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bluedog225
02-15-2010, 05:05 PM
I was looking over this great site:

http://cheaprvliving.com/howtohaveelectricity.html

and noticed the section on charging the house battery.

To summarize (I pasted the section below), they recommend a continuous duty solenoid over a separator. Pretty strongly.

Does anyone have more info on this option? Seems all I hear about is an isolator or a separator. The solenoid seems more reliable and more robust (and cheaper).

I'm not an electrical type so I'd appreciate any info. or opinion.

Thanks

Tom




* There are three solutions to
this problem.


1. The first and simplest is a battery selector switch. You attach the cable
from the starting battery to this switch and run a cable from the switch
to the house battery. When you are going to be using the house battery,
you turn the switch to off. This isolates the house battery from the
starting battery so it can't draw it down. The next day, when you are
done camping and about to drive off, turn the switch to on and now the
two batteries are connected again and the house battery is being
recharged. Simple and easy. But what if you forget to turn the switch
off? You run the risk of running your starting battery down and being
stranded. One way around this is replace your starting battery with a
marine starting battery which will not be damaged if you forget to turn
the switch off. And carry a jumper battery as discussed earlier.
2. The next solution is a little more complex but solves all of our problems.
It is using a continuous duty solenoid between the two batteries. A good
auto store will sell these or you can google continuous duty solenoid and
order one over the net. Don't buy an intermittent duty solenoid, it won't
last. It must say continuous duty. Once you have it, you mount it to the
firewall of your vehicle. A cable runs from the starting battery positive
post to one of the large studs on the solenoid. A cable leaves the other
large post and runs back to the positive post of your house battery. On
some solenoids there will be two smaller posts. One is for a ground to the
frame, the other is to a hot wire in the vehicle wiring harness. Some
solenoids are self-grounding, so they only have one of the small posts.
The screws that secure it to the firewall act as the ground. If that is
what you have, take extra care to have a good clean connection for the
ground. If there is paint on the fender or firewall where you are
attaching the solenoid, you must scrap the paint off so that you have a
clean metal-to-metal connection. That thin layer of paint will prevent a
good ground. Whether you have one or two smaller posts, you must run a
wire to the vehicle wiring harness. Wherever you splice in, it must be
after the ignition, so that when you turn the key off, power is turned off
to the solenoid as well. A good easy place for this is the power to the
radio since we know that when you turn off the key, the radio losses
power and turns off. What happens is that when you turn on the key,
power goes to the solenoid which activates a magnet inside it. The magnet
lifts a bar which makes a connection between the two large posts,
allowing charging current to flow from the starting battery to the house
battery. When you turn the key off, current no longer flows to the
solenoid, the magnet turns off, the bar falls and there is no longer a
connection between house and starting battery. That means that if the
engine is running, the house battery is being charged, and if it is off, the
house battery can not run down the starting battery. The best of both
worlds! Absolutely no drawbacks.
3. Another solution, and by far the most common, is using a battery isolator.
These are commonly available at any auto parts or RV store. Because
these have a half volt drop between the house and starting battery, I
don't recommend them. Therefore, I am not going to cover them very
much. Just follow the instructions that come with them if you want to use
one.

Breakaway
02-15-2010, 05:45 PM
The solenoid connects the house and starting banks (batteries) for emergency starts. That's it.
As for charging, I recommend, have installed and have been using a Voltage Sensitive Relay like those from BEP in lieu of an isolator. In addition to the voltage drop caused by an isolator, these also generate heat, further inhibiting charging.

A VSR senses voltage and sends charge to whatever bank needs it, keeps both banks isolated, and requires no action on the skippers part after install. Its wired like a three-way battery switch ( 1-2-Both). A simple on off switch is installed also. Works like a charm--no heat, no voltage drop, no switches to throw to direct charge. You can install the solenoid wired to a momentary switch for emergency starting as insurance--I did--but a VSR is very reliable.

When sizing your house bank, estimate the amp-hours at 50-85-percent anticipated usage and then go up 15-percent. ( Getting a battery to accept its last 15-percent of charge takes a lot longer than the bringing it up to 85-percent.) That way you should have the juice you need when you need it. http://www.bepmarine.com/

http://www.bepmarine.com/store/web/catalog/Category/Battery%20Management/Battery%20Charging/VSRs/710-125A/710-125A_Lg.jpg

John P Lebens
02-15-2010, 06:37 PM
My electric guy insisted we do a Balmar Digital Duo Charge. It replaced an auto solenoid.

willmarsh3
02-15-2010, 11:35 PM
I put a Battery Link ACR in my system. The alternator is always connected to the starter battery. When the engine is started it senses the higher voltage, waits for one minute then switches in the house battery to start charging it. Once the engine is shut off it waits one minute before disconnecting them. I've had this on board for several years now and there have been no problems.
Also there are two master switches - one each for the house and starting.

tomlarkin
02-16-2010, 12:24 AM
Also there are two master switches - one each for the house and starting.
With the VSR, are the master switches just ON/OFF switches?

Also, would a dual-sense VSR handle a situation where you have 2 battery banks and two ways to charge the batteries, like below?

[110V Charger]==>House===VSR===Starter<==[Outboard Charger]

Breakaway
02-16-2010, 02:02 PM
Yes. Even if you had three or more ways (alternator, charger, generator, solar panel). Wire your charging device to any one battery and the VSR will do the rest.In fact, with a VSR you can charge multiple banks/batteries with a single output charger.

bluedog225
02-17-2010, 07:29 PM
Thanks everyone.

willmarsh3
02-17-2010, 07:44 PM
With the VSR, are the master switches just ON/OFF switches?

Also, would a dual-sense VSR handle a situation where you have 2 battery banks and two ways to charge the batteries, like below?

[110V Charger]==>House===VSR===Starter<==[Outboard Charger]

Mine are both simple on/off switches. If I find the starter battery flat I can unhook the cables and switch the batteries - which I did once.

SandyToes
02-07-2017, 07:31 AM
Hi Breakaway (and others),

I saw these old posts which I found useful, however I have a perhaps slightly more complicated wiring /battery charging & isolation situation and would like to seek some wisdom from people who have done similar before (with VSRs ideally).

Essentially I have a system containing 4x 12V batteries (all different types, and different capacities too!: Marine, car-starter, AGM and deep-cycle), and 3 inputs: generator alternator (25A), solar (200W: = ~16.7A nominal at 12V) and outboard alternator (23A - its a new-ish Tohatsu 50Hp).

The batteries are all in good to brand-new spec; around ~12.6V to 12.7V each.

I am considering hooking all 4 batteries together (in parallel) using 3x (dual sensing) VSRs (all 140A rated-continuous) between them, so they can all be charged whenever any of the inputs is working. (I will use appropriate wiring size etc, and minimise cable length etc. Also planning to use a 100A fuse at each battery positive terminal.)

Two of the VSR are identical: 12.8V cut-out, 13.7V cut-in (unknown cut-out time), and the other is 12.8V cut-out (after 15 seconds), 13.2V cut-in.

Only one alternator will be running at once (either generator or outboard), however the solar will be on simultaneously while one of the alternators are running.

I have a few of questions, if anyone will enlighen me (please!):

- firstly is this set-up fundamentally flawed from the outset? Or, given it is not 'flawed' but is indeed not ideal for charging the batteries, is it ok?

