Gen light on at full air power

[daveola]

Sadly my gen light is staying on even after I reach air pressure, and sure enough, the batteries are not being charged anymore (they used to sit at a steady 27V when I was driving).

Fortunately for now I can run my Genset and keep the coach batteries charged since they are linked to my house batteries, but I'd like to get this fixed.

I've found the solenoids and relays in the compartment to the left of the driver on the outside of the bus, but I don't see anything that describes which terminal is hooked up to what.  Anyone have a wiring diagram around that explains this?

[robertglines1]

ck your voltage regulator .I think it is located in the last bay curb side on a MCI9 --sort of looks like you pic.  28 volt on gauge would be more like it. Also ck individual batt voltage as you could have one bad cell in one= throws whole system off.

[luvrbus]

Check the voltage at the field terminal it should have 12 volts for the alternator to work and go from there

[bevans6]

What bus do you have?

Brian

[baker4106]

Had that problem with my 4106 and found the charging relay not pulling in.   Found the relay that prevents the starter from working when the engine was running had a bad coil and not activating.   

[daveola]

What bus do you have?

Good point, my bad.  I have an 1986 MCI 102A3.

Does anyone have a wiring diagram showing where the voltage regulator and field terminals actually are?

[bevans6]

MCI wiring diagram is here;  http://busconversion101.com/PDF_Files/MCI%209%20Maint%20Manual%20in%20PDF%20format/MC-9%20-%20Maint%20Manual%20Section%207.pdf

I have studied that thing and I can't see for the life of me how the low air switch can control the alternator the way it does on my MC-5C, so maybe it doesn't, but you mention the air is all the way up so I figure you normally expect the alternator to start charging after the low air warning goes off.  If anyone can figure that part out, I would love to know.   See if you have 24 volts at the positive terminal of the voltage regulator  (MCI often hides them behind a hatch on the rear wall of the driver's side luggage bay).  If you don't have 24 volts there, it could be the Field relay and any low air control system.  If you have 24 volts there see if there is a voltage on the field terminal.  If there is a voltage on the field terminal the alternator should be charging.  Check that the ground on the voltage regulator is good.

The low air switch controls the low air tell-tale and buzzer directly, but it controls the no-gen and blower cut in through the blower cut in relay.  The blower cut in relay is a 12 volt controlled relay that gets an output from the relay terminal on the alternator when the alternator is working.  The low air switch provides a ground to the relay, turning it on, which turns the no-gen lights off and lets the AC and heater blowers work.

That's all I got, sorry...

Brian

[B_K]

Brian they never changed the way the not gen light wiring was from your MC5 all the way up to the C or D models. They are really charging but show not charging up until air pressure reaches that point when the light goes out.

Of course as said check the regulator and the field voltage. Also there is a relay in the rear electrical box mounted inside the rear service door on the drivers side by the air filter. (mounts on the back side of the drivers side tag axle fender well)
  BK 

FWIW even if it's charging while the not gen light is on I always told my drivers not to turn on Heat-A/C or other heavy loads until the light went out. (to give the batteries time to recharge from starting it)

[bevans6]

B_K, my voltage meter sits at 24 volts until the no-gen light goes out when it pops up to 28 volts, and if the alt belts are loose they start to squeal like a piglet when the alt starts pulling power to charge, so I really think they are controlled somehow.  I just can't figure out how, per the schematic they should be charging from the start just as you say.  Just another MCI miracle maybe...

Brian