# How do I determine meter electrical limits?

#### MattQ

Joined Aug 23, 2007
2
I found a small (1/4 inch diameter X 1/4 inch deep) meter with no manufacturer/specification markings. I would like to use it in some project but don't know how to figure out the voltage/current limits to keep from cooking it. Any ideas?

Thank you, Matt!

#### recca02

Joined Apr 2, 2007
1,214
is it a multimeter?
in that case
the full scale deflection values specified on the meter display is its rated value.
is there a selection switch/knob?

#### beenthere

Joined Apr 20, 2004
15,819
That is pretty weenie. You might start with a battery and a resistor. With 1.5 volts, placing a 1500 omh resistor in series will give a current of 1 ma. Put the meter movement in series with the battery and resistor, and see if the indicator deflects. If not, put the battery across the terminals to see if that has any effect.

If current produces no deflection, then the meter might be for voltage. Being so small, it's not going to be too useful.

#### mrmeval

Joined Jun 30, 2006
833
A friend use a junk meter movement that had about 1" deflection and was 0.5" high as a microwave high voltage meter. I know he used a voltage divider of some sort but how he accurately calibrated it is a mystery. It was accurate enough to show several failure conditions with microwave ovens.

#### MattQ

Joined Aug 23, 2007
2
Not a multimeter, no selection switch. Plain unmarked metal case, two wires coming out the back, black face with no marking or values, red needle.

#### recca02

Joined Apr 2, 2007
1,214
then go ahead as Mr beenthere suggested,
try applying a small current (so that it shud not damage the meter) and then a small voltage this will help you in determining whether it is a voltmeter or a ammeter. if the meter is linear u should also be able to estimate its range and then apply a somewhat lower value to check that.