Charging 4 banks from 1 alternator?

[Davidhoy]

Let me preface this with the fact that I have a tremendous amount to learn about marine electrics! If my question or terminology are a little off, please help me to understand things better :-)

I have 4 banks of batteries on my boat - 4x deep cycle house batteries, 2x engine start batteries, 1x generator start battery, and 1x windlass/thruster battery. I'd like to have all four banks charge off the alternator when the engine is running. Firstly, is this realistic? If it is a reasonable thing to do, what is the best way to do this without lots of manual selector switches? I've been looking at battery combiners and isolators, they seems to do what I want. However, there do not seem to be any that take a single input and 4 outputs. Can I connect the alternator to two dual-output devices instead of a single quad? Or use a dual input, quad output version? Are there better ways to achieve what I want?

Regards,
David


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[barnakiel]

If all your banks accept the same charge voltage, you can use one alt.

I think this could lead to some banks getting under charged and others maybe overcharged - for banks are hardly ever in the same discharge state before charging starts.

In other scenarios you can either use varied regulators or else use various charge distributors.

b.

[skipmac]

Hi David,

If you spend a few minutes with the forum search functions on charging multiple banks, the 1-2-BOTH switch you will find hours of reading.

Short summary, my opinion and that of many experts and very experienced cruisers this is a simple, foolproof way to wire a boat.

1. All house batteries wired together in one large bank.

2. One good start battery isolated from the house banks and used only to start the engine.

3. ALL charging sources (alternator, solar, wind, battery charger) connected directly to the house battery bank.

4. Install an automatic battery combiner like the Yandina Combiner, Balmar Duocharge or Xantrex Echo Charge. This will connect the start battery to the charging system only when charging is happening. When the engine is off and the alternator is no longer charging (or the sun is down and solar not charging, etc) then the start battery is automatically disconnected so it will always be charged and ready to start the engine.

If the house batteries are the same brand or at least the exact same type and same age then they should charge and discharge equally.

[dlymn]

Bit pricey but will do the job
zero volt drop marine battery isolator

2 inputs means that if you add another 12v source (another alternator, wind power, solar power) you won't have to buy another isolator.
these unit mostly are big diodes that stop the batteries and also the inputs from interacting with each other.

If all of your batteries are identical, you can charge them all straight off the alternator. Just wire them in parallel. But a 60 ah alternator will take 3 1/2 hours of running to recharge 4 x 100 ah batteries from half charge. Will you run your motor this long every day? Things only go wrong when a cell drops out. Currently, I have a 2 in 3 out and a 1 in 3 out to manage 2 alternators and a wind generator.

Thinking ahead, You might be able to replace batteries with larger capacity ones (200 ah say) and this might reduce the number of batteries

[bvander]

Why two start batteries? Two engines?
Here is my tenatively solution. All 12v sources, altn, solar, wind into house bank. Have two isolators, I like the Blue Sea ACRs, one from house to start battery, second from House to Windlass.
For gen start battery use one of the outputs from battery charger when generator is running.

Alternate option is look at two alternators with one direct to start battery and a high amp one to house bank and windlass battery.

[Davidhoy]

Originally Posted by bvander

Why two start batteries? Two engines?
Here is my tenatively solution. All 12v sources, altn, solar, wind into house bank. Have two isolators, I like the Blue Sea ACRs, one from house to start battery, second from House to Windlass.
For gen start battery use one of the outputs from battery charger when generator is running.

Alternate option is look at two alternators with one direct to start battery and a high amp one to house bank and windlass battery.

I'm really not sure why there are two banked starter batteries for a single engine, seems odd to me too. But that's how the electrical system was set up when I bought the boat. I was planning on investigating this setup anyway, one thing at a time. The start bank of two is in a compartment under the companionway ladder, and the gen start battery is in the bottom of what looks like it should be a wet locker - very odd! I'm going to look at keeping both batteries under the companionway, but splitting them so one is for the engine, the other for the generator. One less battery to maintain is a good thing, no? Can anyone think of a good reason to have two banked start batteries?

I was looking at those Blue Seas ACRs online, they look pretty nice. Definitely worth considering. I don't have solar yet, but it's in the future plans, so taking that into consideration now is a good idea.

Question about leading all charging sources to the house bank first. Couldn't this lead to the start batteries not getting charged if the house bank is quite low? Or am I misunderstanding how charging works?

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[S/V Alchemy]

Originally Posted by skipmac

Hi David,

If you spend a few minutes with the forum search functions on charging multiple banks, the 1-2-BOTH switch you will find hours of reading.

Short summary, my opinion and that of many experts and very experienced cruisers this is a simple, foolproof way to wire a boat.

1. All house batteries wired together in one large bank.

2. One good start battery isolated from the house banks and used only to start the engine.

3. ALL charging sources (alternator, solar, wind, battery charger) connected directly to the house battery bank.

4. Install an automatic battery combiner like the Yandina Combiner, Balmar Duocharge or Xantrex Echo Charge. This will connect the start battery to the charging system only when charging is happening. When the engine is off and the alternator is no longer charging (or the sun is down and solar not charging, etc) then the start battery is automatically disconnected so it will always be charged and ready to start the engine.

If the house batteries are the same brand or at least the exact same type and same age then they should charge and discharge equally.

