do I have an alternator problem?

[bevans6]

Just prior to our recent trip I changed the four alternator belts that drive our 50DN oil cooled alternator.  the old ones where old, starting to crack, and would squeal when the alternator started to charge.  What I found on the trip was that, even with the new belts and retensioning them after the first day's run, they still would squeal when the alternator came on line as the bus aired up.  The alternator rotates freely when the belts are off, no bearing roughness at all that I could feel, the belts are very tight (manual turnbuckle to adjust), four brand new matched belts (from Luke), it's just that the alternator seems to take a lot of engine power to turn when the field  coil is energized and it is producing power.  It is putting out 27.5 volts, which is exactly what the manual calls for, and the batteries are not using water.

I wonder why it seems that the alternator is taking so much engine power to turn, that the brand new belts have such a hard time starting it?  If the engine is on high idle when it kicks in, the squeal lasts so long I turn off high idle and it finally catches up and I can turn on high idle again.  I'm pretty sure this isn't the way it's supposed to be.  All lights and accessories, fans, etc, are turned off when I am airing up the bus, so the only  load is basically charging the battery.

Any thoughts?

Brian

[gumpy]

No, that doesn't sound right, but I don't have any idea why it's doing that.

Once the squeal stops, does it come back, say when you turn on all your big loads (headlights, bus A/C if you still have it, etc)?

Would be good to know what current it's putting out when it kicks in. Maybe you have a bad battery that's requiring considerably more current and putting excessive load on it.
Still shouldn't squeal.

Is it possible the old belts glazed the insides of the pulleys?  Maybe some belt dressing? Just punching into thin air here....

[Sam 4106]

Since you got your belts from Luke I'm quite sure you got the right ones but it wouldn't hurt to check the numbers anyway. Also there could be excess wear in the pully grooves, if it was run with worn belts a long time, and even with new belts they are causing the slippage. Check the pulley grooves with a straight edge to see if they are flat, not concave. If that is the case the only solution that I know of would be new pulleys.
Good luck, Sam MC8

[bobofthenorth]

I'm a big fan of belt dressing for heavily loaded belts.  You don't have to run the belts as tight which is easier on the bearings.  As Sam suggested, your pulley grooves may be worn wider but give the dressing a whirl.  I changed my alt belts about a month ago now & the first thing I did after installing the new belts, before I started the noisemaker, was to spray the belts down with dressing.

[Just Dallas]

Removed

[luvrbus]

I don't know about how the 50D works on a MCI but on a Eagle it has a relay to prevent the 50D from full charge on startup and we use 3 belts about the same size as the MCI without that problem.
Probably wrong here but doesn't MCI use air to open the relay for charging.

good luck

[rv_safetyman]

Others have already mentioned the pulley grooves.  I strongly suspect that is the problem.  The belts should be capable of transmitting the full power the alternator can put out, so how it is activated should not cause the problem.

Well Bob, we usually always agree on things, but on belt dressing we don't.  Belt dressing was OK when leather flat belts were prevalent.  The dressing did not affect the leather and did help to some degree.  However, most belt dressing material today are petroleum based and that is not great for the belt.  Worse yet, the belt dressing is obviously "sticky" by nature.  This tends to collect the dust and dirt for the ambient conditions (really bad in a rear engine bus) and then it becomes a good abrasive material.  This can wipe out pulleys pretty fast.  The belt industry is in universal agreement that belt dressing is taboo!

These drives worked well with no "additives". 

Jim

[HighTechRedneck]

If the old belts were slipping, might they have glazed the pulleys?  This happened to a car I had once.  I used some medium grit sand paper to rough it a bit and that worked.

[bobofthenorth]

Well Bob, we usually always agree on things, but on belt dressing we don't. 

Whale oil beef hooked. 

I guess I have to change my practices.  I'm not about to argue with Jim's expertise on this one.  On the positive side, one less can of weasel piss to carry from now on.

[rv_safetyman]

Bob, don't give up so easy .  I really don't know how to react when someone buys into my thought process - scary!

Jim

[kyle4501]

Bob, You are a hell of a guy!
Jim's statement against belt dressing is right in line with what I was taught when I worked for Dodge Power Transmission (gears, bearings, sprockets, v-belt sheaves, etc).

The rule was that the use of belt dressing would reduce the life of the belt at best & at worst, cause failure. It also accelerated groove wear in the sheave.


Brian, if the belt path & pulley diameters are to stock specifications, then there is a problem with the pulley grooves being worn out. Pulley grooves do wear over time & when you consider the transmitted HP & the number of miles on the coach . . . .

You may be able to get a local machine shop to re-machine your existing pulley-
cheapest is to reduce the diameter just enough to clean up the profile,
more expensive would be to weld up & re-machine -OR- have a new one machined to orig specs.

Those options need to be weighed against the cost of a new pulley.

Good luck!

[Ednj]

Brian,
Does it still do it after the Oil is up to temperature?

[bevans6]

Brian,
Does it still do it after the Oil is up to temperature?

To be honest, I'm not sure.  I can't recall airing up the bus when the engine oil is up to temp.  I had focused on the electrical load as the issue, since it spins easily when it's not energized.  Since the alternator is leaking somewhere, I suspect I will be pulling it to reseal.  That will make inspecting or re-machining the pulley (I can easily do a clean-up cut on the sheaves) very achievable.  There seem to be improved seal kits available now.

thanks every one for your thoughts on this.  I'm glad no one said "that happened to me just before the alternator exploded" or something like that...

Brian

[roadrunnertex]

OK check the field wire from the regulator field terminal to the field terminal on the alternator check to see if it had high resistance.If in doubt run a new field wire from the regulator to the alternator.
Or it could be the front drive housing is worn where the bearing is located  and allowing the bearing to cock and causing the rotor to drag at start up.
You can call Mike Martin at Kirks Automotive 1-800-321-5989 ex 1102 and he can help you with repairs or more information.
jlv

[Chopper Scott]

Another old trick was to use toothpaste to rough up the pulleys and belt surfaces. Probably not a good idea to use the whitening stuff however!   The MC's have a switch that prevents a load on the gen until it reaches 70lbs as Cliff stated. That allowed the air tensioner to tighten the belts before a load was place on them. My gen locked up on several occasions when the switch would kick in and would smoke the belts. It would free wheel fine without a load. Try unhooking the power line to it and see if that helps. Mine had a field or something go bad and it would lockup. I went to a 24 volt alternator instead.