DC System Question 101

[CAVOK]

I’m trying to trouble shoot a refrigeration problem & suspect it’s in the electrics. It’s a Danfoss compressor which draws about 3 amps on a 12 volt system. When I’ve used a clamp on amp meter on the positive and negative feed at the compressor control board I get 3 & 1.5 amps respectively.
Is this normal or should the amps be identical. Apologies if this a newbie question, but after 2 expensive technicians not finding the problem unsuccessfully I’m trying myself.

[Joh.Ghurt]

It should be the same. The Amperes going into a box need to be the same as the Amperes leaving it. If you get different results, you either measure different things or there is also an alternative route for half the current to disappear.

If you have half the Amperes on the Ground / negative, the rest is probably leaving via the chassis or some other connection. This can be a problem.

[goboatingnow]

Just be also aware that dc capable clamp meters can have significant application error issues and can give unreliable results. For best results insert a capable ammeter in line

[rwidman]

The current should be the same. In fact, it must be the same.

I suspect a problem with your measuring technique.

[patrickbarbary]

Originally Posted by CAVOK

I’m trying to trouble shoot a refrigeration problem & suspect it’s in the electrics. It’s a Danfoss compressor which draws about 3 amps on a 12 volt system. When I’ve used a clamp on amp meter on the positive and negative feed at the compressor control board I get 3 & 1.5 amps respectively.
Is this normal or should the amps be identical. Apologies if this a newbie question, but after 2 expensive technicians not finding the problem unsuccessfully I’m trying myself.

You may have a bad breaker.

[captstu]

There is usually a third safety ground water on refrigeration equipment. Measure this line, if it is not zero, you have an internal short and the unit is probably broken. This is how my previous compressor failed.

[s/v Jedi]

Put the clamp meter around any grounding wires as well as the copper lines to/from condenser or evaporator, trying tofind the missing 1.5A current. It should all go through the power feed negative conductor so you need to eliminate alternate paths.

[Cadence]

If there is a ground wire check it for any current. It could be a leak internally. In which case you need a need unit.