50DN Alternator Questions

[richard5933]

Couple of things with the 50DN alternator on my 4106 that puzzle me...

1 - The alternator doesn't start to charge (tell tale 'Not Gen' light is on) for a few moments after startup. I'm told this is normal. I need to get the engine RPMs up a bit before it will start charging. Previous owner told me it's acted like this as long as he remembers.

2 - Is there any connection between the level of air pressure and the startup of the alternator? Could be my imagination, but it seems that when I start from near zero air pressure the alternator takes longer to start charging.

3 - Again could be my imagination, but it seems that sometimes for no apparent reason the alternator is a bit more difficult to get charging. Could this be an indication of problems to come or is this something that is normal?

4 - Once charging, the alternator tests well and the shop tells me that it's producing the proper voltages.

The bus's 8V71 was rebuilt around 1990. There are either 20,000 or 120,000 miles on the bus since then. (I'd vote for 120,000) My guess is that the alternator has not been addressed since that rebuild.

Bottom line is that I'm trying to get some idea of what to expect. I've only put a few hundred miles on the bus and have no real point of reference for things like this. Are there signs to look for when an alternator is about to fail? If it does fail (not charge) are the 12v 50DN alternators still available? Or, are they easy to get rebuilt?

I'd greatly appreciate a bit of insight on the 50DN in my 4106 if possible.

Thanks.
Richard

[Tim Bookmiller]

if you have a air throttle you can not rev it up until it reaches 40 lbs after a slight rev the gen light will go off and all is charging

[Van]

The 50DN can still be had. I am pretty sure they won't start charging til a certain rpm has been reached. Your air throttle sounds about right, build some air and zoom! All the best with your new coach and welcome to the wonderful bus nut kingdom! 



    Van.

[neoneddy]

I'm pretty sure I have a 50DN in my 82 mc9.

It acts similar yours except it show charge voltage right at startup . It is lower until the air throttle engages fast idle.  My "not-gen" light is on until it hits 90lbs  but my voltmeter shows 28v once I hit fast idle.

These are oil cooled units, I wouldn't be surprised if they go two or three in frame rebuilds before replacements.


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[TomC]

My 12v 50DN starts charging immediately at startup, without hitting the pedal. I do have to run with my headlights on since when the batteries are fully charged and there isn't a load on the alternator, my NO Charge light will come on. Good Luck, TomC

[richard5933]

I don't have an air throttle.

My initial question about the air pressure was to see if the bus has any interconnection between air pressure and alternator. I've read so many posts on so may sites about the way the 50DN are set up that I don't know what's fact and what's fiction. More importantly, I can't tell what applies to the 4106.

My bus is still pretty much OEM regarding the charging system for the chassis batteries. It's my first bus, so I have no reference point to know if it's normal for an alternator to not charge until revved up.

I also don't know which systems have safety connections to the air system and will not begin to function until adequate pressure is built.

Guess what I'm looking to accomplish here is to get a list in my head of what's considered normal operation and what should give me reason to start shopping for a new alternator.

Also, should the need arise for an alternator what are the recommended sources? Most of what I've found online only list the 24v model, and I've got a gear-driven, oil-cooled 12V alternator.

Thanks.
Richard

[neoneddy]

I think the air pressure delay on charging is for belt driven models where the belt tensioner is air activated. You don't want load on a slack belt, but I think you're good there with the gear driven, if it's spinning it's making power.


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[Fred Mc]

I have a 4106 and a few years ago it started to overcharge the batteries. According to the manual you can adjust the charging rate on the regulator.(not sure why it started to overcharge) At any rate what I found was that as you adjust the regulator up or down, the rpm it takes for the charge lite to go out varies. What I think is that the lite doesnt go out (and it doessn't start charging) until the voltage output of the alternator reaches A certain level. So as I was adjusting the regulator, when I set it to charge less than the suggested voltage (not at home now so I don't know exactly what that rate is but I think it was 14.4) the light would go out quickly and when I set the charging voltage over 14.4 it took a higher rpm to start charging. So in a nutshell the alternator won't start charging the battieries(and the lite goes out) until it reaches a certain voltage which is controlled by the engine rpm.At least that was my experience.

[bevans6]

Does anyone have a schematic that shows the alternator and regulator on a 4106?  That will tell the tale.  Without it, here are my guesses.  Usually the alternator's R output (a half-wave rectified half voltage output from the middle of the rectifier bridge) is connected to the coil of a special relay - the coil voltage has to be half of the normal voltage for the bus.  That relay usually turns on the air conditioning/heating fans and blowers, so it's called the blower cut-in relay, and it turns off the no-gen light.  It's entirely possible that the field coil of the alternator is connected to the regulator through a relay, which could have a delay built in, be sticky, or be controlled by an air pressure switch.  I have read of gear drive alternator systems with an air pressure switch delay, but I don't know if the 4106 is one of them or not, without a schematic.  Anyway, for the no-gen light to go out first the alternator has to be turning, then the regulator has to apply a signal to the field coil (through a relay or not) then the alternator has to produce a voltage to the rectifier diodes, which have to work, then the R output has to send a signal to the blower cut-in relay (if a 4106 has one) which has to switch and turn off the no-gen light.  One thing that comes to mind is the blower cut-in relay could have been swapped with one that has a 12v coil instead of the 6v coil it should have on a 12v bus, or it could just be worn out or faulty.

[richard5933]

Relays... It always seems to be a relay.

Thanks for the reminder to check the relay. I've been through a lot of the connections checking for corrosion, etc. but have not yet checked the relays. I've got a manual with diagrams, so hopefully I can find it.

1964 PD4106-2412

[bevans6]

I had another thought.  I always think first of my bus, which has a 50DN version with three terminals - the big power output terminal, the small F1 terminal (positive field current from the regulator) and the R terminal (half voltage to the control relay for the blowers and the no-gen light).  It also has a F2 terminal, which is the negative side of the field coil, which is locally grounded with a strap to chassis.  On my bus a solid state regulator controls the field current using transistors.  Earlier versions of the 50DN might have additional terminals for use with a mechanical regulator, to energize the various coils and relays inside the regulator.  With a mechanical regulator there needs to be an initial voltage to the field coil to start the alternator in the first place, then the voltage and current control coils start to work after the alternator has begun to produce sufficient voltage to actually be regulated against battery voltage.  Those coils operate electrical points that open and close hundreds of times per second as long as the alternator is running, and obviously can get pitted with arcing, the springs that regulate things can fatigue and set points can change.  If you have such a mechanical regulator (and 1964 is a definite maybe) then that could be your problem.  Solid state regulators are fit and forget, they either work or they don't, as a rule, but mechanical regulators can need maintenance and possibly regular replacement, just like ignition points in a car.  I have no idea if you can upgrade a mechanical regulator to solid state, but others might know.