- will the battery life be inherently diminished (provided they are not run down too much from the outputs); e.g. say when charging is occuring from the outboard alternator to the starter battery, the charging current is spread to 3 other batteries so the starter battery will get less juice..

- will there be a problem with 'back-flow' of charge from say the outboard alternator to the solar unit? (as the voltage is likely to be lower at the solar; e.g. 13.8V on solar vs 14.4V on the alternator; the charge is high enough that the first VSR will be 'open' connecting the two sources, however since their respective voltages are different is there a problem?) - or is there a diode-like systems (or other 'back-flow' preventers) inbuild into the standard MPPT solar controllers etc? (if not what should I use, if such a thing is required?)

- along the same lines; when two different voltages are fed into such a (parallel battery) system; how does that work; will the solar (e.g. 13.8V) still act to charge the batteries when there is 14.4V already acting on them from the alternator?

Sorry for the lengthly post; a picture may have helped (but with my drawing skills as they are, it may be even more confusing!)

Cheers for any help/insight; will be MUCH appreciated..

Norman Bernstein
02-07-2017, 08:42 AM
I have a few of questions, if anyone will enlighen me (please!):


A couple of comments:

AGM batteries require a different charging characteristic than do conventional flooded cells, although if your alternator or battery charger is not properly set for AGM, you'll still charge, you just won't get the optimum charge.

Battery 'isolators' of the type described are really just diodes, which is why they have a meaningful voltage drop (anything from 0.5V to 0.8V or more). There are more sophisticated isolators available, that use MOSFET devices instead of simple diodes, and therefore have a far lower drop.

SandyToes
02-07-2017, 04:59 PM
voltage drop (anything from 0.5V to 0.8V or more)

Hi Norman,

Firstly thanks a lot for the reply.

My understanding is that the voltage drop (and also current draw) is Very neglible across (/through) a VSR (both when 'active' and when 'inactive'; since its effectively a switch really; hence they can be left connected continuously without concern for draining the battery.); no way near 0.5 - 0.8V but a more like a teensy tiny drop I believe; which is why they're so widely used now. (I'm trying to find the specs for my specific models; will post if I do find them).

EDIT: here's a couple of examples; a bit different from mine, but surely most dual-sensing VSRs of this variety are similar enough:
1. https://www.hella.co.nz/en/products/relays-flashers/voltage-sensitive-relays/voltage-sensitive-relay-module-1224v.html (http://www.projecta.com.au/site/DefaultSite/filesystem/documents/PowerManagement/VSR100K_instructions_Issue1.pdf)
2. http://www.projecta.com.au/site/DefaultSite/filesystem/documents/PowerManagement/VSR100K_instructions_Issue1.pdf

(http://www.projecta.com.au/site/DefaultSite/filesystem/documents/PowerManagement/VSR100K_instructions_Issue1.pdf)1. states the current draw is <2mA (active, or 0 in 'storage mode'; whatever that is..)
2. states the voltage drop is "none" (which surely means very neglible..)


As for the AGM; thanks for that - it does specify the correct charging regime on the battery sticker itself; so another thing I could consider is including a voltage regulator for this batttery.

Looking forward to any more insight from others too!..

Cheers..

Garret
02-07-2017, 05:08 PM
Hi -

Mixing batteries is risky. As said, different battery types charge very differently & even run at slightly different voltages. In setting up off-grid power, most professionals will not even hook up batteries of the same type but different ages - much less batteries of different types. Longevity of deep cycle batteries is dramatically affected by how they are charged & discharged.

In the OP - the idea of continuously connecting a starting battery with a house battery really won't work well, as a starting battery should be just like a car battery & the house battery should be deep cycle. Hooking them up together will discharge the one running @ higher voltage.

Norman Bernstein
02-07-2017, 05:15 PM
Hi Norman,

Firstly thanks a lot for the reply.

My understanding is that the voltage drop (and also current draw) is Very neglible across (/through) a VSR (both when 'active' and when 'inactive'; since its effectively a switch really; hence they can be left connected continuously without concern for draining the battery.); no way near 0.5-0.8V but more like 1/10th of that I believe. (I'm trying to find the specs for my specific models; will post if I do find them).

Yes... for a hard contact relay, the drop would indeed be negligible, although all hard contacts have at least SOME resistance, so under very heavy loads, you COULD probably measure a drop... but admittedly, it's far lower than a simple diode-based isolator. I'm not a big fan of voltage sensitive relays, however, because like anything mechanical, they DO wear out eventually, and under accidental loads, the relay contacts could 'weld', which could lead to major problems.


As for the AGM; thanks for that - it does specify the correct charging regime on the battery sticker itself; so another thing I could consider is including a voltage regulator for this battery.

I agree with those who maintain that mixing battery types is a bad idea.... and also, running batteries in parallel (EXCEPT if they're of the same type, and only while charging) is ALSO a bad idea. I've written about this before; it's bad, both strategically, as well as technically, unless it can't be avoided. If you like, I could probably find my write-up somewhere....

SandyToes
02-07-2017, 05:54 PM
I agree with those who maintain that mixing battery types is a bad idea.... and also, running batteries in parallel (EXCEPT if they're of the same type, and only while charging) is ALSO a bad idea. I've written about this before; it's bad, both strategically, as well as technically, unless it can't be avoided. If you like, I could probably find my write-up somewhere....

Excuse my ignorance, I'm a novice at this, but here's my logic why it *may* not be a problem hooking up different batteries together in parallel (all four being separated with (three) VSRs):

- the batteries are around 12.7-ish Volts as it ('resting'/charged).
- the VSR cuts out at 12.8V (after say 15s); so the batteries will never bring each down below this level. (Even with a 25amp load running for 15sec after VSR cut-off is only ~0.1AH so the batteries won't drain much below the 12.8V; even the smallest one of my four (32AH AGM)).
- since the cut-out voltage (12.8V) is above their usual 'resting' level (12.7V) any one battery will never be adversely affected by any other batteries; even disimilar batteries (both size and type), so long as all have ~12.7V 'resting' voltage.
- (and by extension: so long as no battery has a 'resting' level of larger than 12.8V it will not be affected whatsoever by the others; as the VSR ensures they are 100% electrically isolated below 12.8V; e.g. at their currently 'full'/'resting' charge or below; i.e. if not currently being charged).

- however, in saying this, one caveat is that as the alternator charge is split between the batteries (in parallel); the (only?) affect will be a lower charging amperage on each battery. i.e all batteries will recieve the same charging voltage (provided it is above 13.7 or 13.2V; depending on the VSR's cut-in voltage, and also taking into account the voltage drop along the wires connecting them, of course..)

Further, on the note of this caveat, is that as batteries age/die doesn't the internal resistance increase? (If so,) therefore the worst batteries (with the largest internal resistances) will get the least amperage /charge going through them (as electricity takes the easiest path /lowest resistance path): so the good batteries will stay good, but the bad ones may get worse (well, get less charging amperage anyway).


In summary I don't think there is any way (via this logic!) that a good battery will be degraded in this scenario; even by connecting it to a bad one (connected by a VSR); neither by voltage-differences (so long as none are >12.8V), nor by 'current-stealing'.

> is this a correct/reasonable understanding, or am I missing something here?

Garret
02-07-2017, 05:58 PM
My take on batteries is to do exactly what the manufacturer says and any mfr I know of says don't mix. While I've never seen a battery explode in a boat, I have in a car & the damage it did (even with immediate wash down with water) was extensive. Luckily no one was looking at it when it went - or else they'd be blind.

