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I have two seperate solar panels with exact same circuitry connections. This is what I have:

Solar panel -> Sparkfun Buck boost converter (set on 5v) -> TP4056 -> single 18650 AND + and - Power out cables ready for connection (which I'll connect to LM2596 in a way I explain below).

I want to power my board that needs 5v 1-2amp (varies) for as long as possible. My 18650 batteries are 5000mah each.

So I'm going to connect both positive OUTs from TP4056 pins combined together to LM2596 switching voltage regulator and two negative pins from two of my TP4056s to negative IN on LM2596 and set the output voltage of LM2596 to 5V. LM2596 support up to 3A which is great and more than what I need.

Do you see any problems with my board/method? My board will be outside all day, during daytime I think my board will mostly consume the direct solar power and during night it will use power form 2x5000mah 18650 batteries.

If you see inefficiencies, problems, things I can add to improve safety and power efficiency, please share them with me. Thank you

P.S. Each of my solar panels are 6V 1A 6W panels

TLDR:

2xPanel -> 2xBuck Boost -> 2xTP4056 -> 2x18650 5000mah batteries

Outs of 2xTP4096 combined together will be connected to LM2596 and then to my 5V 1-2A board.

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Whenever you parallel supplies, problems arise from the voltages being slightly different. With a high impedance source that can supply amps, even a few hundred uV can create large currents.

The other problem is the converters themselves, they need to be parallelizable (usually by sharing the same clock or some other synchronization method).

So if possible, use only on TP4056 (if it can support two 5000mah batteries in parallel (with a balancer)

Other methods of load sharing are parallel diodes, which are not recommended because of losses.

You might be able to use a circuit like this, although I'd still put 10mΩ resistors on the outputs of Q109B and Q110B to isolate the DC DC ripple, or maybe an LC filter on the inputs of this circuit. Then measure the ripple and check the TPS4056's to make sure there are no problems with synchronization (if one pushes while the other pulls then they start to fight each other, you need to increase the source impedance between sharing the modules at the switching frequency of the TPS4056)

enter image description here Source: Parallel Power Supplies with Ideal Diodes

Or a load sharing IC

enter image description here

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  • \$\begingroup\$ Thanks for the explanation, LTC4370 seems like a great idea. TP4056 doesn't support two batteries. That being said, I have a question, I thought Buck boost converter always have a smooth and constant 5V out. So I thought combining two always 5V outs of TP4056 will not have problem. Same with LM2596, I thought also that will have a smooth 5V out. Apparently I was wrong \$\endgroup\$ – AltoidsCin Jul 14 '19 at 12:59
  • \$\begingroup\$ Question, with LTC4370, I can have two slightly different 3.7V - 4.2V inputs and have static 5V DC out? If that's the case I can definitely add that to my board \$\endgroup\$ – AltoidsCin Jul 14 '19 at 13:14

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