Rev. 2 - LiPo Current Testing and Questions

A project log for CRAPi2040

Chris' Really Awful Pi: so bad, it's good

chrisChris 08/16/2023 at 16:200 Comments

Just a quick log today.  The last log had me checking my biggest "creeped" feature, as it were: the LiPo Charger.

I bought a less sketchy LiPo cell and borrowed a suitably accurate clamp meter from a friend.

Don't let labeling on the meter fool you! The firmware on the meter had been reconfigured to measure 6000 counts rather than 2000. Considering that the charging IC was configured for 100 mA charge rate I would call this a win!

This setup is also convenient for power draw measuring too. Sitting idle with an install of CircuitPython and with the R, G and B LEDs turned on, current draw measured anywhere from ~25 mA to ~35 mA, which seems to be in the ball park for the RP2040. Eventually I would like some more power logging / bench marking.

I also wanted to look into an issue that I mentioned in my last log. 

For some reason, if you unplug the USB cable while charging the battery, and then try to immediately plug it back in, the charger does not respond: no indicator light and no current flow. If I wait for a while, running off battery power (so no power cycle) and try plugging in the USB again, then it will charge as normal.  

I know that these chargers can normally have some sort of hysteresis but  1+ minute seems a little strange. I am wondering if the Schottky is messing with the LiPo charger some how... maybe I should investigate a more graceful switching option for Rev. 3 of the board.

If anyone has any ideas for this issue I would love to hear your input!