Alternator On FIRE!

[jpelc]

***** WARNING *****
This could and can happen to any of you!

My alternator caught on fire due to a very rare failure that in my 50 years of working on cars and trucks I never experienced.
Note, the electrical starter/alternator setup (circuitry) of the M1078-A0 is no different then any other vehicle out there since the beginning of times. There is a question (at the end) that I have no answer to....

I dropped my truck (Yeti) at a shop to fit it with a custom camper box at TRAX in Kentucky.
Just before Christmas, the guys went to check the truck that is starts ok and ready to drive it into the shop for box fitment.
Here are the order of events that ended up with fire:
Engine started
Starter solenoid fused in RUN position (as was confirmed after taking it off)
Engine ignition turned off (fuel off) to stop the engine....
Starter kept turning the engine full speed powered by batteries
TRAX staff turned the batteries disconnect to OFF
Engine kept turning by starter, powered by ALTERNATOR already producing 24V (aka perpetual motion, but really)
Alternator burned out due to over amperage, internally exploded and caught on fire
Alternator quit producing, starter stopped.

Thanks for the quick response by the TRAX staff, the fire was put out w/o any external damage to the truck!
Thank you TRAX!!!!

This sounds like a perpetual motion, if it was not for the alternator to "bail out".
Question: can this happen to any vehicle out there? The reason it happened here is that the alternator started producing 24V when the engine actually started and got up to the needed RPMs, but when turned off, the RPM should have dopped, yet the alternator kept producing until it literally and electrically burned itself out.



My repair and remedy:
I was already planning on turning the alternator to simple 24V, so thanks to a RONMAR post, I am converting the bracket to take an off the shelf basic 24V, 110A, $165 from Amazon alternator. Adding 24-12 converter to produce the 12V and adding a least expensive 12V battery to supply 12V when engine is not running. (the 12V battery is my choice to simplify the conversion and provide 12V for all the cab systems when at rest). Note: when dropping the 12V pickup from in between the 24V twin batteries setup, the PDC will not function since some of the initiating relays are powered by 12V. RONMAR has a great post on how to deal with that, but I choose to leave things as they are for now and add the converter with a separate battery.

The remedy: simple. I will install a battery disconnect between the +24V and the alternator/cab cable. So in case this ever re-occurs, I will disconnect the alternator first, then the batteries. This will stop the failed solenoid starter without any further damage (AND NO FIRE).

 

[NDT]

Problem with your analysis is that when you turn off the ignition, the excite voltage to the alternator is switched off.

 

[fuzzytoaster]

Your alternator to starter relationship in this situation isn't possible. Ignition off = alternator off/ no excitation. Even if the unit somehow failed in an operating state at max output it would only put 60 amps on the 24v side. That's far less than required to turn the engine over.

Starter relay (in cab) failure, remote starter solenoid (on frame) failure, starter relay (failure), or damage/contact with signal wire are your likely culprits. I've seen starter bendix get stuck engaged to the flywheel from age and corrosion and chew up the unit if not break off the engine with prolonged higher rpm engagement.

 

[Jbulach]

***** WARNING *****
This could and can happen to any of you!

My alternator caught on fire due to a very rare failure that in my 50 years of working on cars and trucks I never experienced.
Note, the electrical starter/alternator setup (circuitry) of the M1078-A0 is no different then any other vehicle out there since the beginning of times. There is a question (at the end) that I have no answer to....

I dropped my truck (Yeti) at a shop to fit it with a custom camper box at TRAX in Kentucky.
Just before Christmas, the guys went to check the truck that is starts ok and ready to drive it into the shop for box fitment.
Here are the order of events that ended up with fire:
Engine started
Starter solenoid fused in RUN position (as was confirmed after taking it off)
Engine ignition turned off (fuel off) to stop the engine....
Starter kept turning the engine full speed powered by batteries
TRAX staff turned the batteries disconnect to OFF
Engine kept turning by starter, powered by ALTERNATOR already producing 24V (aka perpetual motion, but really)
Alternator burned out due to over amperage, internally exploded and caught on fire
Alternator quit producing, starter stopped.

Thanks for the quick response by the TRAX staff, the fire was put out w/o any external damage to the truck!
Thank you TRAX!!!!

This sounds like a perpetual motion, if it was not for the alternator to "bail out".
Question: can this happen to any vehicle out there? The reason it happened here is that the alternator started producing 24V when the engine actually started and got up to the needed RPMs, but when turned off, the RPM should have dopped, yet the alternator kept producing until it literally and electrically burned itself out.

View attachment 960299

My repair and remedy:
I was already planning on turning the alternator to simple 24V, so thanks to a RONMAR post, I am converting the bracket to take an off the shelf basic 24V, 110A, $165 from Amazon alternator. Adding 24-12 converter to produce the 12V and adding a least expensive 12V battery to supply 12V when engine is not running. (the 12V battery is my choice to simplify the conversion and provide 12V for all the cab systems when at rest). Note: when dropping the 12V pickup from in between the 24V twin batteries setup, the PDC will not function since some of the initiating relays are powered by 12V. RONMAR has a great post on how to deal with that, but I choose to leave things as they are for now and add the converter with a separate battery.

