Thread: Canepole

Clamp on Amp probe not very accurate for DC current. Even the Fluke meters are not that accurate for DC current. Need an in line meter for DC.
Just my 2 cents :D

I agree with Alan.

It is next to impossible to measure inrush current (impulse) with any standard meter (digital or analog) because of real time and meter dampening.

DC motors at rest are a virtual short. It takes a lot of instantaneous current to get the motor to move initially.

Here is a little engineering brief.

All DC motors are subject to in-rush current. DC motors at rest appear as a dead short! Initial DC motor in-rush current is very high. Small DC motors can have an initial in-rush current of 300% of rated operating current. Medium DC motors can have an initial in-rush current of 400% of rated operating current. Large DC motors can have an initial in-rush current of 500 to 700% of rated operating current. For example, a starter motor could have an instantaneous in-rush current of 1000 Amps when first turned on.

This (inrush demand) is why we have such big crank amp batteries. The older the battery, the less of this ump it will have.

I am not a battery expert, but I understand a little about dc motors.

Keep this inrush requirement when you get a cranker battery.

I ran a few tests comparing it against a Fluke 87 which ain't no cheap meter. Anyway it seems to be well within the advertised 3% accuracy But my tests were limited to 5 amps as thats all my power supply is capable of. ( it came out of a PBX so its a good one). If it hold to that its good enough for me. I also check an old starting cap with it rated at 7.5uf and it read it as 6.8uf. Temp probe seems to work OK but I don't have anything accurate to compare it against.

If you use a 60 amp shunt and a DC militvolt current meter you would see a big difference in current reading. And 60 amps may not be large enough! But it's inrush and only lasts a few mili-secounds.
Just my 2 cents!