Alternator failure

The school owns five buses. Two traditional ‘yellow’ buses manufactured by Thomas and three ‘minibuses’ manufactured by Krystal Koach. All are diesel. They were not used over the Christmas Holiday (2 1/2 weeks). Upon return in January, it was discovered that the alternators to 4 of the 5 buses did not function and had to be replaced. We had experienced what is for us unusually cold temperatures (lows in mid teens)for about a week during this time. The buses were all parked together out in an open area next to our stadium, so they were subject to the weather. Could the cold have damaged the alternators in some way or are there other situations to consider? Thanks for your help.


Lots of vehicles sit out in the cold for periods of time and do not suffer alternator failure. Something else caused the failures.

Considering you lost 4 out of 5 alternators I’m tempted to say someONE caused the failures.

It would help to know what part in the alternator failed, and if all 4 failed in the same way.
There’s four parts in an alternator prone to wear-out or random failure:
bearings, brushes, diodes, regulator.

Lightning can blow the solid state circuitry of the voltage regulators. Lightning doesn’t just happen in the summer. Can you think of a better target for lightning than 5 buses parked in an open field?

Cold will not damage them. Alternators operate reliably in aerospace applications so cold that it would turn an Eskimo into a popsicle in seconds. There are definitely other situations to consider. But that doesn’t mean automatically assume sabotage.

Lightning is doubtful as the vehicle’s metal hood makes a Faraday Cage to protect the alternators from lightning just as the vehicle body protects passengers.

The failure mode of each of the alternators might reveal more of what happened. If the failure modes were identical, then the weather might have been a factor. If there was a variety of failure types, then I would suspect a sneaky thief.

My guess is the cold weather was not the culprit. Well maybe partly. The 2 1/2 weeks downtime did it. Or a combination of the two if you prefer. A number of years ago I had to replace an alternator. A few weeks later the alternator failed on my other car. I elected to take apart the second one to see what made it tick. I had never disassembled an alternaror before but I had had some experience with generators. OK so it was a lot of years ago, 1973, and I was living in Sault Ste. Marie, Ontario, Canada, just across the creek from the Soo that you all know so well. I discovered that there was a film of crusty corrosion on the slip rings that made contact with the brushes in the alternator as well as in the guides that held the brushes, and further that the light springs that hold the brushes against the slip rings were not strong enough to overcome the crud and therefore there was no contact between brush and slip rings. Both failures were noted on start up after the vehicles had been sitting unused for a period of a few weeks. Just like yours. My reassembled alternator worked just fine and was still in use when I finally sold off the car. Then a few weeks later my newly acquired alternator failed. Again the car had been sitting unused for a time. I wondered whether a few whacks to the alternator casing might be enough to free up the brushes. So, waled the bejesus out of it with a piece of 2 by 4 and, voila, the problem was solved. Since that time I always try a solid whack on the casing with a board or rubber mallet to loosen up the brushes before I dash off to replace an alternator. Maybe that won’t work for you, but it is worth a try (I bet it will work)
Jim Savage Canada

Re my last,
Mrlemm, what part of the country are you in? I am curious to know. If this happens again please let us know how you got on.
Jim savage

Wouldn’t lightning have taken out all five, instead of 4 out of 5? Also, a strike strong enough to damage the alternators, surely would have effected the electronic systems in the vehicle, wouldn’t it?

Just outside Houston Texas.

What’s different about the 5th bus? What does it not share with the other 4?