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Author Topic: "not gen" light on my MC9 dash  (Read 3412 times)
bowmaga
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« on: July 14, 2008, 05:50:29 AM »

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.
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Greg Bowman
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« Reply #1 on: July 14, 2008, 06:59:41 AM »

 Do you have a gauge also? does it show the alternator is chargeing?
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« Reply #2 on: July 14, 2008, 07:10:26 AM »

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.
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bowmaga
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« Reply #3 on: July 14, 2008, 07:59:58 AM »

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?
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Greg Bowman
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« Reply #4 on: July 14, 2008, 09:04:50 AM »

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.
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fraser8
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« Reply #5 on: July 14, 2008, 09:07:39 AM »

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
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Fraser Field
Deroche, BC, Canada
Where the milk cows out number the people, but they can't vote
1972 Prevost, Detroit 8-71/740 Allison automatic, Jakes
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bowmaga
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« Reply #6 on: July 14, 2008, 10:51:16 AM »

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...
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Greg Bowman
1979 MCI MC9
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« Reply #7 on: July 14, 2008, 11:48:16 AM »

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
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DrivingMissLazy
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« Reply #8 on: July 14, 2008, 12:12:00 PM »

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
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bowmaga
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« Reply #9 on: July 14, 2008, 12:33:13 PM »

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.
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Greg Bowman
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« Reply #10 on: July 14, 2008, 02:42:24 PM »

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
 
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DrivingMissLazy
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« Reply #11 on: July 14, 2008, 02:45:39 PM »

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
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« Reply #12 on: July 14, 2008, 03:59:56 PM »

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.
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Marcus
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« Reply #13 on: July 14, 2008, 04:38:18 PM »

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
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tekebird
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« Reply #14 on: July 14, 2008, 05:49:04 PM »

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
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RJ
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« Reply #15 on: July 15, 2008, 12:31:23 AM »

Bowmaga -

Another WAG is that the belt tensioner may be allowing enough slack in the belts to allow the alternator to slow down enough to turn on the "not gen" light.

As Doug says, this is something that needs to be troubleshot and fixed, or you may let the smoke out of the entire electrical system - and maybe the coach, too.

FWIW & HTH. . .

 Wink
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RJ Long
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« Reply #16 on: July 15, 2008, 04:49:36 AM »

I'm inclined to go with Richard's explaination, but there is one thing that intriques me and might offer a different solution....

You said there was a click in the lower right hand corner of the bus when the light comes on.  It may be possible this is an air conditioner valve solenoid clicking, and that the light you are seeing on the dash is really the air conditioner hi/low indicator. In other words, the bulb is in the wrong hole in the dash plate. That's not uncommon.

One way to tell if it is truely the not gen is to let air out of your air system till it's down around 50 psi or below (manually pump the brakes several times). Then, when you turn on the main power, before starting, you should see the not gen light come on. I don't think the A/C light does. Then, after starting, the not gen light will stay on until you have 85 psi air pressure. You should also have a buzzer on the low air, as well as a low air telltale on the dash. When you hit 85 psi, the low air telltale and buzzer should go out, and the not gen light should also go out.

Now, that doesn't mean you are not generating power during air up. If you have a gear driven alternator, it will probably be generating power.  If it is belt driven, it probably isn't.

craig
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Craig Shepard
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DrivingMissLazy
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« Reply #17 on: July 15, 2008, 05:30:05 AM »

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.

That is what I would do. Look for the simple things first, especially since the problem started after you had had a long run previously.

Richard
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« Reply #18 on: July 15, 2008, 06:18:50 AM »

A couple of things also could/would cause the light to come on...


Tag axle air pressure. although usually that just lights the TAG pressure light.

One of the air pressure switches is possibly bad. The sound that you describe might be the air pressure switch inside the spare tire compartment cutting in and out. I had a similar problem and changed the air pressure sensor switch on mine.

The switch is fed from the auxillary or accessory air tank. It could just be going bad. I was informed that the light being on does not necessarily mean that the batteries are not getting charged. It is an IDIOT light only.