My 2 cents only!

SandyToes
02-07-2017, 06:05 PM
Yep - that sounds bad alright! - However I will put a 100A fuse on each battery at the positive terminal (before the other connections) which *should* (fingers crossed) stop a battery exploding); and secondarily I will also put each in its own specialised polypropylene plastic battery case (to contain any potential acid spillage).

(Such as this: https://www.whitworths.com.au/main_itemdetail.asp?cat=123&item=4218 for example)


>> I'm more interested in if this crazy set-up is viable or not?!..

(Especially relating to the solar-alternator voltage-mismatches; this is of particular curiosity to me..)

Canoeyawl
02-07-2017, 06:46 PM
Continuous duty solenoids are often not rated for starting current. Starting current can be around 500 amps at 12v. Ask this question before changing your system.

Big battery isolators for 100+ amp alternators typically have "about" a 1 volt drop and the charger regulators on the alternators themselves must be turned up to compensate for this. I usually turn them up to a minimum of 16 volts. Not all regulators are adjustable.
The old Guest switch is pretty bulletproof, but yes you have to remember to switch it. A couple of lights visible from the cabin or wheelhouse indicating which batteries are "on" can help.

edit to add; A designated start system is another way to go, with the isolated start battery in the loop only when the ignition is on.

SandyToes
02-07-2017, 07:25 PM
Hi Canoey,

Thanks for your reply, but I'm refering to a VSR system, not a CDS.

As mentioned above, for VSR's there is not anywhere near a 1V voltage drop across it! (Even up to their rated continuous ~140A; the voltage drop on these VSR's is almost 0 (very negligible); as stated anywhere you see a VSR technical specs sheet for this type of VSR).

As for the 'surge' current on my 50hp outboard alternator and generator alternator (25A); I doubt it's 500A!; but I will look into this to be sure. (I'm running a small boat with this 50Hp outboard, not a huge beasty 500Hp in-board system or something like that!)

EDIT: this is the 50Hp outboard alternator specs: http://www.tohatsu.com/outboards/50tldi_spec.html
At 12V 23A/280W I doubt it can get to a 500A surge!... but now I am interested to what it can actually achieve?

EDIT2: in case anyone (else) is interested in other possible current surges; such as (full)battery to (empty)battery, this is a good read:
http://www.smartgauge.co.uk/nosurge2.html

Norman Bernstein
02-07-2017, 07:30 PM
Excuse my ignorance, I'm a novice at this, but here's my logic why it *may* not be a problem hooking up different batteries together in parallel (all four being separated with (three) VSRs):

Your scheme certainly looks like it's going the very long way around the barn. I wouldn't design a system like this, myself.... but hey, it's your boat (or is it an RV? I'm not sure). I really can't judge whethr what you're trying to do makes sense or not, because I don't know what the context is. For example, why so many batteries, of so many different types? What are the loads and duty cycles? What are the sources of recharge?


Further, on the note of this caveat, is that as batteries age/die doesn't the internal resistance increase?

The concept of 'internal resistance' is a bit like a comic book's explanation of Christianity: it's an idea to help explain what is vastly more complex, in ways that people not versed in the technology can understand... even if the explanation is not really valid.

It would be far more accurate to say that a battery is a complex, non-linear (but monotonic) device. 'Internal resistance' is a deception, because resistance implies linearity... and a battery ain't linear.., not by a long shot.

Regarding VSR's: when batteries are in parallel, bad things CAN happen that you could not notice by terminal voltage alone. For example, if one battery in a parallel combination develops a shorted cell, the good battery may be able to sustain the terminal voltage by dumping huge amounts of current into the bad battery, before the apparent terminal voltage begins to drop. Admittedly, if the bond between the batteries is broken before an explosion occurs, that's good... but why risk it?

Here's a general set of rules which I would recommend: 1) Size your battery to your load... ONE battery.... and use additional batteries sequentially, rather than in parallel. 2) it's OK to parallel the batteries while charging, as long as they are of the same type... but once charging stops, separate them, and 3) It's actually more practical, and more efficient, to recharge batteries one at a time.

Rule #1, as I mentioned, has both technical and strategic justifications.

SandyToes
02-07-2017, 08:04 PM
Thanks again Norman,

I am using such an assortment of different batteries as thats what I already have!, and, if I am theoretically right (as in if my above logic is true), then it makes no difference whatsoever what the battery types/sizes are as they are only connected while charging from a higher voltage source (solar or alternator etc).

The purpose doesn't matter too much (its arbitrary really); its enough to know I'd prefer to keep the batteries separate as they all run separate outputs which I'd like to isolate in the case there's no charging current going to them. (The batteries are roughly suited to their respective outputs /drains in terms of duty cycle etc.)


Here's a general set of rules which I would recommend: 1) Size your battery to your load... ONE battery.... and use additional batteries sequentially, rather than in parallel. 2) it's OK to parallel the batteries while charging, as long as they are of the same type... but once charging stops, separate them. Rule #1, as I mentioned, has both technical and strategic justifications."


I'm following most of your #1 rule (batteries sized according to load; one battery per load). However, to keep all four of them well charged (off of solar and 2 alternators), and to keep the wiring simple enough for me to do it myself easily I need them in parallel (I think?!).
For your #2 rule, as explained (well, postured) in my above posts I don't see why it matters if different batteries are charged together in a VSR set-up? (as they are isolated when not being charged so the differences e.g. in voltage, never have any impact on each other). Maybe someone can explain the reasons (if any) why not to do this in more detail? (still in laymans terms ideally!).


Regarding the 'internal resistance' I mentioned; please don't get too hung up on this; I understand its a simplification of a much more complex process. Its the concept which could be commented on (if needed; as in if my assumption is wrong?: i.e. if the battery ages/degrades (without a cell failure) then it will get less charge than the good batteries in parallel with it so will not act as a current-drain /current-hog in this multiple battery VSR setup.. )



Regarding VSR's: when batteries are in parallel, bad things CAN happen that you could not notice by terminal voltage alone. For example, if one battery in a parallel combination develops a shorted cell, the good battery may be able to sustain the terminal voltage by dumping huge amounts of current into the bad battery, before the apparent terminal voltage begins to drop. Admittedly, if the bond between the batteries is broken before an explosion occurs, that's good... but why risk it?


Regarding a random single cell-failure in a battery; thanks for highlighting this risk:
I will have to consider:
A. the liklihood (I'm guessing its pretty low on newish batteries?),
B. the consequence (when fused; perhaps in terms of potential damage to other batteries = 0? e.g. so long as they can handle up to a 100A surge before the 100A fuse trips?), and,
C. any possible mitigating factors (any suggestions?)


Let me put it another way: why is it ok (and commonly done) to use a VSR in a simple two battery set-up (e.g. with a high capacity deep-cycle house battery and starter battery in parallel), but not ok to repeat this for N batteries; e.g. four different batteries, like I want to do? Or maybe it is ok?!


Appreciate any insightful comment on other potential issues in my proposed set-up; such as solar-alternator voltage difference and if 'back-flow' may occur to a lower voltage solar system: is this possible /a problem? e.g. solar at 13.8V and alternator running concurrently at 14.4V; will both feed into (aka 'charge') the batteries (all connected by VSR)? Will the solar unit output any current into the batteries at all, or sustain any damage from the voltage difference or what?

Thanks heaps!

