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Why am I needing frequently to tighten my alternator belt?


Theo
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I have had a squealy alternator belt three times in the course of a three week trip with few running hours (often less than 4 hours per day.

 

Each time I have tightened it a boit more.  The belt was new at the beginning of the trip so I would expect to have to retighten it once after the initial tightening, but three times seems a bit excessive.  It is a 10mm x 1005mm belt in the correct pulley width.

 

This morning the battery soc was down to about 70% and as soon as the split charge relay connected the domestics the alternator delivered about 55A.  Its a 70A alternator.  As the battery voltage built up and the current delivered by the alternator reduced to about 40A the squealing stopped.

What I don't want to do is to overtighten the belt.  I was told years ago that the alternator would stand lots of lateral force on the bearings but not so the water pump.  So I want to keep the tension as low as I can consistent with not shredding the alternator belt and scattering bits of black dust over the engine.

 

Advice please?

 

Nick

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The following worked / works for me:-

 

Run the engine at higher revs: - say 1400 rpm or a tad more NOT at tickover

Fit toothed belts (Bearing Boys stock them)

Consider replacing pulleys with ridged type (I'll go away and lookup the correct term)

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Is it a good quality belt? Is it a plain belt and not the proper cogged/toothed one?

If it is allowed to squeal at all it will polish the sides and leave it more likely to squeal, a vicious circle.

There should be about 10mm maximum deflection on the longest run between pulleys with firm thumb pressure.

Inspect the pulleys, particularly the alternator, to see if they have worn wider letting the belt bottom in the groove.

The pulleys should not be worn into small grooves on the sides as this reduces the surface contact with the belt.

Ensure the the pulleys are all in line.  Its not unknown for brackets to become bent putting the alternator out of alignment. This reduces the belt pressure on one side of the vee and leads to rapid deterioration of the belt surface.

Edited by Tracy D'arth
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9 minutes ago, Theo said:

I have had a squealy alternator belt three times in the course of a three week trip with few running hours (often less than 4 hours per day.

 

Each time I have tightened it a boit more.  The belt was new at the beginning of the trip so I would expect to have to retighten it once after the initial tightening, but three times seems a bit excessive.  It is a 10mm x 1005mm belt in the correct pulley width.

 

This morning the battery soc was down to about 70% and as soon as the split charge relay connected the domestics the alternator delivered about 55A.  Its a 70A alternator.  As the battery voltage built up and the current delivered by the alternator reduced to about 40A the squealing stopped.

What I don't want to do is to overtighten the belt.  I was told years ago that the alternator would stand lots of lateral force on the bearings but not so the water pump.  So I want to keep the tension as low as I can consistent with not shredding the alternator belt and scattering bits of black dust over the engine.

 

Advice please?

 

Nick


Did you replace the belt with an identical one? (eg toothed). If a new belt has suddenly created this problem, and you are tightening to the same tension as before, surely it points to an issue with the belt?

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You say the belt is the correct width, but is t the correct profile?

There are two profiles for all but the same width belts and if you have the wrong one it may well wear quickly.

 

Are the pulleys all in line? Use a straight edge to check.

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Further to all the good advice above. The cogs/teeth on a cogged/toothed V belt are not to engage with anything, but to allow the belt to more easily flex round small pulleys, giving better contact and force transfer. Check the root of the grooves in the pulleys. If they are polished down there, then the belt is bottoming out, which reduces contact area and leads to slipping. The belt should be riding on the sides of the V, not the bottom.

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Sometimes if you try to lever the alt out a bit too much it will twist and the pulleys will run out of parallel a bit. Used to happen with BMC engines and dynamos.

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For some years (so long ago that I've forgotten the exact details), I used standard belts which didn't last for long and a local belt shop welcomed my business.

Then I hacked around for a mail order supplier and discovered BB.

Read the blurb and tried the cogged belts.

Instantly, from renewing belts several times a season, I 'never' had to replace a belt again.

(Ultimately I fitted a flat belt system and xx years later the set are still in use.)

 

However - as I have a large 24v alternator and a big battery bank I always run the engine at 1400 rpm and cut out the Adverc for the first 1/2 hour or so to stop any belt squeal.

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3 hours ago, Theo said:

I have had a squealy alternator belt three times in the course of a three week trip with few running hours (often less than 4 hours per day.

 

Each time I have tightened it a boit more.  The belt was new at the beginning of the trip so I would expect to have to retighten it once after the initial tightening, but three times seems a bit excessive.  It is a 10mm x 1005mm belt in the correct pulley width.

 

This morning the battery soc was down to about 70% and as soon as the split charge relay connected the domestics the alternator delivered about 55A.  Its a 70A alternator.  As the battery voltage built up and the current delivered by the alternator reduced to about 40A the squealing stopped.

What I don't want to do is to overtighten the belt.  I was told years ago that the alternator would stand lots of lateral force on the bearings but not so the water pump.  So I want to keep the tension as low as I can consistent with not shredding the alternator belt and scattering bits of black dust over the engine.

 

Advice please?

