Frying Alternators

[gijoel]

I am at my wits end... I have fried two alternators and cant figure out way.

I have an original 60AMP M923A2 alternator installed in truck. From this, I took the B+ lead from alternator directly to a battery isolator which goes to two different battery banks. First battery bank is composed of 4 27AGM batteries and the other, to 2 6T batteries. The 27AGM's are for the camper and the 2 6T's are for truck. From this, I have installed to VANNER equalizers for a 12V and 24V DC.

The first alternator did fine for about 200 miles and then just stopped working and gauge stayed in yellow. Second alternator only lasted 100 miles, but would jump back and fourth between the green in yellow for the last 50 miles and then stayed in the yellow.

Batteries are in excellent condition and all checked out good.

Any help or suggestions would greatly be appreciated.

I am using a 100AMP Battery isolator.

 

[ralph3162]

track the wiring I burnt 2 alts and turned out to be that the wire going to batt box had worn through and was shorting out going into batt box

 

[gijoel]

We ran a new wire from alternator to isolator. So it cant be a short.

 

[Suprman]

Maybe the stock 60a alternator just isnt enough to charge both banks. After you installed the second one and before it went bad, what did your voltage gage show?

 

[swbradley1]

If your 100% sure of the wiring and it fries the alternators then you are putting too much load on them. I have fried two and that was the case both times. the stock alternator on an M809 series does not put out enough to charge 4 dead 6TLs. Period.

Your mileage may vary but I would suggest charging up each battery separately and putting in the new alternator. Check voltage before starting and then start it and watch it as you bring the RPMs up a little. You could have a bad battery or cell in a battery.

One at a time is the way to go. You could also take all of them in and have them tested at a shop. In my case I just use a cheapo Harbor Freight load tester and it hasn't steered me wrong yet.

 

[74M35A2]

There is a small possibility the alternators are fine. Could be the single wire going to them to turn them on, just as a possibility.

As another item, you are charging a total of 6 batteries, which is a lot to charge if they are discharged. The factory 60 amp alternator can't hold 60 amps for a long time without burning up. A lot of guys here are learning that when they jump their truck and then drive or let it run to charge their dead batteries. It should be able to handle it, but it just can't. It uses low quality electronics in the regulator that don't hold up well under the heat. It is really just designed to recharge otherwise good batteries after starting the engine, as the trucks don't have much electrical load after that. If you want to keep or retain the original alternator, you could easily install a Delco 24V regulator ($20?) in place of the regulator on the back of the unit now. The regulator is the switch that sends power to the rotor inside, through the brushes. You'd have to check to make sure the diodes are good before doing so, as those are also high heat exposed, and can fail. But typically this will produce lower current when doing so, not zero current like you are experiencing. How old are the batteries, and have they ever sat discharged? Your regulator is just staying on 100% at idle after a start, trying to charge 6 batteries, and it is likely burning up.

In comparison on the amperage, the starter/alternator company I work for, we supply almost 50% of the market now, and are currently supplying 200A brushless alternators for heavy duty (over-the-road trucks), and 250A alternators for passenger car applications, due to 3 rows of heated seat, electric power steering, defrost grid, etc.....

A next step would be to check the current output of the alternator, and see if it is at its limit. It will likely not make 60 amps at hot idle, but it should be close to 60 amps when revved up, fully loaded, and cold. Also check that you have 24V activation signal to "turn on" the alternator.

I have some high quality heavy duty alternators I am getting ready to list for sale here if you find you just need more current. Examples are: 12V 145A, 12V 165A, 12V 200A (brushless), 12V 350A, 24V 120A, and 24V 140A. PM if you are interested. Most would require custom bracketry, a few would bolt right in.

As a lower cost option, hang one of the Delco 24V 70A conversions on there. Even though old technology, it is still a decent unit, and is more durable than the military one. It won't make 70 amps at idle, but two of them may if you really need to. There is an article or two here where folks have done it.

 

[swbradley1]

I just had the pulley machined on my M813 so I can put a civilian alternator on it as soon as it warms up enough to work on it. The spec sheet says it cranked out 84Amp at 6,000RPM. (Remember the pulley is much smaller than the crank so it turns faster.)

I got my bracket from TM America.

 

[Wildchild467]

If my alternator ever dies someday, I am going to save my money and put a civilian alternator on it like 74M35A2 said. That guy really knows his stuff about alternators. My alternator has been fine for 5 years and 30,000+ miles, but it wont last forever. I wish I had a scrap deuce engine to design and build my bracket on. It would be a lot easier than pulling my radiator and stuff to get to the engine. Maybe one of these days I will source an alternator and then go from there.

