LiPo Shim with non-LiPO NiMH Batteries

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1

Hi all,

I recently bought a LiPo SHIM for Pico.
I see that Pimoroni states that you should only use the SHIM with LiPo or LiIon batteries. But I’m new and stupid, and only paid attention to it after soldering it to my Pico.

So my question is:

  • can I use it with NiMH batteries?
  • Can I at least plug the battery to the SHIM just to consume the battery (and charge it with a separate charger)?
  • a more theoretic question, why should I only use the SHIM with specific types of batteries?
2

No, you shouldn’t use a LiPo charging circuit with NiMh batteries. Different battery chemistries need different kinds of chargers with specific safety cutoffs for that type of battery.

The data sheet for the charging chip we use on LiPo SHIM for Pico is here: https://cdn.shopify.com/s/files/1/0174/1800/files/MCP73831-Family-Data-Sheet-DS20001984H.pdf?v=1618417794

3

Even if not charging, this won’t work. The LiPo shim also has a overdischarge protection, which kicks in at about 2.8V. You would need at least three batteries in series to get above this threshold. And putting (any) rechargeable batteries in series has it’s own problems (e.g. one battery discharging into the second).

If you are technically interested you could head over to https://batteryuniversity.com. You will find there everything you need to know about batteries (primary cells and rechargeable cells).