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Bad diode? Check you AC noise levels just for the sake of tracking it down.

 

20141119_134311_resized_zps2d8ea538.jpg

It is possible for a diode to be bad but still show good on the AC portion. I would pull the alternator and have it tested.

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I've had several  internally regulated   Delcos    that  refused to  'shut down'..   and   eventually   drained the  battery...     

 

After you have the  alt disconnected,  wouldn't you just  ohm  each terminal back to the case,  looking for  internal shorts?

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Hey guys

Had to let truck sit - other things going on.

Started to wonder if maybe I had a bad battery and was cross draining ......... so charged them both for 24 hours. The suspect one passenger side  is holding 12.5V and the good one 12.9v. Hard to tell though as no large draw/load.

 

So I disconnected the field wire from alternator ..... no change still 0.5A draw.

Then I disconnected the passenger side battery completely - which is where the alternator is grounded through ...... still 0.5A draw on the positive side from the 140A alternator circuit (which is shared with grid heater and FSS).

So thinking its not the alternator ...... FSS or grid heater .... ???

 

Am I doing this right in terms of isolating ?

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Problem is I cant really - as its shared with Grid Heater and FSS. I already know thats the circuit where the draw is comming from - just about isolating the problem component.

I figured if I disabled the field wire as well as the the passenger side battery that would be enough to take the alternator out of the equation ....... not right ?

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I'll have to post a pic.

Disabled (took off) the FSS wire and no difference.

So basically have 3 more wires on the 140A alternator circuit

 

1 large Red (ties from battery to alternator circuit)

1 large black (ground to side of block near APPS/TPS)

1 mid/small black which feeds into a wire loom back behind engine fuse compartment .........

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pic

alt_fuse.jpeg

 

So Large Red is power for ALT on left terminal under small black wire.

Large Black on right terminal is ground to block near APPS/TPS 

Small Black goes into LOOM that runs behind engine fuse compartment

(I removed the small red wire on the right terminal which was for FSS solenoid)

 

Passenger side battery fully disconnected.

 

If I do an AMP test with the +ve battery cable disconected..... bridging the battery terminal with the positive cable with my multimeter set to 10A Amergae test ....... I get ~0.5A. 

If I disconnect the red wire on the very end of the battery cable (goes to the alternator circuit) the draw stops.

Edited by JOHNFAK
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The beginning of this month the Battery on my work van went dead over night. Recharged battery  and load tested o'k. draw test was 9 amps. AC voltage varied between .7 and 3+ volts. Disconnected red wire at B+ terminal on alternator and no more draw. Replace alternator and no more draw, no more dead battery.
 

Edited by IBMobile
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You would need to disconect the large wire on the back of the alternator itself. That would take the diodes out of the equasion, and I am sure it would stop the draw also. I firmly believe you have failed diodes and need a new alternator. Make sure the replacement is tested for AC noise and is under .1 (one tenth) volt.

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What does that red wire go to? FSS?  It would seem you've isolated the circuit or at least the bus that it's leaking... I don't know much about the P pump, but it would appear you found your problem.  Perhaps there is a leaking relay in the FSS system.  I would step my way through that system as far as possible to try to isolate the leak.   

 

And just for clairification, all these tests were with the engine off?  I am asking that to ensure that there is zero change of any AC in the system.  I had "AC" being backfed into the system through a solenoid from an air dog relay.  Killed a bunch of parts... about 3000 worth. 

Edited by CSM
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You would need to disconect the large wire on the back of the alternator itself. That would take the diodes out of the equasion, and I am sure it would stop the draw also. I firmly believe you have failed diodes and need a new alternator. Make sure the replacement is tested for AC noise and is under .1 (one tenth) volt.

This is where I am leaning.

Going to pull the alternator and have it bench tested - but not sure how much I trust those tests is part of problem - they always want to sell your a new part ..... plus sometimes the tests say fine but not fine.

 

If the ground side of the alternator is disabled ..... (passenger battery fully isolated/disconnected) - why is the alternator circuit still live though ? Multiple grounds ?

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What does that red wire go to? FSS?  It would seem you've isolated the circuit or at least the bus that it's leaking... I don't know much about the P pump, but it would appear you found your problem.  Perhaps there is a leaking relay in the FSS system.  I would step my way through that system as far as possible to try to isolate the leak.   

 

And just for clairification, all these tests were with the engine off?  I am asking that to ensure that there is zero change of any AC in the system.  I had "AC" being backfed into the system through a solenoid from an air dog relay.  Killed a bunch of parts... about 3000 worth. 

Engine off.

The redwire in the pic is loop from the ALT circuit to the battery - basically for charging the battery from alternator. 

There was a smaller red wire for FSS which I removed to take the FSS out of the equation.

 

All roads point to ALT ..... going to bench test it ......... but just want to be 100% sure as not able to return if it turns out to be something else.

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I can't say as I have seen any alternators that were not grounded through the case and through the mounting. That is why I said to disconnect the wire at the alternator and test it. That will be a difinitive test as to whether the alternator is the problem or not.

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