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Thread: 65 amp alternator...

  1. #1
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    Default 65 amp alternator...

    What amp/hour cranking battery?

    Could be short use of engine, could be long 100 mile stretches.

    Thoughts?

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    Default Re: 65 amp alternator...

    Lead acid batteries are usually charged with an amperage of 10-30% the rated Ah, depending on how they are buildt (open/closed, gel, AGM, flooded). Alternators are chosen according to total systems load, meaning all consumers plus battery charging. Example: normal load of the vessel with everything on (lights, instruments, fridge, etc.) is 20A. When you start the engine the alternator has to supply 20A for the boat and 45A are free to charge the battery. If the battery is full before you start the engine the alternator only has to supply full rated power for a short time before the battery can not accept the load anymore and then the amps are gradually reduced until the charghing profile is in "float", and the alternator puts out the 20A for the boat and another amp for the battery. That is how automobile systems work and for what most alternators are buildt. Car alternators are not buildt to provide rated duty continuously, they would overheat and the magic smoke escapes. Temperature rise is significantly faster in enclosed hot spaces like a sailboat "engine room".
    So the question is not what Ah starting battery because a 65A alternator is sufficient to charge any reasonable starting battery you chose. After all a starting motor has around 800W and you use it for 10 seconds. The problems begin when you have big consumers beside the starting battery. This is why you see big alternators on modern cars. Trying to charge a big housebank, electric winches, etc. all add to the load.

    Best system I have seen had a small alternator sized for charging the starting battery only on a completley separate circuit and a big brushless one driven by a shaft that got switched on to charge the big housebank and provide power for winches.

  3. #3
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    Default Re: 65 amp alternator...

    Thanks for that Rumars.

    My intention is to just source cranking batteries first, i am a way off from designing the entire electric system. I thought as a minimum a ratio of 5:1 or 3:1 was the rule of thumb, meaning my minimum AH battery should be around 200.

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    Default Re: 65 amp alternator...

    You can choose whatever capacity you like. The regulator will match the two and taper off the current. Problems only appear when trying to charge a big bank with a small alternator because it keeps it at rated duty for to long and it overheats if the regulator has no temp probe.

    Just as a thread drift since you are still in the planing phases. I am a proponent of the 1 battery (bank) system, meaning no separate starting battery. Redundancy is best served by installing an aditional spring starter. That way you have true black start ability and a house bank will power the electric starters just fine.

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    Default Re: 65 amp alternator...

    Just adding to the good info already given: its important to note at which engine rpm the alternator produces its rated output. Some need to be revving pretty high; others develop full output sooner. The alternator maker ( engine maker if it is an OEM alternator) should be able to provide you with a chart showing rpm versus amps out.

    Kevin
    There are two kinds of boaters: those who have run aground, and those who lie about it.

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    Default Re: 65 amp alternator...

    Thanks all. I understand now. I have Calders book, but it is akin to reading all of Moby Dick when all you want to find out is which fishing bait to use.

    I would indeed like to have some sort of hand / spring start eventually, but for now i am trying to run up 2 rebuilt engines for the first time. They were fitted with hydraulic starters and 24v alternators, now gone in favor of 12v starters and alts.

    Cheers...

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    Default Re: 65 amp alternator...

    I hope you still have the hydraulic starters, they can be configured for black start with the help of an accumulator vessel and a hand pump. You only need to find bellhousings with starter mounting brackets, or modify the existing ones. It's a more complicated system than spring starters, but it allows for greater mounting flexibility.

    24V is a much better voltage for a bigger boat, I would always choose if over 12V. You can keep the electric starters you have, they will also function on 24V. All electronics are normally multi voltage capable, and lights (including LED) and the rest is available in 24V. If you do find something that is 12V only a small DC to DC converter is cheap.

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    Default Re: 65 amp alternator...

    I do indeed have the hydraulic starters, along with accumulators, reservoir tanks, pressure gauges, release pedals, belt driven pumps, hand pumps and 20 ish feet of hose. It's a lot of ugly cumbersome gubbins, although I appreciate it's usefulness. The engines were from rig lifeboats; I have managed to source 12V starters for the existing bell housings. Spring starters are so much more compact.

    Thanks you all for your help, and standby for more stupid questions.

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    Default Re: 65 amp alternator...

    Good for you. What engines are we talking about? Some lifeboats are fitted with dual starting, electric and manual. Usually one of the starters is fitted on the engine block side, the other on the bell housing over the transmission (it's mounted and rotates the other way around). Simplest way to do that is finding a bellhousing with both holes present. I agree that spring starters are more compact and more reliable, but they have a big disadvantage, you have to be able to reach them for winding. If you can do that great, if it's complicated then you could simplify the hydraulic system by ditching the belt driven pumps and keep it only as an emergency hand pumped system. One pump, reservoir and accumulator to serve both engines with a switch valve. After all if one engine runs you usually have electricity for startig the other, or time to pump by hand.
    I really do advise to go for 24V in the final system. For now just make sure the alternator fan is rotating the right way (if it has angled vanes) and that the gearing is appropiate.

