Direct Current for Dummies

[JimD]

And trust me, we are talking seriously dumb here, so please type slowly...

1) My boat will have two 12 volt batteries connected in series to provide power for a 24 volt trolling motor.

2) I need to hook up exterior nav lighting and interior cabin lighting, just a couple LEDs in the cabin. That's it.

3) Can anyone point me to a good source on how to go about this? Please don't start using big words like omhs, amps, and volts.

[paladin]

two wires works good......

[JimD]

two wires works good......

Mr Chuck. That's a good start.

[John B]

There's the plus and minus thing.....

[capt jake]

Quietly hold your hands together and say "Ooohhhmmm" :)

[John B]

and pray that you find some common ground.

[capt jake]

Is this along the lines of what you are looking for?
http://www.dummies.com/WileyCDA/DummiesTitle/Electronics-For-Dummies.productCd-0764576607.html

[capt jake]

Or this?
http://http://www.allaboutcircuits.com/vol_1/index.html (http://http//www.allaboutcircuits.com/vol_1/index.html)

[paladin]

you have two batteries...one battery has a negative terminal that will be the ground wire for both systems.......then you take the positive side of that battery and connect it to the negative side of the second battery...this will be junction one....the positve terminal of the second battery becomes your plus 24 volts, and the negative side of the first will be the ground......
your lights accessories will have a common ground with the first battery, connect all your 12 volt stuff to the junction of the two batteries......
now...ya gots a little problem ..charging...I assume you will disconnect the batteries and charge them independently as single 12 volt batteries, if you do so then there's no problem.....if you charge with a 24 volt charger you need to periodically switch the batteries because you will not have a balanced charge.......write me a private e-mail if you need a picture...my scanner is down and I don't have time to see why..I go into the witch doktors lair tomorrow for 4 days...

[Peter Eikenberry]

Try this basic electricity page http://newboatbuilders.com/pages/electricity1.html

[Hwyl]

you have two batteries...one battery has a negative terminal that will be the ground wire for both systems.......then you take the positive side of that battery and connect it to the negative side of the second battery...this will be junction one....the positve terminal of the second battery becomes your plus 24 volts, and the negative side of the first will be the ground......
your lights accessories will have a common ground with the first battery, connect all your 12 volt stuff to the junction of the two batteries......
now...ya gots a little problem ..charging...I assume you will disconnect the batteries and charge them independently as single 12 volt batteries, if you do so then there's no problem.....if you charge with a 24 volt charger you need to periodically switch the batteries because you will not have a balanced charge.......write me a private e-mail if you need a picture...my scanner is down and I don't have time to see why..I go into the witch doktors lair tomorrow for 4 days...
I've done that, but I thought it was a dangerous practice.

Good luck with the quacks. Don't keep your hands off the nurses.

[rbgarr]

http://www.amazon.com/Boatowners-Illustrated-Electrical-Handbook-Charlie/dp/0071446443

[Tylerdurden]

If I was stuck on a two battery system I would down convert dc to 12vdc.
Look for a dc to dc converter that will handle your 12volt current load.
I would up size your current load by at least half.

http://abp.com/Cool_Power_DC-DC_Converter.shtml

There are cheaper versions of this all over but finding a mil-spec surplus would be the cats ass.

[JimD]

If I was stuck on a two battery system I would down convert dc to 12vdc.
....

I really would prefer to avoid buying more gizmos if there is an easy way to wire a 24 volt motor and a couple 12 volt lights to the two batteries I have. It sounds like it oughta be dead simple. I just happen to be even simpler when it comes to such matters.

[Tylerdurden]

I really would prefer to avoid buying more gizmos if there is an easy way to wire a 24 volt motor and a couple 12 volt lights to the two batteries I have. It sounds like it oughta be dead simple. I just happen to be even simpler when it comes to such matters.

Just tap off one then. You will have to charge each battery separately and one will go bad before the other because of the imbalance.
A Dc to Dc down converter eliminates those issues and can be had surplus pretty cheap.

[JimD]

Just tap off one then. .

