Alternator

[rex unicume]

i have a 1997 Patriot.
It has the Cat 3126.
In 3 years I have lost 4 alternators, just putting in the 5th.
Only 50 000 miles.
Help
Any comments or ideas.
Cheers
Rex

[Edward Buker]

Looks like you might have it under a heavy load. You could isolate each battery by disconnecting them and measure in a charged state to see if you have one with a weak cell (little lower voltage than the other batteries) which may be pulling extra current. If you boondock without bringing the batteries back up with the generator before you start out, it will damage the alternator with a heavy load that it was not designed for. Loose or poor connections at the alternator, isolator, or batteries can consume current. The other issue is heat. Situations where you are not getting good airflow can contribute to this failure.

Not sure if the fail is always the regulator, the stator winding, the field winding....if it was always a common cause I would search for another supplier of that part or alternators. You may also be able to get an alternator with higher capacity if that is part of the problem.

Maybe just bad luck but not too likely....

Later Ed

[Jeremy Parrett]

Hi Rex,
 I concur with Ed  .
  " If you boondock without bringing the batteries back up with the generator before you start out it will damage the alternator with a heavy load it was not designed for."
I overloaded my alternator by starting the coach with low house batteries.

[Gerald Farris]

Rex,
Alternator failures on on our coaches are caused at least 90% of the time by starting the coach up and driving off with discharged house batteries. The alternator is not designed to charge a large battery bank like your house batteries when they are discharged. Doing so will overheat the alternator and burn the insulation on the stator windings causing the alternator to fail. The way to save your alternator is to start your generator and recharge your house batteries to at least 80% of capacity with the inverter before letting the engine alternator finish charging them.

Gerald

[Dick Simonis]

Gerald, what is the rated output of our Alternators??

As an old boater, I never thought our house battery bank was all that large.  At least on ours we only have 4 6V deep cycle batteries which isn't all that much.  Our boat had two banks of 6 trojan T-105's each....about 1200 AH's and we never lost an alternator but I was running a Powerline dual output.

If our alternators are a bit week, wouln't it be pratical to just upgrade them to a better model after a failure???

I'd be interested to know just what the failure is.  If it's the diodes which is what I would expect from and overload, some diode packs are pretty eash to change and rebuilding them is pretty simply and inexpensive.

[Gerald Farris]

The alternator on later 1990s and the early 2000s is a 160 amp Leece-Neville pivot mount. Monaco changed to a 200 amp pad mount on most of the later coaches. The 160 amp rating is the maximum output for the alternator, however the alternator does not have adequate cooling capacity to produce that much current for very long without overheating.

If you start your coach with discharged house batteries, the alternator will be operating at the maximum output, between the chassis needs and the house battery needs, for thirty to forty-five minutes, and that is to long for the marginal cooling capacity of the alternator.

If you want to increase the the alternator capacity, you can go to a much larger alternator if you can find room, or go to a water cooled alternator. However either option would be costly and difficult. I personally do not see the need to change alternators, because if the Onan generator is used at it was designed to be used, the engine alternator will serve quite well in its intended application.

The alternator on my coach failed shortly after I purchased it at 4 years of age with forty thousand miles. I now have 110,000 and I am still running the same alternator that I installed seven years ago.

Gerald    

[rex unicume]

Hi all
Thanks for the great information.
I will make sure my house batteries are at least 80% before moving.
But, can someone let me know how I know when that has happened.
Sorry for my ignorance, but always learning.
Cheers
Rex

[Joel Ashley]

Rex, I'm not sure of your coach model, but my practice would be to watch my Magnum inverter/charger readout panel, and when it went from Bulk Charge to the Absorb Charge cycle, you've reached about 90% of full charge, at least according to my manual.  Your voltage should be high through both cycles, as the charger packs electrons back into the batteries - 14.2v - 14.6v.  I'm sure Ed or Gerald are more informed on this than me, and may offer different input, but after the charger has been off for 20 minutes or more to dissipate surface charge, if the Alladin or inverter readout give a value of 12.5 volts or more, you are in the 80% range.  12.7v is a full charge, 12.2v is about 50%.

Dick, I changed the diode pack in our sport cruiser's alternator, and in fact rebuilt the whole thing myself once, ca. 1980.  I have to agree that, with guidance, it is not difficult, and it was a good learning experience.  Corrosion from salt air, as you probably know, was more of a threat than heat.

But with cold Columbia River or San Juan Islands seawater continually cycling through the engine, my boat's 350 Merc engine bay never got particularly hot, so it was easier for the alternator to rid itself of excess heat.  The ambient air around our motorhome engines is probably much hotter, giving the alternator windings nowhere to shed heat.  As Gerald indicates, I would then surmise that it's the windings insulation that are the most common failure point, as opposed to the electronics, though I'm sure heat is not the diode material's friend either.  

Rebuilding windings is not a do-it-yourself project.  When the inadequate original Chevy automotive alternator and battery isolator (a simple Ford solenoid) gave up on our old '84 Pace Arrow, I thought, "Well, I know how to rebuild alternators - I'll save some money on this".  Not.  The burned stator windings dictated a higher output alternator (not just a new stator) and a new electronic isolator, after which replacement I never had problems again in that dept.  

