Nickel Metal Hydrids - test-drb@ccmp.vtda.org

17 Jan 2005

Hi
 My understanding is that NiMH's have a higher internal
resistance when mostly discharged and should be charged
slowly until the internal resistance drops. They are also
suppose to be less tolorent to over charging than
NiCad's. In general, I'd expect one to get poor battery
life using a NiCad charger on NiMH's.
 0.1C is not a trickle. 0.02-0.01C is. 0.1C will cause
quite a bit of heating in a fully charged cell. 0.1C
is only recommended for normal rate of charging NiCad's,
not as a trickle level.
Dwight

...
 From: shoppa_classiccmp(a)trailing-edge.com

  I have noticed that NiMH prices have gone down
 about half over the last 5 years. 
In many cases they are cheaper than NiCads now.

This raises a question for refurbishing older equipment: is it always
OK to just drop a set of NiMH's in place of same-size NiCad's?  Most
of the "stupid" NiCad battery chargers were just 0.1C trickle chargers,
but the "smart" ones that looked for the voltage rise at the end of charge
of a NiCad may not see this with a NiMH pack.  Anyone have any experience?

Last time I had to put some new Sub-C cells in my Fluke scopemeter I had
to look rather hard to find true NiCads as opposed to MiMH's.

Tim.