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post #1 of (permalink) Old 02-23-2005, 09:11 PM Thread Starter
 
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Overcharging Alternator (Delco 3 wire hook up)

I have had a annoying problem with my 1978 CJ7 [AMC 360, TH400, QT] ever since I've owned it (8 years now) - the battery will go dead if I don't start it after about a week or two.

This has gotten worse since my latest round of modifications. I put in a York compressor from a 1986ish Grand Wagoneer for OBA but I haven't got around to hooking up the electronics so that's not the problem. However, I also swapped in the alternator from the donor because it has a little better amp output (63amp vs 78amp so I thought - still checking on this) and it had the 2 groove pulley. The Waggy had an AMC V8 so I figured the alternator would be a slight upgrade and bolt right in (3 wire hook up).

Long story short - I tried some current draw tests that were recommended on another board and incidentally found that my alternator is putting out 17.5 volts at idle! Any suggestions? I have been screwing around in my CJ in this condition for about an hour total run time - have I done any permanent damage?
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post #2 of (permalink) Old 02-23-2005, 09:45 PM
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Re: Overcharging Alternator (Delco 3 wire hook up)

What is the system voltage?
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post #3 of (permalink) Old 02-23-2005, 10:05 PM
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Re: Overcharging Alternator (Delco 3 wire hook up)

Maybee a bad regulator module??
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post #4 of (permalink) Old 02-23-2005, 10:26 PM
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Re: Overcharging Alternator (Delco 3 wire hook up)

""""found that my alternator is putting out 17.5 amps at rest!""""

You mean engine off there's still 17.5A running through the armature wire (big wire.)
If so, you have a shorted diode inside the alternator. Probably growls when running too.

If you mean that current is running through one of the small wires - engine off, could be a bad regulator inside.

By the way, if your ammeter inside's reading "putting out" - like charging - the ammeter's hooked up backwards, that's a draw (engine off), not a charge.
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post #5 of (permalink) Old 02-23-2005, 10:33 PM
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Re: Overcharging Alternator (Delco 3 wire hook up)

OOO I read rest=Idle.....
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post #6 of (permalink) Old 02-24-2005, 03:03 AM
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Re: Overcharging Alternator (Delco 3 wire hook up)

He He -- if "at rest" means at idle speed, it's a different story.
Then: Need to know how the 17.5 amps was measured - was it the current in the alternator output line? If so, what accessories were on?
Once the battery is charged, the alternator still provides all the current to run the vehicle, including ignition, heter etc. That's normally around 8-10 amps - depending on ignition type and what's on.

As far as the battery running down fast, does it do that when it's disconnected too? If so, defective battery -- or possibly the top of the battery has so much conductive dirt on it that it's discharging it - if so, just clean it off.

Engine off - disconnect/reconnect the battery - see a spark? If so, something's on all the time. Sometimes it's a digital radio with the lighted dial that shows a clock - some draw way too much. I've had 2 like that.
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post #7 of (permalink) Old 02-24-2005, 09:22 AM Thread Starter
 
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Re: Overcharging Alternator (Delco 3 wire hook up)

Sorry - what I meant to say is that the alternator is putting out 17.5 volts at idle (yesterday was a really long day [img]images/graemlins/cussing.gif[/img]). I edited the post and fixed it.
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post #8 of (permalink) Old 02-24-2005, 09:48 AM
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Re: Overcharging Alternator (Delco 3 wire hook up)

THAT makes it easy. Two possibilities come to mind:

1 The regulator is bad.

2 The sense wire is disconnected or has high resistance - more likely in my opinion.

In a stock installation the sense wire is usually a short red jumper from the output terminal to one of the two spade connectors on the alternator housing. It's supposed to tell the regulator what the system voltage is. If it's disconnected the regulator will tell the alternator to run wide open.

A common modification is to run the sense wire to a spot as close electrically as possible to the battery. That tells the regulator what battery voltage is, which will be a little lower than the voltage at the output terminal.

The other wire on a spade next to it provides voltage to bootstrap the alternator when it starts running. It will run to the warning light, if so equipped, and then to the ignition switch.
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post #9 of (permalink) Old 02-24-2005, 02:16 PM Thread Starter
 
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Re: Overcharging Alternator (Delco 3 wire hook up)

Thanks for the replies. I'll check the wiring and get back to you.
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post #10 of (permalink) Old 02-25-2005, 05:10 AM
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Re: Overcharging Alternator (Delco 3 wire hook up)

What should a stock alt put out at idle any way?
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