Chris,
you say it's a DC output type? - This means it includes rectification
and a filter capacitor? - Let's see:
Under normal load conditions, the output voltage is around 0.6..0.7
times the peak voltage of the secondary AC voltage at the transformer,
so you get
Vp * 0.6 = 9V or
Vp = 9V / 0.6 = 15V.
With no load, the filter capacitor will charge up to this voltage
because there is nothing that will discharge it, so this can be
expected.
You may want to try loading the adaptor with a small car bulb (about
12V/3..4W should be fine) and see to which value the measured output
voltage will drop.
Regards,
Andreas
Chris 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>
--
Andreas Freiherr
Vishay Semiconductor GmbH, Heilbronn, Germany
http://www.vishay.com
Received on Fri Jun 07 2002 - 13:10:43 BST