Strange multimeter reading

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I was checking my wife's car for parasitic draw. I attached my Innova 3320 multimeter (has been very accurate so far) leads betweeen the negative cable and negative post. On the 10A scale ( 200mA to 10A) it reads .029. On the 0-200mA scale it reads 0.00. I checked everything repeatedly and have no clue what I'm seeing. 290mA should read 0.290. 29mA should show on the 0-200mA scale.

What is up?

Bob
 
Two possibilities:

1)You need to switch the positive meter lead to the far right jack. The far left jack is ONLY for the 10A range.

2)The fuse for the 200mA scale is blown. Replace it.
 
The leads are in the correct jacks.

I was able to get a reading of 0.01-0.02mA on the 0-200 scale, so I think the fuses are ok.

Interestingly, when I first connect the leads on the 10A scale, it first reads .080 and after about 10 seconds it drops to .029.
I assume something is powering up and settling down (computer, stereo antitheft, etc).

I'm getting the same reading from two multimeters.

This is maddening and embarrassing because I'm a former master mechanic...yes... specialized in driveability.
smile.gif


Bob
 
i am just learning about multimeters + bought an EXTECH #470 just under a buck, thought i was using it wrong + it failed to display at times, bought a Klein recently + know i know the out of warranty Extech is a piece of poop!!
 
Yeah, I could have 2 bad multimeters.
But it is interesting that they both read the same.
 
Originally Posted By: Loogie
Interestingly, when I first connect the leads on the 10A scale, it first reads .080 and after about 10 seconds it drops to .029.
I assume something is powering up and settling down (computer, stereo antitheft, etc).

What cars is this?

When I first connect the battery on my 530i, there is several amps of current being drawn initially as all the various courtesy lights come on. If I tried that with my DMM on the mA range, it would easily blow the fuse.

Silly question, but are you using the DC range and not AC range on your DMM?

I usually prefer to use the 10A range anyway - it's more accurate on most DMMs, even if it gives you less resolution.
 
The meter’s internal impedance is probably very different between the 2 current ranges.
I run into this weirdness even with high-end Fluke meters on various circuits.
Since you have 2 meters, as a check, here is an idea:
With one meter measure current on both ranges,
while measuring voltage drop with the other meter.
 
Originally Posted By: Loogie
The leads are in the correct jacks.

I was able to get a reading of 0.01-0.02mA on the 0-200 scale, so I think the fuses are ok.

Interestingly, when I first connect the leads on the 10A scale, it first reads .080 and after about 10 seconds it drops to .029.
I assume something is powering up and settling down (computer, stereo antitheft, etc).

I'm getting the same reading from two multimeters.

This is maddening and embarrassing because I'm a former master mechanic...yes... specialized in driveability.
smile.gif


Bob



Looks like your 10A scale is working, .080 amps equals 80 milliamps, .029 amps equals 29 milliamps. It you want to further test this......With the meter hooked in series, Take a incandescent test light hooked to the positive battery terminal & probe a good ground on the engine somewhere, The meter should increase to around 1/2 a amp or 500 milliamps.
I use a test light because it's a fairly known low load device for the 10a scale. IIRC some cheap multimeters are not fused on the 10a scale!

It also looks like your milliamp jack fuse is blown, VERY easy to do!!! Never complete the circuit with the 2 amp milliamp jack fuse or the 10a amp jack fuse! Use a jumper wire to do the initial hook-up....Wait a few minutes to let the modules go to sleep. Unhook the jumper wire to allow the current to flow through the meter.

29 milliamps is right where you want to be with a basic modern car. Some upscale vehicles will draw more.
 
The load the vehicles electronics is placing on the vehicles battery could include that of some type of switching voltage regulator that draws power in pulses and there is a wide range of frequencies that such switchers could operate at. When a switcher draws power in pulses it could throw off the readings that an electronic Amp/milliamp meter produces.
 
It would be interesting to put a shunt resistor in series with one of the leads to the vehicles battery and then read the voltage across the shunt resistor with a digital storage oscilloscope.
 
