Hi From Melbourne, Australia (looking to build EV runabout on a student budget)

[mechman600]

What is the typical characteristics of NiMH batteries as far as charging VPC, low and high VPC cutoffs, etc? I guess they do not require fancy BMS like lithiums and are much harder to murder, which makes it great for a starter pack.

[themainstreetexile]

Hi guys,

Sorry but notifications from ecomodder ended up in my spam folder somehow!

NiMh like being discharged, so having them sit for a long time isn't an issue (individual cells at 0.5V). They don't like high temperatures which might be an issue in summer for me, temperatures above 40 Celsius, so need fan cooling when driving. I have a set of fans I can pick up from one of the guys that gave me the cells, but might need to make up some more to be sure.

I'm a bit of an electronics noob, what is VPC?

I ordered a hobby charger so I can charge small strings and work out the usable capacity of the cells. Unfortunately the plug that came with it was broken so that will set me back a while. Basically I have to charge, discharge, charge, discharge again to get an amp hour count and work out which cells won't be suitable. Some are obviously dead as they physically bulge, so they're easy to spot and remove.

After the initial test I imagine I'll have to check cells every few months or so.

The pack voltage should indicate when enough cells are failing.

[mechman600]

Originally Posted by themainstreetexile

I'm a bit of an electronics noob, what is VPC?

VPC = Volts Per Cell.

From what a Google search tells me, NiMH batteries are nominal 1.2VPC.
To contrast, a typical lead acid battery is around 2.1VPC (X 6 = 12.6V).

[themainstreetexile]

Gotcha, Yes you are spot on, they're 1.2 volts per cell. I have about 200 of them to test...