I'm using an battery shield to recharge my battery. I want to use a solar panel, so I bought one (5V 240mA). I'm pretty sure, it won't recharge my battery fully, but that's not the point. I've assembled my board with my shield, soldered the solar panel together with an schottky-diode and put it on USB (since the shield allows charging via USB). All fine, I get some electric power in the sun - yeah!

But my Wemos D1 Mini only runs for say 2-3 minutes and than ... dead? Restarting works, but only lasts again 2-3 minutes. This only happens while the battery shield is charging via solar. I already tested using any USB charging (my computer) - this simply works.

Basically I rebuild the circuit like described on TheAustrian/Wemos-D1-Mini-BME280-Weather-Station but only one solar panel attached and using the Wemos D1 Mini Battery Shield instead of the TP4056.

Any hints what's going on? Why can't I run the board while charging via solar? Did I miss something?

  • 2
    I would hazard a guess that the solar panel needs to be big enough to both charge the battery and run the Wemos D1 at the same time. Lack of current will cause bad things to happen.
    – Majenko
    Commented Aug 6, 2020 at 12:48
  • @Majenko how can I be sure? What specs do I need to read? :-D Commented Aug 6, 2020 at 13:43

1 Answer 1


The TP4056 Module will output a max of 4.2V which is less than the 5V the Wemos D1 Mini is expecting on its 5V connection (Assuming you have connected the circuit as shown in the Github guide). When the solar panel is charging it's likely that the TP4056 is causing a driving issue on the supply of the Wemos causing it to potentially Brownout .

I would not connect the solar panel to the Wemos like this, I would have it connected to the battery then the battery connected to a 5V Step Up Power Converter like shown below (This reduces efficiency but give the MCU a stable supply),

enter image description here

My recommendation for the wiring,

enter image description here

  • 1
    Thank you for explaining, but as far as I can see, this the Wemos D1 battery shield does provide a boost converter (step-up converter?). But I also just noticed: it states 0.5A or max. 1A charging current. Maybe my problems lies in using one solar providing 0.25A? Commented Aug 6, 2020 at 13:36
  • As I stated in my question: I'm using the Wemos D1 battery shield instead the TP4056. Commented Aug 6, 2020 at 13:37
  • Sorry I should have re-read you question, okay so the module is getting 5V which is good. The symptoms still sound like the Wemos is browning out. It's very possible the solar panel is not generating enough current to power the regulator (You could get a multi-meter on the output to see what's going on under load). Is the battery completely drained, do you have a way to fully charge it and repeat the test? In theory the solar panel should only be charging the battery not directly driving the 5V regulator. Commented Aug 6, 2020 at 13:52
  • Yes I do have one. I'm new to electronics, so: where do I need to measure output? On the solar panel or output of the shield (a.k.a input of Wemos)? V or A? Commented Aug 6, 2020 at 14:04
  • I would measure the voltage cross the 5V connection on the Wemos module (So Wemos 5V to GND). Keep measuring it while the Wemos run & see if it changes when the Wemos crashes (The voltage will likely drop < 5V then potentially jump back up to 5V once the crash has occured and the current load has dropped). If the 5V supply is stable during the crash you may need to switch to measuring current (Amps A). So in line 5V as shown here - electronics-notes.com/articles/test-methods/meters/… Commented Aug 6, 2020 at 14:09

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