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.
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.
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.
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.
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.
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.
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.
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.
Sorry, I’m new to electronics fiddling. Guessing that the battery will charge up to the input voltage of the solar? E.g. if my DIY panels can only supply 3.5V the battery will discharge down to that then level out at 3.5V. Is this conceptually correct?
No it wont. You need to reach the input voltage requirement of the charger IC TP4054. For RAK19007, optimal value would be 5.0 to 5.5V with considering some small forward voltage drop on the diode.
Okay starting to figure this out a little more. Two more questions
1.Is there a minimum mA for it to charge? My bare panels put out 5-6 V so should be good there. The mA depends on the amount of light.
2. Does the charging have some sort of threshold before it kicks on? Looks like it didn’t really charge until it dropped very close to 4V yesterday then the other 5W USBC panel it charged very swiftly. (different panel from the first question)
There is no minimum. As long as the voltage requirement is met and you have sufficient current, it will get the current it needs.
There is a 100-200mV hysteresis. So what you see is ok. It will recharge again somewhere on that range. Since 4.2V is the max voltage, it will recharge in between 4.0v-4.1v, without that feature, it will oscillate.
Ah okay, this is making sense now. So what I’m seeing basically is that the solar panel is probably overkill in these current conditions for keeping the single 18650 charged. Appreciate all of your help!
