Marsupial
Well-Known Member
so you want a "higher" authority? try these guys, I think they may just know what they're on about AS DO I; 110a needs a better drive system.
http://www.dg2k.co.uk/alternators.htm
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Alternator Belts: does "wrap" matter?
- Thread starter nigelmercier
- Start date
so you want a "higher" authority? try these guys, I think they may just know what they're on about AS DO I; 110a needs a better drive system.
http://www.dg2k.co.uk/alternators.htm
pvb
Well-Known Member
Actually, the link you provided said that greater than 110A needs dual pulleys. There's a lot of misunderstanding about alternators. The quoted output is a maximum current, and is only achieved when the load connected to the alternator is able to absorb it. I have a 90A alternator, charging about 660Ah of batteries. It rarely manages anywhere near 90A. Most boats have smaller battery banks.
fuss
Well-Known Member
Marsupial... I have read the posts and your comments are right... but unfortunately he does not want to hear it.... so you are wasting your time here.
VicS
Well-Known Member
It look as though the OP's 12 volt 110amp alternator is a Balmar series 7 one.
They are supplied with a single deep Vee pully which will take a 3/8" or a 1/2" belt
The 150 amp series 6 ones are fitted with a double pulley.
It would seem that Balmar, who one would assume know what they are about, consider a single belt ( but perhaps a 1/2" one) suitable for their 110amp alternator but that twin belts are required for larger alternators.
In view of all the arguments and views in the thread it would seem sensible to me to fit a larger belt to the 12volt alternator , even if that means changing the pulley on the crank shaft and on the water-pump.
It would be silly IMHO to risk the mod ( even if it was my suggestion) to the water-pump drive or to go to the extent of swapping the positions of the alternators just to get a bit more wrap without guarantee of success.
They are supplied with a single deep Vee pully which will take a 3/8" or a 1/2" belt
The 150 amp series 6 ones are fitted with a double pulley.
It would seem that Balmar, who one would assume know what they are about, consider a single belt ( but perhaps a 1/2" one) suitable for their 110amp alternator but that twin belts are required for larger alternators.
In view of all the arguments and views in the thread it would seem sensible to me to fit a larger belt to the 12volt alternator , even if that means changing the pulley on the crank shaft and on the water-pump.
It would be silly IMHO to risk the mod ( even if it was my suggestion) to the water-pump drive or to go to the extent of swapping the positions of the alternators just to get a bit more wrap without guarantee of success.
Lakesailor
Well-Known Member
Well I'm only a bit thick, but I would look at putting an idler on the alternator mount bolt (extended) to run on the back of the belt and increase the wrap on the alternator pulley.
Plenty of automotive engines have such idlers. Fiat for instance.
Plenty of automotive engines have such idlers. Fiat for instance.
William_H
Well-Known Member
Alternators
Yes assuming that the belt for the 12v alternator is aligned and correct tension and size then wrap does matter. If the concern is grip then the added circumferential distance with more wrap will give proportionally more grip.
I would suggest that the 24v alternator be fitted in place of the 12v alternator. presumably the 24v alternator being the engine battery charging so not much power needed.
Put the 12v large alternator in the additional place on the dedicated belt and pulley. This should help belt problems.
However one answer rather than fit twin belts is to fit bigger pulleys. If you can find and fit a bigger pulley to the 12v alternator that will give more circumference so more grip. Obviously that will slow the alternator so you will need to proportionately increase the size of the crankshaft pulley. The end result will be a higher belt speed with less pull (torque). All this very much depends on what pulleys are available and it may be just as easy to go twin pulleys/ belts. good luck olewill
Yes assuming that the belt for the 12v alternator is aligned and correct tension and size then wrap does matter. If the concern is grip then the added circumferential distance with more wrap will give proportionally more grip.
I would suggest that the 24v alternator be fitted in place of the 12v alternator. presumably the 24v alternator being the engine battery charging so not much power needed.
Put the 12v large alternator in the additional place on the dedicated belt and pulley. This should help belt problems.
However one answer rather than fit twin belts is to fit bigger pulleys. If you can find and fit a bigger pulley to the 12v alternator that will give more circumference so more grip. Obviously that will slow the alternator so you will need to proportionately increase the size of the crankshaft pulley. The end result will be a higher belt speed with less pull (torque). All this very much depends on what pulleys are available and it may be just as easy to go twin pulleys/ belts. good luck olewill
reeac
Well-Known Member
wrap angle
I'd never thought about wrap angle before but it seems to me that the major effect of increasing it is to apply the belt tension more effectively to press the belt into contact with the pulley. This will be a cosine effect, the relevant angle being half of 360-wrap angle i.e. half the internal angle between the two lengths of belt. In this particular case that is 30 degrees. Cosine 30 is 0.866 so you've only got a potential gain of 16% if you go for a parallel belt layout with zero internal angle or 360 degree external wrap angle. Not a lot of gain. In all of the above I'm assuming that, as in sliding friction, area of contact is irrelevant [Amonton's Law, if I remember correctly]. I the real world I'm sure that it's more complicated. I would consult Balmar.