Though many boat mechanical theories can translate into motor home technology, they are two different animals operating in different environments.

Joel

[MarcRodstein]

Is this an issue on all the coaches or just years mentioned? I have a 2003 Monterey and I have often driven off after a night of dry camping with my batteries at 65 or 70%. Haven't had an alternator problem after 8 years/60,000 miles.

Marc

[Gerald Farris]

Rex,
There are several ways to determine when it is safe to let the engine alternator take over charging the batteries. The best is to have a battery charge state monitor, however since most of us do not have one, I use the charge rate on the inverter remote panel as a guideline. With the generator running, if the charge rate on the batteries is below 50 amps, you should be OK to kill the generator and let the alternator take over charging the batteries.

In regards to Marc's question, yes this is a problem on all coaches. If you are driving off with the batteries at a 65% to 70% state of charge, you are on the line, and apparently within the operating range of the alternator. However the people who drive off with the batteries at a 20% state of charge are the ones that replace alternators yearly. A 80% state of charge is always safe, but the more discharged the batteries are the harder it is on the alternator and the more job security it is to mechanics.

If you do not have time to recharge the batteries before starting to drive in the morning, simply start the generator before driving off and let the inverter recharge your house batteries as you drive. This will take the load off of your alternator without having to wait for the batteries to recharge.

Gerald

[rex unicume]

Hey all
Thank you so very much for your input.
I am now afraid to start my engine without somehow checking my house batteries.
Is there a device to separate the house and starting batteries.
I cannot find a device to indicate my house battery % of charge.
Thanks for the great help and awareness.
Cheers
Rex

[Edward Buker]

Rex,

Without turning this into a science project basically your bank of batteries are charged when the voltage at rest with no load or minimal load is 12.6V. The first chart in this article shows charge level vs voltage. If you have an accurate voltmeter you could check at the house battery bank. You just need to minimize the load while checking. If you have been charging, you will get a false reading, the bank needs to rest until the voltage has stabilized to get a voltage and charge state value that is meaningful. You may have a digital read out Alladin or equivalent built into the coach that may help.

http://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

This was a guideline that I posted earlier on this subject that is looking for the Xantrex to be down to 20 to 30 amps of charging current before stopping the generator and using just the engine alternator.

The critical time for the alternator would be when the batteries start out near or below 12.2v. If the batteries are discharged deeply then without a doubt you want to run the generator and the Xantrex first to start the charging. I would consider looking at the Xantrex voltage output level and if I could, let it climb during absorption, until 13.8V is obtained. What is happening is the Xantrex is putting out max current and the voltage on the battery is slowly rising as it stores the current. The battery voltage at the time you start the engine alternator will set the current level that the alternator will provide. Safest bet might be something like this...

1. Generator /Xantrex only until voltage reaches 13.8V or as long as you have time to wait. The higher the voltage the better.

2. Generator/Xantrex and Alternator until Inverter current output drops to 20-30 amps. That means you are in absorption and the alternator should be able to pick up that added load so go to alternator alone.


This is a reasonable guess as to a rough guideline one might follow to max the alternator life.

Hope this helps.

Later Ed

[rex unicume]

Hey all
Thank you so very much for your input.
I am now afraid to start my engine without somehow checking my house batteries.
Is there a device to separate the house and starting batteries.
I cannot find a device to indicate my house battery % of charge.
Thanks for the great help and awareness.
Cheers
Rex

[Keith Oliver]

What is it about the design of our alternators, that they can't take heavy usage?  On my boat, I routinely charge low (down to less than 60%) batteries from the alternator.  The draw will typically be 90 amps for two hours, then dropping down gradually, so that, on a 4 hr run, I can get to 90% charged.  I have a 130Amp powerline, which is an aftermarket alternator built on a Delco small case unit.  It is regulated through an Ample Power "Next Step" 3 stage regulator that I installed many years ago.  The bank of batteries is the same as on the Beaver, but gets discharged faster due to a DC fridge and freezer.  At 6 yrs old, it isn't showing any signs of old age just yet.  Yes, I have worn out another alternator along the way, but the hard usage given the alternator is considerably harder than anything described here.
The large case alternator on my 3126 CAT should stand up far better than that, Shouldn't it?  When I bought the Powerline, I first tried to fit in a large case, 150 amp Volvo truck alternator, but the physical limitations of the space prevented that retrofit.  That was while of the belief the truck unit would last longer in that type of usage.  After reading about these troubles, I am not so sure.
No way I can alter my usage pattern, but so far, not a problem.

[Edward Buker]

The marine industry is very reliability conscious given that the use may be well off shore. The cooling fan assembly and regulators for sure are more heavy duty. Probably the rest of the components are also.

One issue with the rear engine design and our alternators is air flow. The cooling fan of the alternator was sized for its application which is usually in the main fan wash from behind a radiator and sees a lot of available air flow at the front of a truck. The alternator fan augments the normal flow of air from the front through the alternator to the back. In our case the fan is trying to push air against the natural flow of the vehicle and my guess is that it does not do a very good job and during heavy charge alternator components are running beyond their temperature limits shortening its life.

Later Ed