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post #1 of (permalink) Old 09-09-2006, 11:29 PM Thread Starter
 
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A Tale Of Two Alternators...


So I'm setting on the sofa trying to decide if I'm going to nap or watch something mindless on TV... When the phone rings.

It's 'Chris' at the local Advance Auto parts store, saying he had a guy driving a 'Jeep' and his charging system wouldn't work...
Could I come over and have a look cause this guy is melting down in the driveway...

I tell Chris that if he gives me crap I'm going home, and SOMEBODY better come up with a banana split when this was over...

Turns out, this guy has three very bored kids that want to go home over an hour away, in a jeep that won't run in a strange town.... I felt sorry for him, he seemed like a nice guy with bad luck...

He goes on to explain he's had a new battery in it every three months or so, and he's changed the alternator twice a year for the last three years...
They had just got done replacing a dead battery (warranty) and testing the very out of place CS-144 alternator someone had installed, and it didn't look very old...

The guy had put 4 Ga. cables to his starter, his alternator, and to his engine ground, strapped to his alternator bracket.
(I always suggest your ground should go to a starter bolt, but a dedicated 10. Ga. soul go directly to the starter back...)

He explains the CS cost him over $400 dollars at the Chrysler dealership!
I about passed out!
Over $400 to mount a CS 144 that didn't work just like the rest of the alternators the dealership had installed...
I'm aware it was a 190 amp CS 144, but it was from Advance Auto, sticker still on it!
He got robbed!

Anyway, did the usual tests, the alternator had just been run on the store machine and passed with flying colors, and the jeep owner said all of the alternators except the first one had passed, but just weren't charging, so he had them replaced.

I tested for resistance between the solenoid and the 'Batt' terminal,
I tested for resistance between the alternator housing and the Battery negative terminal.
I tested for voltage at the 'Sense' wire, and at the 'Excite wire.
I Double checked the diodes real quick, no problems.

Start the vehicle up, do the tests again, no problems except for the ground wire is showing resistance that it wasn't before...
Turn the vehicle off, no problem, start the vehicle,-- Resistance again...

I didn't quite understand the problem, but we installed a jumper cable from the battery terminal to the alternator ear.... NO RESISTANCE and the volt gauge jumped up to 14.5 steady!
Took the 4 Ga ground wire off, checked the connections, load tested the wire, cleaned off the terminals, cleaned the bolt & bracket where it was supposed to mount, put it back on, and the same thing...
12.3 or 12.4 volts (battery voltage) .
Made up a 10 gauge dedicated wire with star washers, bolted it to the back of the alternator, touched the other end to the battery cable and the voltage jumped up.
Take it off and touch it to the alternator bracket right next to the connection, 12 volts again.

I ran the wire back to the battery as a dedicated ground and he gets 14.5 volts again...

What gives! Are the brackets made out of something that has such high resistance that the ground won't travel?
I'm very- acutely- aware if rusted, corroded, dirty, greasy or loose connections, but this was none of the above...

Just over an inch of that bracket had over 10,000 Ohms resistance!
And it looked like a factory TJ bracket to me, I couldn't tell the difference...

Anyone have any experience with anything like this?
This is the strangest thing I've ever seen. It defies nearly everything I've learned in 30 years...
The only thing I could see that looked different was a crack had be welded up, I suspect a victim of the alternator wars at the dealership...
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post #2 of (permalink) Old 09-10-2006, 01:35 AM
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Re: A Tale Of Two Alternators...

"""""Just over an inch of that bracket had over 10,000 Ohms resistance! And it looked like a factory TJ bracket to me, I couldn't tell the difference..."""""

Wow, that is weird! It was the slotted bracket? Even if it was missing, I'd think the lower bracket would be enough as the ground.

If you still have the bracket, maybe try a magnet on it? Since it's cracked - but it's hard to imagine even thousands of stress cracks could run that resistance that high.

Good job diagnosing it!

Did you get your banana split?
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post #3 of (permalink) Old 09-10-2006, 05:48 AM
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Re: A Tale Of Two Alternators...

[ QUOTE ]
Just over an inch of that bracket had over 10,000 Ohms resistance!

[/ QUOTE ]

Unless the bracket was made of some kind of plastic that just looks like metal, it makes absolutely no sense. And even if the bracket were a total insulator the belt tension arm should provide plenty of ground, or does it have a rubber bushing?
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post #4 of (permalink) Old 09-10-2006, 07:47 AM
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Re: A Tale Of Two Alternators...

Some years ago a guy broke down in his Dodge Pickup in front of my house. I was out working on a car in the drive way and helped him push the pickup out of the street into my driveway. He said it just quit. He Had lights but no ignition. I suspected a problem with the ballast resistor. It checked fine, the battery checked fine, it had 12 volts under load. For some reason I checked the engine block for ground... and there was none. It took me an half hour to find that the factory had run a ground wire from the engine block to the radiator frame. The radiator frame had broken loose. This lost the ground. After repairing the radiator mount, the ground was restored, and the engine started right up. I told him to go to NAPA the next day and get a good grounding braid and how to install it. I doubt he did, but he was warned.