That easy? Good to know. I don't expect to be using either the lights or the trolling motor very much. This is for a small day boat that might get slept in occassionally, and has a gas outboard motor for power, using the trolling motor mainly as back up and to get in and out of the marina, perhaps.

[Ron Williamson]

Could Jim remedy the imbalance with a double throw toggle switch to tap from alternate batties?
R

[Tylerdurden]

Could Jim remedy the imbalance with a double throw toggle switch to tap from alternate batties?
R

Have to figure time and current draw, there are switching relays to do that but again complexity.

[raycon]

Buying pre-packaged look for LED's with drivers that take input voltages of 6-36VDC.
Buying a little more upfront translates to longer battery life. Same for the trolling motor.

[py]

Jim, I'm probly even dumber than you, and others will tell us why this idea is crap, but I'd have thought that maybe using some electrical one way valves, (diodes?), you could have the 12v charger coming into both batteries from the outboard, or solar panel or shore charger, or all 3, with the batteries wired alongside each other. Is that paralell? Take your 12v supply off one battery. Or maybe even have a couple of seperate 12v supplies, one off each battery. One for starting your outboard if its electric start, and one for "house" stuff. And then have a series connected circuit to power your trolling motor. Not really sure where you'd put the diodes, but that should be possible. Shouldn't it?

[emichaels]

JimD,
I can sympathize with you, I am going thru a lot of this thought right now. I am using Nigel Calder's book 'Boatowners Mechanical & Electrical Manual'

There is more in this book than I will need but he starts from the bottom and works up so you can get what you need and stop. It is a very good reference and teaching book. Good pictures and diagrams and very good explanation. He will give you several ways of doing what you want in your situation and give you the pros/cons of each system.

Eric

[JimD]

From what I have learned so far there are two accepted ways to tap 12 volt from a 24 volt battery bank. One is to have a DC converter hooked up in the series that coverts 24v to 12v. The 12v requirement is then hooked up to the converter. The other way is to tap the 12v from one of the batteries directly and hook up an 'equilizer' to the two batteries' positive terminals. The equilizer draws from the untapped battery and sends it to the tapped battery so that overall, both batteries get equally drawn from. This according to Nigel Calder in the book emichaels mentions and which I have been fortunate enough to borrow for an acquaintence.

Tylerdurden's suggestion to just tap one of the batteries without an equallizer is considered the 'wrong' way to go about it but it is probably the one I will use, since its only wrong because as he acknowleges, it drains the batteries unevenly and creates charging problems if you are charging the entire 24 v bank as a whole. Since I will be charging the batteries individually on a 12v charger on shore its not much of an issue in this case. It (mostly) just means the one battery will need replacing sooner. The battery will be used to power four or five light bulbs on a little boat that likely won't get much use at night anyway (White all around masthead light, port and starboard bowlights off a combination light that uses one bulb for both red and green, and two or three cabin lights which will be LED if I can stand them).

Also, I've found a local guy who is going to help me sort out practical stuff like what gage wire to use, where to scrounge a small, second hand switching panel with fuses, etc, which is the stuff I really need to get this little job done as Calder and other's don't seem to state in the sort of explicit terms that a diy job requires.

[Ken Hutchins]

JimD,
I can sympathize with you, I am going thru a lot of this thought right now. I am using Nigel Calder's book 'Boatowners Mechanical & Electrical Manual'

There is more in this book than I will need but he starts from the bottom and works up so you can get what you need and stop. It is a very good reference and teaching book. Good pictures and diagrams and very good explanation. He will give you several ways of doing what you want in your situation and give you the pros/cons of each system.

Eric


Ditto, an excellent book.

[Peter Eikenberry]

Nigel's book is one of the best there is on practical application of DC circuits. Most of the rest is strong on theory (even mine) but leaves you to sort out the details. I think you are headed in the right direction as long as you charge the batteries separately ashore.

Good luck

[boylesboats]

whatever you do.. Do Not Close The Circuit
I done that before at Johnson Control Battery plant, all 32 12V batteries in series, and Wham! Boom! Sizzles!... What a BIG smoking mess, acid went everwhere, all the cables are crispy fried, fume of melted plastic filled the air..

