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#4757152 - 05/14/18 05:29 PM Strange multimeter reading
Loogie Offline


Registered: 09/17/07
Posts: 131
Loc: Michigan
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

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#4757165 - 05/14/18 05:40 PM Re: Strange multimeter reading [Re: Loogie]
brianl703 Offline


Registered: 05/07/04
Posts: 10597
Loc: Nokesville, VA
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.

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#4757206 - 05/14/18 06:14 PM Re: Strange multimeter reading [Re: Loogie]
Loogie Offline


Registered: 09/17/07
Posts: 131
Loc: Michigan
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

Bob

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#4757229 - 05/14/18 06:36 PM Re: Strange multimeter reading [Re: Loogie]
benjy Offline


Registered: 08/23/10
Posts: 926
Loc: pa
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!!

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#4757235 - 05/14/18 06:40 PM Re: Strange multimeter reading [Re: Loogie]
Loogie Offline


Registered: 09/17/07
Posts: 131
Loc: Michigan
Yeah, I could have 2 bad multimeters.
But it is interesting that they both read the same.

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#4757273 - 05/14/18 07:22 PM Re: Strange multimeter reading [Re: Loogie]
Quattro Pete Offline


Registered: 10/30/02
Posts: 36092
Loc: Great Lakes
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.
_________________________
'02 530i (Edge 0W-40)
'15 Q5 3.0T (Edge 5W-40)
'18 Charger SRT (FF)

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#4757285 - 05/14/18 07:29 PM Re: Strange multimeter reading [Re: Loogie]
SWS Offline


Registered: 04/10/04
Posts: 347
Loc: Tennessee
The meterís 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.

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#4757296 - 05/14/18 07:34 PM Re: Strange multimeter reading [Re: SWS]
Quattro Pete Offline


Registered: 10/30/02
Posts: 36092
Loc: Great Lakes
Originally Posted By: SWS
The meterís internal impedance is probably very different between the 2 current ranges.
Yup. There is something called high internal burden voltage that skews mA range results on most DMMs.

http://www.fluke.com/fluke/uses/comunidad/fluke-news-plus/articlecategories/electrical/burdenvoltage

But I don't think this alone could account for the strange results that OP is seeing. Something else is going on.

_________________________
'02 530i (Edge 0W-40)
'15 Q5 3.0T (Edge 5W-40)
'18 Charger SRT (FF)

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#4757314 - 05/14/18 07:42 PM Re: Strange multimeter reading [Re: Loogie]
JHZR2 Offline



Registered: 12/14/02
Posts: 41975
Loc: New Jersey
Put the two DMMs in series??

In ammeter mode they should read similarly.

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#4757340 - 05/14/18 08:03 PM Re: Strange multimeter reading [Re: Loogie]
clinebarger Online   content


Registered: 12/19/13
Posts: 2080
Loc: Fort Worth, Texas
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

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.
_________________________
2001 Chevy Camaro L92/4L80E
2006 Chevy 2500HD LBZ/Allison 1000
2010 Toyota Corolla 2ZR-FE/Auto

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#4757372 - 05/14/18 08:35 PM Re: Strange multimeter reading [Re: Loogie]
JimPghPA Offline


Registered: 08/22/09
Posts: 3878
Loc: Pittsburgh,PA U.S.A.
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.
_________________________
Boy will I be happy when ALL vehicles on public roads are autonomous.


JimPghPa


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#4757378 - 05/14/18 08:39 PM Re: Strange multimeter reading [Re: Loogie]
JimPghPA Offline


Registered: 08/22/09
Posts: 3878
Loc: Pittsburgh,PA U.S.A.
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.
_________________________
Boy will I be happy when ALL vehicles on public roads are autonomous.


JimPghPa


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#4757494 - 05/15/18 12:32 AM Re: Strange multimeter reading [Re: Loogie]
redbone3 Offline


Registered: 06/09/12
Posts: 669
Loc: Reno, NV
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!!!
_________________________
2014 Passat Wolfsburg, 1995 Miata.

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#4757518 - 05/15/18 03:27 AM Re: Strange multimeter reading [Re: Loogie]
Loogie Offline


Registered: 09/17/07
Posts: 131
Loc: Michigan
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

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#4757519 - 05/15/18 03:36 AM Re: Strange multimeter reading [Re: Loogie]
Quattro Pete Offline


Registered: 10/30/02
Posts: 36092
Loc: Great Lakes
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
_________________________
'02 530i (Edge 0W-40)
'15 Q5 3.0T (Edge 5W-40)
'18 Charger SRT (FF)

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