How To Read Multimeter!

[1905 adam 0]

Hi,

 

I'm trying to see if I have a parasitic battery draw and don't know how to read my multi meter!

 

With the red cable plugged in the 10amp (10ADC) socket and the selector wheel pointed at 10amps I get a reading of 0.34, so I do seem to have a problem!

 

But is this

 

0.34 x 10amps = 3.4 amps or

0.34 x 1amp = 0.34 amps or

something else?

 

Many thanks!

[Anthony 1,003]

I would take that as 0.34 amps, which is far too high.

 

On a 205 in my experience it should be something around 20-50mA which would be 0.02-0.05 amps.

 

Just to check that you're doing the test correctly - with the ignition off, doors closed, lights off etc, you need to disconnect one of the the battery leads and then put the multimeter between the battery and the disconnected lead so that all the current runs through the multimeter.

 

The usual culprits for high parasitic losses are alarms, stereos, and the boot light staying on. If the current draw is higher than expected, you can remove each fuse in turn to see if the current drops dramatically on the multimeter to find the cause.

 

DO NOT attempt to start the car or turn on anything significant electrical otherwise you risk burning out the multimeter - they will normally only cope with approximately 10A maximum.

[Stu 18]

Just to add to Anthony's post, id firstly make sure you're running the meter in series with the battery, people tend to forget that ammeters go in series, voltmeters in parallel.

 

So double check you've effectively bridged the battery terminal with the multimeter.

 

Either way, nearly half an amp is high at static, do Anthony's fuse test first, if theres nowt obvious the alternator could be at fault if one of the diodes in the pack has gone down.

[1905 adam 0]

Hi, yes, I'm doing it properly! Thanks for the advice! And now the hunt for the culprit begins!

[1905 adam 0]

Just to add to Anthony's post, id firstly make sure you're running the meter in series with the battery, people tend to forget that ammeters go in series, voltmeters in parallel.

 

So double check you've effectively bridged the battery terminal with the multimeter.

 

Either way, nearly half an amp is high at static, do Anthony's fuse test first, if theres nowt obvious the alternator could be at fault if one of the diodes in the pack has gone down.

Thanks! In case I need to, how do I test for a downed diode?

[Anthony 1,003]

Disconnect the battery feed from the alternator and see if the current reading on the multimeter drops.

 

Remember to keep the lead well away from the engine block and bodywork!

[1905 adam 0]

Disconnect the battery feed from the alternator and see if the current reading on the multimeter drops.Remember to keep the lead well away from the engine block and bodywork!

Sorry, You mean disconnect at the alternator a wire that goes to the battery?

[Stu 18]

Yeah the main feed that charges the battery

 

Leave your multimeter inline, and disconnect at the alternator to see if you see an improvement.

[1905 adam 0]

Yeah the main feed that charges the battery

 

Leave your multimeter inline, and disconnect at the alternator to see if you see an improvement.

OK, thanks both for all the advice!

[1905 adam 0]

I would take that as 0.34 amps, which is far too high.On a 205 in my experience it should be something around 20-50mA which would be 0.02-0.05 amps.Just to check that you're doing the test correctly - with the ignition off, doors closed, lights off etc, you need to disconnect one of the the battery leads and then put the multimeter between the battery and the disconnected lead so that all the current runs through the multimeter.The usual culprits for high parasitic losses are alarms, stereos, and the boot light staying on. If the current draw is higher than expected, you can remove each fuse in turn to see if the current drops dramatically on the multimeter to find the cause.DO NOT attempt to start the car or turn on anything significant electrical otherwise you risk burning out the multimeter - they will normally only cope with approximately 10A maximum.

T'was the boot light not being turned off on closing the tailgate. Draw now down from 0.34 to 0.03 amps. Thanks again!

[Harni 6]

Thats more like it!

For future reference, on your meter where it says 10a, That will be the max it will read. Most decent meters are auto ranging so you will just set it to amps and away you go but some cheaper ones you have to choose the range like 1a, 10a, 20a.

Also, don't forget that on most meters, the amp circuit is not fused and there is normally a warning above the pin telling you this and not to exceed the total amps the meter can take (normally 10 or 20a)