Hi Mark.
You asked:
<< why do so many battery operated equipments
state that they must not be operated using rechargeable batteries? >>
There is no one all-purpose reason, but the two main ones, at least the ones
I worry about with battery powered stuff, are:
1. As you already implied, terminal voltage.
NiCads are typically 20% lower terminal volts than Alkaline cells, and as
lots of battery operated stuff needs a stabilised supply the headroom
required to produce a stabilised supply can take the volts down too low.
2. Short circuit current is very high with NiCad's. If there is a fault
internally, or as in one case that I had, if you drop it in water, the
resulting current can destroy the PCB and associated components. Alkaline
cells, ar even better, Zinc/carbon cells have a much lower short circuit
cirrent and the liklihood of damage, or even fire, is reduced or even
prevented completely.
The short circuit thing is interesting. My son has a radio controlled car
with a 7.2V NiCad battery pack. The short circuit current was enough to melt
the PVC insulation on the battery wires, 1.5mm^2, and I measured it
subsequently at 82Amps. You could probably start a European car with one of
those!
Chris Dupres
Surrey UK.
p.s. Anyone wrapped up a alkaline watch battery in aluminum foil? Don't!
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