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Old 05-30-2016, 11:39 PM   #1
Bus Crazy
Join Date: May 2009
Location: Columbus Ohio
Posts: 2,491
Year: 1991
Coachwork: Carpenter
Chassis: International S3800
Engine: DT360
Rated Cap: 7 Row Handicap
"exciting" an alternator.

Ok.. im a little lost on how these monsrer alternators work... i finally got the numbers off of my alternator and its a Bosch SB200 (200 AMP)..

it has an external regulator mounted to the alternator itself.. which has several terminals on it..

there are 2 very large terminals... marked "14 volts".. a big red wire is on one but the other is empty... (is this normal?)..

there is another terminal marked 'L' and it is empty..

so when i start my bus.. my alternator isnt charging.. I can turn on every heater, light , A/C etc.. and the voltage needle will drop way down.. the batteries are good so everything runs...

now I take off in the bus and drive.. seems aftyer I drive a couple blocks.. sometimes even a mile or two and suddenly the alternator "kicks in" and it charges perfectly... always between 13 and 14 volts.. even with everythign turned on.. at idle, at cruise.. just works great..

someone told me you have to 'excite an alternator' to get it to 'turn on'.. but they also said usually the 'turn on' is at a low RPM.. so at most you kick the RPM up and it goes.. mine seems to have to go to a pretty High RPM sometimes..

another person told me without the 'L' terminal hooked up the alternator doesnt "see" a good reference resistance and so ther 'L' floats... he said the 'L' is designed to go to a "no charge" lamp on the dash... which i dont have I have a voltmeter.. and that through the bulb filament resistance is what turns on or excites the alternator..

my main thing is i want to know..

1. does it matter I only have large wire on one of the big terminals? am i only getting partial output or are both on the same set of windings inside and so its just a convenience fitting?

2. what do peoiple that dont have a lamp do? should I be hooking a resistor to ground from the 'L' terminal? or is it a resistance to Positive then to 'L'? I cannot find a manual obn my alternator explkaining the terminals and the uses...

or is it just my alternator is getting ready to go bad??

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Old 05-31-2016, 01:56 AM   #2
Bus Nut
Join Date: May 2016
Location: Georgia
Posts: 365
Year: 1987
Coachwork: Carpenter
Chassis: IH
Engine: IH 9 Liter
Rated Cap: 66 + driver
Well, I am of the belief that the factory spent considerable time and money engineering something to work a certain way. If it left the factory without something on one (or more) alternator terminals, then it likely didn't need it. I drive a Volvo with an ISX Cummins engine and the alternator on it has a couple "empty" terminals as well.

Now, as to the low voltage for the first couple miles, that's another issue. Could be voltage regulator beginning to fail - or just dirty/corroded connections. Belt isn't slipping, is it? You try giving the engine a few revs to see if the alternator "kicks in" after start-up?

*Edit* I re-read your post and see you've revved the engine to see if it charges. Check to see if the alternator is turning at full speed/belt not slipping. Loosen the belt and turn alternator by hand (Engine off, of course); see if it turns freely.
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Old 05-31-2016, 02:03 AM   #3
Bus Nut
Join Date: Jul 2011
Location: Winlcok, WA
Posts: 895
I can remember back in the day we had seven Gillig RE buses in the fleet. All seven had huge Delco Remy 150 amp alternators that over time got swapped out for 200 amp Leece Neville alternators.

It didn't matter which one was on the bus. When you first started the bus up, until you got the RPM's well over 1000 RPM the alternators would not get excited and start to charge.

I am wondering if the same thing might be going on with your bus.
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Old 05-31-2016, 05:57 AM   #4
Bus Crazy
Join Date: May 2009
Location: Columbus Ohio
Posts: 2,491
Year: 1991
Coachwork: Carpenter
Chassis: International S3800
Engine: DT360
Rated Cap: 7 Row Handicap
That's the issue is that I can't use the service manual for this , it's not the factory type alternator.. Ihc put a 130 amp SI style on it .,

Carpenter may have changed it but most likely the schools did at some point.

It's rated at a 1500 rpm turn on point .. Alternator rpm and o have a 3/1 drive ratio so that's 500 rpm engine .

I found another terminal on it behind the heater hoses called S, which is supposed to go to an ignition key switched positive. Mine isn't hooked up..

A mechanic may have just assumed this is a one wire alternator and since it does work eventually probably left it this way ..

I found the oem SI connector nearby .. From the OEM, I'm going to try running a lead from it to the S on the alternator and see what happens..

I had heard of some old tricks years ago that had to get their RPMs up.. Mine I can redline it and still doesn't come on.. If I let it run with the air conditioner blasting (60 amps) for 15 minutes then rev it up and down a few times it will kick in...

These alternators though are a huge upgrade over factory.. At $500 a pop! It's 200 amp, and gives 80% of its rated capacity at 1500 alternator rpm or 500 engine rpm. .. That's a nice output at idle!!.. Maybe because I had a wheelchair lift they knew this bus would spend a lot of time idling and pull lots of current.. That lift likely used a lot.. Then in winter if that door was open lots all the heaters would be blasting.. School lights and headlights on..

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