[JimD]

whatever you do.. Do Not Close The Circuit
I done that before at Johnson Control Battery plant, all 32 12V batteries in series, and Wham! Boom! Sizzles!... What a BIG smoking mess, acid went everwhere, all the cables are crispy fried, fume of melted plastic filled the air..

Yep, short cicuits are to be avoided.:D

[Kim Whitmyre]

So, there is no need to have grounding cables to a grounding strap with a setup like Jim is going to have? Mine will be similar, except no electric motor to run, and just 12V. Most books seem to assume an inboard engine as a ground. . .

[Peter Eikenberry]

On most inboard boats the ground is the engine block. On outboard powered boats the ground is also the engine block. Most outboards these days come with a pre-made wire bundle that plugs into the engine. One of the wires in the bundle is the ground wire.

Jim's setup is about as simple as it gets. Any simpler and he would be using oil lamps for running lights.

[Kim Whitmyre]

Most outboards these days come with a pre-made wire bundle that plugs into the engine. One of the wires in the bundle is the ground wire.

Jim's setup is about as simple as it gets. Any simpler and he would be using oil lamps for running lights.

That kind of gets to my point: what if the outboard is in the raised position? (which is where it is supposed to be on a sailboat :D ) Or what about those who don't even run outboards? I don't want to have any thruhulls for a grounding plate!

[JimD]

So, there is no need to have grounding cables to a grounding strap with a setup like Jim is going to have? Mine will be similar, except no electric motor to run, and just 12V. Most books seem to assume an inboard engine as a ground. . .

And this is exactly the sort of question that it is frustrating to try to find a suscinct answer to. One can pore through 500 pages of Calder without finding it. However...sometimes a quick phone call to a knowledgable marine dealer such as the guys at Sherwood Marine in Victoria (shameless plug because they have been very helpful) and the answer is - no, do not ground this system to anything but the neg terminal on the batteries. Do not run any special ground to the outboard or to seawater. Its unnecessary and may be harmful to the wooden hull which can end up conducting current. So my system will look like this: two 12 volt dc batteries in series to run a 24 volt trolling motor. One of the batteries will be tapped for the 12 volt lights. That battery will be wired to a fused switch panel with a fuse for each light (cabin, masthead, and bow running lights). The lights will be wired in parallel to the panel so each light has its own fuse in the panel and each draws a full 12 volts (less the minor transmission loss). To minimize transmisson loss the correct gauge wire will be determined once I measure the exact length of wire needed to run to the lights and the total wattage of the lights, ie four 25 watt lights = 100 total watts. I'm guessing this will probably call for 14 gauge wire but there is a standard look up table I will consult. The only other safety component will be an 'isolation switch' which is between the battery positive terminal and the panel. It is a main kill switch that shuts off power to the panel. At this point about the only serious short that could occur is if a very big conductor such as a wrench were laid directly accoss the battery connecting the two terminals which is pretty well impossible if the batteries are protected in a vented battery box which mine are.

As mentioned in an earlier post, ideally my system would have an equalizer or DC converter in the mix to prevent an unbalanced drain on the two batteries but that will have to wait for another day.

[Gary E]

One of the batteries will be tapped for the 12 volt lights. The battery will be wired to a fused switch panel with a fuse for each light (cabin, masthead, and bow running lights). The lights will be wired to the panel so each light has its own fuse in the panel. The correct gauge wire will be determined once I measure the exact length of wire needed to run to the lights and the total wattage of the lights, ie four 25 watt lights = 100 total watts. I'm guessing this will probably call for 14 gauge wire but there is a standard look up table I will consult. The only other safety component will be an 'isolation switch' which is between the battery positive terminal and the panel. It is a main kill switch that shuts off power to the panel. At this point about the only serious short that could occur is if a very big conductor such as a wrench were laid directly accoss the battery connecting the two terminals which is pretty well impossible if the batteries are protected in a vented battery box which mine are.


You should be fine with that setup... but...
You did not say how you will wire the return line from each lamp. The fuse and switch in a pannel in the hot wire to the lamp is fine...