 

Nick

 

Have you always had a 70amp alternator, or is it a recent more powerful replacement? I replaced the original 35 amp alternator on Helvetiia with a bigger 70 amp one, still using the original 10 x 1050 belt, and experienced a lot of squealing under load. After tolerating it for a while, I arranged for Jonathon Hewitt at UCC to open out the crankshaft pulley V groove, fit a wider alternator pulley, and fit a 13.5 x 1050 belt - problem solved.

 

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Thanks for all the useful advice.  All the advice had already been followed except Tracy D'Arth's "There should be about 10mm maximum deflection on the longest run between pulleys with firm thumb pressure."

 

It is embarassing to admit that I had not got it tight enough.  I had been testing the tension on the shortest length from the water pump to the alternator (Theodora has a BMC 1.5) The longest length is from the alternator to the crank shaft.  Tightening it with a little assistance of the jemmy should have done the trick but I can't test it properly until tomorrow when we will have run the batteries down a bit.

 

David said "Have you always had a 70amp alternator, or is it a recent more powerful replacement? I replaced the original 35 amp alternator on Helvetiia with a bigger 70 amp one, still using the original 10 x 1050 belt, and experienced a lot of squealing under load. After tolerating it for a while, I arranged for Jonathon Hewitt at UCC to open out the crankshaft pulley V groove, fit a wider alternator pulley, and fit a 13.5 x 1050 belt - problem solved. "

 

Actually, the alternator might be 100A.  I fitted a new one when we first had Theodora.  The old one, the original Lucas, IIRC, was not working at all when we bought the boat.  And in my ignorance I thought that a bigger alternator had to be better.  A few years later I got around to fitting an ammeter in the alternator output.  What a worthwhile investment!  I have never seen the output go higher than 85A and that was when we collected the poor old boat from where they had been painted.  The soc (Smartguage) was reading 25%.  I never let it go below 50% normally and usually get concerened when we approach 60%.  I rarely charge the batteries with the engine when moored but when I do I run the engine just fast enough to give maximum current.

 

I observe from the alternator current that at the beginning of the day the alternator output might go as high as 45A, falling back to 25A within five or ten minutes and gradually reducing over the rest of the day's cruising.  Who needs a high paowered alternator?

 

N

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23 minutes ago, Theo said:

Actually, the alternator might be 100A.  I fitted a new one when we first had Theodora.  The old one, the original Lucas, IIRC, was not working at all when we bought the boat.  And in my ignorance I thought that a bigger alternator had to be better.  A few years later I got around to fitting an ammeter in the alternator output.  What a worthwhile investment!  I have never seen the output go higher than 85A and that was when we collected the poor old boat from where they had been painted.  The soc (Smartguage) was reading 25%.  I never let it go below 50% normally and usually get concerened when we approach 60%.  I rarely charge the batteries with the engine when moored but when I do I run the engine just fast enough to give maximum current.

 

I observe from the alternator current that at the beginning of the day the alternator output might go as high as 45A, falling back to 25A within five or ten minutes and gradually reducing over the rest of the day's cruising.  Who needs a high paowered alternator?

 

That should be printed in bold and posted in the stickies as "Why you don't need a huge alternator"

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28 minutes ago, Theo said:

Thanks for all the useful advice.  All the advice had already been followed except Tracy D'Arth's "There should be about 10mm maximum deflection on the longest run between pulleys with firm thumb pressure."

 

It is embarassing to admit that I had not got it tight enough.  I had been testing the tension on the shortest length from the water pump to the alternator (Theodora has a BMC 1.5) The longest length is from the alternator to the crank shaft.  Tightening it with a little assistance of the jemmy should have done the trick but I can't test it properly until tomorrow when we will have run the batteries down a bit.

 

David said "Have you always had a 70amp alternator, or is it a recent more powerful replacement? I replaced the original 35 amp alternator on Helvetiia with a bigger 70 amp one, still using the original 10 x 1050 belt, and experienced a lot of squealing under load. After tolerating it for a while, I arranged for Jonathon Hewitt at UCC to open out the crankshaft pulley V groove, fit a wider alternator pulley, and fit a 13.5 x 1050 belt - problem solved. "

 

Actually, the alternator might be 100A.  I fitted a new one when we first had Theodora.  The old one, the original Lucas, IIRC, was not working at all when we bought the boat.  And in my ignorance I thought that a bigger alternator had to be better.  A few years later I got around to fitting an ammeter in the alternator output.  What a worthwhile investment!  I have never seen the output go higher than 85A and that was when we collected the poor old boat from where they had been painted.  The soc (Smartguage) was reading 25%.  I never let it go below 50% normally and usually get concerened when we approach 60%.  I rarely charge the batteries with the engine when moored but when I do I run the engine just fast enough to give maximum current.

 

I observe from the alternator current that at the beginning of the day the alternator output might go as high as 45A, falling back to 25A within five or ten minutes and gradually reducing over the rest of the day's cruising.  Who needs a high powered alternator?

