On my boat I've got devices that run on 24V and others that run on 12V. Seeing as how the alternator, wind generator and solar panels are all generating 24V, I guess it's fair to say that this is mainly a 24V system.

I have built 3 80AH 24V batteries using LiFePo4 38120 cells, each has its own BMS and these are working just fine. What do I do about the 12V devices though?

The obvious answer is to use the readily available buck converters, and I am OK with that for most of the 12V requirements (such as instrument displays). However, I also have a number of bilge pumps that run off 12V and I am not so comfortable with relying on a converter for these. I would much rather have a 12V battery store running these, to give me a greater safety margin compared with the immediate failure of a broken buck converter.

Before I switched to Li-Ion batteries, I had lead acid batteries. With 2 batteries in series, I could charge them using the 24V source(s) and then just tap off from one of them to give me the 12V I need for the bilge pumps. Included in this setup was a battery balancer that kept both batteries balanced, even though I was drawing power from just one of the 12V batteries. This is an off-the-shelf bit of kit that is widely used in transport applications where additional batteries are used, trucks etc.

Due to the different charge characteristics of Li-Ion vs. lead acid batteries, I don't believe this type of balancer will be suitable to balance Li-Ion batteries since it relies on being able to detect different voltage levels between the 2 batteries in order to do its balancing and Li-Ion maintain full voltage until pretty much empty.

So to my question...

Is there any smart way of performing a similar balancing act between my LiFePo4 batteries?


  • \$\begingroup\$ The smartest way would be to replace the bilge pumps rated for 24V. \$\endgroup\$ – Ale..chenski Nov 2 '18 at 3:48
  • \$\begingroup\$ Yep, I'd already considered that, but it will cost a fair bit of money to purchase 3 large 24V pumps, and I was/still am curious as to whether there is an electronic solution. Judging by the lack of responses, I'm tending to think that there is no simple electronic solution. \$\endgroup\$ – NomadAU Nov 4 '18 at 23:44

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