On Mon, 2009-05-04 at 14:02 -0700, Sean McCoy wrote:
>
> When I bought my used Poly 800 it had no power supply so I went to
> RadioShack and got a replacement. The guy there helped me and what I
> ended up getting was rated at 9V and 800mA. He said he wasn't sure
> what the amperage requirement was so he guessed something in the
> middle. Based on Gordon's recommendation of "at least 700mA" I'd say
> I got a pretty good replacement. It was a little under $20.
Like I said, more current is fine, as long as the voltage is okay.
Some people will say "aha but if you have too high a current you'll burn
stuff out" - but that's only true if the device will actually pull that
much current! Getting the voltage right is important, and having
∗enough∗ current available is important. Too much is fine, as long as
nothing is trying to draw all that current ;-)
A car battery can provide about 500A peak (usually more). The starter
motor will draw a couple of hundred amps (the very large starter motor
on my Citroën CX pulls down over 250A on a cold morning, trying to churn
over a big heavy engine full of thick cold oil). The interior light
pulls about 400mA. Now if the "too high a current will burn stuff out"
people were right, then the interior light would blow as soon as you
opened the door, possibly with a spectacular shower of sparks! Why
doesn't it? Because devices only draw what they need.
If you wire it up backwards, and you can supply a high current, then you
can expect problems. Take care not to do that.
Gordon