Then take the return wire and connect it to a common terminal bar, much like a buss bar...where all the return wires are connected... From this buss bar, a heavier wire to the neg bat terminal.. No need to run a lot of wires all the way to the battery...

Your battery box lid and a disconnect switch is also good... you should have no trouble, but if you do, ask someone that knows what they are looking at to give you a hand...

Good Luck...

[JimD]

You should be fine with that setup... but...
You did not say how you will wire the return line from each lamp. The fuse and switch in a pannel in the hot wire to the lamp is fine...

Then take the return wire and connect it to a common terminal bar, much like a buss bar...where all the return wires are connected... From this buss bar, a heavier wire to the neg bat terminal.. No need to run a lot of wires all to the battery...

Your battery box lid and a disconnect switch is also good... you should have no trouble, but if you do, ask someone that knows what they are looking at to give you a hand...

Good Luck...

Gary, don't most panels these days just have the return terminal bar built in so all that is required is a single wire into the panel and a single wire out? I don't have the panel yet so I guess I'll find out soon enough.

[Gary E]

Yes, they do... the bar is there, you'l see it

Also, I dont know if this has been mentioned, but get a little tube of ... ... ....
ok, CRS has set in and I Cant Remember S... but it's like grease that you put on the terminals to keep the contact good... The place you buy the pannel will know what it is...

[Peter Eikenberry]

Jim, the guys you talked to are right. There is a school of thought that treats wood boats differently when grounding dc circuits. The belief is that any ground that connects the ground system to the water will promote a particular type of corrosion that occurs in the wood surrounding the metal fasteners (screws, boat nails etc) Even the Coast Guard agrees with this. Here is a quote from a Coast Guard pub on wood boats

In the USCG Wood Hull Inspection Guidance (NVIC 7-95), they say “In general, galvanic connections should be avoided in wooden vessels, unless they are made for a very good reason (like cathodic protection) and the consequences (like wood damage around protected metals) have been fully considered and mitigated (such as by painting the protected metals).

What that simply means is don't use the outboard as the ground and don't bind metal fittings in the hull. Bonding is connecting a wire to all underwater metal fittings to put them all at the same electricla potential.

Anyway, do what Gary said.

[JimD]

Peter I don't know how much any of this theory applies to a glass covered plywood trailer boat. Carvel hulls are conductors because the planking soaks up sea water. Not much of that going on with my boat.

[Peter Eikenberry]

It doesn't apply. The metal fittings aren't in direct contact with the water. From your previous posts I thought this was a strictly wooden boat.

[paladin]

Jim...I mailed you a drawing today.....shows how to connect the two batteries and use a double pole, double throw switch to get 12 volts for the cabin/running lights, and periodically flip the switch to the other side to balance the drain from the batteries...If you want I can draw another one to show how to use the same system to charge the batteries at 12 volts individually without removing them from their connections, just run a pair of wires to the charger....

as always, this message will self destruct in 24 hours and leave no visible traces to any and all misinformation in case you blow yourself up and your widow gets mad.:p

[JimD]

...as always, this message will self destruct in 24 hours and leave no visible traces to any and all misinformation in case you blow yourself up and your widow gets mad.:p

Chuck, she wouldn't get mad. She'd get even.;)

[lofting4fun]

My master electrician's licence is crying after reading the above posts. Its too complicated for me to give a electrical 101 class in short story form....if you would like I will draw up what you require including OVERCURRENT/OVERLOAD protection-Im on my way to Idaho then Utah for more trouble shooting projects this week,but will have it for you asap- I will include volt drop/wire calcs if you give me your load requirements inc ah of batteries//wattages Regards, James

[JimD]

My master electrician's licence is crying after reading the above posts. Its too complicated for me to give a electrical 101 class in short story form....if you would like I will draw up what you require including OVERCURRENT/OVERLOAD protection-Im on my way to Idaho then Utah for more trouble shooting projects this week,but will have it for you asap- I will include volt drop/wire calcs if you give me your load requirements inc ah of batteries//wattages Regards, James

James, sorry about the tears :D. I'll take all the help I can get and thank you in advance for yours. But I don't have the load requirements yet as I don't have the lights yet, or their distances from the battery. Can I Private Message you when I do?