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Alternator Speed on Slow Revving engine


steve.sharratt

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Hi,

 

I am looking at installing a Balmar 140amp alternator to charge my lithium house bank.  I have a Lister JP3 and unfortunately the slow revs and pulley size is not sufficient to spin the alternator fast enough.  Ideally, I need the alternator rpm to 5-6000 but my calculations suggest that I will only achieve around 2500rpm (engine revs of 3-500rpm).  This gives a amp output of 30-50 at best. 

 

I am toying with the idea of engineering a ‘geared pulley’ between the alt and engine. e.g.  15-16in engine pulley to 2 in pulley currently gives 2500rpm. If I place a intermediate 2in pulley which is attached to a 4in pulley to the alternator, this should theoretically double the alt speed to 5000rpm. The math is probably a bit rough but is used as an example.   Has anyone overcome the problem of slow revs?  I would love to hear how you solved it.

 

Chers

 

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10 minutes ago, steve.sharratt said:

Has anyone overcome the problem of slow revs?  I would love to hear how you solved it.

 

 

 

I don't think it can be solved if you're looking for 140A out of your alternator. The power transfer into a small alternator pulley like 2" diameter simply cannot be achieved, you'll always get massive belt slip. 

 

 

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Just run the belt round the flywheel….it’s what I do on mine and it’s worked for the last 30 years. You might need two belts so they don’t slip on a 140 amp alternator. Means I can get full alternator output at tickover. 

1 minute ago, MtB said:

 

 

I don't think it can be solved if you're looking for 140A out of your alternator. The power transfer into a small alternator pulley like 2" diameter simply cannot be achieved, you'll always get massive belt slip. 

 

 

With a single belt and a standard Lucas pulley I get zero slip just round the flywheel…that’s with a 70 amp A127 @ 12v 

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2 minutes ago, frangar said:

Just run the belt round the flywheel….it’s what I do on mine and it’s worked for the last 30 years. You might need two belts so they don’t slip on a 140 amp alternator. Means I can get full alternator output at tickover. 

With a single belt and a standard Lucas pulley I get zero slip just round the flywheel…that’s with a 70 amp A127 @ 12v 

 

 

Yep I think twin belts would be the answer, given the OP is looking for twice the current your single belt delivers. 

 

 

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2 minutes ago, MtB said:

 

 

Yep I think twin belts would be the answer, given the OP is looking for twice the current your single belt delivers. 

 

 

Even with matched belts, one is always going to be tighter than the other. Going to a polyvee avoids this and they last much longer meaning you don't have to take the gearbox off as often to replace the belts. Also you can tape up a spare belt around the flywheel housing for the day that the working belt needs replacing.

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5 minutes ago, Tracy D'arth said:

Driving any alternator much over 90A on a single v belt is doomed to failure. Go to a polyvee belt running on the outside of the flywheel will give you plenty of revs with a reasonably sized alternator pulley.

I’d probably go for two standard belts….if you ran a polyvee then I think you’d quickly wear the ribs away. 

1 minute ago, Tracy D'arth said:

Even with matched belts, one is always going to be tighter than the other. Going to a polyvee avoids this and they last much longer meaning you don't have to take the gearbox off as often to replace the belts. Also you can tape up a spare belt around the flywheel housing for the day that the working belt needs replacing.

If it’s a marine JP then the flywheel is at the front where it should be! 

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8 minutes ago, frangar said:

Just run the belt round the flywheel….it’s what I do on mine and it’s worked for the last 30 years. You might need two belts so they don’t slip on a 140 amp alternator. Means I can get full alternator output at tickover. 

With a single belt and a standard Lucas pulley I get zero slip just round the flywheel…that’s with a 70 amp A127 @ 12v 

I did consider doing this originally as then I could use a serpentine belt.  I dropped the idea when Balmar told me the 140a will run with double V belts which would work with the engine pulley.  This was before I realised that I couldn’t achieve the revs.  I will measure the flywheel to see how much more it gives.  A simple solution to the problem if the flywheel is big enough

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6 minutes ago, frangar said:

I’d probably go for two standard belts….if you ran a polyvee then I think you’d quickly wear the ribs away. 

