Alternator squeeks on startup

[DeanS]

A week ago I noticed that the thick belt on the 175A alternator was creating a bit of "rubber dust" on the floor beneath it. There's no evident place that it's rubbing on anything. The belt is about an inch wide...with approx 5 grooves it runs along.

 

It's also been squeeking when starting the engine....but after a minute or two, stops squeeking....sometimes while it's squeeking, I increase the revs, slow it down and the squeeking disappears.

 

Looking at it, it doesnt seem to be slipping at all...but I'm not sure if thats possible to see with an eye.

Is it slipping? Should I tighten it? When I feel the play in the belt while stationary, it feels tight enough...the press down distance is roughly 3/4 of an inch.

 

The voltmeter shows 14V from startup.

The alternator isnt getting hot. It's not overtight.

 

The engines on about 180hrs of running.

 

ETA - once the squeeling stops, the engine can run for hours with no more squeeling...it ONLY happens within the first 3minutes ....the alternator/engine starts up under load....most times.....immediately having to start supplying quite a high amperage

 

???

Edited May 9, 2013 by DeanS

[RLWP]

press down of 3/4 in pretty loose, that's 1 1/2" up and down.

 

About half that sounds better

 

Squealing is usually a sign of slipping

 

Richard

[Tuscan]

I had the same problem, tightening the belt should solve it

[Bobbybass]

I have it in my 'Beta' manual that they specify only 1/2 inch at the belt's longest point.

 

This fits in with what I was always taught with both generators and alternators...and what I have always tensioned too.

[Sir Nibble]

Certainly a belt tension issue. The symptoms you describe mirrors the torque demands of the alternator and the tension you describe confirms it. As a guide, with engine off (obviously) if you can slip the belt by pushing on the fan with your thumb, it's too slack.

[Guest]

Sure to be a sign of a belt that is not tensioned correctly. You will not see it slipping only hear it. There is a dark art to tensioning grooved belts which to do 100% correctly really requires the correct kit.

 

I find a bit of trial an error does it, tighten it till the squeal just stops at all revs.

 

I usually end up with about the same amount of play mentioned by Richard, over tighten and you can stress the alternator bearings.

[DeanS]

I think you are all correct. I did notice that when it was actually running (and squeeling) , if I (carefully) pressed down on the belt.....the squeel stopped. (which kind of gives it away I know...)...I was just wondering perhaps if it was anything to do with the load on the alternator etc, and wasnt sure why the slipping doesnt carry on, but stops....every time...after a minute........perhaps the belt warms up.

 

I'll adjust it tomorrow. Many Thanks.

[nicknorman]

..I was just wondering perhaps if it was anything to do with the load on the alternator etc, and wasnt sure why the slipping doesnt carry on, but stops....every time...after a minute........perhaps the belt warms up.

 

I'll adjust it tomorrow. Many Thanks.

A combination of alternator load dropping off and belt heating and therefore becoming more sticky. So the chances are it was only slipping shortly after start, but that still points to a loose belt which should be tightened.

[Guest]

I think you are all correct. I did notice that when it was actually running (and squeeling) , if I (carefully) pressed down on the belt.....the squeel stopped. (which kind of gives it away I know...)...I was just wondering perhaps if it was anything to do with the load on the alternator etc, and wasnt sure why the slipping doesnt carry on, but stops....every time...after a minute........perhaps the belt warms up.

 

I'll adjust it tomorrow. Many Thanks.

Do you only have the one alternator?

 

Replenishing the loss to the starter battery immediately after the starter has run will load the alternator and cause additional drag on the belt and make a badly adjusted belt sqeal.

[Puddlejumper]

belt slippin re ajust or replace said belt

[jelunga]

Yeh. With the drain on your batteries that you have mentioned before the initial load in the alternator is quite high and your belt is slipping. Tighten it

[DeanS]

This is something I havent managed to get my head around...perhaps someone could explain

 

My understanding is that the engine, fueled by diesel, turns the pulley, which turns the other pulley, which turns the alternator innards, which caused generation of power, which is sent to the battery.

 

How is it then possible for the state of the batteries to cause the engine speed to change?

Why should the state of the batteries, effect whether a rubber belt slips or not?

 

What am I missing?

Edited May 9, 2013 by DeanS

[nicknorman]

This is something I havent managed to get my head around...perhaps someone could explain

 

My understanding is that the engine, fueled by diesel, turns the pulley, which turns the other pulley, which turns the alternator innards, which caused generation of power, which is sent to the battery.

 

How is it then possible for the state of the batteries to cause the engine speed to change?

Why should the state of the batteries, effect whether a rubber belt slips or not?

 

What am I missing?

The state of the batteries determines how much current will flow from the alternator into the batteries at the alternator's regulated voltage. Flat batteries = lots of current.

 

The alternator's regulator is trying to regulate the voltage at say 14.4v so when the batteries want to take lots of current, the regulator needs to increase the alternator field winding current to maintain the 14.4v. Increasing the field current produces more magnetic field interaction within the alternator which makes it harder to turn. if the rpm remains roughly constant this results in more mechanical energy from the rotating alternator being converted into electricity. So mechanical energy is being taken out of the alternator and, via the belt, out of the engine causing it to slow down. Of course the engine's governor compensates to some extent by increasing the fuel flow but there is still some static droop and the engine slows a bit. If the batteries are flat the mechanical energy required by the alternator is large, if fully charged it is small. The energy is transferred by the pull of the belt, and if the pull is too great for the amount of tension (which determines how well the belt sticks to the pulley) the belt will slip.

