Troubleshooting Parasitic Draw - Defender Source
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  #1  
Old August 22nd, 2014, 12:25 AM
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Troubleshooting Parasitic Draw

Last Friday I drove took my truck ('94 NAS 90) on a trip. Should have been short, 2.5 hour 125 miles trip. With all kinds of traffic issues, it turned into a 4 hour ordeal, and at one point, the temp gauge started creeping too close to red for comfort (after sitting for 30 minutes at idle due to an accident up ahead).

I finally made it to my destination with no issues. But on Saturday afternoon, the battery was dead. I assumed my shitty 4 year old WalMart battery as the culprit, bought nice new Optima battery Sunday morning. Drove home Sunday night nervous, but ultimately with no problems.

However, on Monday, the battery was dead again. So here's what I did:

Charged battery and conducted parasitic draw test with multimeter.

Parasitic draw (from black battery cable back to black terminal post): 1.07mA

I removed each and every fuse and relay I could find in the 2 fuseboxes (behind the gearshift and in the engine compartment) - draw remained constant at 1.07mA

I had my original alternator rebuilt last fall, so I did not suspect it as the culprit, but I tested the battery with the truck running:

Battery with truck off, no key in ignition: about 13V
Battery with truck running, engine revving at about 2K: 13.9V

At no point can I get the truck to measure the 14.5V I read it should with the truck running. Does this point to the alternator as my fault?

Any suggestions as to how the hot road trip may have contributed, and whether my interpretations of the readings are correct would be appreciated.

Thanks
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  #2  
Old August 22nd, 2014, 12:38 AM
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How was the alternator after the tests? Was it really hot to the touch?

What was voltage at idle with the usual accessories on (radio, Ac if installed, etc)? Amps?

My first guess is that alternator is failing, not putting enough charge out at idle. Yes there's still some variability in the voltage as indicated by going to 2k rpms, but that's why it's also dying.

There's other crap to check, but horses first before zebras.
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Old August 22nd, 2014, 12:49 AM
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Quote:
Originally Posted by rankar View Post
How was the alternator after the tests? Was it really hot to the touch?
I didn't feel the alternator, I'll check that tomorrow, I did put a long screwdriver on it and it was making screetchy noises, but I can't recall if those were normal or abnormal screetchy noises.

Quote:
Originally Posted by rankar View Post
What was voltage at idle with the usual accessories on (radio, Ac if installed, etc)?
At idle I think it was about the same, 13.8V or 13.9V. Accessories made very little difference (lights, radio, turn signals, wipers)
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Old August 22nd, 2014, 12:56 AM
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Where are you located? If you're close, we can swap my alternator in for a test.

But that screeching noise tells me that the bearings could be going. If it's really hot that's another reason to believe that it's on its way out.
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Old August 22nd, 2014, 01:00 AM
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Quote:
Originally Posted by rankar View Post
Where are you located? If you're close, we can swap my alternator in for a test.

But that screeching noise tells me that the bearings could be going. If it's really hot that's another reason to believe that it's on its way out.
Thanks for the offer, but I'm nowhere near Connecticut. If signs keep pointing to the alternator, I'll yank it and take it back to the shop that did the work.
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Old August 22nd, 2014, 01:08 AM
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My money is on the alternator. Before you pull it disconnect the main lead off the back and retest the battery to see if you still have a parasitic draw.
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Old August 22nd, 2014, 01:09 AM
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Good idea

------ Follow up post added August 22nd, 2014 01:12 AM ------

I bet if you let it idle for ten minutes or more the alternator will be scorching hot and you'll start to lose output.
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  #8  
Old August 22nd, 2014, 02:36 AM
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1 mA? That's really nothing. That's about the draw you would see from a dim LED like the one on most 12V cell phone chargers or car alarms. Are you sure it's 1 mA? For comparison, I once had a parasitic draw of about 196 mA and it would take a couple of days before it drained it too low to start.

Check the range setting on your multimeter.
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  #9  
Old August 22nd, 2014, 05:51 AM
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Alternator is shitting the bed. Replace.
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Old August 22nd, 2014, 11:07 AM
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Pretty sure they'll test your alternator at autozone or any auto parts store.
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Old August 22nd, 2014, 12:59 PM
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Quote:
Originally Posted by chris snell View Post
1 mA? That's really nothing. That's about the draw you would see from a dim LED like the one on most 12V cell phone chargers or car alarms. Are you sure it's 1 mA? For comparison, I once had a parasitic draw of about 196 mA and it would take a couple of days before it drained it too low to start.

Check the range setting on your multimeter.
On the mA setting it's showing 1.07 - am I reading that incorrectly?
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Old August 22nd, 2014, 01:10 PM
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my 2 pennies.


Maybe your old batterie just shit the bed. When you installed the new one did you scuff up the terminals and the clamps so you have 2 clean metal surfaces mating each other?
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Old August 22nd, 2014, 02:00 PM
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Are there any aftermarket accessories fitted? Those are almost always the culprit for draws.

1.07mA would not drain the battery down overnight. FWIW Newer Land Rovers have about an 18-24mA quiescent draw which doesn't drain the battery for weeks at a time.
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Old August 22nd, 2014, 02:11 PM
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You are not reading your multimeter correctly. It sounds to me like you have a draw of 1.07 amps (not milliamps)

There is not a multimeter on the planet that could read mA resolution down to two decimal points.

(It is reading 1070mA and rolling that up to 1.07A on the display)

A 1 amp draw can absolutely drain a battery overnight. You are on the right track by going fuse by fuse. Is there any aftermarket wiring of any kind installed in the truck?
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Old August 22nd, 2014, 02:25 PM
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Quote:
Originally Posted by transientmechanic View Post
There is not a multimeter on the planet that could read mA resolution down to two decimal points.
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Old August 22nd, 2014, 02:28 PM
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That only tells me that it sees absolutely zero current. That's much different than actually measuring draw at that resolution.
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  #17  
Old August 22nd, 2014, 02:33 PM
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Old August 22nd, 2014, 03:18 PM
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Quote:
Originally Posted by transientmechanic View Post
A 1 amp draw can absolutely drain a battery overnight. You are on the right track by going fuse by fuse. Is there any aftermarket wiring of any kind installed in the truck?
That makes sense. No, nothing aftermarket, it's bone stock except for the radio, which doesn't change the drain when I pull the fuse.

Would a bad alternator, as has been suggested, contribute to the battery drain?
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Old August 22nd, 2014, 03:23 PM
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A bad alternator would only cause a draw if one of the diodes has failed. Usually that would be significantly higher than 1 amp but it is possible. (I had a 2005 Range Rover with a shorted diode that was drawing about 5 amps back through the alt)

Hook up your meter again and disconnect the power cable on the back of the alternator.
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Old August 22nd, 2014, 03:29 PM
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Could the ECU be causing the draw?
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