NiMH or Lithium?


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robert.rozee
Guru

Joined: 31/12/2012
Location: New Zealand
Posts: 2302
Posted: 11:26am 22 Mar 2023      

oops... i wrote "midday friday to midday sunday", when i should have put "midday Friday to midday Monday". and "LiFePo" instead of "LiFePO4". thankfully it seems that with a little bit of jiggling one can edit past posts  

fyi: LiFePO4 cells (Fe for ferrous) have a 3.7v maximum charge voltage, and a nominal 3.2v terminal voltage. LiFePO4 is what the current MG ZS EV car sold here in NZ uses, in the form of a 51kWh pack. electrically far more robust, and greater charge cycles, but slightly poorer energy storage per kg. the long-range model, i have heard, uses a 72kWh conventional Li-Ion pack. you can also buy 2-packs of 14430/500mAh (link) LiFePO4 cells from Bunnings for $7.40. or 14500/600mAh (link) 2-packs for $12.

i'd shy away from any sort of pouch ('silver bag') cells, far more prone to being damaged and as a result having a 'poor customer outcome'. fully metal encased is much safer in my opinion.


one enhancement you could look at is using a pin on the MX170/pico to control charging. so, for instance, every week charge the NiMh battery for a minimum of 1 hour or until the terminal voltage reaches 8.4v (or whatever the battery expects), or until some maximum timeout expires. the time taken to charge - which is just to cover self-discharge over the last week - may be usable an indicator (over time) of 'battery health'.


cheers,
rob   :-)
Edited 2023-03-22 21:33 by robert.rozee