Been my experience that a wall wart under no load (or
any transformer under no load for that matter) will go
a LOT higher than its 'rating'. I'd put, like, a 500
ohm resistor across it (if it's less than 1/2 watt,
might get "a little warm"!!) and measure it again. BTW
a surprising amount of equipment has negative tip. If
you aren't sure about the equipment I'd take a meter
and look for ~0 ohm from a ground to the "ring" of the
power connector. Badly made equipment didn't have ANY
protection from reverse polarity.
I like the RS adapers; just about the most
useful+reasonably-priced thing in the darned store.
--- Chris <mythtech_at_mac.com> wrote:
> This is off topic, since the wall wart is only a few
> years old, but there
> are some great electrical people here, so I am
> asking because I know
> someone will know the answer.
>
> I have a wall wart to a modem. I got the modem and
> wart in a box of used
> stuff (ooh, some of which was more than 10 years
> old, so at least there
> is a reference to on-topicness).
>
> The modem failed to work from the day I got it.
> Today, someone that has
> the same modem asked if I had a power supply they
> could have. I planned
> to give them mine, since I have no real use for it.
>
> But before I mailed it to them, a voice went off in
> my head telling me to
> stick it on a meter first. It's label says it is a
> 9vDC, 400mA Pos-tip
> wart. But when I hook it up to a meter, I get 15v DC
> off it.
>
> That seems a little high, even for something under
> no load. Should I
> safely assume the wart is no good, and point the
> person elsewhere (Rat
> Shack sells a usuable unit for only about $14, so it
> isn't like the
> person has no other choice). Or is it normal for a
> 9v supply to put out
> 15 volts? Any that I have measured in the past have
> not been THAT far off
> (I was expecting to maybe get 10 or 12 volts, but
> not 15).
>
> If this thing has been pumping too much voltage,
> that might explain the
> dead modem I have (or the modem could have been used
> as a soccer ball,
> who knows, it was dead when I got it). I just don't
> want to send the
> person a bad supply, and have them fry their modem
> when they try to use
> it.
>
> -chris
> <http://www.mythtech.net>
>
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Received on Fri Jun 07 2002 - 12:33:37 BST