What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Alternator? Issue

dweyant

Well Known Member
I "might" be having an issue with my alternator.

After I start the engine, I'll turn the alternator field on. Sometimes I'll get a squealing noise that I believe is coming from the alternator. This lasts about 2-5 seconds then stops.

I've checked that the tension on the alternator belt is correct, and it does not show any unusual wear.

Any suggestions?

-Dan
 
high pitched squealing for 5-10 seconds after cold startup is typically caused by a loose belt. Many novices don't have a "feel" for belt tightness. Maybe a good idea to buy a belt tension measurement device. My experience is that V belts can be pretty loose and not make noise, that said, when you turn on the field after starting, it is going straight to max output and THAT is going to require something close to the correct tension to not make noise. Once the output backs down it stops slipping.

Larry
 
Need More Info….

What brand of alternator, and is it internally or externally regulated?
 
high pitched squealing for 5-10 seconds after cold startup is typically caused by a loose belt. Many novices don't have a "feel" for belt tightness. Maybe a good idea to buy a belt tension measurement device. My experience is that V belts can be pretty loose and not make noise, that said, when you turn on the field after starting, it is going straight to max output and THAT is going to require something close to the correct tension to not make noise. Once the output backs down it stops slipping.

Larry

I had an A&P friend help me set the tension on it when we installed it. Of course it is possible that the belt has stretched a bit in the last year. I'll double check the tension when I get home.

-Dan
 
I had an A&P friend help me set the tension on it when we installed it. Of course it is possible that the belt has stretched a bit in the last year. I'll double check the tension when I get home.

-Dan

Many adjust belt tension via deflection. This can be a problem, as most cars have free spans around 10-12" and your lyc alt only a few inches. The shorter the span, the less deflection allowed. You may be able to rent a tension gauge at the auto parts store.
 
The proper way to check the tension actually is with a torque wrench on the alternator, twisting until the alternator pulley slips in the belt, and compare that the MFR spec.

Most of us use the TLAR method, I'm guilty of that as well, but the torque wrench is the correct method.
 
When I had a loose belt it too would squeal briefly upon startup. The other symptom I noticed was a transient ammeter drop during both startup and also when I increased RPM to full throttle during takeoff roll.
 
The proper way to check the tension actually is with a torque wrench on the alternator, twisting until the alternator pulley slips in the belt, and compare that the MFR spec.

Most of us use the TLAR method, I'm guilty of that as well, but the torque wrench is the correct method.

Ditto. It's stupid easy and takes longer to get the tools out than to do the job.

-Marc
 
I "might" be having an issue with my alternator.

After I start the engine, I'll turn the alternator field on. Sometimes I'll get a squealing noise that I believe is coming from the alternator. This lasts about 2-5 seconds then stops.

I've checked that the tension on the alternator belt is correct, and it does not show any unusual wear.

Any suggestions?

-Dan
On a side note, that is unrelated to your question turning the alternator on with the engine running can cause the diodes in the alternator to fail. This could happen to some, reducing the alternators output or to all causing complete failure of the unit. The issue is the amount of load on the system when it is turned on. More load more likely to happen. So, if everything is turned off and you have a battery that is really up to snuff, you will be lucky and probably not damage anything. But if you have a battery that really draws after a start, or you have other electrical items turned on, when you flip the field switch on the alternator, you could damage your alternator.
Because of all this, it isn't a good idea to turn the alternator off and on with the engine running either.
Good Luck,
Mahlon
 
After I start the engine, I'll turn the alternator field on. Sometimes I'll get a squealing noise that I believe is coming from the alternator. This lasts about 2-5 seconds then stops.

I've checked that the tension on the alternator belt is correct, and it does not show any unusual wear.

Any suggestions?

Alternator tension method below. However, the Plane Power has exhibited a failure mode in which the bearing boss in the rear cover gets enlarged, allowing that end of the rotor enough wobble to touch the stator. Mine would make a scuffing noise if I moved the prop after shutdown, but only when hot.

The Plane Power facility is here in Montgomery, so I had an opportunity to speak with one of the engineers. They attribute the failure to excessive belt tension, i.e. using the new belt spec with a worn-in belt.

With the belt off, the freeplay was detectable by grasping the pulley.

______________________________________________

Slip Torque Method:

This method consists of installing a torque wrench on the pulley-retaining nut and measuring the amount of torque required to make the pulley slip. Torque the wrench in a clockwise direction, as viewed from the pulley end and adjust belt tension accordingly. Note: Too much tension can cause excessive pressure on alternator bearings. Too little tension can cause the belt to slip thus not turn proper RPM.

3/8 INCH new belt 11~13 ft lbs, used belt 7~9 ft lbs

½ INCH new belt 13~15 ft lbs, used belt 9 to 11 ft lbs.
 
As Dan posted.

Use a torque wrench on the alternator pulley and it should not turn until 12 ft/lb +/- is reached.

Spin the alternator free and check for play and binding.

Look for a glazed belt. It should not be skinny and/or shiny/slick.

GM
RV8
 
Use a torque wrench on the alternator pulley and it should not turn until 12 ft/lb +/- is reached.

That's where Plane Power was placing blame for the bearing boss failures; owners and mechanics using the new belt slip spec rather than the used belt spec. I'm just sayin'...
 
I don't see that the OP has stated what starting battery chemistry is installed. A LiFePO battery will draw quite high amps after a start and could result in high alternator torque.

BTW - belts are formulated to shrink in length with elevated temps (negative coefficient of expansion), so loading could go up with under cowl temps compared to cold.
 
Back
Top