DMM Showing Current without Current Source

[lothian]

I am attempting to use my DMM to identify a parasitic drain in my car's electrical system using a Chinaseum-brand DMM with an amp clamp.

After I set the thing to DC amps and before I clamp it to the target conductor, it displays a range between 0.1A and .22A. This makes t'shooting with this tool impossible. I can't figure out how to "zero" it within this mode; nor can I determine if--like voltage measurements--extraneous ambient readings are normal. The user manual is useless,

Thoughts? Suggestions?

 

[DPG]

You really need to know the specs of the device. How accurate is it at low current readings? ie at the current levels you are needing to measure.

If you can't find this from the manual do you have a bench power supply where you can set the max current? Or maybe set something up with some resistors? Then you could compare readings from a normal DMM.

To be honest it's probably unlikely to be accurate at low currents.

 

[lothian]

I believe 5mA is the "at rest" datum current for the make/model car I'm t'shooting. A reading above that value indicates a problem. I'm still looking for the actual milliamp value from the manufacturer, however.

As for your other qustion: uh... no.

 

[Marvo]

The clamp meter lowest range is 60Amps so it's not suitable for measuring small currents under an Amp.

As long as the current you're measuring is less than 10Amps rather use a cheap multimeter and disconnect one lead of the battery to get the tester in series.

 

[DPG]

The clamp meter lowest range is 60Amps so it's not suitable for measuring small currents under an Amp.

As long as the current you're measuring is less than 10Amps rather use a cheap multimeter and disconnect one lead of the battery to get the tester in series.

View attachment 89475

Remember to remove the meter before switching the lights on or starting the car!

 

[lothian]

"The clamp meter lowest range is 60Amps so it's not suitable for measuring small currents under an Amp.

Right. I don't understand how a meter that specs 6A (+/- 5%) as its lowest current detection can read milliamps. The manual isn't much help in this regard.

 

[James]

quite Simpley if it says 6A is the lowest current it can measure to a tolerance of 5%
you have not a lot of chance in measuring the difference between 500mA and 600mA let alone figures below that.

 

[Marvo]

Yeah, bottom line is it's the wrong tester for the job. A cheap multimeter will work to measure parasitic draw but as DPG points out it won't handle the current of things like headlights or if the ignition key is switched on.

The best option would be an AC+DC earth leakage type clamp meter that's designed to measure current in the miliamp range but the purchase price of this kind of tester would be too high for most DIY'ers so a cheap multimeter is probably the way to go even with its limitations.

To check parasitic draw you also need to monitor the current over a couple of hours because it takes a long time on some newer vehicles for some of the control modules to shut down completely.

 

[PEG]

Hi,on the lower ranges,some of the cheaper meters are not much more use than writing the word "amps" on a dice,and throwing it ?

A cheap meter which measured amps via the leads.would be more use,although the 10A standard limit would require care,due to modern vehicles tendency to sort windows,locks,seats and other ancillaries,on locking - whether wanted or not.....

I take it you have read the operating manual for that meter,and zeroed the scale by pressing the "Z/F" button for 3 secs?

Just for comedy,some of the many things i have encountered,whilst researching a parasitic drain,include...

Bad battery,bad new battery,faulty ECU,alarms,alternators and wiring. Owner rolling around on couch all evening with fob in pocket,locking/unlocking doors......member of family using spare keys to sit in car during early hours,to listen to radio and smoke weed....and many,many more ?

Please never discount,the mysterious drain,which despite days of testing,data holding and scenario changing,only ever happens on returning the fault-free vehicle,to it's angry owner ?

 

[UNG]

I would start out by testing the battery,
For a tester I would recommend the Foxwell BT100 as a cheap battery tester I've had one for a few years and it certainly identifies failing batteries