4.8 nimh with 7.5v charger?  Wine opener

ttylamg · 2019-09-16T03:12:41.000Z

So I had this wine opener for ages, not used it much because we just use the “rabbit” manual opener usually. Today it finally appears to have died, and I thought this would be a good project and opened it. To my surprise it’s 4 nimh for 4.8v but the charger shows output of 7.5v. Is that a bit excessive? Should I replace with 4x nimh or 1 or 2 lithium ion? 1 might be too weak and 2 might be too much? But the nimh doesn’t seem right either. Thoughts?

Pete7874 · 2019-09-16T03:46:41.000Z

Charging of NiMH cells requires more voltage than their nominal voltage. Typically, when charging a NiMH cell, it will terminate around 1.6V. 1.6Vx4=6.4V, so your 7.5V charger may be well suited for that NiMH pack because you always need a little extra to account for efficiency losses.

If the device came with 4 NiMH originally, then that is what I would use.

Is this actually a pack or 4 individual/separate cells?

ttylamg · 2019-09-16T05:33:03.000Z

Ah thanks. So, I used a meter and found the 4 pack to be putting out ~4.2v and 8.4 amp, yet it fails to turn the motor. The motor is good as when I used a pc bench at 5v it runs. Are the battery pack shot and I am just not understanding the amp properly or what’s going on?

Edit, okay I found the culprit, only 1 out of the 4 pack is dead and that’s what caused this problem. TIL