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DMM Showing Current without Current Source

lothian

Jan 5, 2021
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I am attempting to use my DMM to identify a parasitic drain in my car's electrical system using a Chinaseum-brand DMM with an amp clamp.

After I set the thing to DC amps and before I clamp it to the target conductor, it displays a range between 0.1A and .22A. This makes t'shooting with this tool impossible. I can't figure out how to "zero" it within this mode; nor can I determine if, as with voltage measurements, extraneous ambient readings are normal. The user manual is useless,

Thoughts? Suggestions?
 

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dave9

Mar 5, 2017
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In the manual, page 7 reads "Correction of Zero correction for DC measurement" "with no conductor inserted... press and hold the Z/F key (approx 3 seconds) until a beep sounds and the Zero symbol appears on the display"

https://m.media-amazon.com/images/I/C1+4pwuzOSS.pdf

Although the above version of the manual is human readable, it doesn't appear to be searchable so you might eventually want to find a better version for easier use.

However, another way to measure for this "IF" you have major brand (not generic chinesium which may be off-spec) fuses, is measure mV across the fuse, but don't forget to check the alternator cable too in case it has a leaky diode pack.

https://www.powerprobetek.com/wp-content/uploads/2018/12/fuse-charts.pdf
 
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lothian

Jan 5, 2021
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b'woof.. Thanks for reading the manual to me.

<zero'd>

I'm getting a seemingly more appropriate current reading now: >100mA across the pos. battery cable. I'll let the DMM monitor things for an hour, then check the min/max and see if it detected a spike Otherwise, it may be that my problem isn't a parasitic drain afterall...
 

dave9

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100mA is excessive once a vehicle enters its lowest power state but (that or even higher than 200mA) is to be expected in its higher power state before that times out... depends on the age/model vehicle.

If your vehicle senses a hood switch or door latches (or disconnect/reconnect battery too) to trigger a higher power state, you may have to wait for that to time out to get the deep sleep state current draw reading, or in the case of the door latches, with the door open you can flip the latch mechanism closed manually to toggle the door sense switch (assuming that is how they designed it, as it has been decades since I saw vehicles with door open sense switches using a pin/plunger instead of the switch integrated into the latch mechanism)... just don't forget to flip the latch back open before trying to shut the door. :)
 
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lothian

Jan 5, 2021
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right... I've done all that--doors, hood, latches latched and triggers clamped. The car has been sitting since 9am in this state. I've been monitoring the battery as well: 14.48 at 9am/14.30 ten minutes prior to this post. Recent meter readings show similar current draw values as previously posted--nothing like true zero or just above, which bothers me..

I'm following the procedure here:

Time to start pulling fuses, methinks.
 

Bluejets

Oct 5, 2014
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I'd be disconnecting the alternator first.
Beats me why you need a tong meter when it's only small current drain where the meter can measure direct.
 

Martaine2005

May 12, 2015
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Otherwise, it may be that my problem isn't a parasitic drain afterall.
What is the problem?
Are you having a flat battery after a day?
Or 3 days?.
What vehicle is it? year?
Newer model cars have 50mA or lower after it goes to sleep. 100mA is excessive but not necessarily a fault.

Martin
 

Kiwi

Jan 28, 2013
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Having been an automotive electrician for 40years, I have a little bit of experience finding current leaks.

upload_2021-9-1_18-29-29.jpeg

I fit one of these terminals to the negative battery post and turn the knob to ON.
I then start and run the vehicle for a couple of minutes and then turn it off.
I then turn my multimeter to the 10A scale and connect one lead to the vehicle side and the other lead to the battery side.
The meter will show the discharge current when the green knob is turned to OFF.
Some vehicles can take ages to go to sleep before you can confirm if there is a leak or not. Grrr...
I usually turn the knob back to ON, turn the meter off, and walk away for a while.
I come back to it occasionally, turn the meter on, and turn the knob OFF to see if it has gone to sleep.

My clamp meter is a 1000A model, so is not very accurate with the small currents that are usually found as leaks.

Not sure whether a 60A clamp would be totally accurate at these small currents either. Might pay to compare it with an inline multimeter.
 

lothian

Jan 5, 2021
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2006 Hyunda GLS v6

The story
6yo battery suddenly would be drained between jumps; citing age we replaced it with new. That battery was also dead inside 24hrs. Time to hunt for a leak.

An issue of datum...
We need: 1) Hyundai's official module-shutdown procedure--aka, "sleep"; 2) the time-to-module-shutdown; and, 3) the expected current draw under module-shutdown condition (really important, that). One might expect the Electrical Troubleshooting Manual portion of the Hyundai 2006 Sonata Factory Service Manual (here in front of me) to provide important information. It doesn't, Sooo... we resort to averaging the gamut of resources found on the Internet and proceed. Not ideal.

An issue of equipment...
Most amp clamps aren't well-suited to detect milliamp current--the tool we're using is no exception. It does display readings two values to the right of the decimal when set at 60A--iow, milliamps. But without an OEM datum for expected module-shutdown current draw, we have no confidence in any readings.

An issue of procedure...
There are three general procedures when investigating leaks, with myriad hybrids. The amp clamp does provide readings, but not with the specificity to move on thru the rest of that particular procedure. We'll hook the DMM in series and continue t'shooting.
 

dave9

Mar 5, 2017
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Absolute values are not really needed, just to make sure you don't toggle any of the circuits that cause it to come out of it's deepest sleep state for ~1 hour, then measure mV across all fuses (no need to remove them unless they don't have access at the top for meter probes which most do). Practically (if not absolutely) everything is going through a fuse besides the starter and alternator, though if anything aftermarket is installed it might have an inline fuse instead (or none if poorly installed).

Deepest sleep state current should be under ~60mA, would have to be substantially more than that, to drain the battery quickly, though if it is an intermittent fault like a wiper motor, you might only get a momentary few-amps drain every few minutes on certain vehicles.
 

davenn

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Sep 5, 2009
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6yo battery suddenly would be drained between jumps; citing age we replaced it with new. That battery was also dead inside 24hrs. Time to hunt for a leak.


very few batteries last 6 years these days


An issue of equipment...
Most amp clamps aren't well-suited to detect milliamp current--the tool we're using is no exception. It does display readings two values to the right of the decimal when set at 60A--iow, milliamps. But without an OEM datum for expected module-shutdown current draw, we have no confidence in any readings.

You are wasting your time with a clamp meter


The amp clamp does provide readings,

but they wont be useful
 

hevans1944

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Jun 21, 2012
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I'd be disconnecting the alternator first. ....
Yep, there are six stud-mounted rectifiers connected to rectify three-phase AC in the stator windings, produced by DC in the rotor winding when the alternator shaft is rotated by the engine. If any one (or more) of these diodes develops excessive reverse leakage current, it can easily drain the battery.
 

Kiwi

Jan 28, 2013
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"That battery was also dead inside 24hrs"
Please define "dead".
Was the battery voltage so low that it wouldn't even light up the dash indicator lights, or was it just that there wasn't enough charge left to crank the engine fast enough to start up and run?

Not all alternators have only 6 diodes. Many have 8, 9, 11, or even more.
It is really only the positive diodes leaking that cause current leaks, usually by causing current to flow through the rotor coil.
Often the alternator will feel warm when the engine has not been running for some time.
 
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