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Direct Drive Alternator
My bus is in the shop at Elite Coach in Ephrata PA for some A/C work and the mechanic mentioned that I have a direct-drive alternator on my 8V92 that is operating below spec. He said it is a bear to get to, likely by entering under the bed. I would like to understand what this alternator drives vice the belt-driven alternator and why two alternators.
Thanks.
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7 Replies
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Liam,
Your alternator is a 50DN and it is readily available from here:
I had one fail on my 8V92 and there was no way I could do it myself because of the weight and location. So I took it to Prevost in NJ. They didn’t even consider going in from the top. They raised the coach, did all the loosening and bolt removal from below, and when it was free, they brought it down across the top of the bell housing. Installation was done the same way. They had the coach on the wheel lifts and during removal and installation they raised and lowered the coach by a little bit to aid in getting the alternator in the best position to install or remove.
If a tech tries to remove it from the top (under the bed through the cover in the floor) take special precautions to protect the coach from the grease and oil that is going to get everywhere. That alternator is around 135# if I remember and I think it would be very hard to try to work around the bed frame to lift it up to carry it through the coach.
FWIW, the first replacement failed before I got the 400 miles to the house. I returned the next week so they could replace the replacement. They used the same method for R&R. Ironically the second one they were about to install was binding when they spun the alternator so the next one they pulled from stock was OK so out of three Prevost had in stock one worked.
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Wow, what a drama!
What items does that alternator drive and why do I need two?
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Liam, are you sure you have 2? I had a ’90 Country Coach with 8v92 and it had only one, the 50dn that has been mentioned. It charges both the house and chassis batteries. My current bus has two, but that is because MCI does not make a conversion shell so it has stuff related to passenger service. Mine has a small alternator to allow limp home if the big one gives out.
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Liam,
If your house battery bank is 12V then you likely have 2 alternators, one 12v and one 24v.
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Liam.
If you have 2 that means the house and chassis have their own dedicated charging system for their respective battery banks. You don’t even have to look at your engine to know. Look at the gauges for each system, and if one is not showing the correct charging voltage and the other is, then one of the alternators or regulators likely needs attention.
Before deciding to replace the 50DN if that is in fact what appears bad, check to make sure the regulator is not bad. Also the 50DN as installed by Prevost had a recurring issue with a broken field wire connection at the alternator. I don’t know if it was vibration or some other cause but on two occasions with my 87 coach I had to replace the field wire terminal because it fatigued and literally broke in half.
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8v92 detroit that have 2 alternators
usually are setup that if one fails the other will take over until the faiiled one is fixed
the rear one is usually at fault due to dirt grime and other associted nasties
We sell ELREG alternators for coaches 12 and 24 volt and 50 dn oil and air cooled also voltage regulators
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Stephen,
On Prevost conversions (excluding later model Bosch alternator equipped coaches) there are several alternator configurations with none used as redundancy or backup.
One single alternator coaches, usually 50DN the alternator is coupled with an isolator so it can charge both house and chassis batteries, but neither set can draw down the other due to the isolator.
On some coaches with 50DN alternators and over the road air and a 12 volt house the converter uses a second alternator with 12 volt (usually 145 amp) output for the house.
When the house is 24 volts, the second alternator is not used generally speaking.
When the coach has no over the road air the 50DN is usually dedicated to the house and the second alternator is a 24 volt dedicated to the chassis.
So bottom line the second alternator is usually a different voltage than the primary and only when OTR is used is the chassis batteries supplied by the 50DN
Some coaches do not use the 50DN, but have two alternators, each dedicated to the house or chassis.
Our back up for an alternator failure is usually to run the generator and charge the house through inverters and the chassis via an on board charger. When the chassis battery fails loads have to be minimized, such as no use of the OTR.
I’ve dealt with Elreg and always recommend them.
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