Question about measuring amps with DMM

[stovebolt6]

Yesterday I was trying to determine if a vehicle had a parasitic draw. I set up my DMM in series with the negative battery cable & post and had my meter on the A setting with the red lead in the 10A jack. Reading was 0.00. I thought this was weird because there should at least be SOME draw, right?

So I plugged the red lead into the mA jack, and switched to the mA setting. I can't remember if it was 3.2 mA or 32 mA, but either way, shouldn't that measurement be reading on the 10A high current setting as well? Not just 0?

I thought the 10A fuse might have been blown but I checked, it's not.

Is my meter maybe expecting at least 1A on the high current setting to register?

 

[firebox40dash5]

I'm going to go with yes... at least that's how my Extech works. I always use it on 10A for that, and it reads in mA.

Does it have a range button?

 

[larry_g]

Yesterday I was trying to determine if a vehicle had a parasitic draw. I set up my DMM in series with the negative battery cable & post and had my meter on the A setting with the red lead in the 10A jack. Reading was 0.00. I thought this was weird because there should at least be SOME draw, right?

So I plugged the red lead into the mA jack, and switched to the mA setting. I can't remember if it was 3.2 mA or 32 mA, but either way, shouldn't that measurement be reading on the 10A high current setting as well? Not just 0?

I thought the 10A fuse might have been blown but I checked, it's not.

Is my meter maybe expecting at least 1A on the high current setting to register?

With hundreds of meters out there, and you not giving up your make and model your question is impossible to answer...

lg
no neat sig line

 

[stovebolt6]

Klein MM200. It is auto ranging.

 

[POS Camaro]

3.2 mamp would be .0032 amps. That would not show up on a meter that read 0.00.

 

[zkling]

The auto ranging name can be a bit misleading especially on current measurements. As Camaro said above, the minimum on the resolution on that meter is probably in the 10ma range for the 10A jack.

 

[theoldwizard1]

3.2 mamp would be .0032 amps. That would not show up on a meter that read 0.00.

Yep !

But the OP is doing the testing the proper way. Start with the highest current range and work down.

 

[logixjock]

Not really applicable in the OP's situation but something I just remembered, when using a clamp meter to measure small currents you can loop the wire around the clamp, then cut the reading in half. Makes it easier to get a reading on very small currents that way.

 

[stovebolt6]

Thanks for the replies, guys.

 

[theoldwizard1]

The quickest and reasonably accurate way of measuring current in a car is by measuring the voltage drop across the fuse. Knowing the resistance of the fuse and the voltage drop, it is simple to apply Ohm's Law (Current = Voltage Drop / Resistance).

 

[awdblazer]

now are you sure you have correct polarity? cause i have seen cheap meters give false values
and polarity does matter in dc!!!

 

[theoldwizard1]

now are you sure you have correct polarity? cause i have seen cheap meters give false values
and polarity does matter in dc!!!

Not really when you are chasing a parasitic draw on a car.

 

[Zrexxer]

Not really applicable in the OP's situation but something I just remembered, when using a clamp meter to measure small currents you can loop the wire around the clamp, then cut the reading in half. Makes it easier to get a reading on very small currents that way.

Most clamp meters will only measure AC current. There are DC clamp meters out there, but they're in the minority for sure.

 

[stovebolt6]

now are you sure you have correct polarity? cause i have seen cheap meters give false values
and polarity does matter in dc!!!

Yeah with this current test if the polarity is reversed all that happens is the "-" symbol shows up. Value doesn't change.

 

[Schurkey]

Not really applicable in the OP's situation but something I just remembered, when using a clamp meter to measure small currents you can loop the wire around the clamp, then cut the reading in half. Makes it easier to get a reading on very small currents that way.

Thousands of years ago, the shop I was at had a Sun VAT-40 (more-or-less the "industry standard" analog volts/amp meter with DC current clamp for automotive electrical diagnosis.) We'd use a piece of 12-guage wire looped ten times, bundled tightly, and secured with tyraps, with an alligator clip on each end of the wire. We'd just "move the decimal point" when taking low-amperage readings using the DC current clamp.

Nobody ever tested the ten-loop bundle to see if it really was an accurate 10x multiplier. I've since heard that the wire loops have to lie perfectly aligned, and become an inductor which could conceivably screw with the accuracy of the meter reading. I can't say for sure...but we used it a lot and it seemed to work fine.