Alternator Problem

[MScott]

First of all, I am entirely off grid. I have a solar powered system using a 48 volt battery pack. My primary backup generation is a custom made 'generator' powered by a 3 cyl Perkins/Caterpillar diesel engine driving a large alternator which I am told was designed for the US army's Abrams tank.
Recently, the alternator stopped generating power. Instead of the usual 60+ volt output, it was producing only about 12-15 volts. I took it to a nearby alternator repair shop who tested it on their test bed. They claimed it was putting out over 60 volts. When I took it back home, it still only produced 12-15 volts. After several go-arounds with the shop, I found that the alternator would produce 60+ volts if running free without being hooked up to my system but that, as soon as a load was placed on it (ie. my battery pack) the production dropped to the lower output and it would stay there even when disconnected from the load.
I discussed rebuilding the alternator but the repair shop doesn't believe they can get parts so they were not willing to attempt a rebuild. Since a replacement alternator is around $1800, I thought I would run the problem past the minds at GJ to see if anyone has an idea of what is happening here and if there is a solution or whether I should just bite the bullet and get a new alternator.

 

[wyliesdiesels]

Sounds like there may be an issue with the load ie the batteries or charge controller.

Does the repair shop have a load bank they can test it on?

 

[MScott]

Not sure whether they have a load bank, but the batteries charge OK with the portable generator and with the solar panels. The alternator charges directly into the battery bank with only a cutoff breaker. AFAIK there is no charge controller.

 

[matt_i]

The fact that the alternator would still stay at 15ish volts after being disconnected from load says to me that the (presumably internal) voltage regulation is not working well.

Im linking a Delco alternator diagram, you can see the voltage regulator is a system of transistors. Possibly a component in that part of the alternator has gone bad. The regulator has to affect field -- it has to be strengthened to get a higher voltage from the alternator. Its just a guess but I would not think that the voltage regulator would have been re-invented very much from the basic automotive offering.

https://alternatorparts.com/10si-15si-type-116-136-repair-manual-page-2.html

 

[theoldwizard1]

Matt-i is on the right path, but let's back up a step or two. Alternators are very simple with only a couple of parts, case, bearings, slip rings, brushes, rotor and stator. The simplest (non-automotive) alternators have no voltage regulator and rely on the constant speed of the engine. Older alternators used mechanical voltage regulators.

There are some videos on YouTube that talk about testing/rebuilding alternators. None will likely be the same as what you have. The simplest way to test an alternator is to bypass the regulator and apply "full field voltage" to the field windings. This is typically the voltage of the battery. This will put a large load on the engine and the output voltage will exceed its typical output (>60V maybe even >80V !)

If you are getting that, you know it is the regulator.

 

[TheEquineFencer]

Post more info/pics of the alternator?

 

[MScott]

Thanks for the suggestions. I will pass them on to the repair shop to see if that changes their opinion on repairs. I'm afraid rebuilding would be beyond my abilities even if I can source the parts so I may just have to bite that bullet.

 

[TheEquineFencer]

Thanks for the suggestions. I will pass them on to the repair shop to see if that changes their opinion on repairs. I'm afraid rebuilding would be beyond my abilities even if I can source the parts so I may just have to bite that bullet.

I'd like to know more about the "specs" for the alternator, mounting, amp output and rated voltage. I know where you might be able to get another surplus or something that might replace it.

 

[MScott]

I'd like to know more about the "specs" for the alternator, mounting, amp output and rated voltage. I know where you might be able to get another surplus or something that might replace it.

I don't know much about the alternator other than that it was apparently designed for the Abrams tank. It has no markings or numbers to identify the model or manufacturer.
The alternator puts out 60 + volts DC and, when charging, had an output of up to 100 amps at the battery bank. (Would drop to about 75 amps as the batteries became fully charged.) The mount is a standard 4" mount on a 1/2" bolt. The distance from the mount to the center of the drive pulley is 2". There is a mount for adjustment at the top, but in operation the adjustment is by a contoured pad against the side of the body. The alternator body itself has a length of 7 1/2" and the diameter is 7 1/4". That's about all I can tell you.
Thanks for your input.

