Re: Can a rechargeable device using NiCd battery be replaced by NiMH?

njchen24@xxxxxxxxxxxx wrote: 
Greetings:

I have a cordless sweeper (Shark EuroPro) which uses 6 Cells Sub C NiCd
1300 mAh. The cost to replace these cells is equivalent to 10 Cell Sub
C NiMH 3300 mAh. Is there any problem if I replace any device
(Cordless Vacum, Drill, Screw driver etc.) design for NiCd with a
different type i.e. NiMH? In other word, will the charger for NiCd be
able to charge NiMH?
Any insight thoughts would be greatly appreciated.


I'd say the answer is a definite maybe...
The situation is improving over time, but there are some general guidelines.
NiCd seem to be better in high drain applications because of their lower
internal resistance and slower self discharge.
Cells are optimized for different purposes. For a fixed size and technology, there's an inverse tradeoff between capacity and fast charge capability.
For slow charge applications, NiMH are somewhat less tolerant of long-term overcharge.
For fast charge applications, the charge termination characteristics can
be sufficiently different that charge does not terminate when NiMH cells
are used on a NiCd charger. This is much worse because a charger designed for one hour now takes three. This c/3 may not be enough to cause the internal processes that are detected to terminate charge based on C.
There may be a safety timer that times out based on 1300mAH and only gives you 1/3 charge.

Safest thing to do is use the battery supplied by the vendor.
mike

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