^^^This. All charging to your biggest bank. Biggest bank keeps the others, via EchoCharger or ACR (basically a one-way gate) topped up. Refinements include the ability to use the start bank (or others) to power the house loads through on-off isolation switches, and external regulation on the alternator to do "off the dock" equalizations of that house bank.

I found this an interesting article and my own setup resembles it, save that I have both positive and ground disconnects, a particularity with metal boats with floating DC grounds. A DC positive distribution buss - Ocean Navigator - January/February 2016

[S/V Alchemy]

Originally Posted by Davidhoy

Question about leading all charging sources to the house bank first. Couldn't this lead to the start batteries not getting charged if the house bank is quite low? Or am I misunderstanding how charging works?

No, you have that correct. But that's a different situation: if you are unable to charge your house bank adequately, you shouldn't be attempting to keep your start bank "downstream" charging. The ACR/EchoCharger have presets (which you can in some cases program/alter) to specifically prevent the house bank from "draining" in favour of the start. The idea is rather than the charging doesn't happen to the start bank unless the house bank is sufficiently charged itself. The other side of the coin is that if your house bank is close to 100%, and you're motoring, or it's sunny, that "excess" power is absorbed by the other batteries in the circuit and not just put to no use.

[Davidhoy]

Originally Posted by S/V Alchemy

No, you have that correct. But that's a different situation: if you are unable to charge your house bank adequately, you shouldn't be attempting to keep your start bank "downstream" charging. The ACR/EchoCharger have presets (which you can in some cases program/alter) to specifically prevent the house bank from "draining" in favour of the start. The idea is rather than the charging doesn't happen to the start bank unless the house bank is sufficiently charged itself. The other side of the coin is that if your house bank is close to 100%, and you're motoring, or it's sunny, that "excess" power is absorbed by the other batteries in the circuit and not just put to no use.

Can you help me understand why to prioritize charging the house bank over the engine start battery? I would imagine that the start battery would be more important, as if you can at least start the engine you will eventually be able to charge the rest. But if the start battery never gets charged due to the house being too low, and the engine shuts down (intentionally or otherwise) before the start battery gets its charge, you could be dead in the water. What am I missing in this scenario?

I'm learning a lot for you guys, thanks!!


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[Davidhoy]

Originally Posted by S/V Alchemy

I found this an interesting article and my own setup resembles it, save that I have both positive and ground disconnects, a particularity with metal boats with floating DC grounds. A DC positive distribution buss - Ocean Navigator - January/February 2016

Great article, thanks for sharing it! The diagrams in particular really help me to visualize what you and others have written. I created a PDF and saved it for later reference. For my purposes I can just add an ACR for each of the other two batteries, and I'll have a comprehensive chairing system for all my batteries. I also like that the author shows where to put the Ah shunt - I just bought a Blue Seas M2 SoC monitor, and now I have a better idea of how to install it.

Regards,
David


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[bvander]

Originally Posted by Davidhoy

Can you help me understand why to prioritize charging the house bank over the engine start battery? I would imagine that the start battery would be more important, as if you can at least start the engine you will eventually be able to charge the rest. But if the start battery never gets charged due to the house being too low, and the engine shuts down (intentionally or otherwise) before the start battery gets its charge, you could be dead in the water. What am I missing in this scenario?

I'm learning a lot for you guys, thanks!!


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If your start battery is isolated from everything except the engine circuit it has enough reserve power to start your engine 20/30 times. As well, it will not take much to top it up after it starts your engine, where as your house bank many times will take hours to top up. If you prioritized the start battery the regulator will quickly top off your start battery and then shift into absorb or float mode, thereby taking days to top up your house bank.

[Davidhoy]

Originally Posted by bvander

If your start battery is isolated from everything except the engine circuit it has enough reserve power to start your engine 20/30 times. As well, it will not take much to top it up after it starts your engine, where as your house bank many times will take hours to top up. If you prioritized the start battery the regulator will quickly top off your start battery and then shift into absorb or float mode, thereby taking days to top up your house bank.

👍👍👍


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[RaymondR]

Been through all the manual switching and automatic switching relay setups and sooner or later one comes to grief with them. The only really reliable way to do it is entirely separate the house and cranking systems and put two alternators on the engine, one for each. Probably the lowest cost in the long run.

[Davidhoy]

Originally Posted by RaymondR

Been through all the manual switching and automatic switching relay setups and sooner or later one comes to grief with them. The only really reliable way to do it is entirely separate the house and cranking systems and put two alternators on the engine, one for each. Probably the lowest cost in the long run.

Hi Raymond, can you elaborate on the issues you had? I prefer to learn from the mistakes of other ;-)


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[skipmac]

Originally Posted by bvander

If your start battery is isolated from everything except the engine circuit it has enough reserve power to start your engine 20/30 times. As well, it will not take much to top it up after it starts your engine, where as your house bank many times will take hours to top up. If you prioritized the start battery the regulator will quickly top off your start battery and then shift into absorb or float mode, thereby taking days to top up your house bank.

Exactly. Starting an engine might use 1/2 of an amp hour from the start battery. House loads like lights, electronics, fridge, etc could use 50-100-200 amp hours in a day, depending on your boat and systems. So obviously the house bank is the one needing the most charging.

Of course it's critical to keep the start battery good, hence isolating the start battery from all house loads and installing your preferred brand of auto combiner to keep it topped off.

By the way, the combiners mentioned here are very KISS devices and very reliable. As a final check monitor start battery voltage to make sure you're good.

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