 

[TheEquineFencer]

I don't know much about the alternator other than that it was apparently designed for the Abrams tank. It has no markings or numbers to identify the model or manufacturer.
The alternator puts out 60 + volts DC and, when charging, had an output of up to 100 amps at the battery bank. (Would drop to about 75 amps as the batteries became fully charged.) The mount is a standard 4" mount on a 1/2" bolt. The distance from the mount to the center of the drive pulley is 2". There is a mount for adjustment at the top, but in operation the adjustment is by a contoured pad against the side of the body. The alternator body itself has a length of 7 1/2" and the diameter is 7 1/4". That's about all I can tell you.
Thanks for your input.

Does the APU it's mounted on have any numbers? BTW, as far as I can tell, an Abrams tank is 28VDC.

 

[TheEquineFencer]

FWIW http://www.gdls.com/

 

[nelstomlinson]

I can think of a couple of possibilities. Did the shop test it under load? If not, the problem may be that there is a high internal resistance. That could be as simple as a bad connection. This would look fine with an open circuit, and the voltage would be low when loaded.

Does it have an internal voltage regulator? What controls your field current? This is the trail that Matt_i is going down, and it's likely your problem. Do as old wizard said and apply DC voltage to the field coils when you're running under load.

 

[TheEquineFencer]

 

[MScott]

Does the APU it's mounted on have any numbers? BTW, as far as I can tell, an Abrams tank is 28VDC.

No numbers or other identification on the Alternator. Not sure what "APU" stands for but this is a custom built stand. I could be wrong about this being from an Abrams tank. That is what I was told but I have no evidence to support it.

 

[MScott]

I can think of a couple of possibilities. Did the shop test it under load? If not, the problem may be that there is a high internal resistance. That could be as simple as a bad connection. This would look fine with an open circuit, and the voltage would be low when loaded.

Does it have an internal voltage regulator? What controls your field current? This is the trail that Matt_i is going down, and it's likely your problem. Do as old wizard said and apply DC voltage to the field coils when you're running under load.

The shop did not test it under load but I did when I brought it home. When running free it produced 60+ volts but as soon as I hooked it up to the batteries the voltage dropped to around 12-15. When I unhooked the load the voltage stayed low. After a period of time it would recover to the higher voltage when not under load.
I have no idea whether there is an internal voltage regulator or what controls field current. I don't know how to apply DC voltage to the field coils other than hooking the cables up to the battery bank.

 

[MScott]

I have some problems obtaining and attaching pictures but I will try to get some tomorrow.

 

[TheEquineFencer]

I have some problems obtaining and attaching pictures but I will try to get some tomorrow.

Don't feel bad, it took me forever to figure out what I was doing wrong when I first tried it. BTW, APU = Auxiliary Power Unit.

From what I've been reading tanks have an APU so they don't have to keep the "big" engine running at times of "idle" or standby.

 

[MScott]

No luck yet on the pictures (might get some help on the weekend) but I did discover that this is a PMA (permanent magnet alternator.) That might make a difference in diagnosing the problem.

 

[TractorJeff]

Not sure why you would want 60 volts on a 48 volt battery bank? Seems like it would boil your batteries?

 

[MScott]

Not sure why you would want 60 volts on a 48 volt battery bank? Seems like it would boil your batteries?

Don't forget, charging a 12 volt lead acid battery requires 13.8 volts. That would be over 55 volts for a 48 volt battery, These batteries are AGM, not lead acid batteries so they do not boil. It would probably be OK to use a 55 volt alternator to charge them but this system was designed for 60 volts so???

 

[48RON54]

Is there any noticeable change to the engine speed when you apply the load? Im having a hard time seeing how the generator output voltage would drop only when load is applied without it making a noticeable change to RPMs/exhaust output.

 

[48RON54]

Does this shop have a DC load bank you can rent or can they point you in the direction of a place that you could rent one from so you can make sure the issue isn't actually on the battery pack end?

 

[MScott]

Is there any noticeable change to the engine speed when you apply the load? Im having a hard time seeing how the generator output voltage would drop only when load is applied without it making a noticeable change to RPMs/exhaust output.

No change. That's how I first noticed the problem. Usually when I flip the breaker to start charging there will be a slight but noticeable change in the engine speed. Change in output seems to be instantaneous.

