Ken wrote:
I have a beard trimmer that runs on a Ni-cad battery that I recharge
about once a month when the battery runs low. Recently, the battery
stopped being able to hold a charge. I charged it for ~12 hours,
tested the voltage, and got zero. OK, fine, so I soldered in a new
ni-cad, and everything works fine now. The trimmer is only a few
years old, so I thought the battery died earlier than I would have
expected.


Then I got to thinking about the charger, which is just a simple wall
wart. The battery is one AA ni-cad, 1.2 V 600 mAh. The wall wart
charger is labeled 2.3 V, and I measured 7.5 V DC actual output. The
charger is what came with the trimmer, and molded into the trimmer is
something about "use only charger # such-and-such", which is also the
number on the charger. So I'm sure that the charger is the one that
the manufacturer intented to be used with the trimmer.

Did the higher than expected voltage on the charger lead to the early
demise of the ni-cad battery? Should I find a new wall wart that has
a voltage closer to 1.2 V? If so, what current output should it have?
(I save each and every wall wart from every dead appliance that I have
ever owned, so I have a wide selection to choose from a box in the
attic, although I think most of them are 5V and up.)

Ken

You found that voltages change depending on how you measure them.

The battery is rated at the voltage it can deliver (likely under a
specific load).

The charger is rated at the voltage it delivers under a certain load.

The voltage you measured was likely with a modern digital meter that
have a very high resistance, resulting in the high voltage recorded.

If you were to measure the voltage when you first put a battery in need
of a charge on it and then measure it again when the battery is fully
charged you are going to get two more measurements, the last likely near
that 2.3V specified for the charger.

Measure the voltage output of that 5V vampire with that same meter and
no load and you might get something about 10V.

The moral of the story, stick with the one designed for the use you
have.

--
Joseph Meehan

Dia duit