"not gen" light on my MC9 dash

[bowmaga]

Just got back from taking super Betty on another excursion....she made her to our destination and back. But on the way home soon after we left, the "not gen" light on our dash would come on when we would get up above 35-40mph.  When we'd slow down coming into a town, less 30 or lower, it would turn off....leaving gt back up to speed it would come on.  Then later on that night after we got home I drove her a little more with only me for some quietness, and when the light would come on I could here a single click down just inside the curb door, then the light would come on.  I've looked at a not gen post here on the page but it confused me more...Is my bus safe to drive with this light on?  Could i have hurt anything driving with it on for 2 hours?  How do i fix it?  where do i start?  Couldn't find anything in the manual about this.  My bus has and 8v71 with 740 Allison auto, and the alternator is belt driven and I do have that air belt tensioner valve in the back.  I actually replaced it right after we got it cause it was leaking air.

[jjrbus]

 Do you have a gauge also? does it show the alternator is chargeing?

[HighTechRedneck]

My RTS is a much different system than yours (50DN direct drive alternator), but I have found that once the batteries are fully charged, if there is no electrical load on, then that light comes on.  If I turn headlights on, putting a load on the system, then the not gen light goes off.  Since my insurance company wants the lights on when driving, I have made a habit out of running with them on and haven't seen the light come on since.

I don't know that your's works the same way, and there may be something on yours that does need looking at.  I'm just offering my experience as one idea.

[bowmaga]

yea, we have a volt gauge and it appears that they are being charged.

Its interesting that you say that when there is a load on it, that the light goes off.  While we were at our destination, I did some "field work" and relocated a main power wire that fed our back up camera and interior bus lights, ac stuff.  I got it off the bus starting batteries and hooked it up to our house batteries so that it wouldn't draw the starting batteries down dead.  Now you say that if there isn't a draw on the batteries that maybe this is why it doesn't need to generte power.  maybe if i rehook up that wire and see if it goes off maybe I can narrow it down. 

But why does the light go off if we are slowed down?  does the bus only generate power at high speed?

[HighTechRedneck]

You're right, that doesn't make sense that it would go off at lower speeds if it was the same as mine is doing.

The power tap you moved, was it one you had installed or was it OEM?  If it was OEM, and the timing seems to coincide, then I would start looking there.

[fraser8]

I had the same 'not gen' light problem. It came on at highway speeds, I found that turning on the lights or other power draw would put the light out. The volt meter shows a charge so I took the advise of others on this page and just ignore it. One of those things, I guess

[bowmaga]

the power tap was something the previous owner installed....the installed a new power switching center above the drivers head that ran different sets of lights through the bus.  Down lighting, kitchen lighting, bathroom lighting, back up camera, etc.  My bus was a limo bus, so things were a little different.  I just took a long lunch, and drove it around my dads farm where i keep it, and the light didn't come on, I didn't have time to take her out on a 30 minute drive to see if the light will come on.  I will this week and then, try the head light trick and hopefully that will make it "go away".  I like my bus a whole lot better when she doesn't make me nervous...

[Dallas]

Greg,

I would venture a WAG that you have one of two problems,

Either the belt is glazed or worn out or the pulley is worn out.

At low RPM in any gear, the belt/pulley interface can generate enough friction to handle the load being called for by the regulator. As the engine reaches higher RPM, the load is the same but the torque of the engine is much higher causing the belt to slip.

One neat little trick you can use to see if it is either of those problems is to grab your handy dandy can of WD40 and squirt the peewaddin' out of the belt at idle, do this in 10 second or so bursts for a series of 5 or 6 bursts. Do Not Use PB Blaster or belt dressing or any other brand of belt lube. The other lubes won't break the glaze on the belt and the pulley, and belt dressing is only going to make a build up on belt and the pulley, eventually making matters worse.

Once you've done the above mentioned application, drive around the county or even across the state line and see if the light on problem has changed, if it has, you've narrowed down the problem to belt or pulleys, if not, you've narrowed down the problem to electrical.

Good Luck,

Dallas

[DrivingMissLazy]

My WAG would be that the batteries are fully charged and as the engine speeds up, the alternator cuts off as no more charge is needed. I also suspect that the regulator is a mechanical device instead of solid state device.

Richard

[bowmaga]

what do you mean "I also suspect that the regulator is a mechanical device instead of solid state device".

will it hurt anything if i drive my big bus with this light on?  Does this not "not gen" light stand for Not Generating....as in not generating power....as in power to charge the batteries....which that is what the bog @$# alternator does....right?  I'm trying to piece all the parts together to understand how things work. 

when you say idle speed, is that slow idle, or fast idle with the fast idle switch on?

I think what i first will do is take her for a spin and see if the headlight thing works......

If not, i will come back and try the lube job.......

if that doesn't, I'll begin to drink heavily.......again,  and be back with lot more questions.

[jjrbus]

My not gen light has been on for years, stays on all the time. It is a simple fix, but a BIG job to pull the alternator. When the altrnator needs to come out I will fix it. In the mean time I pulled the bulb.  I watch the gauge to make sure the alternator is chargeing. I will not get the mechanic of the year award for this approach, but works for me!! I may even have to admit this at the next Busaholics Anonymous meeting!!!

HTH jim

[DrivingMissLazy]

To me, the Not Gen light is indicating that the battery(s) are fully charged. I believe this happened on your return trip so that ample time would have passed to charge the batteries to full charge.

Richard

[Lin]

DML,
     Could one test that by running the battery down a bit, like leave the headlights on for an hour, and see if the light stays off?  I ask because mine would be on all the time if I put the bulb back.

[Marcus]

Lin, I have a mci 9 and I can't leave my headlights on for an hour because they shut off automaticly if the engine is turned off. They stay on for a little bit ,but not long. Only the running lights stay on. Marc

[tekebird]

thje Not Gen light is an indicator showing that the system is not generating

can't tell you why yours is on but it indicates a flaw somewhere...serious or not