The remedy: simple. I will install a battery disconnect between the +24V and the alternator/cab cable. So in case this ever re-occurs, I will disconnect the alternator first, then the batteries. This will stop the failed solenoid starter without any further damage (AND NO FIRE).

This theory makes no sense, even if it did the alternator would only have produced as much power as it could without harming itself. These batteries have enormous potential that most likely caused the fire if they were not disconnected properly and completely while the starter was stuck on. Check your slave port connection, if like my 5 ton, and a battery disconnect is added incorrectly into the negative circuit, you will still have at least some battery connection through the slave port mounting.

 

[jpelc]

Problem with your analysis is that when you turn off the ignition, the excite voltage to the alternator is switched off.

That may be, but how else do you explain starter kept running after batteries were disconnected? Were did the 24V energy come from?

 

[NDT]

You mentioned the truck is an “A0”. Those did not have battery disconnect switches. Did you add this switch? If so did you interrupt BOTH ground cables connected to the batteries?

 

[jpelc]

You mentioned the truck is an “A0”. Those did not have battery disconnect switches. Did you add this switch? If so did you interrupt BOTH ground cables connected to the batteries?

See my post diagram, is how it is wired. Previouse owner installed the battery disconnect between the negative lower battery post and starter negative cable via the shunt. Other then the battery disconnect, that is the OEM wiring.

 

[jpelc]

See my post diagram, is how it is wired. Previouse owner installed the battery disconnect between the negative lower battery post and starter negative cable via the shunt. Other then the battery disconnect, that is the OEM wiring.

Also... when testing post failure (two weeks after fire), I had the 12V pickup cable from in between the 2 batteries disconnected. Straight 24V to the starter primary solenoid. Turning the disconnect to ON would instantly power the starter!

 

[jpelc]

However.... there is one other part of the wiring I did not show but exited during the event.
The 12V pickup from in between the two bats was connected to the alternator 12V terminal and not affected by the battery disconnect on the negative side. I do not know if this played any role in this event or able to explain what may have been happening inside the alternator. But I see possible circuit between the starter, 12V battery (the upper side of the 24V bank) and the alternator 24V and 12V terminals....

 

[GeneralDisorder]

This is why the battery disconnect is not wired that way from the factory. The battery disconnect in the A1 trucks breaks BOTH of the +12v and +24v leads isolating both positive battery paths.

This is a result of poor choices - but not by the engineers - so this is a lesson in how not to do electrical - rather than a warning to other FMTV owners. This cannot happen with the stock wiring configuration or if the disconnect is wired per the A1+ schematics.

And I don't trust TRAX in general. Lookup their litigation history. Regardless of "change in ownership" - birds of a feather and all that. Could be as they say. Could be other factors left unsaid. Who knows. Probably will never know.

No great loss if it's a 100A. That was a door stop to begin with.

 

[Jbulach]

However.... there is one other part of the wiring I did not show but exited during the event.
The 12V pickup from in between the two bats was connected to the alternator 12V terminal and not affected by the battery disconnect on the negative side. I do not know if this played any role in this event or able to explain what may have been happening inside the alternator. But I see possible circuit between the starter, 12V battery (the upper side of the 24V bank) and the alternator 24V and 12V terminals....View attachment 960302

And that explains why your alternator caught fire, your 12v should be pulled from the other battery with the negative disconnected that way.

 

[jpelc]

Thanks for the replies! I was not aware of the A1 factory disconnect, but now it does make sense.
So than this is a warning to those that find their LMTV with a simple negative battery disconnect as I did on my A0.

Knowing all this, what disconnect would you recommend?!

 

[Ronmar]

There is no way that alt powered that starter cranking an engine, PERIOD! You said the mythical words yourself, perpetual motion is a myth with the conversion efficiencies in play here, let alone the mechanical drag of an engine strapped to its back... As mentioned a normally functioning alt drops offline without ign power provided by K11 anyway...

Since you were not there, everything in that scenario and the order in which things occurred that you were told about is suspect. You only have 2 sources of energy strong enough to rotate the engine, fuel and the batteries...

so it kept cranking after the ground disconnect sw was activated? How did they stop it, or did it just slow down and stop by itself?

here is a more likely scenario:
1. Started truck, start solenoid/start ckt fused keeping the starter engaged(I have had this happen twice over the years). "Hey what's that noise" if they were paying attention and could hear it over the kitty purring...
2. Truck kept running, alt was online feeding the starter and the probably depleted batteries(overloaded).
3. somewhere in here the alt shorted and started letting smoke out. "Holy Krap! shut it off, shut it off"
4. Ign off, fuel cut, shorted starter kept cranking using batteries, shorted alt kept smoking
5. Open battery ground cut-out, shorted alt continues to provide a ground path and smoke, as shorted starter soldiers on at reduced power/12v until the shorted alt finally melts down and opens the 12V path to ground...

 

[Ronmar]

And that explains why your alternator caught fire, your 12v should be pulled from the other battery with the negative disconnected that way.

that 12v looks correct, it must be connected between the series wired batteries...