I'm still puzzling over that repair. Why wasn't there another, better ground path? It was the Rust Belt of the Midwest. I guess every other ground path was rusted providing a heck of lot of resistance.... or an open circuit.
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post #5 of (permalink) Old 09-10-2006, 09:51 AM
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Re: A Tale Of Two Alternators...

Well when you think about it - the engine's mounted in rubber, the trans, throttle and shift linkages, linkages, the exhaust, even thinking the current will travel down to the diff - oops, springs are in rubber. It's totally isolated - unless somethings worn through.
I was explaining that to one of my customers once - he said he had no body to engine ground strap (Chevy II he'd converted to a V8) - turned out he'd added an aftermarket oil gauge - with a copper line. We turned the lights on and disconnected the cpper line - lights out! Since it was a body to engine problem, it started and charged fine - but all the body stuff, lights, heater etc went through that oil line.

Some older Chryslers, Mercs etc - with a floor mounted Automatic shifter used a cable to operate it. When you lost the ground, that cable was the conductor - it'd weld itself stuck in gear!

I can't imagine any vehicle using composition material for the alternator bracket - but stranger things have happened.

JYC - was it the slotted strap or the base bracket? Seems like even if one was bad, the other would take the current.
That took some thinking and diagnosis beyond the "box."
Good job!
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post #6 of (permalink) Old 09-10-2006, 10:17 AM
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Re: A Tale Of Two Alternators...

First off JYG, good logical and methodical troubleshooting...and OT....it also reinforces the fact that a 'good' multimeter should be a part of evey jeeps tool bag....I never leave home without it....

About the only thing I can think of is that the bracket was made in some foreign country using cheap steel....most likely that part of the bracket has excessive impurities that is increasing the resistance....Not all metals are highly conductive....take for example certain magnetic materials....they hold a nice strong magnetic field but have very poor conductivity....

Make me want to go outside and measure the voltage drop between the altenator case and the block.........
post #7 of (permalink) Old 09-10-2006, 10:21 AM
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Re: A Tale Of Two Alternators...

I've been trying for a long time to trace down a voltage drop in my own system on the Zuk . Using a Delco single wire 100a alt, it just never wants to stay at it's rated 14.2 volts anywhere other than the battery. The voltage is so amazingly consistent at the battery terminals but everything else drops to 12.5 the instant there is much of any load . Even the a/f meter changes with a touch of the brake pedal, nearly half the guage range . I'm starting to wonder now if maybe I have the same issue, not enough ground return despite the many heavy ground wires I've added to the engine bay . Maybe I'll try a nice strap directly to the alt case itself today....
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post #8 of (permalink) Old 09-10-2006, 10:52 AM
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Re: A Tale Of Two Alternators...

""""single wire 100a alt,""""

Single wire? You mean the only wire to it is the output wire?
If it is - There's the rub. They monitor the output right at the alternator itself, it has no idea what the battery is doing, or if it's even connected at all!
It's about the same as asking a politician if he's honest - "of course" he'll say, as he steals your wallet.

Real alternators sense the voltage at the battery, or at least "system voltage.".
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post #9 of (permalink) Old 09-10-2006, 04:36 PM
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Re: A Tale Of Two Alternators...

[ QUOTE ]
First off JYG, good logical and methodical troubleshooting...and OT....

[/ QUOTE ]

why is it OT? [img]/ubbthreads/images/graemlins/confused.gif[/img]
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post #10 of (permalink) Old 09-11-2006, 03:44 AM Thread Starter
 
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Re: A Tale Of Two Alternators...

"Good job diagnosing it!"

I didn't diagnose it, I just dumb luck found it.
Couldn't have been more of a surprise if it would have been Pam Anderson naked...[img]/ubbthreads/images/graemlins/grin.gif[/img]
That's just the way the old tractor mechanic taught me when I was about 13 and I've been doing it so long it's just habit.
This is the first time I've seen a problem with an actual good, heavy duty ground wire to the alternator or alternator bracket like this...

How may times have me, CJ Dave and LEVE preached about dedicated grounds...?
--------------------------------

"Did you get your banana split?"

YES I DID! The guy gave me $5 the night of for the banana split. He kept trying to give me more, but my price was a banana split that night! (Guess I soul raise my prices! [img]/ubbthreads/images/graemlins/blush.gif[/img])
And the guy called yesterday morning to say 'Thanks' again, and invited me and Debbie out for dinner on him.
We had BBQ Baby Back Ribs! (I we paid for our own)
--------------------------------

"...it makes absolutely no sense."

You are telling me?
How did they weld the thing with that much resistance?
I'm kind of book stupid when it comes to welding, but how could you get an arc to do it's thing with that much resistance?
---------------------------------

"why is it OT?"

I think he was saying his Multi-Meter recommendation was Off Topic, but I don't think so.
With Harbor Freight giving them away for under $5. you should have one in every vehicle.
They may not be totally accurate, but they work and I get to keep the $500 Fluke in a locked garage!
--------------------------------

The guy talked me into doing some more work on his Jeep this week (regular shop rates apply!), and he's bringing it up this evening (mon.)...
He's bought some lights, now that he has enough charging system to pull them...
I'm wanting to have a closer look at that bracket anyway...

I'll keep you posted, but right now, your guesses are as good as mine, and if someone can explain this, I'm all ears!
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