Canoeyawl
02-07-2017, 10:12 PM
EDIT: this is the 50Hp outboard alternator specs: http://www.tohatsu.com/outboards/50tldi_spec.html
At 12V 23A/280W I doubt it can get to a 500A surge!... but now I am interested to what it can actually achieve?


I was referring to starter current draw, and that using a continuous duty solenoid may not be up to it.

SandyToes
02-07-2017, 11:55 PM
I was referring to starter current draw, and that using a continuous duty solenoid may not be up to it.

Ok - but I'm not sure what you mean by this though /how it's relevant?

1. I'm looking at using VSRs (which I think are different from CDS?)
2. The outboard came with its own alternator so it's surely ok to start that motor?! (and has any required current surge protection already installed - Similary for my generator and its alternator/battery setup).

Are you suggesting that if the solar is on and the VSRs are all in the 'closed' state (connected: i.e. >13.7V), that if the motor is started at this point there could be a current surge running from all 4 connected batteries to the outboard? (And that this would be a problem for the 140Amp (continuous) rated VSRs?)

Or, if you're talking about a surge in the other direction (to the batteries, from the alternator); surely this also isn't a problem as its never been a problem for the starter battery in any car/boat; so hooking up what is effectively a larger battery (battery bank in effect, when the VSRs are closed) can't make it worse (so long as the wiring between the batteries is up to it, of course).

Norman Bernstein
02-08-2017, 08:14 AM
Thanks again Norman,

I am using such an assortment of different batteries as thats what I already have!, and, if I am theoretically right (as in if my above logic is true), then it makes no difference whatsoever what the battery types/sizes are as they are only connected while charging from a higher voltage source (solar or alternator etc).

Multiple batteries of differing types, connected in parallel, will not necessarily charge at even remotely equivalent rates; each battery will have a different acceptance current at a given voltage. In particular, your AGM battery will probably not get a sufficient charge, since it wants to be charged to a slightly higher terminal voltage.

You haven't explained WHY you have the arrangement you do; I think it runs contrary to good practice.... but hey, as they say, it's YOUR boat.... so, whatever floats it... :)


The purpose doesn't matter too much (its arbitrary really); its enough to know I'd prefer to keep the batteries separate as they all run separate outputs which I'd like to isolate in the case there's no charging current going to them. (The batteries are roughly suited to their respective outputs /drains in terms of duty cycle etc.)

Makes no sense, to me, but whatever.


Regarding a random single cell-failure in a battery; thanks for highlighting this risk:
I will have to consider:
A. the liklihood (I'm guessing its pretty low on newish batteries?),

Yes, the likelihood is low.... but the consequences are severe. I know of one fairly nice sailboat who had a failure like this: a shorted cell in a two battery parallel combination. The acidic gasses that filled the cabin ruined the headliner, all upholstery, and all the woodwork... the cost to repair was huge. It's not a risk I'd care to take lightly.


Let me put it another way: why is it ok (and commonly done) to use a VSR in a simple two battery set-up (e.g. with a high capacity deep-cycle house battery and starter battery in parallel), but not ok to repeat this for N batteries; e.g. four different batteries, like I want to do? Or maybe it is ok?!

The use of a VSR in a two battery areangement does make sense... ASSUMING that 1) both batteries are of exactly the same type (most commonly, flooded wet cells), and 2) one battery is a deep discharge type used for house loads, and the other is a starting battery. It's purpose is simply an alternative to a battery isolator. Personally, I'd rather use a more sophisticated battery isolator in a setup like that... the kind which is MOSFET-based, which has very low voltage drops.

It's NOT an issue of whether it's 'ok'... you can do it, and do what you like. The result you get will be what it is. With differing battery types, you will not get efficient charging for all of them.

I can't really comment on the appropriateness of the arrangement because you haven't provided enough information about loads and devices to be able to judge whether this makes sense, or to be able to recommend a better arrangement.


Appreciate any insightful comment on other potential issues in my proposed set-up; such as solar-alternator voltage difference and if 'back-flow' may occur to a lower voltage solar system: is this possible /a problem? e.g. solar at 13.8V and alternator running concurrently at 14.4V; will both feed into (aka 'charge') the batteries (all connected by VSR)? Will the solar unit output any current into the batteries at all, or sustain any damage from the voltage difference or what?

In such a mish-mash of a system, there are going to be all sorts of issues. If, for example, you've got solar and alternator running concurrently, and the alternator is raising the terminal voltage to 14.4 volts, your solar panel will likely contribute next to nothing, to charging. If you've got all batteries connected together during charging, the ones with the highest acceptance rate will probably consume the majority of the current. I don't think there's any problem with reverse current back to the alternator; the alternator output comes from a diode pack which shouldn't leak more than a tiny amount of current.

SandyToes
02-09-2017, 05:22 AM
Hi Norman,

Thanks again for taking some time to consider my proposed power set-up and offer some thoughts on it.
(On the viability of what I thought (possibly incorrectly) might be an easy, reasonable setup! - to keep everything charged yet isolated.. maybe it's just not that simple huh!)


Multiple batteries of differing types, connected in parallel, will not necessarily charge at even remotely equivalent rates; each battery will have a different acceptance current at a given voltage. In particular, your AGM battery will probably not get a sufficient charge, since it wants to be charged to a slightly higher terminal voltage.

Yes, this seems likely to be a problem - it might be worth actually trying this set-up and actually measuring the amperages & voltages while it's all working since I have everything for it already.. sometimes people (like me) just need to fail themselves first to learn I guess!

Otherwise I wonder how to get around it /optimise it without either too much energy loss in the system, or spending too much $$); changing the whole setup using specialised battery isolators and individual charging arrangements doesn't sound cheap (unless I could do all the electronics from scratch myself instead of buying plug-and-play solutions?)



..but hey, as they say, it's YOUR boat.... so, whatever floats it...

For now it does yes! But if I don't heed to some sound electrical advice I'm not sure how long that will last!..


Yes, the likelihood is low.... but the consequences are severe. I know of one fairly nice sailboat who had a failure like this: a shorted cell in a two battery parallel combination. The acidic gasses that filled the cabin ruined the headliner, all upholstery, and all the woodwork... the cost to repair was huge. It's not a risk I'd care to take lightly.

This one is an open-air aluminium run-about boat with almost no wood or upholstery (somewhat sadly on all accounts! - will get a nice wooden sailboat one day.. I'll consider this my electrical learning curve before I get to that point!) - but still, point taken. No battery failure is 'fun' when stuck out on the water..


The use of a VSR in a two battery areangement does make sense... ASSUMING that 1) both batteries are of exactly the same type (most commonly, flooded wet cells), and 2) one battery is a deep discharge type used for house loads, and the other is a starting battery.

This is perhaps where the heart of the problem lies; your 1). and 2). cannot be true together: house batteries are usually large capacity deep cycle; different from starting batteries... so there's an inherent difference in most dual/multi-battery set-ups. The batteries may (often) be different types of batteries, different size of batteries (capacity), different manufacturers, and different age of batteries too. (I think this goes for RVers as well as boaties).

So once again; if its ok for a dual battery set-up, why not for 4 batteries?!
Or maybe it is simply not ok to use a VSR set-up on any dual battery system unless both batteries are identical (but then they'd both have to be starters?!).


I can't really comment on the appropriateness of the arrangement because you haven't provided enough information about loads and devices to be able to judge whether this makes sense, or to be able to recommend a better arrangement.

