Alternator Parasitic Drain??

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Alternator Parasitic Drain??

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Alternator Parasitic Drain??

Postby WKU Toppers » November 8th, 2018, 11:08 am

Gents,

I’m desperately in need of some schooling here, I’m hoping to be educated. My problem centers around what I believe is parasitic draw (ignition switch off) and a newly rebuilt 60 amp alternator.
My vehicle is an M151A1 with a new wiring harness. In brief, I’m getting current draw at the battery, immediately upon installing the alternator (ignition switch off).

Prior to installing the alternator, I have absolutely no draw at the battery (ignition switch off). When I connect the alternator, my multi meter shows approximately 0.70m draw. I have a faint spark when terminal is connected. The alternator is rebuilt. I’ve tried two newly rebuilt alternators—both with the same result.

Here’s how I’ve got the alternator is wired:

(1) Alternator ground lug connected to vehicle chassis (good ground).
(2) Alternator field wire ( #586) to switched side of ignition. That is, power to field only when ignition is on.
(3) Alternator output (#5) directly to foot starer terminal joined with the cable running directly to battery ( + side).

To trace the problem I’ve disconnected everything from the foot starter switch except:

(1) Alternator output cable (#5) and
(2) Battery cable to foot starter
(3) Disconnected starter cable from foot starter switch.

This leaves only the alternator cable attached to the foot starter terminal with the a common connection to the battery cable. Nothing else is connected to the electrical system. After all of this I still have a 0.70 draw at the battery.

Given that the system shows no signs of draw without the alternator in circuit, and that I’m getting the same problem after trying two different rebuilt alternators, my thinking is that the alternators internal regulator might be responsible. I'm not smart enough to know how these regulators work -- but I'm sure others have seen and solved this problem but I can’t seem to figure this one out.

As a last ditch effort, tonight I’ll start the MUTT to see if I’m getting any AC voltage at the battery. If so, I assume that would indicate leaking diode(s) in the alternator. Which might help explain the problem. I just don’t know enough about these circuits to trouble shoot them. And I would doubt that I’ve had to identical problems on newly rebuilt alternators.

Please educate me. There is a lot of smarts on this board, I need to some guidance. Any help would be appreciated.

Thanks
Bob
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Re: Alternator Parasitic Drain??

Postby SEABEE62 » November 8th, 2018, 11:15 am

Hi Bob, Welcome aboard......you'll get responses on this matter, so enjoy this G . Seabee
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Re: Alternator Parasitic Drain??

Postby rickf » November 8th, 2018, 1:46 pm

Hi Bob, Welcome and I am pretty sure your diagnosis is on the right track but here is a link to a manual you can download that will help you out.

http://radionerds.com/images/c/cb/DA_Pa ... 750-33.pdf
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone
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Re: Alternator Parasitic Drain??

Postby muttguru » November 8th, 2018, 5:14 pm

It would be unusual (but not impossible) for you to have a couple of rebuilt alternators that were both having diode problems.
There is another possibility. You have an M151A1 and unless you say otherwise, let's assume that the floor start switch is not new. Other owners have had similar problems to you and at least one owner disconnected and removed the floor start switch and replaced it with a known good one. The electrical drain was cured. Those floor start switches sometimes have a buildup of carbon which allows a very slight leakage. Worth a look....and cheaper than another alternator !
Ken
Kind regards....
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Always wanted - Details and pictures of M416 Trailer data plates & M151 data plates & body-tags for my research. Thanks!

Contact address - - muttguru@aol.com

Notes for 2018...... Doing nothing is ALWAYS an option !
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Re: Alternator Parasitic Drain??

Postby svramselaar » November 9th, 2018, 2:51 am

hi

if the wire no 5 is disconnected from the alternator and the draw is stil there one off the positive diode`s have a leak

george
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Re: Alternator Parasitic Drain??

Postby m3a1 » November 11th, 2018, 9:16 am

...another source for a power drain is the brake light. If you have one of those brake pedals that doesn't quite want to return all the way back up and coupled with that, if you leave your signal light switch on (because you can't remember to turn it on every time you drive) is can run a very low current across the brake light bulb. This current may be so low you may not even notice the bulb is lit unless you're looking right at it. This particular gremlin had me chasing my tail for some time until I figured it out.

Cheers,
TJ
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