Community Forums

Timw99 · 09-20-2013, 04:55 PM

I just purchased a 1995 bonder and today the Alternator went out. I looked and it had been replaced in 2005 with a 105 amp unit. Would it be wise to upgrade to a 200 amp Alternator since it looks like it might have a large load on it ?
New rv owner
Tim

**CLIFFTALL** · 09-20-2013, 04:56 PM

Welcome to irv2.

Cliff

Timw99 · 09-20-2013, 05:19 PM

Thank you.

vsheetz · 09-20-2013, 08:48 PM

Welcome!

If GM alternator and it needs excitation, ensure the excitation voltage is present to the alternator. A blown fuse in the excitation line will shut down the alternator.

Is there a battery isolater? Ensure it is not the problem.

I have experienced both these issue on a previous coach - on a 95' GM P30 chassis.

Timw99 · 09-20-2013, 08:59 PM

Thank you I will check that tomorrow as it will be a lot cheaper to fix then to replace an alternator

Loren Rice · 09-20-2013, 09:30 PM

I had a Winnebago that had a similar sized alternator as yours. One day My wife and I decided suddenly to go to the beach about 100 miles away.

My coach batteries were a little on the low side as was the starting battery, in fact I had to charge it a while to get it started. I knew I had a 100 amp alternator-- so no problem --right? That's way bigger than my car alternator at that time. Last it was getting dark when we left so the lights were on as well.

Turns out when you have low batteries those small frame 100 amp alternators over heat and fail. So the alternator servicer told me to make sure your starting battery for sure is up. Since then I never have had a problem even when my coach batteries are down from boon docking, as long as my starting battery is up.
Loren

Timw99 · 09-21-2013, 09:25 AM

Where is the exciter fuse located on the p30.. All fuses are ok on the battery control center and none labeled exciter ?

vsheetz · 09-21-2013, 10:19 AM

Quote:

Originally Posted by Timw99

Where is the exciter fuse located on the p30.. All fuses are ok on the battery control center and none labeled exciter ?

First I would suggest to ensure you have an GM alternator that needs excitation. There will be a third smaller wire that goes to the alternator. It should have 12vdc on it with the ignition key on. Troubleshoot it back from there. I have seen the fuse in a panel under the dash, or inline with the wiring.

Timw99 · 09-23-2013, 06:58 PM

Checked the 3rd wire going to the alternator and it has 12 volts on it so my guess would be the alternator is bad. So I guess I should have it changed. This will be the second one this has had. Next question would be should I have a 200 amp put in since the smaller ones have had problems ? I also noted that there is a 1 mil phantom load that will take the battery down just sitting. Guess that is what the knife switch is for.
Tim

Loren Rice · 09-24-2013, 09:52 AM

Tim,

If you have plans to keep your mh, for a while I would probable go 200 amp route. I think I understand that there are large frame alternators, and small frame alternators, which came with the chassis, to the motor home builder. It's my understanding that the large frame alternators handle heat much better--like when you have low batteries, lights and heaters going. (wintertime)

So I think even a large frame 100A would be better than the compact frame, but if you tend to boon dock, the chances of finding yourself with a pretty high charging demand at times, the 200 is the way to go. Remember it only takes one event to cause alternator failure.

The chassis under your motor home gets built for a variety of uses. Some are turned into trucks, which do not have the battery banks for house lights etc. So a small frame alternator works just fine for them. They perhaps don't know or choose not to address the rigors of an alternator that is in a chassis sold to a motor-home builder.

This information is what I was told when I had a 100 amp small frame alternator fail in my Winnebago, with a gm chassis

Hope this helps,

Loren.

mgscott4 · 09-25-2013, 10:39 AM

You are going to pay a lot more for the 200 amp alternator.

Amazon.com: ALTERNATOR HIGH OUTPUT 200 Amp 7.4L 454 CHEVY GMC P VAN 91 92 93 94 95 96 TRUCK: Automotive

monkey · 09-26-2013, 07:19 AM

Is the wiring the same size for a 100A to a 200A alternator? I know some vehicles are not compatable unless you change other things. Is a P30 chassis ok to go from 100 to 200 A ? Also when I recently replaced the belts on ours, (a 350 engine), I "guessed" it had the larger 124amp alternator in my case, but it had a 105 amp one, so the belt was a different length... Something else for you to check.... Might be the same on a 454... Monkey

Timw99 · 09-30-2013, 07:04 PM

Quote:

Originally Posted by monkey

Is the wiring the same size for a 100A to a 200A alternator? I know some vehicles are not compatable unless you change other things. Is a P30 chassis ok to go from 100 to 200 A ? Also when I recently replaced the belts on ours, (a 350 engine), I "guessed" it had the larger 124amp alternator in my case, but it had a 105 amp one, so the belt was a different length... Something else for you to check.... Might be the same on a 454... Monkey

Thanks.
I had it
Changed wow 153 for the unit and 400 for
Labor. I think I need to
Learn more about how
To do this kind of stuff my
Self .

Papa_Jim · 10-01-2013, 05:47 PM

Do you have a chassis battery and house batteries? If so, do you have an isolator? If you upgrade to a larger output alternator, you must make sure that you upgrade the isolator to match.

The biggest mistake many people make is to rely on the engine alternator to charge up house batteries that have been depleted. That's a HUGE load on the alternator, one that it was never designed to handle. This is true whether you have a 100 amp or 200 amp alternator. You need to size your alternator based on the 'on the road' loads it will have to handle, assuming that the house batteries are fully charged when you head out on the road.

The best procedure is to make sure the house batteries are fully charged using shore power or your generator before starting your engine to head out on the road.