Smoking Alternator

BDFulbright · 08-27-2019, 03:47 PM

I have a 1997 Thomas SAF-T-LINER MVP with an 8.3L 6-cyl diesel with 62,000 miles. I am just starting the conversion. Little work has been done. Other than disconnect some lights - I haven't done any electrical work. Last week the bus cranked fine. Let it idle for about 15 minutes (waiting on registrations from VT - lol). Went to crank this week and it was completely dead. It has 2-12 volt commercial batteries configured for 24-volts. Went to put on a charge -- charger showed 0 volts and would cut off (this charger is "smart" and it has never done that before). Put on a 100 amp boost. The lights on the panel lit up, but when I tried to crank it -- the voltage gauge danced all around. Went back the the charger to take a look. Smelled hot electrical. Saw the back of the alternator was smoking so I shut everything down. Just got two new batteries. As soon as I connected the first battery, the alternator started smoking. Any advice on what to check for this newbie would be greatly appreciated.

brokedown · 08-27-2019, 03:57 PM

I haven't seen a bus that was configured for 24 volts. 24 volt vehicles I've worked with in the past used a pair of 12v alternators and an isolated ground to get that 24v power. Without knowing more I'd expect that your bus was actually a 12v bus with batteries wired in parallel (very common, basically every bus ever) that you've mistakenly connected in series (never seen this on a bus) and you smoked the alternator and possibly other components by giving it twice the voltage it can handle.

But that's sight unseen.

Brad_SwiftFur · 08-27-2019, 03:58 PM

I'll skip a smart-Alec response that I was tempted to give and simply ask - are you *ABSOLUTELY* sure this bus has a 24 volt system? 24 volt systems are exceedingly rare on school buses in the U.S. (I've never even seen one myself and even on coach and city transit style buses they aren't terribly common). The vast majority are 12 volt systems and if so, you've probably got a fried voltage regulator (inside the alternator) ... and who knows what else. Virtually all these buses with 2 batteries run on 12 volts, the batteries are wired in parallel to give more amps.

Brad_SwiftFur · 08-27-2019, 04:05 PM

Also, I've never seen a Cummins engine factory painted yellow, are you sure it's not a Cat engine? Or is your profile info reflecting a different bus?

BDFulbright · 08-27-2019, 04:08 PM

You are both correct -- There are 2-12 volt batteries run in parallel. Trying to put everything down -- miss typed. That is and was the configuration. Thanks

Brad_SwiftFur · 08-27-2019, 04:16 PM

Still, a smoking alternator is bad news. I'd swap it out, could be a failed voltage regulator or something else inside ... it would also account for dead batteries and the charger not wanting to charge. Could be something shorted in the alternator.

Might wanna double check your engine, Yellow is the color of Cat's. Yours being a '97, it was the year the 3126 came out but some 3116's may be equipped. Easy way to tell - the 3116 is a mechanical engine and the 3126 is electronic. The 3116 lists as 6.6L and the 3126 is 7.2L. A VIN check should also reflect your engine.

cadillackid · 08-27-2019, 04:45 PM

that sure looks like the layout of a 3126. . hard to tell since I cant see the valve cover area.. if you havent futted the bus yet, the thomas sticker above the driver window will tell you the engine model number..

the front cover of a cummins 8.3 looks different and its usually painted a light tan color..

brokedown · 08-27-2019, 05:21 PM

Look online for a local alternator rebuilder. They can test your current unit (letting the smoke out is usually fatal) and likely have a fresh compatible unit on the shelf.

CMORGANSKOOL · 08-27-2019, 05:53 PM

Quote:

Originally Posted by Brad_SwiftFur

Still, a smoking alternator is bad news. I'd swap it out, could be a failed voltage regulator or something else inside ... it would also account for dead batteries and the charger not wanting to charge. Could be something shorted in the alternator.

Might wanna double check your engine, Yellow is the color of Cat's. Yours being a '97, it was the year the 3126 came out but some 3116's may be equipped. Easy way to tell - the 3116 is a mechanical engine and the 3126 is electronic. The 3116 lists as 6.6L and the 3126 is 7.2L. A VIN check should also reflect your engine.

Quote:

Originally Posted by brokedown

Look online for a local alternator rebuilder. They can test your current unit (letting the smoke out is usually fatal) and likely have a fresh compatible unit on the shelf.

These guys/gals are absolutely right. You had a dead short in the alternator and I bet once replaced everything will be good to go. And yes, have someone rebuild the alternator and keep it as a spare.

o1marc · 08-27-2019, 06:58 PM

You just need some of this to fix it right up.

somewhereinusa · 08-27-2019, 07:08 PM

Quote:

Originally Posted by o1marc

You just need some of this to fix it right up.

It may be next to imposable to get negative earth Lucas smoke.

o1marc · 08-27-2019, 07:21 PM

Quote:

Originally Posted by somewhereinusa

It may be next to imposable to get negative earth Lucas smoke.

You just blow it in backwards.

Rivetboy · 08-27-2019, 08:03 PM

Quote:

Originally Posted by somewhereinusa

It may be next to imposable to get negative earth Lucas smoke.

As some one who had a positive ground MG with a negative ground radio it was interesting to say the least, when I took that first fast corner and my keys swung over and hit the radio and immediately welded to it turned red hot and melted balls of brass burning my pants and the carpet. Good times. When I saw that picture, actually googled "negative ground replacement smoke". No luck

o1marc · 08-27-2019, 09:10 PM

Quote:

Originally Posted by Rivetboy

As some one who had a positive ground MG with a negative ground radio it was interesting to say the least, when I took that first fast corner and my keys swung over and hit the radio and immediately welded to it turned red hot and melted balls of brass burning my pants and the carpet. Good times. When I saw that picture, actually googled "negative ground replacement smoke". No luck

You have to ask for it by name. Lucas is the only one who makes it.

BDFulbright · 09-04-2019, 08:18 AM

Follow-up: There was a short in the alternator. Was able to get it rebuilt. Looks like new. FYI - the rebuild was $145. Thanks

BDFulbright · 09-04-2019, 08:28 AM

Follow up on the engine look-up comment. Interesting how the VIN and spec card in the window differ. The VIN has a "B" in the 7 spot which translates "6-cyl diesel". The spec card say the engine is an "ER3116TA250". There is a code "5" for a "3116TA 250 HP". Not sure why they didn't code the VIN with a 5. Need to investigate.

BigPaul367 · 09-07-2019, 03:46 PM

Something is wrong, that bus should be 12 volt, only Greyhound uses 24 volts. That Alternator will need replacement no matter what, they are NOT supposed to smoke. The charge controller, in the alternator, has three diodes, they are fried. Hopefully the starter is not fried. When you take the alternator to a rebuilder, that rebuilder will be able to tell you if it is 12 or 24 volt. BEFORE you install the new alternator, tape off the wire ends and connect your batteries. There should be no smoking, when you turn the key on, there should be no smoke, then turn the key off and DISCONNECT THE BATTERIES, THEN install the alternator, then repeat the previous procedure. AFTER you complete that procedure, THEN you can try to start the motor.

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