Battery max voltage charging

WisBlock
1

When does the 19007 stop charging when connected to solar? I’m testing different panels and can’t tell if it’s not getting enough light or the unit is just doing maintenance charging. Here the ramp up was USB then I added 1 small panel, then another small panel and the voltage has remained flat.
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This node has a much more powerful solar panel and the voltage has been dropping as if it’s moving down to some max charge level.
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Would be great to know what the max and min the unit will run and charge via solar. Docs say 3.3 to 4.2 but doesn’t seem like it wants to charge above 3.9 ish. Also, these are both on 18650s without a BMS – going to install a BMS soon though.

2

RAK19007 has TP4054. Max voltage is 4.2V so it should go above the 3.9v you have in your graph. Lower cutoff is 2.9V which it will go to trickle charging to slowly rampup the voltage to safe level before charging.

It might be best to check the actual voltage on Vbatt. It can be that there some issue panel input voltage (might be low) or some issue on the ADC reading.

3

Is the TP4054 what the solar goes through as well?

I have a USB voltage tester so I can check what the big panel is putting out tomorrow. Odd that the smaller panel didn’t seem to change at all when wiring another up to it. I’ll break out the multimeter for that one and see what’s up. Thanks for the insight.

4

Yes. Solar panel connector of RAK19007 goes to TP4054.

5

Is there any advantage to using a battery management unit on an 18650 considering the 19007 has that chip? Or is something like this redundant Amazon.com: ACEIRMC 12pcs 1S 3.7V 4A 18650 Charger PCB BMS Protection Board for Li-ion Lithium Battery Cell : Electronics

Also, is there any difference in using the usbc to charge via a solar panel as opposed to the JST? I read the telemetry gives you battery voltage instead of charging voltage but not really seeing a difference in the data.

6

The link you shared in a protection board, it doesn’t facilitate charging but it protects the battery on shortcircuit, undervoltage, etc. It can help as added protection.

USB and Solar Panel goes to the same charging IC. If it provides stable 5V and rated charging current, it wont have any difference.

7

okay great, that’s good to know.

Is there a minimum threshold of voltage or current for the TP4054 to start charging?

Side question, would something like the RAK16000 allow telemetry/logging of the solar charging voltage?

8

If you go below 2.9V, it will go to trickle charging mode. This will allow the voltage to go up to safe level before it starts to follow the standard CC-CV charging profile.

You can probably use RAK16000 since it has INA219 which is supported by Meshtastic.