Alt. output? - Defender Source
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  #1  
Old August 30th, 2007, 01:20 PM
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David Marchand
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Alt. output?

I'm chasing down a volt drop issue and a problem I'm having where sometimes using the headlights shuts down the truck. Intermittant battery light and volt meter reading 11-12 volts

I'm getting 12.5 volts out of the altenator, 12 each on the batteries both when they are running and when they are not. I've checked almost all ground and the only thing left I have is disconnecting the aux headlight wiring harness to make sure that is not the problem (although the wires themselves look good and it is grounded. But my volt meter at the battery, is showing 12 volts when driving when it use to show 13+. Headlights on and I see a big volt drop under 12, about .5 and sometimes 11, while driving (high RPM).

Manual says alt. should be 14 +/- 0.2 volts. Is that correct and what folks have experience with? And I should see 13 at the battery or close, due to drops from connections?

I still need to test the batteries (two 6 month old odyssey's) outside of the truck. But I doubt they are the problem. I haven't seen any tach. issues which at first lead me to think it couldn't be the Alt. Anyone experience something similar?
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  #2  
Old August 30th, 2007, 01:34 PM
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Quote:
Originally Posted by dmarchand
Manual says alt. should be 14 +/- 0.2 volts. Is that correct and what folks have experience with? And I should see 13 at the battery or close, due to drops from connections?
My experience has been that you will see around 14.1 to 14.4 volts from a healthy alternator, but I'm not a mechanic, so take it for what its worth... 12 volts at teh alternator is definatley low though, and not enough to charge a 12v battery. To actually charge a battery, the potential (voltage) has to be higher than the voltage of the battery you are charging.
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  #3  
Old August 30th, 2007, 04:02 PM
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13.8 to 14.2 would be an acceptable output from your alternator.
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  #4  
Old October 1st, 2007, 10:32 PM
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Quote:
Originally Posted by dmarchand
I'm chasing down a volt drop issue....I'm getting 12.5 volts out of the altenator
I'm having same situation, 11.7 volts output.
Could you solve your problem ? any suggestions ?
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Old October 2nd, 2007, 08:36 AM
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I ended up replacing my alt. with a spare but am still experiencing the voltage drop and truck shut off so it seems to be something else.
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Old October 2nd, 2007, 02:32 PM
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Quote:
Originally Posted by dmarchand
I ended up replacing my alt. with a spare but am still experiencing the voltage drop and truck shut off so it seems to be something else.
Disconnect any accessories you don't need for the engine to run (i.e. pull fuses and/or relays) and see if the output of the alternator is correct (~14V as mentioned earlier). If not, then take it to Advanced Auto Parts (or similar) and have them test it (for free). Also make sure your ground is good. The alternator (and a lot of other bits) can not function properly if the ground is bad/not that great.
Also, make sure you belt has the right tension so that the pulley does not split on it.
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Old October 3rd, 2007, 10:59 PM
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Ground seems to be good.
Same low voltage with everything off.
Diodes ? Regulator ?
Damned... I hate electrical troubles
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Old October 4th, 2007, 09:13 AM
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Quote:
Originally Posted by JFD
Ground seems to be good.
Same low voltage with everything off.
Diodes ? Regulator ?
Damned... I hate electrical troubles
I'd guess regulator (I'd expect a bigger drop if a diode dies, obviously, you could test them! ;-) ), but on my 1995 D90 alternator, diodes and regulator are in one piece, so.....
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  #9  
Old October 4th, 2007, 09:27 AM
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A quick test you may want to perform. Start the truck and disconnect the battery. If the truck keeps running your alternator is still putting out something. A reading that low may just be the battery and the alternator is completely dead. From there, make sure there is a positive running to the battery in order to generate a charge. If this gets cut somehow, the alternator won't put out anything. Good luck.
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  #10  
Old October 4th, 2007, 09:37 AM
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one other thing to check is the chassis to engine block ground. I had one break on my J**P and you wouldn't believe the impact it has on the charging system.
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  #11  
Old October 4th, 2007, 10:00 PM
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Julien Dalbin
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Thank you guys

I'll try those tests this week end.

So far I'm checking output on the cigare lighter 2 or 3 times
a day with a DMM and i'm getting beetween 11.6 and 12.1 volts @ 1500 rpm.
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