Thread from 2017:
I am a total newbie at electrical issues, and I am trying to diagnose a parasitic draw on my battery. The problem is, my digital multimeter (a Klein MM300) doesn't seem to want to read amps all of a sudden. It seemed to for a second, now it just reads 0.00. I am wondering if I fried it when I accidentally left the lead in the Amp port and switched the knob to Volts and measured the battery. Just so you know what I'm doing to try to read the amps: I'm touching the red lead to the negative terminal and the black lead to the ground lead on the car. Thanks!
Most meters have an internal fuse on the Amp port to protect the meter when you do something like connect it to a 12v source with no series resistance. I'd say yours is blown.
Okay, thanks. I thought it might be, but wasn't sure since the Volts port is still working, and because even on amps it reads 0.00.
Fuse is most likely. You either touched something you shouldnt have, or there was too much load on the circuit you were testing.
T.J.
UltimaDork
6/14/17 7:52 p.m.
Open it up and replace the fuse. It is fairly easy to blow them. Realize a voltmeter is designed to have a high input imefence, but an ammeter is the opposite. It has a very low input impedence and if you connect it across 12v it essentially is a short and the fuse will blow to protect itself.
CyberEric wrote:
Okay, thanks. I thought it might be, but wasn't sure since the Volts port is still working, and because even on amps it reads 0.00.
You're welcome. The fuse is in line with the jack the leads plug into not the rest of the meter so it essentially disconnects the lead when it blows. That's why you get a zero reading on Amps and everything else is unaffected.
^Gotcha, that makes sense.
I replaced the fuse, works good as new! Thanks again!
Just a tip. If you suspect a blown fuse in your meter, it's super-easy to check it using the meter itself. Just set your meter to read resistance (ohms), take the red lead (positive) and touch it to the contact in the "Amps" socket on the meter. If you get any resistance reading (usually less than 1K Ohms), your fuse is good. If you get "Infinity" (Usually read as "OL" or "Out of Range" on new digital meters) then your fuse is blown.
NOTE: Be sure to replace it with a fuse of the exact same current rating and type. Some meters, usually the higher-quality ones, use a special fuse, that is filled with a sand-like material that turns to glass when the fuse blows to prevent possible internal arcing inside a blown fuse. This can happen if the meter experiences any high-voltage transients. Not a big deal in an automotive application, but still needed to maintain the safety rating of the meter.
CyberEric said:
^Gotcha, that makes sense.
I replaced the fuse, works good as new! Thanks again!
Just a small reminder that it's the amperage that kills, not voltage.
