Parasitic Auto Battery Testing

In summary: It was a "car" type multimeter and had a scale of 40mA.In summary, the car's electronics do not work when a battery is hooked up to a serialized multimeter. The current should flow through the meter to the car's electrical system, but it doesn't. The meter was in amps and the fuse was not the issue.
  • #1
mearvk
133
0
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.
 
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  • #2
Did you try to start the engine?

BTW What's your meter's maximum current specification?
 
  • #3
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 .
 
  • #4
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.
 
  • #5
How do you "test for amps"?
 
  • #6
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).
 
  • #7
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).
 
  • #8
Yeah, I'm trying to see where the overnight battery drain is coming from. Not worried about CCAs.
 
  • #9
berkeman said:
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 [Broken]

.
 
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  • #10
mearvk said:
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...
 
  • #11
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.
 
  • #12
mearvk said:
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 [Broken]

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
 
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  • #13
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.
 
  • #14
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..

N501203001.jpg


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.
 
Last edited:

1. What is parasitic auto battery testing?

Parasitic auto battery testing is the process of measuring the amount of electrical current being drawn from a vehicle's battery while the car is turned off. This can help identify any components or systems that may be draining the battery, causing it to lose its charge.

2. Why is parasitic auto battery testing important?

Parasitic auto battery testing is important because it can help prevent unexpected battery failure. If a component or system is continuously draining the battery, it can lead to a dead battery and leave you stranded. Regular testing can help identify any issues and prevent this from happening.

3. How is parasitic auto battery testing performed?

Parasitic auto battery testing is typically performed using a multimeter. The multimeter is connected between the negative battery terminal and the negative battery cable. The current draw is then measured, and if it exceeds the recommended amount, further testing can be done to identify the source of the drain.

4. When should parasitic auto battery testing be done?

Parasitic auto battery testing should be done periodically, especially if you have noticed any issues with your vehicle's battery. It is recommended to do it every 3-4 months or whenever you have performed maintenance on your vehicle's electrical system.

5. Are there any risks associated with parasitic auto battery testing?

There are minimal risks associated with parasitic auto battery testing as long as proper safety precautions are taken. It is important to disconnect any aftermarket devices or accessories before testing to avoid any damage to the electrical system. It is also recommended to have a professional mechanic perform the testing if you are not familiar with the process.

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