DC clamp meters

Not really, they're all quite expensive, particularly at low currents, cheapest you'll get one is about £30 from ebay.

You won't get a clamp meter that can measure small DC. The one's that can do this are very expensive. You need a cheap digital multimeter from Maplin. See the thread called "Multimeter?" back at the start of Dec. We covered it all there with instructions how to use measure current drain by removing one of the battery terminals. If you still have questions after reading it, then post back here.

Mark

Easily done. A normal DVM measures AC and DC current so why not a clamp one?

They are more expensive but more to the point not very accurate. Or at least a general purpose one isn't. Especially since with a car most will be looking to measure very low quiescent drain from the battery. Most will be ok to tell if the starter is taking about the correct current, though.;-)

To accurately measure very low currents the sensor coils need to be very carefully positioned round the conductor - not really possible with general purpose types.

Mark W wrote on 27/12/2008 :

They are expensive and accuracy goes down dramatically as the level of current is reduced, so not really much use to measure small discharges which flaten car batteries.

For that you need a meter able to measure with reasonable accuracy in the 10ma range, which even a cheap meter can do providing it is in series with the load. Wire the meter up in series with the battery terminal, a 21 watt lamp, the meter and the cables removed from the battery - with it set on the 2amp range. Initially the current demand could be quite high, but given time it should fall as things shut themselves down into power saving mode - mine takes an hour to do this, but doesn't completely shut everything off until a month after it has been parked undisturbed. Even the bonnet open might draw extra current

- if there is a bonnet sensor, find some way to fool it that the bonnet is closed.

Why do you need a clamp meter? A decent AVO can do the job.

--=20 Conor

I only please one person per day. Today is not your day. Tomorrow isn't=20 looking good either. - Scott Adams

Seconded. The clock in my Capri shows an 8mA drain so you definitely=20 need something that's quite sensitive.

--=20 Conor

I only please one person per day. Today is not your day. Tomorrow isn't=20 looking good either. - Scott Adams

My Sierra takes about 25mA (same as the previous Sierra I had). I would imagine modern cars would take at least that, even if using lower power for each item on standby. All mine has to do is keep the radio memories and the digital clock time. If I disconnect the clock and the radio, I cannot measure any current drain at all. My old MK1 Escort used to draw zilch. Same with my 1980's VW LT van. No drain at all and happily starts after six months without use. Has a big battery for the 6 cly diesel, but not bad considering it has to run six glowplugs for a minute before I can crank it over.

Mark

we had this discussion before. A few hundred will buy a suitable dc clamp meter.

A clamp meter would be *very* useful if only they worked. To measure current means disconnecting the battery and inserting a DVM in series with it. But you don't need a 'decent AVO' - even a DVM at under a tenner is likely to better 1% accuracy.

That's exactly it. A meter that could just somehow 'sense' a DC current in a wire without dismantling, that would be great!

They exist. I used to use one for work. The bad news is that they are MUCH more expensive than the standard coupled-inductance AC variety.

Ian

They're called a dc clamp meter oddly enough. CHeap ones on ebay, good ones come from lem-heme that fluke have bought. They're hall effect though, so the zero error is tricky, normally you have to manually null them.k