Here's a little more info, hopefully it helps. (all 12V DC):
System Inputs: petrol motor alternator (25A), outboard motor alternator (23A), and solar system (200W).
System Outputs: 1. water pump (7.5A), 2. car radiator fans (for cooling petrol motor in housing)(~16A combined, max), 3. compressor (45Amps max @ 1/3 duty cycle; 15Amp average), (and of course the petrol motor and outboard motor; for sparking (?A)).

Batteries, connected to Outputs as numbered: 1. 32AH 45RC AGM, 2. 55AH 90RC /550CCA lead car starter, 3. 1250CCA (110AH) marine (dual purpose: starter/deep-cycle type), and, 4. 900MCA/720CCA 160RC Marine starter battery.
(Current (resting) voltages (~28deg C), respectively: 1. 12.50V, 12.65V, 3. 12.71V, 4. 12.71V -- may or may not be in their best /fully charged state!)


If, for example, you've got solar and alternator running concurrently, and the alternator is raising the terminal voltage to 14.4 volts, your solar panel will likely contribute next to nothing.

This is what I am perplexed by; but I don't fully understand 'why'; surely the solar system energy has to go somewhere??

e.g.
Taking it to the extreme case (as it can be easier for me to understand things): if the solar unit is putting out say 14.3999V and the alternator is putting out 14.4V, does this mean the solar unit it not contributing anything to charging the batteries?! - seems unlikely to me that it wouldn't contribute something; that ~200W has to go somewhere.. Using this logic I would *assume* (cough!) that even if the solar is only putting out 13.8V while the alternator is putting out 14.4V that BOTH would be contributing to charging the (VSR-connected) batteries (somehow)...surely?!

- can anyone explain this to me simply? - is it simply that the battery acts as a 'bank' and will accept any 'deposits' higher than a threshold (minimum) value? (even simultaneously?)


If you've got all batteries connected together during charging, the ones with the highest acceptance rate will probably consume the majority of the current.

This is an interesting point for me; and I would (ideally) like to know how the current is going to be split between the batteries. (or how to control how it is split; for as cheaply as possible)...

Thanks again for the thoughts and raising some important questions too!

SandyToes
02-09-2017, 06:21 AM
In case anyone else is following this thread /is interested, this post (below) provided me with some very useful insights on the dual-charging aspect of what I'm looking into, using VSRs:

http://forum.expeditionportal.com/threads/142118-Charging-battery-bank-via-solar-and-alternator-simultaneously

(In the post, just swap 'ACR' (Automatic Charging Relay) for 'VSR'; it looks like they're one and the same).

I hope that helps someone..

Norman Bernstein
02-09-2017, 09:42 AM
.
(On the viability of what I thought (possibly incorrectly) might be an easy, reasonable setup! - to keep everything charged yet isolated.. maybe it's just not that simple huh!)

you're right... sometimes, it's NOT simple :) However, amateurs sometimes have an advantage over professionals; they're often willing to try something that MIGHT work, when the professional is fairly sure it won't... and sometimes, the professionals can be wrong. I'm an electrical engineering professional... but I've also been wrong on many occasions throughout my career... so take my judgments with a grain of salt.


sometimes people (like me) just need to fail themselves first to learn I guess!

Failure is a great way to learn. However, sometimes, the failure is hard to recognize, often expensive, and the results can be deceiving.


Otherwise I wonder how to get around it /optimise it without either too much energy loss in the system, or spending too much $$); changing the whole setup using specialised battery isolators and individual charging arrangements doesn't sound cheap (unless I could do all the electronics from scratch myself instead of buying plug-and-play solutions?)

My general impression is that your setup is unnecessarily complex... and complexity can be expensive. 'Simple' is often best.


This is perhaps where the heart of the problem lies; your 1). and 2). cannot be true together: house batteries are usually large capacity deep cycle; different from starting batteries... so there's an inherent difference in most dual/multi-battery set-ups.

On this point, I have to say you're wrong. When referring to flooded lead-acid cells, the difference between a 'starting' battery and a 'deep discharge' battery is strictly in the physical construction of the battery... the electrochemistry is absolutely identical. Starting batteries have thinner plates, intended to allow very high (but short duration) discharges of current, for heavy starting loads. Deep discharge batteries have thick plates, designed to deliver long periods of moderate loads.

The difference is often also indistinct: witness the 'dual purpose' batteries on the market. They're a compromise between the two types.


So once again; if its ok for a dual battery set-up, why not for 4 batteries?! Or maybe it is simply not ok to use a VSR set-up on any dual battery system unless both batteries are identical (but then they'd both have to be starters?!).

I wouldn't consider using even a single VSR in a system where the batteries aren't of the SAME electrochemistry. With 4 batteries of the exact same electrochemistry, using 4 batteries with 3 VSR's is possible... it just strikes me as massively overcomplicated, for little reason that I can detect.


Here's a little more info, hopefully it helps. (all 12V DC):
System Inputs: petrol motor alternator (25A), outboard motor alternator (23A), and solar system (200W).

System Outputs: 1. water pump (7.5A),
2. car radiator fans (for cooling petrol motor in housing)(~16A combined, max),
3. compressor (45Amps max @ 1/3 duty cycle; 15Amp average),
(and of course the petrol motor and outboard motor; for sparking (?A)).

Batteries, connected to Outputs as numbered: 1. 32AH 45RC AGM,
2. 55AH 90RC /550CCA lead car starter,
3. 1250CCA (110AH) marine (dual purpose: starter/deep-cycle type), and,
4. 900MCA/720CCA 160RC Marine starter battery.

What is the 'petrol motor' for? What is the water pump for? (7.5A for a water pump seems high... my boat has a number of water pumps, none of them are more than 4A, and thy're only used intermittently). And is the compressor for diving purposes?

OK, to start off: if you got rid of the AGM battery, at least the remainder of the batteries would all be (I assume) flooded lead-acid, so at least they'd share the same electrochemistry.

The most significant load you've got is the compressor.... and if it's really pulling 45 amps when cycled on, I don't think your battery #3 (which appears to be what we call a 'group 31' battery, here in the states) is sufficient. You're talking about pulling 40% of the total aH rating of the battery, and that rating is based on typically 20 hours, not one hour... and that's extreme... that battery might out-gas quite a bit, even suffer warped plates, under a load like that. I think I'd want to use a group 4D battery, at the very least, for a load like that. Secondly, recharging that battery, after a period of time, from a 25A alternator, is going to be a challenge.

Depending on the purpose of the 'petrol motor', I could see the need for three batteries: 1) a more-or-less conventional automotive type attached to the 'petrol motor', whose alternator would supply the water pump and radiator fan loads while running, as well as serve for starting the 'petrol motor'... 2) a starter battery for the outboard, and 3) a rather massive battery for the compressor.

The battery for the petrol motor, as well as the battery for the outboard, don't really need any special recharging consideration; their loads are either engine start (in which case, their alternators very rapidly replenish the starting power), or they have loads that are consistent with their alternator ratings. The big problem is getting the compressor battery recharged... I assume that this is the purpose of the petrol motor, but it's alternator isn't sufficient to run the water pump load, AND the fan loads, AND recharge the big compressor battery. You COULD recharge the compressor battery from the outboard's alternator, albeit inefficiently.

So, based on your description of your loads, and the description of your recharge sources, I don't see how this could work.



