I knew someone would ask sooner or later.
I am using a clamp-on AC/DC ammeter. The model is Intertek 5009374 / Voltcraft VC330. There are quite a few similar clones available all basically made by the same company. They usually differ only in the case color and are priced around $45 or so.
I am using it clamped around the negative return lead(s) at the battery.
John, I asked because I have been through this in past on my Mercedes - looking for causes of stray currents. I have a different but similar clamp on meter and know I should have bought a Fluke or similar!
On the Outback, it is hard to attach the clamp meter properly because there are two conductors at least, on positive and negative terminals. Meter should only go around one conductor (not two) and that conductor should be centered and at 90deg to meter opening (I think I tested both pos and neg one at a time and added measurements) Polarity should also be correct, but which side is positive on a battery ground cable?? Maybe meter should be other way around?
The accuracy of these meters at very low currents is usually not very good. The manual for the model you have says (+/- 2% of reading +8). where Specified accuracy is ± (% of the reading + display errors in counts = number of least significant digits). What the heck does that mean?? OK, I checke with Fluke - see at bottom of post.
All my test on my Subaru told me, was that current with everything off and no FOB nearby was something under 100mA and with FOB nearby about 2 amps. Someone said leakage current should be about 70mA. Thats just the way it was designed, so nothing I can do about it except attach battery maintainer when car is not used for long period. And keep FOB well away from car when it is parked.
ccuracy for a clamp meter is usually expressed as a percent of reading. An accuracy of 1% of reading means that for a displayed reading of 100 amps, the actual value of the current could be anywhere between 99.0 and 101.0 amps.
Specifications may also include a range of digits added to the basic accuracy specification. This indicates how many counts the digit to the extreme right of the display may vary. So the preceding accuracy example might be stated as ±(2% + 2). Therefore, for a displayed reading of 100.0 amps, the actual current could then be estimate to be between 97.8 and 102.2 amps.
So for +/-(2%+8) for 100mA, would that then be between 97.2 and 102.8 mA?. Good enough for our purposes!