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Old 10-05-2007, 07:38 PM
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Powermaster 140A Overcharging

My 140 amp powermaster (#37294, one wire) GM style alternator has started overcharging recently. At idle it charges at 16A, at 2000 rpm pegged on 18A. I verified voltages with my DVOM at the alternator and battery. All connections/grounds are tight. Battery is in the trunk and using 00 wire. I can also see corrosive liquid damage inside my battery box, like splattering on the inside surfaces, can't see any battery cracks but it came from somewhere. It's an Optima battery and appears the liquid came from one of the corner top seams possibly. Less than 50 miles on the car.

I can take the alternator to NAPA for a check; my question is who makes an internal regulator for this alternator if that's the problem? Powermaster has given zero support through email and an internet search hasn't turned up any parts or repair kits for a Powermaster 140A unit. Did GM ever make a 140A alt and if so, would their regulator be compatible with Powermaster?

Anyone have an idea what else it may be? When I turn on the fans and switch the fuel pump on and off, it dips but comes right back up to 18V.

I'm not driving the car now concerned about my ignition and other electrical components, near as I can tell no damage done.....yet.

Man, like all of us here, I sure miss Doc, may he rest in peace...Larry

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Old 10-05-2007, 08:42 PM
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I'm no doc, but...

Doc sure knew his stuff. and I'm no expert on alternators, but some here's some initial thoughts.

Just because a ground is tight, that doesn't mean it's a good electrical connection. Remove the cables and clean with a wire brush. a star washer bites into the metal for a better connection. If you have it, or can get it at a local auto parts store I like using dielectric grease to help prevent corrosion.

That means cleaning cleaning the battery terminals as well.

Now you said that at idle your meter is showing 16A. I am guessing you mean 16V - you were measuring volts right and not current (amps)? It's critical to know this and the WAY you measure amps is totally different than the way you measure volts.

If you think your battery may be damaged, I'd find out for sure. Yank it and the alternator and take it to your local parts store that can test and remove all doubts. If they are a good enough parts store to be able to test, then they might be able to find a regulator for it if it's even bad.

If they can't help you, there are other aftermarket vendors out there that would love your business. Haywire is one I like so far.

With you putting your battery in the trunk, did you also put in any other special parts such as a battery switch for emergency cut off?

Just curious, put your meter on ohms and measure the resistance in the positive battery cable (with the battery disconnected) from the battery end to the starter, if your leads length will permit. Then do a test from the negative cable terminal to the block, the body and the chassis.

Steve
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Old 10-05-2007, 10:19 PM
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Steve, yes I was measuring voltage not amps. My leads aren't long enough to reach from the battery area to my grounding lug on the front frame. I may pull it out tomorrow (it runs through the frame rail) and test it. What value am I wanting? I did measure the ground lead from the lug to the block, saw .5 ohms there, connected.

Everything on this car is new, every piece of wire, etc. It's possible I suppose that the battery shop did a poor job crimping the cable ends but doubt it. I found the high voltage accross the battery terminals, and from the charging lug at the alt to ground. I actually have three ground lugs on the car, all welded, one on each frame rail in front and one under the dash. Also, no blown bulbs anywhere. My alt charge wire goes to a heavy duty power block on the firewall where it splits, one 00 wire to the battery, one 00 wire to the starter and the MSD box powers from ther as well. My fuel pump is behind the bumper grounded directly to the battery, powered through a relay, wired through a painless switch panel on the dash, as are my fans, ign, etc. I haven't installed the electrical shut off switch at the rear yet.

Just odd to me it just started happening, I'll will recheck all my ground contacts. I ****ume the shop can test the voltage regulation, not just alternator output, load it and all that? My battery never lost any charge, checked it before I started it today, it was at 12.98V after sitting for probably a month connected. The alternator is acting right, begins to charge at about 1500 rpm and stays charging until shut off.

Do you suppose I can ust an OEM GM regulator in this alt? Does it matter it's a 140A alt when considering the voltage regulation?

Thanks for the fast response...Larry
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Old 10-05-2007, 11:27 PM
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Charge!

Larry,

Sounds like you're in pretty goos shape overall then.

Let's eliminate one more thing. Put a battery charger on your battery to top off the charge. Make it so the alternator doesn't NEED to charge a low battery.

I'm betting you'll see the normal 14.xx volts after your battery is charged.

The voltmeter on my truck goes to 16 volts fairly frequently, but it comes down after it's charged the battery back up.

Steve
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Old 10-05-2007, 11:47 PM
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I'll put the charger on it tonight, and still check the entire ground and primary wiring tomorrow.
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Old 10-06-2007, 01:34 PM
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Naw, that didn't help, i'm taking the alt to be tested.

Are internal regulators ampere sensitive or simply voltage controlling, if i can find one for this 'generation' or style alternator? No pun intended....

Thanks guys, Larry
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Old 10-08-2007, 10:30 PM
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The problem and fix

Well I pulled all my cables and examined the crimps, etc. No problems. Took the alternator to auto electric for testing, sure enough, regulator went south. Got talking to the tech, he offered a tip - grind the chrome off the grounding stud in back, chrome makes a poor ground. Said the poor ground is (and was in my case...) a sure thing to take out a regulator in a one wire alternator.

Whodathunk? Parts were only $34.00 and I'll fix it myself.
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Old 10-08-2007, 10:42 PM
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Testing 1,2,3

I love the fact that they can and will test alternators at the parts store these days! The only way to really troubleshoot a charging issue.

Interesting statement on the ground.

Let me see ....$34 Alaska price, must mean I coulda got them here for about $12? But! They tested it for ya, gave you the result and had the parts in stock. A lot cheaper that buying a new alternator ....that isn't chrome even Sounds like they earned your business and loyalty.

I'll have to remember that ground on chrome. I have a chrome 120 amp I am putting to work.

Steve
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Old 10-08-2007, 10:53 PM
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I guess $34 is a fair price, I got so sick and tired of shipping costs when building this car. If he had told me $24 plus $10 shipping, I'd not take it as easy.

NAPA and Shucks-Kragen don't carry internal regulators any more and neither could test this alternator. Said their tester is computerized and needs an OEM part number to input!

I figured it was well grounded through the bracketry to the block, but then it's all chrome and aluminum. This time I'll run a lead to my grounding lug.

Larry
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