Clayton Family wrote:
Dear Esteemed and Learned List Members,
I was fooling around with a wall wart that is listed as 24V and 500mA,
and had it hooked up in series with my radioshack multimeter. It
tested as 30.6V, and after I switched it to mA, the meter failed. Now
it just reads micro volts and won't read anything else. Dang! Maybe I
had it on micro amps instead of milliamps, and would that break it?
Maybe, but probably not. I would expect it to fail if you put it on
milliamps. If you have a wall wart that is open circuit then short
circuit it without any limiting resistor, you can expect a surge of 100
to 1000 amps or so. This will take out any meter easily. Most
multimeters have a fuse in them, and if yours does, then replacing the
fuse should fix it.
BTW if you wanted to know the steady state short circuit current, you
could come pretty close from the measurements you have already made.
Assuming no saturation, you measured 30.6 volts on a device rated 500mA
@ 24 volts. Thus 500 mA drops 6.6 volts, and is thus 13.2 ohms. If you
short it out, you could expect a current of about 30.6/13.2 = 2.3 amps.
I need another multimeter! But I don't want to just turn around and
break this one too.
Don't measure an unlimited voltage source with a current meter. If you
want to measure the current through something, like a CS cell, that is
fine, but never the unlimited source itself. If you really want to
measure the short circuit current, then use a small resistor, like .1
ohm, and measure the voltage across the resistor, starting at 50 volts
and going down. Do it quickly, or the wart may burn up if they don't
have any thermal limiting in it. Even if they have a thermal link in
it, if that blows the wart will stop working..
Marshall
Thanks,
Kathryn
--
The Silver List is a moderated forum for discussing Colloidal Silver.
Instructions for unsubscribing are posted at: http://silverlist.org
To post, address your message to: [email protected]
Address Off-Topic messages to: [email protected]
The Silver List and Off Topic List archives are currently down...
List maintainer: Mike Devour <[email protected]>