The different ranges have different impedences and change the readings because the higher the impedence the lesser the current. Plus, the accuracy of a multimeter is normally a percentage of full scale, on the 10 amp range the acceptable error is probably greater than the reading!!!
 
Wow, some excellent observations and ideas, thanks!

My skills are very rusty, I haven't practiced in nearly 25 years.

The car is a 2003 CRV. It does have some type of electronic voltage or current management system. I replaced the part maybe 8 years ago.

Anyway, what was throwing me off is I thought the multimeter's scale wasn't matching the readings. I used a couple of meters at the dealer (one was a Fluke, I think) that absolutely would not give a reading unless on the proper scale.
I will assume the mA scale is goofed, and the 10A is reading correctly.

Funny, I started on the 10A scale and waited for it to settle. Only then did I switch to mA. I wonder if there is some sort of electronic switching going on that pulsed higher current, torching the mA scale.
I'll hook up a Nichia and see if the mA scale is torched.

Bob
 
Quote:
Funny, I started on the 10A scale and waited for it to settle. Only then did I switch to mA. I wonder if there is some sort of electronic switching going on that pulsed higher current, torching the mA scale.
I'll hook up a Nichia and see if the mA scale is torched.

Bob
Switching from 10A to mA range would require you to move the test lead from the 10A socket to the V/mA socket on your 3320. This would temporarily break the circuit and be perceived by the car as reconnecting the batterry again which may result in high initial current being pulled by the car again.

If you did not move the test lead to mA range and only shifted the range dial, then no wonder you did not get any reading.
smile.gif
 
Ok, get outta my Head!
Not 5 minutes ago that I had the same theory.

You would think that if the car is pulling 80mA initially, then falling to 29mA, then changing to the mA setting wouldn't be an issue.
It appeared safe to use the lower scale (though the readings were odd).

BUT, as you surmised, there may have been some brief inrush current or fluctuation. Poof.

My wife's car seems to be turning over a bit slower than usual, so I checked the (less than 2 year old) battery after sitting overnight. 12.41.

I then checked for parasitic draw with the results listed above.

Yesterday, I had Advance Auto test it, and it was fine. At that time it was reading 12.61, as my wife had driven it 3hrs earlier.
This morning, it reads 12.45.

Parasitic draw vs bad battery.
I'm leaning toward bad battery because the alternator is charging hard, putting out 14.65v, but the battery quickly settles to about 12.60, and seems to be drifting down from there.

I remember attending a full day course on batteries around 1993.
We learnedd that they can fail in remarkably complex ways, eluding even some fairly advanced testing. Thus, only rarely could the battery be ruled out.
AKA, the battery remains suspect unless another culprit is found.

This weekend I'm going to assure it is charged, isolate it, and see if voltage drops overnight. That will provide my answer.
 
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Your battery behavior sounds pretty normal to me.

Parasitic drain of 29 mA is quite low. My old 530i pulls about 80 mA, and even then, the car can still sit for weeks and start normally afterwards.
 
If we see anything under 100mA, we consider it to have a negligible parasitic draw and look elsewhere. Normally, if a vehicle has a parasitic draw that is actually affecting overnight draining, it will always be above 300mA. CCA and storage capacity are not really related. Need a good modern battery tester to measure storage capacity. We have several here at work, but they are around $10k each.
 
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Yeah, I agree that the small drain is ok.

But I don't trust the drop in voltage. I think the battery is trying to tell me something.
Ok, that sounds kinda weird.

$10k for a battery tester? Wow! I recall there was some high tech equipment at the battery course I attended.
Maybe I could pick one up at Harbor Freight for $5k.
smile.gif
 
Just random stuff

When you disconnect your battery cable to do a current draw, use a decent jumper lead to complete the circuit. Wire your meter on the amps scale of choice parallel to the jumper. Give the car 5 minutes to let the modules go to sleep and then disconnect one end of the jumper and run all the current through the meter. Lost a few 10 amp fuses in the Fluke 88 when the air suspension would kick on in Lincolns and Mercs. Generally 50 milliamps is the cutoff point for an allowable draw.

I miss having a Sun VAT40 to play with for diags.
 
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