Some coaches were/are wired with the/a switch that actually signals a relay to cut off charging on air pressure loss. I haven't run into that myself.

The light will come on whenever the accessory air tank is below 85 to 90 psi.

The other thing is that if the not-gen light comes on while going down the road it could be that the batteries are fully charged and will no substantial electrical load the alternator is being shut down. When the voltage drops again the charging starts back up... The blinking Not-Gen light business.

You could have a faulty voltage regulator or it may be out of adjustment. The newer electronic ones handle loading better than the old delco remy units.

This is just a guess....

Dave....
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« Reply #19 on: July 15, 2008, 09:03:49 PM »

I agree with almost everyone...the belt could be slipping, or the batteries may be fully charged.   And you could have a charging problem.   
Now for my SWAG.... Wink
Operating the coach with a faulty belt-driven alternator isn't going to hurt the bus.   It could reduce you to walking however....if ignored over long periods, if the batteries wouldn't restart the bus after a shutdown.   
The not-gen light will come on if there's no load on the electrical system and the batteries are fully charged.   Turning on any voltage hungry source should shut the light off if that's your situation.  If the light goes off with a load, and the system maintains 26Vdc plus, you don't have a problem. 
if the light stays on with a load on the batteries, you may have a bad relay?   You can check the battery voltage with a dig voltmeter.  If the voltmeter reads 26-28Vdc, you don't have a problem.     
It the voltmeter reads less than 25Vdc, something's not right.  Then we get to start new SWAGS!
In a bus' designed function, it's rare that there's no load at all on the electrical system.  AC or heat is almost always on...or both.  Big loads all.   
One other item, which you haven't mentioned is that if any charging device such as a genset is running and charging your batteries, the not-gen light will light up. 
Any time the regulator senses fully charged batteries, the alternator may quit charging. 
Craig brings up an interesting point with the light locations.  He explained how to verify the air switch that controls the alt relay.
It's possible that it's air pressure related (as Dr. Dave sez).  The relay is in the rear junction box.
JR


 
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« Reply #20 on: July 16, 2008, 09:17:28 AM »

I ran the test as suggested by DML; left the headlights and markers on for an hour or so.  The Not Gen light still remains on.  The voltage at the batteries is 27+.  I guess mine is some sort of relay issue.
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« Reply #21 on: July 16, 2008, 09:32:52 AM »

Lin, on My mc7 there is a lead from the alternator, wire #33 which provides voltage to a relay in the junction box on the driver side rear engine door.  There is a diode that provides the dc voltage from the alternator stator to the relay circuit.  There is a pressure switch that causes a not gen light and prevents the alternator from operating until there is sufficent pressure to tension the alternator belts.  The light will function even if the batteries are charged.  While loss of the light may not be a true indication of alternator function it is in My opinon very valuable on a rainy night in downtown atlanta.  Check for voltage from the alternator and if it is present at the relay coil then check the low air pressure switch by jumping it to see if that causes the light to go out.  Hope I helped.  John
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« Reply #22 on: July 16, 2008, 10:17:02 AM »

I concur......fully charge batteries have nothing to do with the Not gen light.

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bowmaga
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« Reply #23 on: July 17, 2008, 01:04:48 PM »

well.....now that i have know idea what to do or where to look or where to begin......but i did begin....I took super Betty on a nice easy 20 mile drive today, got her wound up....no lights turn on.  They all stayed off as they should have.  When we came home from our last trip, it only took about 5 miles after getting on the road for the light to come on.  NOW WHAT??
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Greg Bowman
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« Reply #24 on: July 17, 2008, 03:56:02 PM »

You'll have no worries until you start on a 1000 mile trip with your family...

Nothing like depending on it to have all the faults show up at the worst possible time.

Maybe use that  big rubber hammer as inidcated in another post to test it.

Lots of good ideas here when it does act up again.  Guess you'll have to keep driving it!!
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Jim Stewart
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