If it’s a marine JP then the flywheel is at the front where it should be! 

Strangely they don't seem to wear away.

I am really pleased if you have a marine JP, most I see are old lighthouse units with the flywheel at the wrong end.

I did see one with a rubber faced alternator pulley running on the flywheel, seemed to work OK and easy to replace.

Edited by Tracy D'arth
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30 minutes ago, frangar said:

I’d probably go for two standard belts….if you ran a polyvee then I think you’d quickly wear the ribs away. 

If it’s a marine JP then the flywheel is at the front where it should be! 

It is! Although I don’t think it is a marine version.  The original builder just set it up with the flywheel to the front.

Edited by steve.sharratt
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I think a polyV (serpentine?) should work and I know you can reverse them and use the smooth side.  I have also checked the Balmar Output curves chart and I think I will be able to get the rpm high enough to make it workable at around 70amps at idle.  The upside of the PolyV is that the Balmar pulley is smaller (than the double V) which adds to the rpm.

 

My math is this:

 

Currently: Using a double v pulley onto the engine pulley is 2.2in / 15.5in = 0.142 velocity ratio.  300rpm (engine idle) / 0.142 = 2112 rpm at alternator.

Flywheel: PolyV pulley onto engine flywheel is 1.9 / 23in = 0.083. 300rpm / 0.083 = 3615 rpm.

 

That takes it from around 20 amp to 70 amps at idle.

65 amps to 135 amps at running speed.  

 

That’s looking good.  Just need to take some measurements now.

 

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4 minutes ago, steve.sharratt said:

I think a polyV (serpentine?) should work and I know you can reverse them and use the smooth side.  I have also checked the Balmar Output curves chart and I think I will be able to get the rpm high enough to make it workable at around 70amps at idle.  The upside of the PolyV is that the Balmar pulley is smaller (than the double V) which adds to the rpm.

 

My math is this:

 

Currently: Using a double v pulley onto the engine pulley is 2.2in / 15.5in = 0.142 velocity ratio.  300rpm (engine idle) / 0.142 = 2112 rpm at alternator.

Flywheel: PolyV pulley onto engine flywheel is 1.9 / 23in = 0.083. 300rpm / 0.083 = 3615 rpm.

 

That takes it from around 20 amp to 70 amps at idle.

65 amps to 135 amps at running speed.  

 

That’s looking good.  Just need to take some measurements now.

 

 

If you use the smooth side of the polyvee the power it can transfer will be much smaller than using the grooved side, the angle of the vees increases the torque that can be transferred by several times (2x-3x is my estimate depending on vee angle).

 

This will make your problem of getting power into the alternator even worse, it'll slip on the alternator pulley.

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7 minutes ago, steve.sharratt said:

I think a polyV (serpentine?) should work and I know you can reverse them and use the smooth side.  I have also checked the Balmar Output curves chart and I think I will be able to get the rpm high enough to make it workable at around 70amps at idle.  The upside of the PolyV is that the Balmar pulley is smaller (than the double V) which adds to the rpm.

 

My math is this:

 

Currently: Using a double v pulley onto the engine pulley is 2.2in / 15.5in = 0.142 velocity ratio.  300rpm (engine idle) / 0.142 = 2112 rpm at alternator.

Flywheel: PolyV pulley onto engine flywheel is 1.9 / 23in = 0.083. 300rpm / 0.083 = 3615 rpm.

 

That takes it from around 20 amp to 70 amps at idle.

65 amps to 135 amps at running speed.  

 

That’s looking good.  Just need to take some measurements now.

