Just installed the 4th reman alternator on my GenII after getting a mere 800m out of the last one. All have been covered by a lifetime warranty, but the job of replacing them is getting tedious. Hence,I started prowling for why they were failing when the OEM lasted nearly 130k.

I compared the spec sheets that came with the just-failed and "new" units, and interestingly, the just-failed unit supposedly pumped out 138A at6k on the bench when sold. The new one manages a mere 106A at6k. Both are nominally 90A. Seems to stand to reason that anything much over 90A is either a problem (poor rebiuld) or is going to cause problems. My guess is the failed unit overheated.

The output graphs on the spec sheets look about the same - key is they are scaled differently (0-125 vs 0-150). On cursory review, there's no apparent difference. There's also a reassuring statement that "the output meets all specs"

Moral of the story - read the fine print. Don't get suckered into a reman unit that exceeds stock performance by such a wide margin!

FWIW these were/are WorldWide reman units that list for $250 each (!!!)


Paul

I had one built to replace my 75A 3.0L unit that supposedly bench tested at 160A.... I haven't tested it myself to verify the output. The difference may be that I had mine wound as a new unit and not just rebuilt. It has a much heavier stator winding (with little room for cooling air flow) and it probably has a beefier rotor, voltage regulator and rectifier as well, because it's still working fine after 7000 miles.... it recharges a Group 27 95AH AGM battery with a huge charge acceptance rate like a champ. Unfortunately, the fellow who built it has vanished and as long as it's working I don't want to take it apart to see what's in it. <img src="/forums/images/graemlins/cyclops.gif" alt="" /> <img src="/forums/images/graemlins/shame.gif" alt="" />

Most alternator rebuilders replace only the parts necessary to make it work on the bench load test and if the parts aren't compatible you can blow the new one pretty quickly... as you found out.

Frank

Do you know what part was failing on them?

Kevin

You might want to try this place - I don't know anything about them or their product quality:

Mr. Alternator

Frank

A properly functioning alternator (and regulator) cannot, repeat CANNOT be made to fail by putting less than peak demand on it.

What this means to you is that an alternator designed for 160 amp that is installed in a system which only requires 50% or less from it is causing less wear and tear on the alternator than a system which requires more.

Bottom line, you replaced factory stuff with crap. That crap failed quickly and was replaced with more crap. Now you're stuck in this seemingly endless crappy cycle probably due to remanufacturing/rebuilding qc crap issues.

Sorry. Keep your tools clean and organized. Won't be long before you can replace alternators faster than anyone else.

Clay

Clay -

If the alternator was designed for 90A and output was jacked up to 160A via new stator/rotor without replacing the rectifier/diode set/voltage regulator with stouter ones - and IF the battery and accessories were capable of drawing more than 90A - it would seem to me that there is a good chance of blowing one of the parts that was not designed for the higher load.

If the load never got above 50A (as you suggest) there would be no problem, but if the load is high and the alternator either runs at/near full output for an extended time, there is a danger of burning it up. Like engine life, alternator life isn't very long at maximum output.

I had my alternator built to partially take advantage of the AGM battery's ability to absorb a very fast high-amperage charge:



web page

Given the charge acceptance rate of Concorde AGM batteries, I could conceivably draw 4x AH capacity (95AH) = 380A while charging - IF the alternator was capable of that output. Since the battery is capable of the higher acceptance rate, the alternator goes to full (or near full depending on heat) output until the battery demand tapers off. If the alternator winding is capable of higher output than original, heat is greater and parts not designed for the job suffer.

There's a big difference in AGM batteries compared to flooded cells. Flooded cells have a charge acceptance rate of about 25% of AH capacity - so if you have a standard Group 24 battery at ~70AH you might be capable of only charging that battery at a rate of 18A - a huge difference from the 180A in the above example of my battery. The lower charge acceptance rate of a standard battery serves as a limiter to alternator output if no accessories are turned on. When accessories and/or higher charge acceptance rates are added, the alternator starts to work harder.

I guess my point is that he could have made a change to his electrical system that is calling for more juice and burning up alternators that are capable of higher than 90A output, but not without burning up due to all of the parts not being up to the task.

Frank

I agree, that normally, running the alternator below peak output, shouldn't be an issue. However:-
-the output at lower rpm is still high (at least by comparison to the latest replacement).
-Unless someone is generously adding windings, giving me the wrong unit, etc..getting well over stock amperage must imply problems somewhere.

In terms of failure modes:-
#1 Died suddenly, battery light on.(10k)
#2 Flaky voltage regulation for about 1500m (lights dimmed/brighten with rpm. Then saw about 100m of "odd" voltage readings - jumps from 12V-16V. Then just 12V, but battery light did not come on (i.e something was coming out of the unit)
#3 Voltage went off-scale (>16V). Then pegged at 12V but battery light stayed off.
#4 Alive and well after 200m.........

All of which leads me to believe the regulator is getting fried, either directly or due to a faulty rectifier pack.

A few other considerations:-
1) Compass/themo LCD display goes blank at >16V (who knew..?)
2) Considered, tested , checked and discounted a bad battery connection. Running the unit open could cause the above behavior, but all connections were tight and showed no unexpected resistance.
3) Questionable battery? If there's an intermitant internal break, the alternator could powering into an open load. So far though, the battery seems happy and has given no signs of failure.
4) The reg/rectifier, being at the back of the unit sit very close to the header. I don't know if this is the case for other mitsu applications, but IMHO, this must mean the electronics get nicely heated.


The rebuilders could be reusing components or installing incorrect pattern parts. They could just be botching the rebuild. Point is check the paperwork (test results) before walking out of the store. I "trusted" the price of the unit and now know how to replace the alternator in my sleep.

Paul

Perhaps I mis-stated what I meant. It was a little late.

He didn't mention anything about upgrades to his electrical system, only that the alternator was capable of producing twice or near twice the amperage of stock.

On the other hand, if you have a small output alternator and make it capable of prodicing a higher amperage than it was designed for, without upgrading all the other weak links int he system, somthin' is going to die. This fall under my "not working properly" blanket catagory.

My point is this;
It's kinda like the idea of putting a built Chevy 350 in a Montero and only using enough of the power available to move like a stock v6. That engine is going to last pretty much forever.

If you demand more power from the engine than the Montero was designed to use, something is going to break.

If you built the engine with crap parts and or didn't do a complete build, chances are that engine won't last. Like if you put domed pistons and a fat cam in and did nothing else (stock heads, no crank upgrades, etc.). Sure. it'll make a lot of power, but for how long? And how long will it last at a lower power output?

In the case of a Chevy 350, probably still quite a long time. So, for the sake of my little object lesson, let's say that you took a 6G72 and pumped it up to 410 hp (I've seen lots of small blocks doing this, so it's not unreasonable). But you did it by only replacing the cam, the pistons and the fuel injectors.

What's going to happen to that big bad engine at only 50% load?

Clay

I always wondered why GM was using glass mat batteries in the corvettes.

I was too lazy to look up what they actually are (I would keep forgetting, since I try to forget everything I experience when I work on corvettes).

Thanks Frank!

Clay

You won't get higher output unless something is demanding current to satisfy need. IOW, the ABILITY to produce more output doesn't mean that the higher output is produced unless something calls for it..... it could be that the battery has an internal short - get it checked at a reputable shop.

If your voltage regulator allowed the alternator to pump 16v into the battery, there's a chance the battery is damaged.

Frank