 

N

I should add that there is good and simple mathematics behind the advice to run the alternator fast:

Power output of the alternator at any instant = VI.

Power input ( just a bit more than power input)  = Torque (in N-m) x angular velocity (radians/second)

 

So for a given power input increasing the angular velocity (think RPM) the torque will reduce.  So running the engine faster will reduce the force on the alternator belt.  However running the engine faster means that it is wasting more power in overcoming friction so you will use more fuel.  That's why I run the engine as slowly as possible consistent with maximum current.

 

N

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One thing that hs occured to me, a 1005 alternator belt is quite short for a BMC1.5, unless you have misquoted the size in your original post. A larger crankshaft pulley wheel would increase the revs of the alternater at a slower engine speed. (or a smaller alternator pulley - not illusrated) Does yours look this size ?

 

984465237_25EngineGearbox02.JPG.bef6f0277bdd487a6bd3744950dc9b16.JPG

 

 

Edited by David Schweizer
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9 minutes ago, David Schweizer said:

One thing that hs occured to me, a 1005 alternator belt is quite short for a BMC1.5, unless you have misquoted the size in your original post. A larger crankshaft pulley wheel would increase the revs of the alternater at a slower engine speed. Does yours look this size ?

 

984465237_25EngineGearbox02.JPG.bef6f0277bdd487a6bd3744950dc9b16.JPG

 

 

I would guess that it's about that size.  There is the added pully on the crankshaft.  It's a small one and is used for the pelt drive to the raw water pump.

 

Edited to add:  An extension to the maths will show that the force on the drive belt to the alternator does not change as the pulley size on the alternator changes.  I find that quite interesting.

 

N

Edited by Theo
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Just now, Tracy D'arth said:

The general consensus is that an alternator larger than 90A will not run reliably on a single Vee belt. So you are doing well.

Ah, yes, but as I said it almost never produces anything like 90A.  Thought! 🗯️ Perhaps it is a 90A alternator.  After all it did only produce 85A when the soc was 25%.

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49 minutes ago, Alan de Enfield said:

 

That should be printed in bold and posted in the stickies as "Why you don't need a huge alternator"

Except that it’s wrong, and is misinformation promoted only by people who have never had a huge alternator.

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Just now, nicknorman said:

Except that it’s wrong, and is misinformation promoted only by people who have never had a huge alternator.

I would be really interested in your reasoning.

 

N

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Just now, Alan de Enfield said:

 

He has all sorts of electronics overiding the alternator.

But at safe voltages you can only put so much current into the battery bank.  At 80% charge and 14.4V my nominal  810AH (very old) battery bank is only accepting in the region of 18A.  This will, of course be due to surface charge, but can such chemistry be overcome by lots of electronics?  I am using an Adverc, and very excellent it is too, but I can't see how I would manage to keep my alternator working flat out any more than it is now.

 

 

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22 minutes ago, Theo said:

I would be really interested in your reasoning.

 

N


A couple of reasons, firstly and simply a large alternator can run a large load (via an inverter of course!) - washing machine, tumble drier, electric kettle etc. without using any battery juice.


But in the context of battery charging, people seem to think that because their (eg) 70A alternator only charges at 40A from a few minutes after starting charging, that a 175A alternator would only be charging at 40A under the same circumstances. This isn’t true.

 

It’s to do with the regulation curve of an alternator’s rather basic regulator. The current supplied by an alternator is related (inversely) to the terminal voltage. So if we presume for example that the regulated voltage is 14.4v, at 14.4v it is producing no current. At 14.39v it is producing  maybe 1% of its output. At 14.3 maybe 10%. At 14.2v maybe 25% You have to get right down to perhaps 13.7v before it is producing 100% of its output. (Figures made up, but the principle is right).

 

You’ll notice I’m quoting the current as % of maximum output, so of course if the max is 175A vs 70A, the actual amount is much bigger at any particular voltage. It is of course true that with more current the battery voltage will be a bit greater, but even so the charge current will be significant more.

 

Example: with our Trojans, on first starting at maybe 60% SoC we would get 175A. This would fall off pretty quickly but still be 120A a long time later. It would take several hours to get down to 70A. Of course it is true that the tail end of the charge takes the same length of time, but a lot of time can be saved in the early and mid stages. So if you want to add a hundred Ah without fully charging, you can do it in under an hour.

 

Linked to this of course is the other myth that “the battery determines the charge current”. Well not quite a myth, it is of course true in theory, but in practice the soft relationship between an alternator’s current vs voltage is a very significant factor. This was brought home to me when I installed my home made alternator regulator which holds maximum current until the regulated voltage is reached within about 0.1v. I seem to recall posting something on here where the charge current was around 120A despite the SoC being 85%.

 

And now of course with Lithiums, my only limitation is the risk of overheating the alternator. I limit it to about 90C and that gives a continuous 125A or so, right up to about 99% SoC. But short term I can put 175A in at virtually any state of charge. And with the Travelpower and 100A Combi playing as well, 275A. That’s a day’s worth in well under an hour.

 

Edited by nicknorman
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