 

You could use the smooth side against the flywheel, but I don’t see how that would work at the alternator end. You’d still need to have the polyV side against the alternator pulley grooves and to do that you’d need 2 idler pulleys and a lot of belt contortion! It seems that having the polyV side against the flywheel isn’t too bad a solution.

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21 minutes ago, IanD said:

 

If you use the smooth side of the polyvee the power it can transfer will be much smaller than using the grooved side, the angle of the vees increases the torque that can be transferred by several times (2x-3x is my estimate depending on vee angle).

 

This will make your problem of getting power into the alternator even worse, it'll slip on the alternator pulley.

 

19 minutes ago, nicknorman said:

You could use the smooth side against the flywheel, but I don’t see how that would work at the alternator end. You’d still need to have the polyV side against the alternator pulley grooves and to do that you’d need 2 idler pulleys and a lot of belt contortion! It seems that having the polyV side against the flywheel isn’t too bad a solution.

Agreed. I read that it could be done but didn’t give it much thought.  Rough side down it is!

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12 minutes ago, steve.sharratt said:

 

Agreed. I read that it could be done but didn’t give it much thought.  Rough side down it is!

But then you might get slipping on the flywheel side (no grooves), the tension in the belt is the same at both pulleys -- you might be lucky though because the flywheel is so much bigger diameter.

 

Even without this, a polyvee belt running on the tips of the vees on the flywheel is likely to wear them away quickly... 😞

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I have not looked at the manufacturers sites for a while but I am pretty sure that both Gates and Continental are quite clear that running a poly V belt on a flat faced pulley is perfectly acceptable above a certain pulley diameter ( which was less than a JP flywheel diameter) .  The demanding end is the alternator.  Here you want all the belt width you can get,   at least a 180 degree wrapround on the pulley and the makers reccomended belt tension.  At 140 A and,  say, 14v output  you will need to be putting about 2.5 to 3 kW into the alternator, depending on the efficiency.  I would look for  at least a 6 or 8 rib K groove size belt for that.

 

 I did try a "geared up" pulley drive on my Kelvin. With a 4:1 first stage from a 12 in flywheel pulley (all I could swing to cut the grooves)  and a 3:1 second stage into a 2 in alternator pulley,  It worked well for short periods but the bearings on the intermediate shaft were overloaded and did not last long enough.  If you are going to try this I would now suggest at least LJ 1 1/4 bearings  and do not overhang both  the pulleys at one end of the intermediate shaft.

 

N

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3 minutes ago, BEngo said:

I have not looked at the manufacturers sites for a while but I am pretty sure that both Gates and Continental are quite clear that running a poly V belt on a flat faced pulley is perfectly acceptable above a certain pulley diameter ( which was less than a JP flywheel diameter) .  The demanding end is the alternator.  Here you want all the belt width you can get,   at least a 180 degree wrapround on the pulley and the makers reccomended belt tension.  At 140 A and,  say, 14v output  you will need to be putting about 2.5 to 3 kW into the alternator, depending on the efficiency.  I would look for  at least a 6 or 8 rib K groove size belt for that.

 

 I did try a "geared up" pulley drive on my Kelvin. With a 4:1 first stage from a 12 in flywheel pulley (all I could swing to cut the grooves)  and a 3:1 second stage into a 2 in alternator pulley,  It worked well for short periods but the bearings on the intermediate shaft were overloaded and did not last long enough.  If you are going to try this I would now suggest at least LJ 1 1/4 bearings  and do not overhang both  the pulleys at one end of the intermediate shaft.

 

N

 

Which means an idler pulley is needed, like this... (alternator is a 48V 100A Electrodyne)

 

 

beta_big_alt.PNG

Edited by IanD
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17 minutes ago, BEngo said:

I have not looked at the manufacturers sites for a while but I am pretty sure that both Gates and Continental are quite clear that running a poly V belt on a flat faced pulley is perfectly acceptable above a certain pulley diameter ( which was less than a JP flywheel diameter) .  The demanding end is the alternator.  Here you want all the belt width you can get,   at least a 180 degree wrapround on the pulley and the makers reccomended belt tension.  At 140 A and,  say, 14v output  you will need to be putting about 2.5 to 3 kW into the alternator, depending on the efficiency.  I would look for  at least a 6 or 8 rib K groove size belt for that.

