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post #1 of (permalink) Old 02-11-2002, 05:33 PM
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Charging System

What would cause my amp-meter to read low (about 10 volts) at start up and only show a charging state when I rev up the motor to about 2000 rpm. If I dont rev up and then drive around town my batt. goes dead. If I initally rev it up I can drive around all day. I swapped out the alternator with a rebuilt from the local auto parts store. I would suspect the rebuilt alternator, but the rebuilt has the same crazy symtoms as the one I pulled out. Its a 82 Cj, with the stock straight six in it. The rebuilt was a delco with slight variation in the terminal placement compared with the old alt..

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post #2 of (permalink) Old 02-11-2002, 06:42 PM
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Re: Charging System

If you have an external regulator, it could be that.

"It's a Jeep thing... and I DO understand"
Duct tape, WD-40, and a BFH, what else do you need?
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post #3 of (permalink) Old 02-11-2002, 06:44 PM
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Re: Charging System

Or just a loose belt, but I would think you would hear that thing squealing.

"It's a Jeep thing... and I DO understand"
Duct tape, WD-40, and a BFH, what else do you need?
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post #4 of (permalink) Old 02-11-2002, 07:01 PM
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Re: Charging System

Arkon,
When you get time please fill out your BIO, at least on your jeep. It makes it easier to help you....at a minimum, we need the model and year.
You on the right track. As 97TJ said, if you have an external regulator, that could be it. But you would have to have a really old jeep. There is not a lot to go wrong here. You will most likely need a voltmeter to troubleshoot the problem.
1. With the engine off, measure the voltage at the battery. You should have at least 12 vdc. If it's less, take the battery to your local parts house. They will test if for free.
2. Start the engine and again measure the voltage. At idle you should have at least 13.5 to 14 volts at the battery. Your dash meter should also read the same as the DVM. If you have to rev it up to get up to 14 and the battery is good, then you could have gotten a bad rebuilt.
3. While you have the voltmeter, measure the voltage from the battery neg terminal to the block and the frame. You should not have more than about .2 vdc difference. If you do, check for a bad ground.
4. Don't be afraid to pull the altinator off and take it back to have it checked.

It is possible to have a loose fan belt that is sliping real bad, but I think you would notice that. Just a side thought? Did the new rebuilt come with the pully or did you have to swap them out? Drag racers will sometime put a larger pully on the altinator to reduce the load on the engine. I would be real surprised if that happened to you.

Was it working fine before? Did anything happen just before this problem?

Get back with us and we will help you in any way we can.

John...southern CA
84CJ7, 3"lift, 32"BFG, 4.10's, ARB Rear, Detroit Front, Solid Axle's, Durabak, York Air

They say we learn by our mistakes......I guess thats why we are all so smart.
post #5 of (permalink) Old 02-11-2002, 07:27 PM
 
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Re: Charging System

*What would cause my amp-meter to read low (about 10 volts)*

Amp meters read amperage, not volts.
Volt meters read volts.
I'd say since you referred to '10 volts', you have a volt meter.
----------------

*at start up and only show a charging state when I rev up the motor to about 2000 rpm.
If I dont rev up and then drive around town my batt. goes dead. *

This is a dead give away here!
When you first start up, If you rev up the engine until the volt meter starts to move, the alternator will charge all day?
This is classic, but only a guy with experience in alternator rebuild or an education in automotive alternators will know this one...
----------------

*If I initially rev it up I can drive around all day. I swapped out the alternator with a rebuilt from the local auto parts store.
I would suspect the rebuilt alternator, but the rebuilt has the same crazy symtoms as the one I pulled out.*

(If I can keep that lying KC mutt from butting in long enough to explain this...)

The alternator is not externally exciting, meaning that there is a problem with the wiring harness to the alternator.
All automotive alternators use an external 'pulse' of DC from the battery to start the charging process, your external source is not getting there for some reason.

You are having to rev up high enough that the residual magnetism in the rotor is producing enough current to internally excite and it will work from there.
That's why you have to rev the engine way up at startup...
<hr>
You didn't fill out your profile, or tell us what alternator you are using, so I don't know what test proceeders to give you...
Post your jeep type here, or give me the manufacturer of the alternator and we'll trouble shoot this problem.
This is not going to take long, I have good graphics for this one.

So many cats, so few recipes...
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