Does this shop have a DC load bank you can rent or can they point you in the direction of a place that you could rent one from so you can make sure the issue isn't actually on the battery pack end?

I don't believe so. They are about an hour away so I can't check right now. The battery pack does charge with either the solar array or the portable AC generator that I have as a second backup.(it charges through the inverter and not directly into the battery pack like the problem system.

 

[48RON54]

Did you take it to a generator place, or a place that specializes in rewinding/repairing alternators?

 

[MScott]

They advertise as repairs to generators and alternators. There are not a lot of choices in this area and they have seemed competent on previous contacts. This time, however, they seem a bit out of their element.

 

[48RON54]

I agree. Any generator place should have conducted a load test right off the bat and then moved on to troubleshooting from there. DC load banks rather uncommon though so I imagine that is a hurdle to begin with. I wish I was more knowledgeable on the alternator side.....but unfortunately most of my knowledge is on the diesel engine side of the problem. Good luck on your search!

 

[Radix2]

Are there other connections to the alternator? There are often connections to monitor or switch the regulator beside the power connections.

 

[MScott]

I agree. Any generator place should have conducted a load test right off the bat and then moved on to troubleshooting from there. DC load banks rather uncommon though so I imagine that is a hurdle to begin with. I wish I was more knowledgeable on the alternator side.....but unfortunately most of my knowledge is on the diesel engine side of the problem. Good luck on your search!

Thanks for trying. Fortunately, the diesel engine side of the problem is working well. It's just the alternator that is a problem. I'll keep looking.

Are there other connections to the alternator? There are often connections to monitor or switch the regulator beside the power connections.

There are only three terminals on the alternator. One is positive, one is negative ground and the third is marked RPM (possibly for a tachometer) but has not been used.

 

[TheEquineFencer]

OK guys, tell me if I'm looking at this wrong. It's a PMG generator, that means it puts out AC voltage and gets rectified to DC. A rotating magnet inside a coil (STATOR) puts out AC voltage right? That has to go though a rectifier to be made into DC right? If the stator was shorted, the smoke would come out and the engine would bog down, neither is happening. If the stator was open, it wouldn't have any DC output right? So the only thing it can be is the rectifiers (DIODES) are bad, breaking down under a load. This is assuming it is an UNREGULATED DC output.

My question is, are you sure this is from a tank? After googling around, it appears most tanks are 28VDC output, even the upgraded AUX units in them are 28VDC.

I even tried to find a 60VDC generator end and could find one of any real size.

Am I missing something as far as what's wrong with it? I think his rectifier/rectifiers are bad and breaking down under load.

 

[Radix2]

OK guys, tell me if I'm looking at this wrong. It's a PMG generator, that means it puts out AC voltage and gets rectified to DC. A rotating magnet inside a coil (STATOR) puts out AC voltage right? That has to go though a rectifier to be made into DC right? If the stator was shorted, the smoke would come out and the engine would bog down, neither is happening. If the stator was open, it wouldn't have any DC output right? So the only thing it can be is the rectifiers (DIODES) are bad, breaking down under a load. This is assuming it is an UNREGULATED DC output.

My question is, are you sure this is from a tank? After googling around, it appears most tanks are 28VDC output, even the upgraded AUX units in them are 28VDC.

I even tried to find a 60VDC generator end and could find one of any real size.

Am I missing something as far as what's wrong with it? I think his rectifier/rectifiers are bad and breaking down under load.

PMG?

The base assumption is it is a conventional lundell style (automotive) alternator?

A picture of what it actually is would be great.

One advantage of a lundell Machine is that the output voltage can be regulated over a very wide range, basically limited by the diode ratings. So for something like this, you could use a common part with proper diodes and get the required 40-60 volts needed with the correct regulator.

It could be many things, some pictures to see what it is are a must.

Permanent magnet machines are harder to control for this sort of job so I am guessing that this is not one?

 

[MScott]

My question is, are you sure this is from a tank? After googling around, it appears most tanks are 28VDC output, even the upgraded AUX units in them are 28VDC.

As I mentioned, I was told this was an Abrams tank alternator. I have no proof of this and there are no identifying markings to tell me if that is true or not. It may have been seller's hyperbole.

