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I'm looking for a way to be able to connect a Solar Panel (5.5 V / 540 mA) and a Water turbine generator (3.3 V / 120 mA) together to charge a LiPo Battery of 4,000 mAh.

While using the solar panel alone, the LiPo Rider Pro from SeeedStudio did the job, and I was powering my Arduino MKR WAN 1310 without any problem. Now I want to add the water turbine generator to charge the battery as well, but it doesn't output the same voltage.

How would I go about this?

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2 Answers 2

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You have three separate things to accomplish here:

  1. Solar panel MPPT
  2. Combining sources with different voltages
  3. Battery charging

There are plenty of ICs out there that charge batteries from solar panels but none to my knowledge that allow you to simultaneously draw charging power from another source. There are a few ICs that will let you combine two sources with widely differing voltages - they are essentially paired boost converters feeding a common output bus - I think your best bet is to perform each step with its own IC, most of the highly integrated ones are DFN/QFN/BGA packages that are difficult for (I assume) hobbyists to work with anyway. The "combining sources" is going to be the hard part since they are not designed to be paralleled - each source doesn't "know" how much the other is providing and how much it should supply to the load and, in the case of the solar panel and maybe also the hydraulic generator, the power input is highly variable. You could try one of the dual-converter chips out there but it might be easier to have two separate batteries with their own charging circuits (that can also supply a connected load) and simply diode-or them into your Arduino.

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  • \$\begingroup\$ So essentially if I understand correctly, I can charge 1 battery using the solar charger and another battery using the water turbine, then plug them in parallel to the arduino (with each battery having a diode before the connection node)? And do the batteries need to have the same capacity (4,000mAh) or not since there are diodes? \$\endgroup\$ Commented Nov 19, 2023 at 15:53
  • \$\begingroup\$ They do not need to have the same capacity. There are somewhat more sophisticated systems than diodes for managing current draw from two sources of roughly (a few hundred mV) the same voltage that you could use here as well. \$\endgroup\$
    – vir
    Commented Nov 19, 2023 at 15:55
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FYI, we ended up using SeeedStudio's LiPo Rider Pro. We connected the solar panel to the "Solar 5V Adapter" JST connector and the water turbine to the micro USB port (with a 5V voltage step up/step down regulator in-between because this input only supports 5V).

We obviously cut a USB cable to connect its positive and negative cables to the output of the voltage regulator. After running some tests, it looks like this setup is working as expected.

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