Ubergeekian
Well-Known Member
The major effect of increasing the wrap angle is to allow a larger tension difference between the slack side and the power side. The capstan equation describes this:
T(load) = T(slack) x exp(mu theta)
The maximum torque which can be transmitted is therefore
radius x T(slack) [ exp(mu theta) - 1 ]
which multiplied by the angular velocity gives you the power.
boatmike
Well-Known Member
Thats precisely the point pvb and the fact that I have run one for two years with the single pulley that it was supplied with proves it. For those who insist on arguing for the sake of it my alternator is exactly the same as the one shown although the wrap around the pulley is greater. I actually contacted Prestolite direct when I originally fitted it as I was a little surprised that it only had a single v pulley supplied as standard. Their reply was that if the alternator was expected to run at maximum output for long periods a double vee or flat belt drive would be an advantage. On a boat with a stirling smart charger the maximum output is confined to occasional boost when the service batteries are at their lowest so the single belt is sufficient. The point is that the single belt is quite capable of transmitting the power without danger of breaking. It will however wear more rapidly if run at maximum for a long time which means it needs careful maintenance. Its a matter of what is ideally desirable and what will suffice in practice.
boatmike
Well-Known Member
Agreed, and you make the same point as the original poster and myself, namely that the manufacturer wouldn't fit a single pulley if they thought it insufficient. I think however it's a prestolite rather than balmar and he may well have the same problem I had when I fitted mine, in that its a solid turned imperial sized pulley with a metric sized belt and may be very near the bottom of the groove.
boatmike
Well-Known Member
Yes indeed Lakey. In this instance you are not thick
and if the pulley proves to be the right width (which I suspect it isn't) that's worth a try and only requires a flat idler pulley that would be quite easy to rig up.
oldharry
Well-Known Member
Interesting conflict of professional opinion here! Just a lateral thought: are all the pulleys on the belt that keeps failing correctly aligned with each other? It's the single biggest cause of early belt failure, and characteristically shreds belts in the way you describe.
Avocet
Well-Known Member
For what it's worth, I got fed up with bits of rubber dust so I put a toothed belt (yes, a timing belt!) on and it seems to work very well! I realise that if something seizes I'll snap the belt, but that's something I'm happy to live with!
DownWest
Well-Known Member
Funny, that was my first thought too. But the mechanical problems re fitting one to the crank might be tricky. The OP asked where to get a spacer. If he needs to ask that, then a toothed belt conversion would have to be handed to a professional outfit, at lord knows what cost. (and it is outside his question)
Blueboatman
Well-Known Member
Two h'aporth. I assume the OPs batteries and charging regulator are all sound? If the alternator is being encouraged to cut in and out far more than it 'should' then any drive belt(s) will wear correspondingly more quickly.
Def the cheapest sensible option is to measure/replace the Imperial pulley first and observe!
Def the cheapest sensible option is to measure/replace the Imperial pulley first and observe!
reeac
Well-Known Member
This is all a bit "chicken and egg" as you will only get that tension difference if the belt gets enough grip on the pulley [and the pulley offers resistance to rotation]. I'm suggesting that that grip will be increased by reducing the angle between the two lengths of belt.
Heckler
Well-Known Member
Its an MD22 engine, the 12v alternator is the std fitting, the std belt from Volvo Penta is a 9.75 mm by 975 mm. Ive just changed the one on mine, it looks the same as the one in the pic, dust everywhere, I tightened it up well this weekend and its working better. However what I have done is sourced a Gates 10mm by 975mm toothed belt and hopefully the extra width will make up for any wear in the pulleys. I use a Sterling booster which, according to Charles, can make a std alternator produce up to 100 amps and I suspect that is what is causing the extra wear, I have dialled in to the controller to tell it to charge at 14.2v which has eased the load somewhat. (it was charging at 14.6)
Stu
pvb
Well-Known Member
The 12v alternator looks to me like an aftermarket product, not standard fit. The original poster also said it was a 110A alternator, but Volvo generally only fitted 60A alternators on the MD22. But you're right, a good-quality Gates belt is worth getting.
saltwater_gypsy
Well-Known Member
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Balmar warn that,although a single belt will do for 110A, that belt life may be considerably shortened...as you have confirmed! Lots of good suggestions but getting double pulleys for afterfit may be difficult.
It may be easy to fit a nylon jockey wheel and a longer belt to give a better wrap. There look to be plenty of potential fixing points
It may be easy to fit a nylon jockey wheel and a longer belt to give a better wrap. There look to be plenty of potential fixing points
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scottie
Well-Known Member
reinvent the wheel <pulley>
been here before
you seem to have the std Volvo add alt kit but 110 rather than 60a
change the the drive to either twin pulley or see if you can get a toothed <timing belt> this is what volvo did on the 2030 etc and csn be retro fitted dont know if you can get the same for the 22
also worth checking what load you can take from the front end of the engine
if you can find the accessorie cat for the 22 it will have all the options
been here before
you seem to have the std Volvo add alt kit but 110 rather than 60a
change the the drive to either twin pulley or see if you can get a toothed <timing belt> this is what volvo did on the 2030 etc and csn be retro fitted dont know if you can get the same for the 22
also worth checking what load you can take from the front end of the engine
if you can find the accessorie cat for the 22 it will have all the options
