need help with mc9 new alternator.

[mike802]

I am installing a new alternator in the 83 mic mc9.  There is a jumper wire going from the big post to the small post on the left, I don't think this wire is original, any suggestions?  I do not find anything in the manual about a jumper wire and I am considering just leaving it off.

[hargreaves]

What kind of alternator is it?

[mike802]

I am not sure what the model is, but it is a direct drive oil cooled unit that bolts up to the back of the engine. Access is through the floor in the rear of the bus.  The one I removed had two oil line connections, but the replacement only has one.

[Lin]

I don't know myself, but if no one here responds you could show the old unit to an alternator shop and see if they can tell you what the jumper wire is for.  Having had no experience with oil cooled alternators, I am a bit confused.  I would have assumed that two oil connections were needed for separate supply and return.

[hargreaves]

It probably is a DN50 in which case there are two smaller terminals on the back of the alt.  One is labeled (R) it is  for idiot the lite if there is one ,also used for tach on some models. The other terminal is the (F) terminal for the fields. 

[Hard Headed Ken]

I am installing a new alternator in the 83 mic mc9.  There is a jumper wire going from the big post to the small post on the left, I don't think this wire is original, any suggestions?  I do not find anything in the manual about a jumper wire and I am considering just leaving it off.

I found this in the archives. As Sean describes, with this system one side of the field is tied to the battery terminal and the regulator controls the field strength through the negative side of the field. The opposite of this can work also, where one side of the field is grounded and the field strength is controlled through the regulator using positive voltage.  It seems your system is like the one in Sean's post. Jumper wire from the battery post to small field terminal.

Do some more research, I'm usually wrong.

Ken

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Title: Re: Setra 50DN Alternator wiring
Post by: Sean on August 02, 2009, 01:00:59 PM
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The regulator you have should work fine with the alternator listed.

Note that this is an "A-circuit" regulator, which means it regulates the ground side of the field.  Your alternator connections should thus be as follows:

Large (1/2") terminal, marked "+", "DC", or "BAT": Main output, to batteries.  Use 0000 (four-ought) with a properly swaged lug.
F1: Field positive, wire directly to main output with a jumper.
F2: Field negative, connects to "F" or "FLD" terminal on regulator.
R or Relay: Relay terminal, connects to 12-volt relay that operates blower circuits and "No Charge" light on dash.

The regulator should be wired as follows:
F or FLD: goes to F2 on alternator
I or IGN: goes to a 24-volt circuit switched by the master switch ("Ignition")
G or Gnd: ground
B or BAT: Sense lead, should be connected directly to battery positive at the battery (resist the temptation to connect it someplace else more convenient).

Hope that helps.

-Sean
http://OurOdyssey.BlogSpot.com (http://OurOdyssey.BlogSpot.com)

[luvrbus]

This is what I find when they have a jumper line I removed one and the 50D on a MCI and it would put out 31 or 32 volts and regulator would not cut back to normal charging

I have GM at the shop without a jumper wire and it putting out 31 or 32 volts with no control had Tom a GM guy from the board here look at and he can't figure out we are thinking a bad reg

[Sean]

Ken, thanks for digging that out of the archives.

It sounds like you picked up an alternator from an A-circuit (also known as "N-type") application.  However, the regulator on your MC9 is probably P-type, which requires a different jumper.  If you post the part numbers for both the alternator and the regulator we can tell you for sure.

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