Why do mA and A settings on multimeter give different result?

[Rob Plant]

With apologies in advance for the newbie question...
I'm using a multimeter to figure out the source of my battery drain, so attempting to measure the leakage current between my battery terminal and its lead. When taking the readings shown below, they are quite steady, but as you can see, on the 10A setting I get a measurement of (-)69 mA, while on the mA setting I get 1.5 mA. Is this just because of the lower resolution (and higher error) in the 10A mode? I ask because online how-to information for doing this say to do the check in the 10A mode, and to be concerned if the current is more than about 50 mA. Based on the mA settign reading, I see no problem, but is there reason for concern based on the 10A reading?
I'd appreciate any pointers - thanks!
Rob

 

[PEG]

Hi,what is the vehicle,the means of connection,and alarm/locks/bonnet position?

 

[Rob Plant]

Subaru Outback, prongs of multimeter clamped to battery terminal and the disconnected lead (I used the positive, although I understand now that neutral would have been safer). All doors closed, key not in ignition - only the hood open.

 

[Mikegh]

I'd probably discard the reading on the 10amp scale

You can get disconnectors as a short term measure

 

[brianmoooore]

A quiescent current of 1.54mA for any vehicle made in the last 40 years is incredibly low. I'd expect it to be north of 40mA as a minimum, so, the 69mA reading is the more realistic.
Are you sure the meter is working correctly.? It's likely to have separate internal fuses for the two ranges.

 

[pc1966]

Beware that the surge when connecting a meter can be enough to pop the fuse on the low current range.

Make sure you ALWAYS replace the fuse with the correct type, both in amps rating and the high-rupture capacity ceramic style. If you put in a low-rupture glass fuse and make a mistake on a high energy circuit like the mains supply you run a serious risk of it exploding in your face in flames.

If you want a graphic display of what a high fault means this video shows it, though at industrial plant levels so a bit more than domestic fault currents:

 

[Mikegh]

Yes that was the concern when I saw the fuse changed and meter now working

 

[brianmoooore]

Beware that the surge when connecting a meter can be enough to pop the fuse on the low current range.

This is something I state regularly on another internet forum with which I am involved.
The technique I recommend is to loosen the negative clamp on the battery, but leave it still pushed down on the pole, maintaining contact. Connect the black lead of the meter to a good body earth, and push the point of the probe on the red lead vertically down onto the top of the negative battery pole, then lift the terminal clamp off of the battery, up around the battery clamp. Take the meter reading, then replace the clamp again.
The battery isn't disconnected at any time, so no problem with radio codes or anything else resetting itself.

 

[Rob Plant]

Thanks for all the pointers. I'll check the fuse, and try the measurement method Brian describes.

 

[Simon47]

I don't know what the specs are for that meter, but if it's (just to pick easy numbers) 1% of FSD +/- 2 counts, then the accuracy on the 10A range is basically + or - 100mA (1% of 10A) and a bit (2 counts). So you might have 171mA, or -33mA, or anything in between actually flowing and the reading is "in spec". If the other reading is on a 2mA range, then the meter spec says you should have +/- 20uA (1%) and +/- 2uA (+/- 2 counts) so your current is between 1.32 and 1.76mA. Furthermore, that 1.32 to 1.76mA lies fully within the range of readings the spec of the meter would allow for the 10A range.
(Sits back and waits for someone to point out a daft error ?)

That's why it's important to understand the specification of the instrument that you are using and how that relates to what you are measuring. Too many people take a number of the display and accept it without question as being "the" current/voltage/whatever that is being measured.

 

[Marvo]

Yeah, trying to measure a current of less than 0.1 Amps with a multimeter using the 10 Amp scale will not give an accurate result. I would use the tester on its miliamp scale but I would probably do a quick calibration check using a known value resistor with the battery to make sure the tester is accurate and functioning correctly. For example a 1 kiloohm resistor in series with your car battery should give you about 12-13 miliamps, this would be a good value to test the meter accuracy.

 

[johntheo]

Should't the red lead be in the 10A socket whatever reading is been taken, no?. the 69ma on the 10A scale is certainly more accurate IMO, all my cars bar 1 read 40 to 60ma, the exception, a 2005 Polo reads 95ma even after the ECU goes to sleep.

 

[Lucien Nunes]

No, the right-hand socket serves for the lower current ranges and includes the markings μA and mA. In most meters the 10A shunt is connected to a separate socket to avoid having to switch this current with the function selector, while allowing the use of a higher-value shunt for the lower ranges.

 

[johntheo]

I use my one in the 10A socket which has 3 different scales 10, 200m and 20m.
Connected it between a 12.46V battery and a 14.3ohm resistor = 0.871amps and got 0.86on the 10 scale and 08.6 and 0.86 on the other two scales. (not bad on the 10A scale?)

 

[johntheo]

With apologies in advance for the newbie question...
I'm using a multimeter to figure out the source of my battery drain, so attempting to measure the leakage current between my battery terminal and its lead. When taking the readings shown below, they are quite steady, but as you can see, on the 10A setting I get a measurement of (-)69 mA, while on the mA setting I get 1.5 mA. Is this just because of the lower resolution (and higher error) in the 10A mode? I ask because online how-to information for doing this say to do the check in the 10A mode, and to be concerned if the current is more than about 50 mA. Based on the mA settign reading, I see no problem, but is there reason for concern based on the 10A reading?
I'd appreciate any pointers - thanks!
Rob

View attachment 90599View attachment 90600

I didn't realize how accurate these M.meters are even on very low measurements. I have a a 6200ohm resistance that I use to test/trip my RCDs (30ma) and when i connected this across the ma scale I got 2.1milliamps, theoretically 2.026 milliamps with the battery at 12.56V.