  10. #10
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    Default Re: 65 amp alternator...

    Engines are Westerbeke 40's (Perkins 4108's) with Paragon gearboxes.

    They looked like this...

    IMG_2145.JPG

    IMG_2147.jpg

    Now they look like this, except now they have their Bowmans fitted.

    IMG_20190124_220006_1.jpg

    IMG_20190124_215414_0.jpg

    port shiney 2.jpg

    Here's my build thread...http://forum.woodenboat.com/showthre...erring-Drifter

    I am dealing with the water cooling system and electrics now, with a view to first run up...

    I have so far sourced my navionics, nav lights, house lights and a few other things as 12 volt, but I imagine I am not so far gone not to be able to use 24v. As you say, many items are multi voltage capable. I have gone 12V largely because of worldwide availability and interchangeability with vehicle components.

    I know that 24 volt motors are by default smaller than like for like (hp) 12 volt motors, but what other advantages does 24 volt have?

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    Default Re: 65 amp alternator...

    Nice engines, and probably lightly used, they will serve you well.

    24V has one big advantage, half the amps on the same load. That means less voltage drop, thinner (and cheaper) wires, and an overall more robust system. Inverters function better on higher voltage, especially high power ones. Battery life is also better (lead acid) because of the reduced amps. Basicly everything that's high power is happy. You still source most of the stuff from vehicle components, but it's from the heavy trucks, commercial sector.

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    Default Re: 65 amp alternator...

    Good info, thanks Rumars.

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    Default Re: 65 amp alternator...

    Quote Originally Posted by lupussonic View Post
    My intention is to just source cranking batteries first, i am a way off from designing the entire electric system. I thought as a minimum a ratio of 5:1 or 3:1 was the rule of thumb, meaning my minimum AH battery should be around 200.
    I always thought the important thing about a crank battery is less the amp hours and more the Cold Cranking Amps (CCA). Your donk will need a minimum kick to turn it over sufficiently.
    Philip K. Dick 'Reality is that which, when you stop believing in it, doesn't go away'.

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    Default Re: 65 amp alternator...

    This is the one you want - big bubbles, no troubles ! Proven in service, tales a lickin' but keeps on tickin' !

    http://www.delcoremy.com/Alternators...el-Family/50DN

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    Default Re: 65 amp alternator...

    ^ begs the question; whats the difference between a generator and an alternator?
    Philip K. Dick 'Reality is that which, when you stop believing in it, doesn't go away'.

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    Default Re: 65 amp alternator...

    In automotive language "generator" designates the older type of electricity generating machine, one were the rectification of the alternating current is done by a mechanical comutator instead of a diode bridge.

    As for the CCA's in theory you are right, in practice it's more complicated. Batteries hold a finite amount of energy, and are limited by chemistry and physical construction in how they can give it up. Depending on these two factors a battery needs a certain capacity in order to be able to generate a certain amount of CCA. For example a flooded lead acid battery will need more overall capacity to generate the same amount of CCA as a smaller AGM, even if both are thin plate starting batteries. Significant differences also exist between the different lithium chemistries.
    To all this there are also standards regarding reserve capacity of starting batteries, meaning the number of minutes it can sustain a 25A discharge.
    This is all more or less irrelevant to sailing vessels for the following reasons: battery bank size is usually dictated by the expected hotel loads. Any deep cycle battery sized for modern electrical necesities is fully capable of starting the small motors sailboats employ, even if they are solar storage FLA. Using a separate starting battery is just an anachronism. Some racing rules require one, so the practice will live on.

  17. #17
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    Default Re: 65 amp alternator...

    'Hotel loads' I've learned a new term today!
    Thanks Rumars for a good explanation.
    There is nothing quite as permanent as a good temporary repair.

  18. #18
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    Default Re: 65 amp alternator...

    Yes, same for me.
    Great info Rumars! Thanks mate.
    Philip K. Dick 'Reality is that which, when you stop believing in it, doesn't go away'.

  19. #19
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    Default Re: 65 amp alternator...

    There's still a good case for a separate starting battery/ies, being as the house batteries will need careful monitoring to ensure you retain enough power to start the engine/s. Obviously back up Hydraulic/spring starters will help negate this, but back up starters are rare as hens teeth, and with a twin engine installation, really not worth the effort.
    True deep cycle batteries may start an engine if the bank is big enough, but a start battery gives the high CCA needed for starting and are relatively small and light, making them easy to place near the engine.