 

[Radix2]

As I mentioned, I was told this was an Abrams tank alternator. I have no proof of this and there are no identifying markings to tell me if that is true or not. It may have been seller's hyperbole.

Any pictures if this bad boy?

Since the Abrams is powered by a turbine (jet) engine, I'm kinda sceptical on that, maybe from the aux? Don't know if that is a turbine too?..

 

[TheEquineFencer]

Any pictures if this bad boy?

Since the Abrams is powered by a turbine (jet) engine, I'm kinda sceptical on that, maybe from the aux? Don't know if that is a turbine too?..

They are now I sure. Aux units for MIL Spec aircraft are I know.

 

[theoldwizard1]

Any pictures if this bad boy?

Since the Abrams is powered by a turbine (jet) engine, I'm kinda sceptical on that, maybe from the aux? Don't know if that is a turbine too?..

On the tank, I am pretty certain it is driven somewhere off the gear box, so it does not see anything close to shaft speed.

 

[Captain Spaulding]

Don't forget, charging a 12 volt lead acid battery requires 13.8 volts. That would be over 55 volts for a 48 volt battery, These batteries are AGM, not lead acid batteries so they do not boil. It would probably be OK to use a 55 volt alternator to charge them but this system was designed for 60 volts so???

AGM batteries will boil. The problem is the process isn't reversible since you can't add water to replace what is lost when they vent. Most AGMs have a charging voltage limit at 14.6V max to avoid this.

 

[TheEquineFencer]

AGM batteries will boil. The problem is the process isn't reversible since you can't add water to replace what is lost when they vent. Most AGMs have a charging voltage limit at 14.6V max to avoid this.

I think the term is "out gassing" for AGM batteries. I know at the place I was working in Raleigh,NC they use AGM batteries in the solar towers, if they wired them wrong or a charge controller failed, they'd "vent" or "out gas" and would never hold a charge or real load once they were over charged.

 

[Captain Spaulding]

I think the term is "out gassing" for AGM batteries. I know at the place I was working in Raleigh,NC they use AGM batteries in the solar towers, if they wired them wrong or a charge controller failed, they'd "vent" or "out gas" and would never hold a charge or real load once they were over charged.

Gassing is the correct term for all lead-acid batteries, and when it gets extreme enough an AGM will vent, but the term boiling is so commonly used that I've given up on convincing people that batteries don't actually boil.

 

[MBfreak]

To the OP.
I have extensive knowledge and experience of generators from typical car size, 14,2 V 60 A and up to 1700 MVA 25 kV units in nuclear power stations.
And I love to repair stuff. Been at it for 55+ years, I am 72.
Can you please post some pictures of the nameplate, connection box, voltage regulator, rectifier bridge and slipring assembly with brushes. ( I surmise it is an alternator)
I can the probably point you in the right direction.
Culprits are sliprings/brushes or the regulator.
There is a very easy way to test, will advise once I see pics.

And if it is the regulator, please send it to me and I will repair at absolutely no cost to you. I will be in Clarksdale MS the next three weeks, you can send the regulator there.

Will only be to happy to help out.

Ola

 

[TheEquineFencer]

To the OP.
I have extensive knowledge and experience of generators from typical car size, 14,2 V 60 A and up to 1700 MVA 25 kV units in nuclear power stations.
And I love to repair stuff. Been at it for 55+ years, I am 72.
Can you please post some pictures of the nameplate, connection box, voltage regulator, rectifier bridge and slipring assembly with brushes. ( I surmise it is an alternator)
I can the probably point you in the right direction.
Culprits are sliprings/brushes or the regulator.
There is a very easy way to test, will advise once I see pics.

And if it is the regulator, please send it to me and I will repair at absolutely no cost to you. I will be in Clarksdale MS the next three weeks, you can send the regulator there.

Will only be to happy to help out.

Ola

Good luck on the pictures, we've been trying to get him to post some so we'll know what it actually looks like.

If he'd take a picture and send it as a message attachment to someone they could post it for him.

 

[MScott]

Sorry about the pictures. My camera is not working and my cell phone is not able to send pictures. I tried to get someone to take some pictures on the weekend but, with the ice/snow we have had it hasn't worked out. I am still trying so I should be able to post some pictures in the next few days. I am a bit of a technical neophyte I'm afraid.