Using a Mulit-metre

Submitted: Wednesday, Jul 18, 2007 at 09:05

ThreadID: 47828 Views:2437 Replies:4 FollowUps:2

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John R (SA)

Could someone point me at an article which tells me how to use a mulitmetre on 12v systems?

I'm sure I've seen one referrred to before, but can't find the post (so sorry if I'm repeating previously asked questions!!).

Something continues to drain my battery. I want to figure out how much is being sapped, and what it is. I have a sneaking suspicion the solenoid wiring has something to do with it (on a hilux which has negative active headlights).

Thanks! JR

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Reply By: Mike Harding - Wednesday, Jul 18, 2007 at 09:23

Wednesday, Jul 18, 2007 at 09:23

I posted one a few weeks ago but can't find it again either :)

See if this answers your questions:

Site Link

if not, ask again.

Mike Harding

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Follow Up By: Member - bungarra (WA) - Wednesday, Jul 18, 2007 at 09:56

Wednesday, Jul 18, 2007 at 09:56

Mike

excellent advice to give the link that you did. I am sure it will help many.

I purchased one of the DC clamp meters pictured about 2 weeks ago (online from that same web site) and found it invaluable. Has a resolution of 0.01 and 200 amps max. AC & DC. Much easier than using the conventional multi meter with probes which are usually limited 10 to 20 amp DC range and having to break into the line.

I found that that if you look for a DC clamp meter with a range greater than 200 amps then you usually compromise on the resolution to 0.1 which is less useful if chasing small current flow in trouble shooting

For the record I have checked the calibaration on the one I purchased against another multi meter and an analogue meter and found it satisfactory (low amps test only)

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Reply By: Member - Phil G (SA) - Wednesday, Jul 18, 2007 at 14:50

Wednesday, Jul 18, 2007 at 14:50

John,
To check for the parasitic loss, loosen the negative terminal. Turn your multimeter onto the 10amps setting. You will also have to move the red pos lead on the multimeter into the third socket which should be labelled 10amps. Put one multimeter lead on the battery terminal itself and the other multimeter lead on the earth wire, and it should read zero. Then disconnect the earth lead from the battery and see what the reading is. If its a lot, you can probably disconnect things, pull fuses or whatever to find the source of your problem.

Common causes are
- sticking brake light switch
- reversing cameras and screens that are left on
- second battery systems.

Your solenoid should not be energised unless the vehicle is running. The usual source of fused IGN power for dual battery systems is the wiper motor. The headlight wiring on Toyotas is that the pos side is always active, and the switching is on the earth side, so you wouldn't want to use that to energise your solenoid.

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Reply By: equinox - Wednesday, Jul 18, 2007 at 20:57

Wednesday, Jul 18, 2007 at 20:57

Remember to never put 12 volts (or any voltage) across the leads when the meter is on the Ohms setting (resistance).

It may blow an internal fuse or even the meter!!