This is what I am perplexed by; but I don't fully understand 'why'; surely the solar system energy has to go somewhere?? e.g. Taking it to the extreme case (as it can be easier for me to understand things): if the solar unit is putting out say 14.3999V and the alternator is putting out 14.4V, does this mean the solar unit it not contributing anything to charging the batteries?! - seems unlikely to me that it wouldn't contribute something; that ~200W has to go somewhere.. Using this logic I would *assume* (cough!) that even if the solar is only putting out 13.8V while the alternator is putting out 14.4V that BOTH would be contributing to charging the (VSR-connected) batteries (somehow)...surely?!

- can anyone explain this to me simply? - is it simply that the battery acts as a 'bank' and will accept any 'deposits' higher than a threshold (minimum) value? (even simultaneously?)

Batteries, alternators, and solar panels are all non-linear monotonic devices; their terminal behaviors are dependent upon what they are connected to. Your solar panel output is completely dependent on what load it is driving... and it's current output is dependent on what voltage it sees. You can think of the solar panel, if you like, as a 'highly resistive' source (even though that's not really true, but it might help)... if you connect the solar panel to a device whose terminal voltage is higher than optimum for the panel, the panel will not output maximum current. The solar panel's mximum output will occur at some specified terminal voltage, and will NOT be constant if the load voltage varies. Certainly, if the alternator is charging the battery and is sustaining 14.4 volts, the solar panel's contribution may be very small indeed, if it's maximm output is specified at a lower voltage.

.

Breakaway
02-09-2017, 10:12 AM
Let me say that VSR/ ACR's are, and have been, in widespread use in the production powerboat market for at least a decade now. Many new boats are fitted with them, and they are reliable and work as advertised to separate two batteries, or two battery banks.




Let me put it another way: why is it ok (and commonly done) to use a VSR in a simple two battery set-up (e.g. with a high capacity deep-cycle house battery and starter battery in parallel), but not ok to repeat this for N batteries; e.g. four different batteries, like I want to do? Or maybe it is ok?!

If I understand your setup, it's really just one " battery" ( its one battery bank). A VSR// ACR is used to separate two batteries ( or two banks) and ensure both are always charged.

o
RE: Your outboard. That alternator only puts out its max amperage at high rpm. At lower engine speeds, the charging output will be less. Dig deep into the specs to discover what you can really expect.

Kevin

EDITED to add: I also agree that you should not mix battery types in the same bank.

k

Norman Bernstein
02-09-2017, 10:25 AM
.
RE: Your outboard. That alternator only puts out its max amperage at high rpm. At lower engine speeds, the charging output will be less. Dig deep into the specs to discover what you can really expect..

Excellent point, and one that people often miss. It's not just a problem of maximum RPM, though. The temperature coefficient of copper is 0.4%/degree C. As the alternator heats up, the windings become more resistive, and the output goes down. So, at the moment the engine starts, and if the RPM is at maximum, the alternator will put out it's rated amperage... but as the windings heat up, and when the RPM is NOT at the maximum, the output can be substantially less than the rating.

SandyToes
02-09-2017, 05:15 PM
Cheers again Norman,


My general impression is that your setup is unnecessarily complex... and complexity can be expensive. 'Simple' is often best.

For me I think there couldn't be anything easier than 4 batteries connected in parallel! (using VSRs to keep them all charged); that's precisely why I was considering running with this (because its cheap and I can do it myself, and I thought it might work - although, I am planning on refining the design now after these discussions; thanks! - see below..).

> Whats an alternative way to set this up then, given what I've got, what I want to do, and without spending much money?


When referring to flooded lead-acid cells, the difference between a 'starting' battery and a 'deep discharge' battery is strictly in the physical construction of the battery... the electrochemistry is absolutely identical. Starting batteries have thinner plates, intended to allow very high (but short duration) discharges of current, for heavy starting loads. Deep discharge batteries have thick plates, designed to deliver long periods of moderate loads.

Just to be a bit nit-picky: I wasn't only referring to flooded lead-acid; many people use an AGM as their house battery. So many dual-battery set-ups do indeed use different batteries. In fact I'd go as far to say that Most dual battery set-ups (using VSR) have a specialised deep-cycle house battery (AGM or lead etc) and a seperate starter battery.

Also the 'electrochemistry' is still different between a starter and a deep-cycle; in the sense even though it may mostly come down to only a plate thickness difference (and potentially other additives; e.g. silver); their 'internal resistance' /'acceptance rate' /whatever you want to call it is distinctly different. Right?

e.g. If one has a huge CCA (/MCA) battery then its likely it will also accept charging current more readily than a 'sluggish' deeg-cycle. To me this is an 'electrochemistry' difference; even the thought the chemistry is roughly (or identically) the same (both being lead-acid +/- minor specific additives), the physical plates are different thickness (and maybe orientation etc) giving different electrical properties. Hence different 'electrochemistry' (by one definitioin of the word anyway..). I think to call a deep cycle and a starter battery the same 'electrochemistry' is a little bit misleading perhaps; especially for us amateurs who may misunderstand the nuance in which this is said..



The difference is often also indistinct: witness the 'dual purpose' batteries on the market. They're a compromise between the two types.

Agreed; this is precisely why I went with a marine 'dual-purpose' battery as my main 'deep-cycle' /Aux/house battery; to be hooked up to the boat starter via VSR; so they are as close as possible to each other. (So I agree with you and everyone else on the principle that the more similar, the better (where possible).


With 4 batteries of the exact same electrochemistry, using 4 batteries with 3 VSR's is possible... it just strikes me as massively overcomplicated, for little reason that I can detect.

It's actually very simple in terms of wiring etc (make a break in the positive, add the VSR unit, connect the negative/ground); and its relativey cheap; and it makes sure all batteries are charged from a variety of charging systems (provided the right voltages & amps are getting to each battery).

> There may be better ways to ahieve all this: I am all ears! :)


the compressor....if it's really pulling 45 amps when cycled on, I don't think your battery #3 (which appears to be what we call a 'group 31' battery, here in the states) is sufficient.

Interesting; I wondered what the 31A CMF stood for; must be a USA thing. (Now I know its a group 31).

The battery is 130AH, and bear in mind it will be connected to a 200W solar (= ~16.7A) which is on (max!) almost constantly (it's sunny here; too much so!), while the compressor (15A average) will only run several hours per day. For the discharge rate at 45A peak; it's a largish 1250CCA-rated battery so I don't think this will be a problem for short durations; as in its on (45A) for say 1min then off for 2min cycles etc.. Furthermore, it's also a dual-purpose battery, so it won't mind if a cloud comes along and it has to discharge say 15AH (one hours constant use). Finally, the engine alternator will provide a kick every now and then (via VSR) when I'm moving /when the engine is on (even if not at full revs; this is seen as bonus really!).


So, based on your description of your loads, and the description of your recharge sources, I don't see how this could work.

Granted: my rough calculations are simply amperage based.
As above I think the compressor (15A), solar (16.7A output), and outboard alternator (23A when on) set-up is fine.
Similary I think the petrol motor alternator (25A output), pump (7.5A) and radiator fans (16A) are ok together (so long as the engine is at max revs).

