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I'm working on a solar powered project which requires two voltage levels - 3.2v-4v @ 2A for one element an 6v-12v @ 500mA for another.

My initial plan was to use a 12v lead acid battery with a solar panel and a charge controller. I would then regulate the voltages. However, the size and weight of lead acid batteries is a bit of a concern for this particular project and so I looked into using a lithium battery. The problem I had with this was that I could only find solar charge controllers for 3.7v lithium batteries, nothing for higher voltage lithium batteries (no decent ones at least).

I came up with the idea of using two 3.7v lithium charge controllers. I could then use one of them to power the 3.2-4v element while also using them in series to power the 6-12v element. Of course the overall Ah rating would be the lowest of the two and they would discharge at different rates. I'm wondering if this is still a feasible solution though. I've added a block diagram of my idea below. I'm open to other suggestions too.enter image description here

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  • \$\begingroup\$ I think the main thing to look out for would be the possibility that one battery discharges before the other. Have you looked at whether you can use other modules? e.g. can you use a "non-solar" charge controller? \$\endgroup\$ – user253751 Jan 9 at 1:56
  • \$\begingroup\$ It’s not an unfeasible solution. If there’s enough solar power that the cells never run flat then it could be a good solution, but if they might run flat you’d need to satisfy yourself that the resulting condition would be acceptable (one or other cells flat, or both). \$\endgroup\$ – Frog Jan 9 at 3:46
  • \$\begingroup\$ @user253751 Unfortunately it's for an installation away from any sort of mains power which means it has to be solar really. The 3.7V batteries aren't too expensive either so I can get some with fairly high Ah ratings as well. \$\endgroup\$ – zt42 Jan 9 at 10:47
  • \$\begingroup\$ @Frog I can get 3.7V batteries with fairly high Ah ratings and solar panels which are able to charge at the maximum rate the system can handle. Besides, the application is not too power hungry anyway. It would also save me having to use regulators and save me a lot of space and weight. \$\endgroup\$ – zt42 Jan 9 at 10:51
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    \$\begingroup\$ Not a great idea. Better to map out the current required from each supply, (add that info to the question!) and supply the lower current load from a buck or boost convertor, and choosing the right battery voltage for the higher power load (and capacity to run both of course!). \$\endgroup\$ – user_1818839 Jan 9 at 14:13

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