Ordered a Prestolite 24V 150A alternator. Back in March the last time I ran the engine, I measured the voltage at the batteries while the engine was running. The alternator had been changed out by the previous owner due to a succession of alternator problems with the old 50DN alternator. So he removed the original setup and installed an aftermarket smaller alternator. It appeared that the alternator was not putting out a charge. With one of the wettest spring seasons on record, I was unable to do much work on the bus for months. After much research and a lot of going from one place to another talking to one shop and then another I ended up ordering a new and larger output alternator online from www.ereg.com.
While the old alternator was out it gave me the opportunity inspect some of the engine room wiring. Several major wiring runs across the engine room were run inside of plastic wire wrap. On inspection, I found a horror. Approximately 5 foot of 1/0 cable was completely bare of insulation. It evidently had dry rotted and fallen off and someone is the past covered it up by putting it in wire wrap. While it was somewhat protected, it sure looked like an electrical fire just waiting to happen. So I removed it all. Nandino Industrial Electric made up new cables for me and did a great job. When I get ready for a house battery bank they will be the ones I go to to have all of the cables made up. I also replaced the "pass through stud" in the rear panel box that the alternator and this 1/0 cable hooks to. Had new cables made for the new alternator and cleaned up some wiring in the rear panel box.Pictures below are some of the new cables and replaced wiring run inside of new wire wrap and tied up secure.
Greasy ME working from the street side rear access cleaning up the wiring, removing the old alternator and installing the new.
After several months of work off and on around working and the weather, I finally got the job completed and was ready to start up the engine and test the alternator. Started it up Thursday the 7th of July... lit right off and ran for about 5 minutes then started to faulter and die. I suspect that I'll find the fuel filter canisters partially empty, which means she has lost prime.
For the brief few minutes that she ran, I hooked my meter to the alternator and was not getting a charge at idle. At first I thought something was wrong, but after researching the specs on the new alternator, I think my problem is lack of idle RPM's for the alternator. The cut-in RPM is 1400 and it turns no where near that at engine idle. The driven pulley diameter is 3" and the driving pulley diameter is 5", which means the alternator will not get up to 1400 RPM or better until the engine is at about 850 RPM.
I suspect when I get the lost prime issue resolved and the engine running again, that when I increase the RPM's that the alternator will put out the proper voltage. I am not sure of the options of either increasing the driving pulley diameter or reducing the driven pulley diameter, but either way would help the alternators idle RPM situation, but that is another battle for another day. At this point I can live with it the way it is for a while as I have more important issues to resolve.
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