So ideally I would seperate these and have two battery banks; not connecting between them, however as the second system is cutting it fine (while the first has a little spare capacity) I would ideally utilise that spare capacity and shimmy it towards the second system (somehow; maybe not using VSRs, but something else?)


if you connect the solar panel to a device whose terminal voltage is higher than optimum for the panel, the panel will not output maximum current. The solar panel's maximum output will occur at some specified terminal voltage, and will NOT be constant if the load voltage varies. Certainly, if the alternator is charging the battery and is sustaining 14.4 volts, the solar panel's contribution may be very small indeed, if it's maximm output is specified at a lower voltage.

Agreed - this seems to be the rough consensus from the link (site) I posted above too; that if the (smart) solar controller sees the 14.4V from the alternator it will go into standby mode (low output). This shouldn't be a big problem for me as the (outboard) alternator will only be on briefly compared to the solar which will be on all day; so if the alternator 'over-rides' the solar for short periods its no big deal in my case really (I'm not counting on using both simulaneously). However, if I did run with the 3x VSR system it would be a big problem from the generator alternator; which does need to be on while the solar is on.

So now, thanks to this discussion, I am looking at breaking up my proposed 4-battery & 3-VSR system; instead of using 3 VSRs to connect all 4 batteries (to effectively make a single charging-bank; now only use 2 VSRs to connect two batteries each; to make 2 separate battery charging-banks.

> Is there any way to connect the two seperate banks smartly?; so that the alternator and the solar can both charge both banks (all 4 batteries) simultaneously; some sort of voltage and current regulating system?

Many thanks again for the thoughts..

SandyToes
02-09-2017, 05:25 PM
Hi Breakaway (Kevin),

Thanks for coming back to this.


If I understand your setup, it's really just one " battery" ( its one battery bank). A VSR// ACR is used to separate two batteries ( or two banks) and ensure both are always charged.

Actually I have 4 battery banks (each containing one battery!), and was intending to connect them all using 3 VSRs; so that all may charge, from a variety of sources; depending what is on at any particular time..

However, now I am strongly considering keeping two separate systems (which are isolated except when charging: AKA 'charging-banks') - for fear that a higher voltage alternator output will deem the solar system 'idle'/'standby' if they are on together /simultaneously (as the solar unit has a smart voltage regulator that changes output depending on what it sense across the battery; which would be the alternator voltage if that is on?!).
I need the juice from both solar and the alternator at the same time; but can separate into two VSR-charging-banks if needed... (hence have the petrol motor alternator in a separate charging-bank from the solar).

So I'll still have 4 separate battery banks but only 2 VSRs (not 3); keeping the 2 systems isolated.

(Unless (hopefully!) I can find a way that allows both systems (all 4 batteries/banks) to be connected and charge from both a solar system and an alternator concurrently - not only one source at a time). - looking for input on this; any ideas?


RE: Your outboard. That alternator only puts out its max amperage at high rpm. At lower engine speeds, the charging output will be less. Dig deep into the specs to discover what you can really expect.

Yep, make sense: Good idea thanks - to look into the specs; as in to find the alternator voltage (and current) output vs engine RPM.

Breakaway
02-09-2017, 06:54 PM
It's not just a problem of maximum RPM, though. The temperature coefficient of copper is 0.4%/degree C. As the alternator heats up, the windings become more resistive, and the output goes down. So, at the moment the engine starts, and if the RPM is at maximum, the alternator will put out it's rated amperage... but as the windings heat up, and when the RPM is NOT at the maximum, the output can be substantially less than the rating.

Very informative and interesting, Norman.




(Unless (hopefully!) I can find a way that allows both systems (all 4 batteries/banks) to be connected and charge from both a solar system and an alternator concurrently - not only one source at a time). - looking for input on this; any ideas?

I don't THINK you can set that up to be an automatic thing, where the relay switches to whichever charging source is better at the time. You'll need, I surmise, to install manual switches to switch your batteries/ banks between charging sources.


Kevin

Norman Bernstein
02-09-2017, 09:02 PM
Just to be a bit nit-picky: I wasn't only referring to flooded lead-acid; many people use an AGM as their house battery. So many dual-battery set-ups do indeed use different batteries. In fact I'd go as far to say that Most dual battery set-ups (using VSR) have a specialised deep-cycle house battery (AGM or lead etc) and a seperate starter battery.

Not in my experience... and regardless, it's still wrong, if they're not using separate regulators to provide the correct charging voltages. People do LOTS of dumb things. I'm not suggesting that such a setup doesn't 'work'.... but I AM suggesting that it abuses one or the other battery, and doesn't give the best efficiency. I certainly wouldn't do it.


Also the 'electrochemistry' is still different between a starter and a deep-cycle; in the sense even though it may mostly come down to only a plate thickness difference (and potentially other additives; e.g. silver); their 'internal resistance' /'acceptance rate' /whatever you want to call it is distinctly different. Right?

No. NO!

The physical construction of a battery is independent of it's electrochemistry. Deep discharge, starting, or dual purpose, if it's a flooded cell lead-acid battery, its electrochemistry is EXACTLY the same. Sorry, but there's NO difference.

see http://www.engineersedge.com/battery/electrochemistry_lead_acid_battery_cell.htm


I think to call a deep cycle and a starter battery the same 'electrochemistry' is a little bit misleading perhaps; especially for us amateurs who may misunderstand the nuance in which this is said..

You ARE indeed misunderstanding, but your error is in presuming nuance where there is none.


this is precisely why I went with a marine 'dual-purpose' battery as my main 'deep-cycle' /Aux/house battery; to be hooked up to the boat starter via VSR; so they are as close as possible to each other.

You are fooling yourself... a 'dual purpose' battery has the SAME elctrochemistry as a starting or deep cycle type, if they're flooded cell lead-acid batteries.


The battery is 130AH, and bear in mind it will be connected to a 200W solar (= ~16.7A) which is on (max!) almost constantly (it's sunny here; too much so!)...

It may be 'on', but the amount of current it delivers depends on what it's trying to deliver current to. Your panel might be capable of delivering 16.7A... but only into a load whose V-I characteristics match the panel.


while the compressor (15A average) will only run several hours per day. For the discharge rate at 45A peak; it's a largish 1250CCA-rated battery so I don't think this will be a problem for short durations; as in its on (45A) for say 1min then off for 2min cycles etc..

'CCCA' ratings are not engineering ratings... they're marketing ratings, intended to impress the customer with how many amps can be delivered in a very short period of time. '1 min on, 2 min off' is NOT a characteristic that relates to the 'CCCA' of a battery. If you're pulling 45 AMPS off of a group 31 battery, you're abusing it, even if it's 1 min on, 2 min off. 'Average' current draw does have meaning... but there are bounds on that. A 130aH battery CANNOT supply 130 amps for one hour. The rating is usually based on 'C/20' (i.e., what current can be sustained over a 20 hour period, presuming that the load is constant and not varying.

SandyToes
02-09-2017, 10:29 PM
People do LOTS of dumb things.

Indeed we all do! Some of us more than others...

In saying that I am trying to do this as smartly as possible without paying multiple $100's for specialised chargers etc (and trying to do the charging automatically, ideally - as there's enough charge being produced throughout the day; it's [*only*!] a distribution problem).
- I know there will be some compromises (it's life afteral!).


You ARE indeed misunderstanding, but your error is in presuming nuance where there is none.

I was just trying to be nice by saying there is a nuance. Actually there is a very apparent difference between a starter and a deep cycle; even at my limited level of understanding..


You are fooling yourself... a 'dual purpose' battery has the SAME elctrochemistry as a starting or deep cycle type, if they're flooded cell lead-acid batteries.

