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alternator charging weird


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So i just did a 100 amp GM swap and i tested it with my multimeter, and i got 12.3 volts at 400 rpm idle. when i revved it, it charged at 15 volts and the meter continued to climb. When i checked my stock loyale for comparison, it read 13.2 consistently.

 

What is going on? Or is this normal? I don't want it to overcharge, because that when things go bad...

 

Oh yeah, and now my headlights dont work. i checked the fuses and they are good, bulbs are not burned out and the taillights work... WTF?

Edited by Markus56
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First, was your battery fully charged? You might also check your fusible links. The GM alts are not the greatest quality. I bought the lifetime warranty one for an extra $10 and I change it out probably once a year. I have also received one that was bad out of the box. That could be what you have got. If you bought it at a store, go back and have them check it.

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The higher output alternators usually charge to a slightly higher voltage and 2000 rpm. I wouldn't be concerned with 14.3V (I think the max should be around 14.5) and 13.5 to 13.8 is pretty typical. But for sure the 15V and continuing increase with rpm is a sign the internal regulator is not working. Take it back and get another.

 

As to the headlights not working, check the bulbs again; 16V or more will fry the filament pretty quickly. As a matter of fact, having both low beams burn out together is a pretty common indication of a faulty regulator in the alternator.

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One of the reasons I use the 90A Nissan Maxima units is they seem much better quality than the GM stuff besides being easier to fit up. Though it of course depends on the rebuilder but I haven't had a bad Maxima unit yet and I'm using mostly junk yard units. I don't imagine my EA's put much strain on them either.

 

GD

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Nope - 14.5 should be the max. If it's higher than that then the regulator is not working or the sense lead is telling it the voltage is low at the main junction. Where are you checking the volts? The alt is designed to put out enough voltage so the reading is 14.5 at the main junction (fusible links). Sometimes that means putting out more at the back of the alt though that generally indicates a poor wiring connection between the alt and the junction if it's more than a few tenths of a volt. 14.5 at the junction and 14.8 a tthe alt I wouldn't worry about - but over 15 is a problem.

 

GD

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One of the reasons I use the 90A Nissan Maxima units is they seem much better quality than the GM stuff besides being easier to fit up. Though it of course depends on the rebuilder but I haven't had a bad Maxima unit yet and I'm using mostly junk yard units. I don't imagine my EA's put much strain on them either.

 

GD

 

I was gonna flame you on this, but, once I read your second sentence I just decided it should be highly emphasized instead. :):lol:

 

The problem with doing these swaps is that most people doing them go to Schucks, and get the cheapest POS rebuild they can find. That doesn't speak anything to the quality of the original GM unit. The one wire GM high output swap is probably THE most common swap for alternators to any other type of vehicle in the world. You'll see this swap on anything from Jaguars to Subarus to offroad forklifts. It didn't become that popular with all the alternators being garbage. Another thing to emphasize is that you need to be aware of the wiring of the car you are putting it into. These alternators were originally destined for emergency response vehicles like cop cars, and ambulances. They were wired to run larger load lighting, and heavy duty everything. Alot of them had dual batteries. Thusly, charging at 15 volts for those vehicles really isn't a problem. I've never had a GM with these systems that idled under 14v. If they did, I knew something was on its way out. Put that same alternator in the midst of a bunch of light duty wiring; be prepared to chase some smoke, and do some splicing. Needless to say; you're going to have a few problems.

 

I'd be willing to bet I've sold over a thousand of these alternators. Probably well over that. I've sold them in multiple rebuilt brands, and brand new ones. We sold alot of Raylocs where I worked, and it was the damndest thing. I'd sell 100 in a row with no incident, and then out of nowhere we'd get a string of 10 that were garbage right out of the box. The rule back then was that a Gm alt should cost about $1 per amp. So a 100 amper should be around $100. Unfortunately recently the price has stayed pretty close.... the quality has just plumeted. If you stay with a decent parthouse like Napa, or Carquest, they will warranty them until you die, but, changing them can get a little annoying. If you want a better one; go with a high quality rebuilder like Bellingham's Romaine Electric. I have a bunch of their stuff I've had for years. Never had a problem with any of it. Even a newer GM alt recored for heavy sub-woofer useage. Or, go with a new AC-Delco unit, and you will be plenty happy.

 

A Schucks $80 unit is just going to keep going poof though. Probably at the expense of other parts on your car. That's just how it goes.

Edited by 3eyedwagon
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The one-wire swap is stupid on anything but a race vehicle or something that has basically no electrical devices. It's only done so much because people don't understand the 3 wire remote sensing system. It's a much better system delivering more consistent power and has no real drawbacks other than it takes more than 2 brain cells to install it.

 

I agree though - the quality of rebuilds in general seems to be really poor. I get the Bosch reman's for a good price and they seem fine for the half a dozen I've bought.

 

Rebuilt parts in general are very poor these days. Axles, alternators, starters, etc are all largely junk and are almost worse in many cases than a carefully selected junk yard part.

 

GD

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The one-wire swap is stupid on anything but a race vehicle or something that has basically no electrical devices. It's only done so much because people don't understand the 3 wire remote sensing system. It's a much better system delivering more consistent power and has no real drawbacks other than it takes more than 2 brain cells to install it.

 

GD

 

I agree with you completely. But, that's the thing about these alternators. They have voltage sensing. Nobody chooses to use it. That's not the alternators fault. It's just so easy to hook up the one wire and run with it. They all have 3 wire hookups, but they only need the one "excitor" wire to take off and charge. Look at what these alternators originally came on, and you'll see that they probably ran more electronics than most cars today. Given, those electronics weren't nearly as advanced as todays electronics with needs for ranges of voltages, etc., but, they can run ALOT of stuff.

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I was testing it between the alt and the battery.

 

 

I topped off the water in the battery (which should have been the first thing i did:-\) and the voltage output dropped, so that helped. i will test the power at the fusible links to see what i get. Now that it is starting to snow, i want this car to last till march :rolleyes:

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the big wire into #1 and the small wire into #2

I have done this swap on two ea81s and the "sense lead" or "field sensor" wire goes on the #2 spade on the narrow case 7157. I think the older version of the GM had the sensor on the #1. I don't know about ea82s, but the big wire might be your sense lead.

 

http://www.teglerizer.com/alternator/wiring.htm

 

 

 

As far as quality goes, it seems like if the ubiquitous chain-store reman alts make it through the first test drive, they last about as long as a standard mid-grade reman alt. I have really liked mine, but I also monitor my car constantly and trade in the old unit at the first sign of sub-standard performance. Swapping out for a new one at the store has always been hassle-free. If I didn't essentially have an unlimited supply of replacement alts, I would probably spring for a higher quality one somewhere.

 

The nice thing about narrowing the alt. bracket to accept the GM is that you can easily put on the Nissan, stock alt, or others. I plan on pulling a Nissan alt from the yard (unless GD gets there first) and adapting it for a spare in case the GM decides to suddenly fail instead of the usual slow failure.

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