 

[swbradley1]

You don't have to pull anything off except the alternator bracket to the one on I use. Just pull the old one off and put the new one on.

 

[Swamp Donkey]

I don't see anywhere in your post where you used anything other than the gauge to gather your information. You might have, and not posted the fact, but it would be better to use a little more accurate and reliable device to test with. Just making an observation...

Also keep in mind that a bad PCB can cause charging issues, to include intermittent charging. If the batteries run down from intermittent charging due to the PCB and it decides to start charging with depleted batteries, there will be a heavy load on the alternator. This happened with mine and I think I lucked out since I'm only currently running 2 batteries and caught it pretty early.

 

[74M35A2]

If my alternator ever dies someday, I am going to save my money and put a civilian alternator on it like 74M35A2 said. That guy really knows his stuff about alternators. My alternator has been fine for 5 years and 30,000+ miles, but it wont last forever. I wish I had a scrap deuce engine to design and build my bracket on. It would be a lot easier than pulling my radiator and stuff to get to the engine. Maybe one of these days I will source an alternator and then go from there.

Not really. I just guess and see how many believers I can gather.

 

[ralph3162]

I went civilian after my second alternator. I went with the whole dual setup for the price of an original military alternator. Now I have 12v & 24v system and they push a whole lot more amps and are cheaper to repair or replace.

 

[gijoel]

Will that work on the M923A2 engine? Anyways, I can purchase a 400 AMP 12/24VDC alternator. What would happen if I replaced the one that fired with one of these? Could I cook my batteries?

 

[74M35A2]

Will that work on the M923A2 engine? Anyways, I can purchase a 400 AMP 12/24VDC alternator. What would happen if I replaced the one that fired with one of these? Could I cook my batteries?

No. A properly regulated alternator will not "fry" a battery, no mater what its amperage capability is.

Most of the dual voltage alternator units require an external voltage regulator box, so be sure to obtain that also.

 

[jonesal]

I do not agree that "The factory 60 amp alternator can't hold 60 amps for a long time without burning up." The military standard is many, many hours at 60 amps continuous load. I pulled over 60 amps on mine (on an alternator testing machine) for over one hour. I had to stop because the machine generated too much heat (more heat than the generator). I do agree that these 60 amp generators can be finicky, but if in good service, will perform well. I tried to run one wide open (shorting the brush to ground will do that) and it still did the job - the machine stalled out.

Four dead 6TL batteries definitely draw much more than 60 amps - especially when most of the time there is a shorted cell that will draw even more. Very few generators or alternators are designed to charge the dead battery scenario.

I've found that poor grounding is the result of an early death. This cannot be verified by a visual inspection with the connections in place - you need to disassemble each and make sure it's at full grounding capability. Also, for some reason, the large carbon resistor in the regulator does not seem to be up to the job to me (the usual cause of failure of the regulator). Have you disassembled the generators to diagnose them? What is the point of failure? Regulator? Brush? ??? Diagnose, man.

I suspect your custom setup. Check to make sure the isolator is not causing the regulator to run wide open. Also, how do the batteries "test out and are good"? More information there too, please. I have to spend more time thinking of how your setup interacts with the generator regulator. Have you taken measurements at the generator to see how it's behaving to a deep cell.

Al Jones
M923
M38A1
And other 'n such.

 

[zout]

Detroit 60 series had a major issue with the blowby gasses coming up into the alternator and frying them - running an extension tube below the steer axle cured this. Then they started mounting the alternators higher.

could be could not be may not be related could be a shot in the dark - may not have anything to do with anything.

 

[74M35A2]

An alternator is also at a higher failure risk if fully loaded at an idle, as that is when cooling airflow is the lowest.

 

[ralph3162]

Will that work on the M923A2 engine? Anyways, I can purchase a 400 AMP 12/24VDC alternator. What would happen if I replaced the one that fired with one of these? Could I cook my batteries?

My setup is on a deuce but they make them for the 5 ton as well here is a link that I think will be helpful http://wolverinetechnologiesllc.com/

 

[Doug Roberts]

I'd 2nd what Swamp Donkey just told you . Your PCB might be bad , all this logic , but all this history, your PCB is bad man

 

[DOUBLE ALT]

Any one with Alternator trouble can call us for Help. As a Veteran, We specialize in helping you out. The old Alternators just were not reliable.

Regards
Ron from Double Alt