In one sense of the 'same' (electrochemistry) then yes I agree with you (as in they may incorporate the exact same chemicals and undergo the same electrochemical process). But in terms of the specific differences between a starter and a house/Aux battery I don't agree; the way they each work to absorb and discharge electrons is different (at different rates, with different internal impedences etc: different electrochemical properties); hence different 'electrochemistry' on that level of understanding at least.
(I knew you'd prefer the use of 'impedence' vs 'resistance' in this case! :) )

Otherwise why doesn't everyone always use two identical (starter) batteries in a dual-battery situation then?! - because they are different from deep cycle ones; each suited best to its purpose.


'CCA' ratings are not engineering ratings...

I disagree - they are in fact engineering ratings.

While they may be manipulated for marketing reasons, there are engineering standards which exist (which may vary by geographic regions).

I stumbled across this which you might enjoy reading; to see (some) of the engineering standards for CCA which exist:
http://batteryuniversity.com/learn/article/how_to_measure_cca_cold_cranking_amp


If you're pulling 45 AMPS off of a group 31 battery, you're abusing it.

I disagree again.

I don't think it will be upset (feeling abused) from either the Depth of Discharge (DoD), or the Rate of Discharge (RoD) in this case.

Regarding the DoD:
This is only 0.75AH from a 130AH battery (neglecting the almost equal solar input). (45Amps for one minute = 0.75AH).

Regarding the RoD:
Are you suggesting that a battery that is rated to take 1250 Amps (over 30seconds) will be upset with a mere 45A draw (over a minute)?! (Not to mention there is some % of 16.7amps of solar charge going into it concurrently in this case).

Granted this 1250 Amps is a CCA rating. However, as CCA rating is at -18'C and the CA increases with temperature so a 1250CCA (at -18deg celcius) is actually a ~1560 MCA (at 0deg celcius), and probably more like 2000CA at an operational temperature (here) of say 25deg celcius!

Here is a good calculator if you want to test this yourself:

http://www.bgsoflex.com/ccatemp.html e.g. these results: http://www.bgsoflex.com/cgi-bin/ccatemp.cgi?cca=1250&ccatemp=0&temp=77.0

(beware: temperatures are in non SI units).

Interestingly enough, conversely to the resistance of copper (increasing by ~0.39%/degree kelvin increase), a battery's internal impedence must actually decrease with an increase in temperature (to an extent) to achieve this (likely non-linearly) increase in CA. (I found that interesting at least...)

Norman Bernstein
02-10-2017, 08:25 AM
Indeed we all do! Some of us more than others...

In saying that I am trying to do this as smartly as possible without paying multiple $100's for specialised chargers etc (and trying to do the charging automatically, ideally - as there's enough charge being produced throughout the day; it's [*only*!] a distribution problem).
- I know there will be some compromises (it's life afteral!).



I was just trying to be nice by saying there is a nuance. Actually there is a very apparent difference between a starter and a deep cycle; even at my limited level of understanding..



In one sense of the 'same' (electrochemistry) then yes I agree with you (as in they may incorporate the exact same chemicals and undergo the same electrochemical process). But in terms of the specific differences between a starter and a house/Aux battery I don't agree; the way they each work to absorb and discharge electrons is different (at different rates, with different internal impedences etc: different electrochemical properties); hence different 'electrochemistry' on that level of understanding at least.
(I knew you'd prefer the use of 'impedence' vs 'resistance' in this case! :) )

Otherwise why doesn't everyone always use two identical (starter) batteries in a dual-battery situation then?! - because they are different from deep cycle ones; each suited best to its purpose.



I disagree - they are in fact engineering ratings.

While they may be manipulated for marketing reasons, there are engineering standards which exist (which may vary by geographic regions).

I stumbled across this which you might enjoy reading; to see (some) of the engineering standards for CCA which exist:
http://batteryuniversity.com/learn/article/how_to_measure_cca_cold_cranking_amp



I disagree again.

I don't think it will be upset (feeling abused) from either the Depth of Discharge (DoD), or the Rate of Discharge (RoD) in this case.

Regarding the DoD:
This is only 0.75AH from a 130AH battery (neglecting the almost equal solar input). (45Amps for one minute = 0.75AH).

Regarding the RoD:
Are you suggesting that a battery that is rated to take 1250 Amps (over 30seconds) will be upset with a mere 45A draw (over a minute)?! (Not to mention there is some % of 16.7amps of solar charge going into it concurrently in this case).

Granted this 1250 Amps is a CCA rating. However, as CCA rating is at -18'C and the CA increases with temperature so a 1250CCA (at -18deg celcius) is actually a ~1560 MCA (at 0deg celcius), and probably more like 2000CA at an operational temperature (here) of say 25deg celcius!

Here is a good calculator if you want to test this yourself:

http://www.bgsoflex.com/ccatemp.html e.g. these results: http://www.bgsoflex.com/cgi-bin/ccatemp.cgi?cca=1250&ccatemp=0&temp=77.0

(beware: temperatures are in non SI units).

Interestingly enough, conversely to the resistance of copper (increasing by ~0.39%/degree kelvin increase), a battery's internal impedence must actually decrease to achieve this (likely non-linearly) increase in CA. (I found that interesting at least...)

Good luck with your project.

SandyToes
02-10-2017, 06:00 PM
Cheers Norman - I might need it!

(Sorry if I came across the wrong way, I guess I was being a bit defensive..)

Thanks for your input; a lot of your comments inspired a research effort on my behalf so I have learnt a lot in this process; and as a result I'm changing my proposed 4battery+3VSR system to 2x(2battery+1VSR) system (effectively isloating the two halves) - which is 'ok'; great in terms of installing a cheap, automatic, charging system, but not ideal in terms of the charging regime for each specific battery (not ideal like a 3-stage charging regime).

Also I'll have more input (charging) on one half of the system than the other so its not spread as well as I'd like (yet).
So... I'm still looking for a way to combine the two battery banks if possible (well; they're really 'charging-banks' as they're isolated when not charging).

The proposed VSR between the two charging-banks doesn't look like a good idea; as (like you and everyone has said): the 4 batteries are quite different to each other; maybe to the point where the charging current won't be allocated well. (However the 2 batteries in each bank are 'close-enough' to one-another that this should be ok, but between the 4 of them; the difference is probably too much).

Does anyone have a good idea to connect 4 batteries to 3 chargers (with only two chargers working at any one time)?
(Ideally with some sort of voltage & current regulation for each battery!)

The (proposed) system is roughly:

alternator==battery==VSR==battery (componentX) solar==battery==VSR==battery==alternator

Or, more specifically:

alternator1==battery1==VSR1==battery2 (componentX) solar==battery3==VSR2==battery4==alternator2
.....||.................||........................ .||.........................................||.... ..........................................||
..motor1...........load1....................load2. ...................................load3.......... .............................motor2


(the dots are spaces: because I can't have more than one white space side-by-side here).


(Ideally I'd have something at "(componentX)" to connect both sides when charging to more evenly spread the charging load across both sides: a VSR3 doesn't seem ideal...the main concern being that the voltage at 'alternator1' would be higher than the voltage at 'solar' so only one would work at a time; when I reallly need the full power from both when both are on concurrently).


Here's a couple of good links if anyone is going through this learning curve (too):

Types and differences of lead-acid batteries: http://www.mpoweruk.com/leadacid.htm

Battery charging theory: http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery