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daifu avatar image
daifu asked

How to best wire up 2 battery banks and 4 charge sources?

Hi, I am trying to figure out to wire up two battery banks (house batteries, and starter battery) with multiple charging sources in my boat and getting confused about how the charge sources work out what to do and when to connect/isolate the batteries to avoid discharging.

I only have mains and alternator charging at the moment and am looking to add an MPPT solar charge controller, then later a wind charger.

Is this a typical setup?

Any help/guidance much appreciated.


Existing set up

Mains: Currently the battery banks are normally isolated and the mains charger has two separate outputs for each bank.

Alternator: It looks like there is a relay that connect the starter and house batteries when the engine is running.

Target setup

1. Mains charger when on shore power

2. Alternator charging when engine is running

3. Solar power during the day/no wind

4. Wind power when there is more wind than sun.





battery charging
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4 Answers
ludo avatar image
ludo answered ·

Normally all chargers have protection against backward current, so everything should work fine. You can check all sources with a dc-clamp ampère meter, of you really have current flowing the wrong way try putting a diode in the wiring.

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christern avatar image
christern answered ·

Usually you put charging from solar panels and wind on the house bank since the starter battery is only used for starting and maybe equipment that is used only when enginge is running. This assumes that the relay that connects the house bank is working correctly which it seems when reading your post.

It is always a good idea to have an ampere clamp meter onboard. (Make sure it can read DC if you buy one.) With that you can see i.e. if there is any draw from the starter battery that shouldn't be.

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daifu avatar image
daifu answered ·

Thanks both for the tip on a clamp-on dc ammeter - will definitely get one of those.

Its sounds like the best approach is to build up the system in steps and check its not discharging at any time - something like:

  1. Add solar charging for house batteries only
  2. Add a house-to-starter relay for when there is enough solar charge voltage available (the existing one only appears to 'connect' when the engine is running)
  3. Add a wind charger to house batteries (which would also charge the starter battery if there is enough charge voltage)


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christern avatar image christern commented ·

Skip the house-to-starterbattery relay. The starter battery lives a ”quiet life” if not used for other purposes than starting (=misused) and wouldn’t need any charging. You may also get some strange results if you have one relay connecting starter battery to house battery and at the same time have another relay working in the opposite direction. This last thing is, I admit, just a guess ;-).

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Kevin Windrem avatar image
Kevin Windrem answered ·

A DC-DC charger is the best way to interconnect battery banks. These generally work in one direction only. So in your system you'd connect it so the alternator/starter battery would charge the house battery.

If you needed the house battery and all it's charging sources to charge the starter battery, you' connect the DC-DC charger in the other direction.

If you needed both, you'd need two DC-DC chargers wired in opposite directions and interlocked so they both could not activate at the same timer. You could also use a bi-directional DC-DC charger.

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