NiCad vs. NiMH Battery Chargers

C

Cass Lewart

Guest
Can NiCad chargers be also used for NiMH batteries? If not what
precautins should be taken? Most chargers cut off around 1.4 Volt which
is ok for both kinds of batteries.

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_/ Cass Lewart Voice (732) 264-9541 Fax (630) 566-0349/_/
_/ e-mail: rlewart@monmouth.com _/_/_/_/_/_/_/_/_/_/_/_/_/
_/ N 40 deg 23' 41.9", W 74 deg 11' 29.7"/_/_/_/_/_/_/_/_/
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Yes and no.

It's not a good idea if the charger is a fast charger (>2C for example ).

Good quality fast chargers for this type of cell use a technique called
Delta V cut-off. This relies on the fact that (when charged by a constant
current source) NiCad and NiMH cells have a characteristic voltage "peak"
and subsequent slight _reduction_ in voltage when nearly full. The
reduction in voltage is small and filtering must be employed to remove
noise. The peak is smaller for NiMH than it is for NiCad cells.

This means that NiCad chargers can look for an absolute fall in voltage,
whereas NiMH chargers have to be more sensitive and usually look for the
gradient changing from +ve to -ve. If you use a NiCad fast charger on NiMH
cells, there is a danger that the peak won't be big enough to trip the end
of charge detector leading to a possible overcharge. However most chargers
of this type use a timer or temperature sensor as a safety backup or
similar.





"Cass Lewart" <rlewart@shell.monmouth.com> wrote in message
news:bqtre7$7c5$2@news.monmouth.com...
Can NiCad chargers be also used for NiMH batteries? If not what
precautins should be taken? Most chargers cut off around 1.4 Volt which
is ok for both kinds of batteries.

--
_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
_/ Cass Lewart Voice (732) 264-9541 Fax (630) 566-0349/_/
_/ e-mail: rlewart@monmouth.com _/_/_/_/_/_/_/_/_/_/_/_/_/
_/ N 40 deg 23' 41.9", W 74 deg 11' 29.7"/_/_/_/_/_/_/_/_/
_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
Click to expand...
 
At least Maxim MAX713 can charge both NiCd and NiMH batteries. I built one
charger with that IC for my kids RC car. It is very simple and also seems to
charge the battires well. No I'm going to build another charger with the
same IC for NiMH batteries. If you know how to solder, I suggest you should
check that IC. It needs only few additional components and is very simple to
get it work.

TSa

"Cass Lewart" <rlewart@shell.monmouth.com> wrote in message
news:bqtre7$7c5$2@news.monmouth.com...
Can NiCad chargers be also used for NiMH batteries? If not what
precautins should be taken? Most chargers cut off around 1.4 Volt which
is ok for both kinds of batteries.

--
_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
_/ Cass Lewart Voice (732) 264-9541 Fax (630) 566-0349/_/
_/ e-mail: rlewart@monmouth.com _/_/_/_/_/_/_/_/_/_/_/_/_/
_/ N 40 deg 23' 41.9", W 74 deg 11' 29.7"/_/_/_/_/_/_/_/_/
_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
Click to expand...
 
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