Charging System Problem???

[MyPrevost]

I just returned from a trip to Palm Springs on Sunday and noticed that while the engine was running, the voltmeter on the dash fluctuated between 26 and 28 volts. Additionally, the dashboard lights were dimming and brightening in sync with the changing voltage.

After parking and just before turning off the engine, the red battery indicator on the dash lit up.

I started the engine again 48 hours later, and the same fluctuating voltage was present, but the battery indicator light was off this time.

What could this mean? Is it an issue with the 24-volt alternator?

Lee

[MyPrevost]

It sounds like you might be dealing with a similar issue, Lee. Back in 2001, I experienced a related problem while driving down the interstate. The headlights were pulsing, and it turned out to be an issue with the 24-volt alternator—not the one on the 8V, but the auxiliary alternator.

[MyPrevost]

Lee,

It sounds like your alternator or voltage regulator may be starting to fail. If you have the 8V92, check the field wire that runs from the voltage regulator to the alternator. There have been issues in the past with the field wire connection at the alternator.

Good luck with this—it can be tough to see the wire and its connection under there. If it turns out to be an alternator failure, I recommend letting someone else handle that job; changing the alternator is a challenging task that can only be done from underneath the coach.

[MyPrevost]

Jon,

My coach is a 1997 Liberty 40′ with a 60 Series engine. The 24V alternator is located next to the cooling fan and is belt-driven from the gearbox, so it looks easy to access.

There are only two wires attached to the alternator, which are the size of battery cables. Where can I find the voltage regulator for this setup?

I just examined the belt and noticed it has a crack and a lump at the point where it’s cracked. It’s possible that it’s slipping whenever it hits that crack. I’ll replace the belt first and see if that improves the situation.

Lee

[MyPrevost]

Lee,

Make sure to check the voltage regulator. From my experience, it’s not a good idea to run the bus for long with that warning light on. Last fall, my voltage regulator failed, and the red light illuminated. It caused the battery isolator to catch fire, which fried a lot of wiring and destroyed both the chassis and coach batteries, creating an expensive mess. Thankfully, I managed to put out the fire before it turned into a full-blown disaster.

In the end, I had to replace the alternator, voltage regulator, isolator, battery equalizers, a lot of wiring, and both the chassis and coach batteries.

Good luck with it!

Loc

[MyPrevost]

Your voltage regulator is located on the forward bulkhead above the bus batteries.

If your alternator is indeed failing, at least it will be easier to change compared to the setup on the 8V92.

[MyPrevost]

I realize now that I made an error. The small Delco alternator is a 12V system with a 145A output, designed for charging the house batteries, and it has an internal regulator. I’ve replaced the belt.

Upon further consideration, I’ve noticed that the dash volt/amp meters are labeled for both the engine and the house systems. The house system operates on 12V, while the engine alternator is a 24V unit with a hefty 270A output.

It seems the issue lies with the 24V system rather than the house system. I’ve located the regulator in the engine compartment, and I’ll do some research on how to test both the alternator and the regulator. I’ll keep you updated on my progress.

[MyPrevost]

Lee,

Are you sure about the 12V? I thought the small alternators where for the start batteries and the 24V 270 is for house.
Tom Chilcote
Trans-Specialists RV Batteries
tom@transpspecialists.net

[MyPrevost]

Tom,

I had the same confusion initially. My Prevost Build Sheet indicates that the 12V 145A alternator was an optional add-on when the coach was manufactured.

Since I have Prevost Bus Air, the blowers utilize large 24V DC motors. The engine is equipped with a 24V starter and four 12V engine batteries arranged in two banks to create the 24V system. That’s why my coach is outfitted with the hefty 270A 24V alternator.

For the house system, I have three 8D gel cell 12V batteries connected in parallel, so the small 12V 145A alternator takes care of charging them while I’m on the move.

Lee
97 XL 40 Liberty

[MyPrevost]

I can’t fully explain the reasoning behind this, but I believe I’m on the right track.

In earlier coaches, particularly those with 24V lighting, the alternator was 12V and charged the 12V house batteries through an equalizer. In later models, possibly those equipped with 12V lighting, the bus alternator was upgraded to 24V.

That seems logical, doesn’t it?

[MyPrevost]

On my 97 Liberty Classic, the house is 12v, the house alternator is 12v, 145amp. The engine batteries are charged by a 24v alternator.

Mike

[MyPrevost]

Thanks Lee, I surrender!  Glad I only have one big fat alternator.
Tom Chilcote
Trans-Specialists RV Batteries
tom@transpspecialists.net

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