Why Don't My Car's Electronics Work During Parasitic Battery Testing?

[mearvk]

Hello all.

Was wondering when I test for amps on my car's battery when sitting in my driveway why doesn't the car's electronics work when I hook up the battery via a serialized multimeter? The current should still, theoretically, go through the meter to the car's electrical system but it doesn't.

Perhaps you guys could explain this weirdness.

Thanks.

 

[dlgoff]

Did you try to start the engine?

BTW What's your meter's maximum current specification?

 

[jim hardy]

what is meant by "serialized" ? In series with a battery lead?

i would guess either:

A. You have the meter on volts
B. You have blown the internal fuse in your meter.

If B, be aware it is IMPORTANT that you replace fuse with one rated for same voltage, probably at least 250 or maybe 600 volts, and NOT a glass automotive fuse they're just 32 volts...

Look at this link,
http://support.fluke.com/find-sales/Download/Asset/2041429_6001_ENG_A_W.PDF

for a quick tutorial with photo of what the wrong fuse can do .

 

[mearvk]

Yeah, in series with battery ground specifically.

Meter was in amps. The meter was brand new and it was showing some minor amperage which makes me doubt it was the fuse.

No, I didn't try and crank the engine; I meant the interior light, electric hood pop, etc did not work when the ammeter was hooked up in series with ground terminal of car battery.

 

[russ_watters]

How do you "test for amps"?

 

[mearvk]

Multimeter set for 40amps DC hooked up in series to battery ground.

More specifically, the ground connector (the 10mm nut holding the wire to ground) was removed from the ground terminal. Then I connected the ground of the ammeter to the battery's ground terminal and the positive ammeter terminal to the wire acting chassis ground (the wire previously attached to the battery's ground terminal).

 

[berkeman]

To test for starting current in your car, you will need a high-current Hall sensor-based current clamp. That will either have its own display, or some models let you plug them into your DVM (and you read it out on the voltage setting of your DVM).

 

[mearvk]

Yeah, I'm trying to see where the overnight battery drain is coming from. Not worried about CCAs.

 

[berkeman]

To test for starting current in your car, you will need a high-current Hall sensor-based current clamp. That will either have its own display, or some models let you plug them into your DVM (and you read it out on the voltage setting of your DVM).

Like this 400A unit from Fluke:

http://www.torontosurplus.com/test-equipment-1/probes-sensors-rf-sources-noise/fluke-80i-410-i410-dc-ac-clamp-on-hall-effect-current-probe.html

.

 

[berkeman]

Yeah, I'm trying to see where the overnight battery drain is coming from. Not worried about CCAs.

Oh, nevermind. As long as you don't try to start your car or turn on any lights, a DVM should be fine for tracing parasitic currents...

 

[mearvk]

So my question is what's the reason that we can't turn on the interior lights, for instance, with the multimeter connected in series like described? It completes the circuit so current should flow. Not sure what I'm missing.

 

[jim hardy]

So my question is what's the reason that we can't turn on the interior lights, for instance, with the multimeter connected in series like described? It completes the circuit so current should flow. Not sure what I'm missing.

and

Multimeter set for 40amps DC hooked up in series to battery ground.

40 amps? Multimeter? what make and model is it , so i can look up a manual?

40 amps requires heavy test leads and connectors. That'd be one expensive piece of test equipment.

A multimeter scale of 4xxx sounds like a digital meter with 4000 count ADC, like this cheapie:
http://www.extech.com/instruments/resources/manuals/dm110_um.pdf

which has a scale of 40 MILLIamps not amps

which puts me back to my guess B in post 3.

Another possibility is - better multimeters require you to move red lead from the V/Ω jack to the current jack. Is yours so equipped, if so did you move the lead?

If you have a second meter or continuity checker,
place your multimeter in 40 (milli?)amp position and measure resistance between its leads with the other meter. Should be less than ten ohms if 40 milliamps, way less than one ohm for 40 amps..

good luck !

old jim

 

[berkeman]

Yeah, 40 Amps is pretty stiff. My Fluke has a 10A scale and a lower current scale. Each uses a different fuse and a different in-line test resistance.

 

[jim hardy]

My old Beckman has a 2000 count ADC, resistor sized to provide 200 mv drop at full scale current.

Note to OP - That fuse voltage rating is quite important. Better hardware stores carry suitable fuses, so does Radio Shack. Buy several and make a place to keep them.

EDIT late addition..

For automotive work i prefer an ancient meter i found at a yard sale, i think it is from the 1930's..
It looks just like this but is calibrated in amperes, +/- 30, and the font is almost Olde English..

It has a small guide on back to place against the wire and it measures DC current through the wire by the magnetic field (think gauss) .
One gets reasonable readings without disconnecting any wires. But it won't resolve fractions of an amp...

point being - if you're handyman keep an eye open for one. Very handy for checking alternator output.