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Subject: RE: Batteries?
From: Fred Maxwell (rockbox_at_anti-spam.org)
Date: 2003-12-17


Eddie wrote:

> Thank you everyone for your input. SteamShip thanks for the url, I also
> found this FAQ which benefits as all.
>
> http://www.thomas-distributing.com/maha-educate-batteries.htm
{Snip}
> Rechargeable batteries actually develop around 1.4 to 1.45 volts when
> fully charged even though they are marked as 1.2V.

That's fine when using NiMH batteries in device designed for 1.5v alkalines,
but it's missing some important information when going the other direction.
I just took a freshly charged NiMH AA cell and measured the voltage at
1.42v. I then took a somewhat old, but unused, alkaline AA cell and
measured 1.59v. So there's a difference of .17v. Multiply that times four
and you've got 5.68v vs. 6.36v. That's significant.

That also ignores the question of load. What happens to the voltage when
there is a load? How much does the voltage drop? I know someone who ruined
an audio device. He measured the voltage off of the wall-wart with no load.
He then hooked the device up to a benchtop supply that was regulated to the
measured voltage. The device was dead in under a minute. The reason was
that the wall-wart's voltage, being unregulated, dropped several volts when
under load. Thus it worked fine. The benchtop supply did not and thus,
fried the device.

Regards,
  Fred Maxwell



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