Alternator/Regulator failure

[jack14r]

I was on the road to Asheville,NC last week and the voltage began to fall on the dash gauge and the battery icon showed up on the dash,I knew that I had a Guest charger hooked up to the coach batteries and I cranked up the generator and the voltage came up to 25.5-26.I only had 25 miles to go so I continued to my destination,the strange thing is that neither the alternator or the regulator have any thermal protection but when it all cooled down it began to work again.Today I left Asheville and in about 30 minutes the same failure happened again,the Guest charger could maintain 25+ volts for about 1 hour but then it fell to 24 volts so I stopped and hooked up a 30 amp charger that I carry with me and made it home.Prevost says that there is no thermal protection so I am trying to figure out if this is a alternator or regulator failure.Prevost has recommended a bus shop nearby and the shop foreman is convinced that the regulator is the problem.How can I verify that the alternator is not at fault and it really is the regulator.This coach has the 270 amp alternator and the Delco regulator.

[garyde]

I replaced my regulator last year when the voltage started acting up. Fixed the problem. Mine went bad when I overcharged my batteries with the on board charger while plugged in.

[Jon Wehrenberg]

Jack,

I am assuming the alternator you are talking about is the big one.

It is cooled via an oil bath. The rear of it, as seen from the RH side door is actually an oil chamber that bathes the diodes. If you suspect it is shutting down due to heat(?) the oil supply line can be removed and you can check the flow by starting the engine. Do a rear start and rig up a way to catch the oil. If you suspect the alternator will have a high output in amps when you run this test, remove the field wire so it does not try to charge with no oil cooling. Any output in excess of 100 amps without oil cooling will damage the diodes.

The return line is the big line coming out the center bottom of the alternator.

The only way I can imagine heat being an issue, assuming the oil supply is adequate (there is a spec that I think I can find if needed) is if the alternator is really working hard, such as to charge dead batteries, or if you are pulling heavy loads off the inverters.

As to the regulator, I can't figure how it would get hot. All it does is sense the battery voltage, and open or close the circuit supplying 24V to the alternator field. The regulator is in the simplest of terms a switch that opens when the voltage reaches a specific point, like 28 volts, and then closes when the voltage drops below that voltage. All that switch is doing is limiting the voltage output of the alternator by removing power to the field. If it did not do that the alternator output voltage would go far beyond 28 volts.

[phorner]

We had a very similar problem last summer.

The chassis charging voltage would drop, and the dash indicator light would come on, when starting out on our travel for the day. Would not usually stay on, but would occasionally happen.

Anyway, with Jon's invaluable help, I made a diagnosis of a bad regulator, which is what we had suspected.

Sounds like your charging problem, and any "warming" may be just coincidental.

I would suspect the regulator first..... but I have no idea why you weren't able to resolve it temporarily by running the generator with the charger running. That was always my "back-up" plan....

[JIM KELLER]

I replaced my regulator last year when the voltage started acting up. Fixed the problem. Mine went bad when I overcharged my batteries with the on board charger while plugged in.

Gary, I don't understand. Tell me more, please.

[jack14r]

Jon,I don't believe that the oil is not flowing because it would have opened the diodes and the alternator would not have ever charged again.Paul the charger is only ten amps at 24 volts and it was adequate until I had to turn on the wipers and then the voltage began to drop.I will check it this afternoon and try to get it to fail and check the field voltage.

[Jon Wehrenberg]

I don't envy you chasing an intermittent problem Jack. It still could be a bad alternator although it sounds as if the regulator is the real culprit.

When the alternator gets hot it could be an issue relating to the slight dimensional change of things when it is hot, but my first guess would be the regulator. iF you suspect heat nothing saus it has to be re-installed in the engine area if you can find a cooler place. Just lengthen the wires.

[jack14r]

I verified that it is the regulator,I ran the system with a large load and it finally shut down,then I jumped from the field post on the regulator to the battery post on the regulator and the alternator put out 33 volts which would be the unregulated voltage at hi idle.I am going to take it to a shop that Prevost recommended tomorrow morning,I will report back on how things go there.

[phorner]

Changing out that regulator was a pretty simple job on our bus. I was able to order a replacement from a local auto electric shop and have it the next day.

If yours is as accessible as ours, you probably can do it yourself easily.

[jack14r]

Its in warranty,I bet it would be cheaper to buy it than the fuel to drive to have it replaced,but I want to visit the place for possible future maintenance.It might take 10 minutes to change it out,the regulator must be the weak link,from talking to the service people they replace them on a regular basis.