 

 I did try a "geared up" pulley drive on my Kelvin. With a 4:1 first stage from a 12 in flywheel pulley (all I could swing to cut the grooves)  and a 3:1 second stage into a 2 in alternator pulley,  It worked well for short periods but the bearings on the intermediate shaft were overloaded and did not last long enough.  If you are going to try this I would now suggest at least LJ 1 1/4 bearings  and do not overhang both  the pulleys at one end of the intermediate shaft.

 

N

The flywheel is 23in so I assume this will be within the parameters of acceptable. The alternator is 24v and I believe the pulley is a 6 rib but have asked Balmar for more detail.

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1 minute ago, steve.sharratt said:

The flywheel is 23in so I assume this will be within the parameters of acceptable. The alternator is 24v and I believe the pulley is a 6 rib but have asked Balmar for more detail.

 

If the alternator is 24V 140A then that'll be about 4kW output, which means about 7kW/9hp input, which is a *lot* -- make sure this doesn't overload the engine, you'll probably need an alternator controller like the Wakespeed which pulls back current at low rpm.

 

IIRC Balmar specify a 180deg wrap, if you don't have an idler pulley with their standard (6-rib?) polyvee pulley you risk it slipping -- see picture above for a recommended layout.

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If you have the rib side on the alternator then you will also have the ribs on the flywheel, not the flat side 😀. I think the idea of using the flat side refers to idlers as in the picture above.  An issue with a big pulley or flywheel is that it results in very poor wrap at the alternator, unless you include an idler. I have seen installations where this is partly solved by mounting the alternator some way from the engine rather than on the engine.  mtb???.

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16 minutes ago, IanD said:

 

If the alternator is 24V 140A then that'll be about 4kW output, which means about 7kW/9hp input, which is a *lot* -- make sure this doesn't overload the engine, you'll probably need an alternator controller like the Wakespeed which pulls back current at low rpm.

 

IIRC Balmar specify a 180deg wrap, if you don't have an idler pulley with their standard (6-rib?) polyvee pulley you risk it slipping -- see picture above for a recommended layout.

 

10 minutes ago, dmr said:

If you have the rib side on the alternator then you will also have the ribs on the flywheel, not the flat side 😀. I think the idea of using the flat side refers to idlers as in the picture above.  An issue with a big pulley or flywheel is that it results in very poor wrap at the alternator, unless you include an idler. I have seen installations where this is partly solved by mounting the alternator some way from the engine rather than on the engine.  mtb???.

The alternator will be mounted separate from the engine but it is a narrowboat so it will never be too far away 😳! I will need to design a new alternator mount anyway so I can include an idler pulley.  

 

The installation will include a multi-stage controller as part of the setup.

Edited by steve.sharratt
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It is quite OK to run the ribs on a flat pulley surface, provided the diameter is big enough.  If you look at the ribs there is quite a large spacing between them, especially for the belts with larger ribs. Combined with it being impossible to mould a sharp point onto the tips of the ribs this provides plenty of contact area.

N

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41 minutes ago, steve.sharratt said:

 

The alternator will be mounted separate from the engine but it is a narrowboat so it will never be too far away 😳! I will need to design a new alternator mount anyway so I can include an idler pulley.  

 

You don't want a very long unsupported belt run between flywheel and alternator anyway, it can make the belt prone to vibrating/resonating from side to side (like a plucked string) driven by engine torque fluctuations -- especially with a big (heavy) alternator spinning quite fast, which has a lot of inertia.

 

FYI Beta recommend using a freewheeling pulley with big alternators like this to reduce vibration and belt wear, but these are only available in certain sizes (diameter and V count).

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