Thread: Leaking Voltage?

Originally Posted by Wilbur

Altronics do an AC/DC clampmeter - very, very useful.

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Thanks Wilbur. I am sort of at a loss as to how a clamp meter would measure DC current. My understanding is that it measures AC due to the EM flux expanding and contracting and cutting the inductive coil in the "clamp" and therefore measuring the current. Still I am not up to speed with all the latest technology so it might just be possible.

Mike

Originally Posted by Mike&Loz

Thanks Wilbur. I am sort of at a loss as to how a clamp meter would measure DC current. My understanding is that it measures AC due to the EM flux expanding and contracting and cutting the inductive coil in the "clamp" and therefore measuring the current. Still I am not up to speed with all the latest technology so it might just be possible.

Mike

Hi Mike
DC clamp meters measure direct current using a magnetic hall effect sensor. I bought one but its not very accurate at low currents as any stray field can set them off. Good for current changes though.

Originally Posted by Mike&Loz

Thanks Wilbur. I am sort of at a loss as to how a clamp meter would measure DC current. My understanding is that it measures AC due to the EM flux expanding and contracting and cutting the inductive coil in the "clamp" and therefore measuring the current. Still I am not up to speed with all the latest technology so it might just be possible.

Mike

Hi Mike,

Bee Utey is right, they use a hall effect device which measures static (DC) magnetic field strength. As he says, they are not terribly accurate but still very useful.

I think you will find your battery is on the way out. A good battery will likely take 50+ amps from the alternator when a bit discharged, so ten minutes driving puts in about 8~10 amp/hours. That should be enough to make up for the small static drain while the car is idle for a few days.

A failing battery will only take a few amps from the alternator so that 10 minutes driving may only put 1 or 2 amp/hours into the battery, not enough to make up for a couple of days of static drain.

Cheers,

Paul

Mike, as soon as I have the time to set out a few test for you, I’ll post them up so you can see whats happening with your battery(s).

BTW you don’t need a clamp meter to test if your battery is good or not but you do need time because Calcium/Calcium batteries are a little tricky to test.

Wilbur, a good cranking battery, even when in a half discharged state will NOT draw anything like 50 amps and a fully charged cranking battery will only pull a few amps after the motor starts and the energy used to start the motor is replaced.

Originally Posted by drivesafe

Wilbur, a good cranking battery, even when in a half discharged state will NOT draw anything like 50 amps....

Mine does.... 2011 D4, original battery.

And how did you measure the voltage and the current?

Originally Posted by drivesafe

And how did you measure the voltage?

I didn't measure the voltage, I measured the current (there is a difference) with my DC clamp meter which I had previously calibrated against a Fluke 19 Digital multimeter.

You still didn’t answer the question, one would hope you used some form of map meter, but where did you get your reading from?