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Low output from alternator?

March 27, 2013, 12:56:20 am

Had my coach in the shop.  Long term project.  Go to pick it up and they are scurrying to start it.  Said terminals were corroded.  New red tops 9 month ago.  No dielectric grease used on cables or terminals. 


They jumped started the select plus 450 and I went home.  On the freeway the charge was at the normal mid 13's on the gauge then suddenly dropped to less than 12.  And stayed there.  Stopped for fuel and left the motor run.  Got home and shut it off.  Barely cranked.  No start.

Redid all the battery connections correctly ten started fine but dash gauge says 12 volt max at mid rpms. 

What died?  97 u320.  And what does it take to trouble shoot and repair this?

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Re: Low output from alternator?

Reply #1 – March 27, 2013, 01:29:14 am

Start with alternator belt tension. Belt(s) should not be glazed and should be able to be just turned 90 degrees between the alternator and drive pulley. Check batteries (if not sealed) with hydrometer for specific gravity, fluid level and voltage at the batteries with a digital voltmeter. Don't rely on the dash voltmeter. Batteries could be fully charged but connections/cables may be corroded. Inspect and clean. Depending on battery type, a fully charged battery should indicate about 12.7 volts AT THE BATTERY. Isolate each battery from the other when checking voltage. One battery could have gone bad. Voltage at the battery with the engine running will be higher than 12.7 volts, depending on the level of charge in the battery.

A good place to start. Alternator and isolator connections after that.

Pierce

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Re: Low output from alternator?

Reply #2 – March 27, 2013, 08:20:49 am

Had a very similar problem when I took delivery on my 1998 U270 at MOT in January. Left MOT on a Tuesday morning, being a newbie was not used to watching the gauges for any would be troubles. Left NAC heading to Seguin, got to Bastrap and stopped to make a phone call. Made the call, turned the key and NOTHING, dead. Did not know what to do. It was late, 8PM so MOT was closed ended up staying in Buc-ees overnight.

Got a hold of MOT in the AM they gave me a few things to do; Flip the boost switch to on, this will tie the house batteries together with the engine batteries, start the generator, this will charge both sets, watch the gauge, it will come up, when it gets to 12 volts engine should start.  Yes it did. They also advised me to drive with the gen running to keep the batt. charged. I did so and limped back to NAC.

Bottom line, the alternator was toast. A new one was about $1000, rebuilt $500, have the rebuilt in now and after 3000 miles I would say it is fine. FOT & MOT have the rebuilt ones.

Good luck.

Norm

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Re: Low output from alternator?

Reply #3 – March 27, 2013, 12:27:09 pm

We have the same issue. Driving down the road, everything fine, next time I glance at the gauges alternator shows12 volts. Did a bit of trouble shooting and found that one
of the posts on the alternator was loose. Strike that, I could pull one of the posts right out of the alternator. Thought I would take it apart and fix it but I cannot get the alternator off. Seems a gorilla bonded the hardware that mounted the alternator to the engine but left the terminal posts loose. On our way to Mecca to get the thing replaced. Been running with the boost switch on and letting our solar keep the chassis batteries charged.

Roland

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Re: Low output from alternator?

Reply #4 – March 27, 2013, 05:04:44 pm

About a year ago, I took our coach out for its monthly exercise run. Dash gauge was at 12V. It normally runs 13V with headlamps off, about 12.5 with headlamps on. Did some checking with a meter and found no output from alternator. Ran with generator and boost to FOT. New alternator was about $750 installed. Charging and voltages have been normal since.

It looked like alternator was probably original equipment. It quit suddenly with no apparent aggravating factors. It had been working fine during the previous trip with the coach. Coach remains plugged to 50A RV outlet when parked at home. Charger/inverter were working properly. Batteries were fully charged. All indications were that the alternator failed at the end of the previous trip, or when I started the coach for the exercise run.

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Re: Low output from alternator?

Reply #5 – March 27, 2013, 06:06:41 pm

OK, a couple of points:

Work around if alternator stops working while you are on a trip and would prefer to continue on the trip:  Turn on generator and "Boost" switch.  That way, the generator will power the charger which will charge the house battery.  And through the boost switch, it will keep the chassis battery charged.

Now, before spending big bucks on an alternator, assuming it hasn't self destructed-- that perhaps it is not charging and/or you can hear bearing noise-- go to a factory authorized reman shop. Stress FACTORY AUTHORIZED, not Bubba's Gas Grill and Electric Shoppe.

If a Hehr Powerline: Distributors of Hehr Power Systems products

I have taken my alternator to Pearland Alternator who put bearings and brushes in mine as preventive maintenance for under $120.

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