 

Or to put it another way, its conservation of energy (energy cannot be created or destroyed, but it can be converted into different forms). You are putting more electrical energy into the batteries if they are flat, that has to come from more mechanical energy so slowing the engine or burning more chemical energy (diesel).

 

As an aside, the mechanical energy going into the alternator is the combination of torque and rpm. So if the rpm is high, the torque (which is the same as the pull on the belt) is not that much, but at the minimum rpm to get the required current, the torque/belt pull is at a maximum. This is why the belt slips at low rpm but not at high rpm.

Edited May 9, 2013 by nicknorman

[DeanS]

The state of the batteries determines how much current will flow from the alternator into the batteries at the alternator's regulated voltage. Flat batteries = lots of current.

 

The alternator's regulator is trying to regulate the voltage at say 14.4v so when the batteries want to take lots of current, the regulator needs to increase the alternator field winding current to maintain the 14.4v. Increasing the field current produces more magnetic field interaction within the alternator which makes it harder to turn. if the rpm remains roughly constant this results in more mechanical energy from the rotating alternator being converted into electricity. So mechanical energy is being taken out of the alternator and, via the belt, out of the engine causing it to slow down. Of course the engine's governor compensates to some extent by increasing the fuel flow but there is still some static droop and the engine slows a bit. If the batteries are flat the mechanical energy required by the alternator is large, if fully charged it is small. The energy is transferred by the pull of the belt, and if the pull is too great for the amount of tension (which determines how well the belt sticks to the pulley) the belt will slip.

 

Or to put it another way, its conservation of energy (energy cannot be created or destroyed, but it can be converted into different forms). You are putting more electrical energy into the batteries if they are flat, that has to come from more mechanical energy so slowing the engine or burning more chemical energy (diesel).

 

As an aside, the mechanical energy going into the alternator is the combination of torque and rpm. So if the rpm is high, the torque (which is the same as the pull on the belt) is not that much, but at the minimum rpm to get the required current, the torque/belt pull is at a maximum. This is why the belt slips at low rpm but not at high rpm.

 

Fantastic Nick! Thanks for that

[bizzard]

To prove its belt slip just splash a little water on it whilst its squeaking and the squeak should stop.

It beats me why most of these so called marine engine marinizers can't fit automatic spring loaded tensioners as per road vehicles, lord, they demand enough money for their engines.

Edited May 9, 2013 by bizzard

[Timleech]

This link shows a page from the Fenner handbook which offers two ways to get the right belt tension, page 5. It doesn't give figures for PK section, you would have to interpolate between J and L to get approx. figures.

 

Tim

[dmr]

Belts slip and squeal most when cold so once its got a bit warmer it stops squealing.

One or two fancy alternator controllers actually give a slow ramp up of the current to avoid this problem!

What you describe is a "polyvee" belt. These do need to be quite tight. One "rule of thumb" is that if you grip the belt with a thumb and finger you should just be able to twist it through 90 degrees. though this is a bit approximate as it depends on how strong your hands are!!!

I would tighten it just a little, just enough to stop the squealing, or maybe just run the engine a little faster. Do not over tighten it as the engine main bearings might suffer.

 

.............Dave

[BEngo]

SNIP>

I would tighten it just a little, just enough to stop the squealing, or maybe just run the engine a little faster. Do not over tighten it as the engine main bearings might suffer.

 

.............Dave

You will do the alternator bearings in long before it's tight enough to affect the engine main bearings.

 

N

[Ray]

I have a similar problem with my Beta 43, save that the sqeak lasts a little longer sometimes. We've tried adjusting the tension to no avail and my (more technically minded than me) colleague suggested that the alternator may be slightly out of line. Is this a possibility or is it simply a case of us not getting the tension exactly right - he was a tad concerned that tightening the belt too much might knacker the bearings.

[DeanS]

A little TWEAKING

has fixed the SQUEAKING.

[bizzard]

Its fast reaching the point when these high output alternators are going to need either gear drive, chain or Fenner toothed belts to drive them, or at least a proper automatic tensioner. or massive great pulleys to attain more belt to pulley grip.area.

[RLWP]

massive great pulleys to attain more belt to pulley grip.area.

 

Larger diameter pulleys is all that is needed. A bigger diameter means that to achieve the same torque the pulling force is being exerted at a greater radius . So the tension in the belt is less, and therefore less likely to slip.

 

Richard

[luctor et emergo]

To avoid the high inital load on the alternator, you need to instal solar panels which will help charging the batteries..

[bizzard]

Larger diameter pulleys is all that is needed. A bigger diameter means that to achieve the same torque the pulling force is being exerted at a greater radius . So the tension in the belt is less, and therefore less likely to slip.

 

Richard

Yes quite. Normal size pulleys could be used if arranged modern vehicle style by using many jockey guide wheels to get maximum pulley wrap around. The multi V belts on vehicles are nicknamed Serpent belts and of course use the auto tensioner. To fit all that lot on the front of a marine engine a special large thick mounting plate would have to be fitted for every thing to poke through and bolt guide wheels and tensioner to.

[bigste]

With today's high output alternators they do take some turning. The more powerful the alternator the more leverage it takes to turn the pulley. Belt tension is very important and should be checked weekly. First sign of under tension is a squeal coming from a slipping belt. It you visit a belt stockist like Bearing Services Ltd (BSL) they all keep belt dressings in aerosol tins. A quick squirt now and then will help to keep your belt in tip top condition and prevent slipping. The stuff puts a sticky residue on the belt to prevent the slipping and has properties to prevent the rubber from decaying. A £5 tin will last years.