 

[Ronmar]

the proper disconnect breaks both the 12 and 24v lines where they connect to the batteries, which is what they used on the A1 trucks, 4 terminal dual pole.

The problem with only lifting the single ground is that you can still have 12V roaming around thru the system via the installed equipment which is probably what happened here the alt shorted that 12v to ground keeping 12v from the 12-24 batt applied to both the starter and ground...

If you ultimately convert to straight 24, you will have no 12v connection to the batteries so will only need a single 24v disconnect...

 

[Ronmar]

My repair and remedy:
I was already planning on turning the alternator to simple 24V, so thanks to a RONMAR post, I am converting the bracket to take an off the shelf basic 24V, 110A, $165 from Amazon alternator. Adding 24-12 converter to produce the 12V and adding a least expensive 12V battery to supply 12V when engine is not running. (the 12V battery is my choice to simplify the conversion and provide 12V for all the cab systems when at rest). Note: when dropping the 12V pickup from in between the 24V twin batteries setup, the PDC will not function since some of the initiating relays are powered by 12V. RONMAR has a great post on how to deal with that, but I choose to leave things as they are for now and add the converter with a separate battery.

The remedy: simple. I will install a battery disconnect between the +24V and the alternator/cab cable. So in case this ever re-occurs, I will disconnect the alternator first, then the batteries. This will stop the failed solenoid starter without any further damage (AND NO FIRE).

what will charge the 12v battery? You don't need the 12v batt anyway, the 24-12 converter will provide the 12 from 24 when the engine is not running same as the batteries provide 24 when not running. you only need to convert ignition control to 24v to make it bulletproof, same as they did on the A1 trucks(swap 1 wire and 1 relay)...

 

[NDT]

There is no way that alt powered that starter cranking an engine, PERIOD! You said the mythical words yourself, perpetual motion is a myth with the conversion efficiencies in play here, let alone the mechanical drag of an engine strapped to its back... As mentioned a normally functioning alt drops offline without ign power provided by K11 anyway...

Since you were not there, everything in that scenario and the order in which things occurred that you were told about is suspect. You only have 2 sources of energy strong enough to rotate the engine, fuel and the batteries...

so it kept cranking after the ground disconnect sw was activated? How did they stop it, or did it just slow down and stop by itself?

here is a more likely scenario:
1. Started truck, start solenoid/start ckt fused keeping the starter engaged(I have had this happen twice over the years). "Hey what's that noise" if they were paying attention and could hear it over the kitty purring...
2. Truck kept running, alt was online feeding the starter and the probably depleted batteries(overloaded).
3. somewhere in here the alt shorted and started letting smoke out. "Holy Krap! shut it off, shut it off"
4. Ign off, fuel cut, shorted starter kept cranking using batteries, shorted alt kept smoking
5. Open battery ground cut-out, shorted alt continues to provide a ground path and smoke, as shorted starter soldiers on at reduced power/12v until the shorted alt finally melts down and opens the 12V path to ground...

I was about to type this exact scenario but Ronmar beat me to it. This is what happened. They are trying to deflect blame.

 

[G744]

Allegiance to 12V systems in 24V tacticals is just stupid if DIY, or dumb on the part of the factory engineering team.

I've never needed to consent to any 12V device in any tactical I've ever owned or worked on for people, tho I've ripped out many jake-leg 12V attempts at something.

I know, lots of the later rigs come that way, and the CUCV & M880 series were the early & worst ever design.

Still, there are lots of 'em out there, and owners spend time & money on failures.

G744, your friendly tactical truck dinosaur.

 

[GeneralDisorder]

Allegiance to 12V systems in 24V tacticals is just stupid if DIY, or dumb on the part of the factory engineering team.

Like the rest of the FMTV, one of the main driving ideologies behind the concept was to use as many commercially available parts as possible to lower costs to produce and maintain. In that vein it was decided to use 12v lighting because the bulbs are cheaper. This later became irrelevant when LED's came to market and now all the combination light housings used by the military are 10-30v so they don't care what you feed them.

Yes in retrospect it was dumb. But at the time it solved a problem someone thought they were having - and overall the mission was accomplished in dramatic form! The CAT engine and Allison transmission were great successes leading to variations on them being used across the entire wheeled vehicle fleet. The 12v lighting was just one small piece that ended up kinda silly but no one knew that would be the case. The overall concept was a great success.

 

[Reworked LMTV]

This is why the battery disconnect is not wired that way from the factory. The battery disconnect in the A1 trucks breaks BOTH of the +12v and +24v leads isolating both positive battery paths.

This is a result of poor choicns - but not by the engineers - so this is a lesson in how not to do electrical - rather than a warning to other FMTV owners. This cannot happen with the stock wiring configuration or if the disconnect is wired per the A1+ schematics.

And I don't trust TRAX in general. Lookup their litigation history. Regardless of "change in ownership" - birds of a feather and all that. Could be as they say. Could be other factors left unsaid. Who knows. Probably will never know.

No great loss if it's a 100A. That was a door stop to begin with.

Interesting. I talked to this guy about 1.5 years ago about the possibility of combining with my CSX rail shipments.