I am trying to find out if I can run a badger from 2 coin cells (CR2032) in series. The spec sheet says max input voltage is 6V which I am not sure is enough for fresh cells.
Do you think it is possible to run a badger from these batteries without damaging it? Do you think you can have decent run times with changing the display maybe just a few times a week?
I would like to mount it as a nameplate on my office closet and AAA Batteries would make it much too thick, Lipos I do not want to leave unattended.
I could of course just refresh the display and leave it there unplugged but I thought it might be cool to be able to leave a message activated by button press or have some sort of time scheduled content.
Coin cells are not built for high loads. And although the badger2040 draws “only” about 30mA during screen update (for roughly 7 seconds, depending on what you do), this is not the target use-case for coin-cells. The nominal capacity will be much lower on these loads and they will degrade faster.
I wouldn’t worry about voltage. These coin cells are used for LEDs, and this works because the voltage drops on typical LED loads to something below 2V.
I have run the Badger 2040 W with one CR2032, just updating the screen, for example scrolling the menu, loading the badge app etc. works ok, but if I try to run something that uses the WiFi it browns out, measured the battery and it drops to 1.7v, so there is a possibility that 2 cells might do the trick. For the W version connecting them in series would go over the the max voltage, but parallel, or just using a thicker cell might fix the brown out problem. Going with the smallest pouch LiPo would be the best of course, one of those 50-150mA that are usually used on bluetooth in-ear headphones.
Connecting them in parallel would keep you in the input limits but give you a better C rating, of course you would get the same results from a larger cell, but I suspect you want to keep it as compact as possible.
PicoW VSYS is rated up to 5.5V. I would not expect that two coin-cells in series would be even near that value. You will always have a voltage drop and find yourself below that threshold.
You could try this with a normal PicoW (less risk). And the PicoW is robust … I once made an error and operated it with 6.5V for quite some time without any visible impact. But I would not repeat this.
yes, 3V nominal, but as soon as you have load, you won’t be near that. Like Oscar already stated, he had 1.7V. So two times 3V is 6V nominal, but in reality you won’t be out of spec.
That is also why battery-testers have a special mode for coin cells - just measuring the voltage like on normal cells is not enough.
Note that voltage-drops under load is absolutely normal for every power suppy. The specific amount depends on your supply, and we are talking here about coin-cells which have a nominal continuous power-delivery of 0.2mA.