    Back to the original question of what A/H battery. If it were my system I would go for a standard starting battery around 1000CCA (land rover size), one for each engine, with a switched link wire to enable starting of either engine from either battery.
    I would also have (money no object) second alternators for the house bank, (split chargers are a cheaper alternative) allowing the house bank to do just do the house duties, I suspect your house bank needs will be less than ours (used to run the washing machine and central heating off the inverter).
    12V vs 24V - as already mentioned 24v reduces cable sizes but with the new 12v LED lights and their reduced current needs, makes it less of an issue.
    Bilge pumps and anchor winches are where the careful attention to cable sizes will be required.
    Avoid dual purpose batteries (leisure batteries) we chewed through a few of them very quickly (supposedly the best available at the time) until I got Rolls Surrete for the house bank.
    All the above applies to conventional lead based batteries, Lithium based systems are completely different. I would seriously be looking at a Lithium based system if I was going to do a new installation

  20. #20
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    Default Re: 65 amp alternator...

    The starter battery on my old furgy tractor is 120amp, however, i have managed to start it with a 55amp battery without any issues; the bigger capacity is usefull if you have an engine that cranks a lot before it actually fires, but that old Perkins is an instant starter hot or cold.
    A small dedicated starter battery is easier to keep topped fully charged. Going down this route myself, i will probably have a 2 battery system, with a domestic battery of around 180-200amps. Given todays LED lighting, consumption is a lot lower than in the past, when running a 25watt tricolour masthead light would have me arranging the 15watt solar panel throughout the next day to replace the used amps.

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    Default Re: 65 amp alternator...

    I am fully avare that my opinion regarding starting batteries is and will not become mainstream, and I am OK with that. 24V is a question of installed consumers and boat size. Someone having only some LED lights, a few instruments and a VHF has no problem with 12V. Someone having electric winches, bowthruster, fridge, freezer, and a bunch of other electric things is better served with 24V, especially in a boat over 40 feet.
    Regarding the capacity of deep cycle FLA batteries to start engines, it's simple. The expected load for a 1,7L diesel will be in the region of 500A for half a second followed by 2-300A for 2-3 seconds until it starts (amps given for 12V starter). This you can measure with a clamp on type ampmeter if you want to know the exact numbers for your specific engine. A 400Ah deep cycle battery will start the engine if it's not under 80% SOC.

    For boats with small house bank sizes (racer/cruiser, 100Ah) instead of going to the expense and complications of a separate starter one can buy a lithium boost pack. It can sit happy at 50% SOC for a year or more, provides USB sockets for charghing phones, some have integrated flashlights and is a portable power pack for the dinghy.

    The term "hotel load" is used in the ship business, sailors usually say "house loads". It is seldom for a sailboat installation to have backup power for instruments (or for them to run on a complete separate system), so I suppose "house loads" is the better term. But I am happy to hear that you found my postings usefull, I thank you for that.

  22. #22
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    Default Re: 65 amp alternator...

    Quote Originally Posted by artif View Post
    used to run the washing machine and central heating off the inverter
    Class!

    I think the most power hungry thing I'll be running off the house bank will be a radar in due course.

    Any advantage to wiring all the navionics to a third bank?

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    Default Re: 65 amp alternator...

    Quote Originally Posted by lupussonic View Post
    Any advantage to wiring all the navionics to a third bank?
    Redundancy the dreaded word. Making sure the freezer and TV does not let you without radar. Of course if the nav department is by far the biggest load it makes no sense to efectivly back up the cabin lights.

  24. #24
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    Default Re: 65 amp alternator...

    Typical politician answer.......... It depends

    Assuming you'll be living on board off grid (weekender/ shorepower hook up will change the requirements)
    In your case, its primarily a sailing boat, running the navionics of the house bank is probably preferable

    Apologies if you know this already
    For the alternator size you, need to work out the expected power consumption, lights, heating, pumps, nav gear, inverter, laptop, phone charger etc etc We found the fridge was the biggest consumer of power on board (domestic triple A rated as well)
    Next decide how long you want between charging e.g. one day or one week.
    You now have a figure that will indicate your battery bank size (for lead batteries I always multiply by 3, to help with battery life i use a maximum depth of discharge of 33%), which will give you a guide to your required alternator/charger size.
    Engine/Genset will be the primary method of charging , solar and wind are supplementary (if living aboard in the UK, unless you are very frugal with power use). Think of Solar and wind as range extenders (In the UK, before all the tropical dwelling forumites jump on this).
    You'll now realise you need a bigger boat for the all the batteries and a 100KVA genset

    Quote Originally Posted by lupussonic View Post
    Class!

    I think the most power hungry thing I'll be running off the house bank will be a radar in due course.

    Any advantage to wiring all the navionics to a third bank?

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