Drivebelt conversion to get higher alternator speed?

[wetfoot]

My sons boat has a Yanmar 4JH4AE engine and a ALT 4036 70A Unipoint alternator. 

As a expected, there is almost no output from the alternator at idle and only at a relatively fast idle , or slow boating speed, is there any charging of the battery.

 

I'm investigating changing pulley sizes to increase the alternator speed so that it charges at idle.

I found this conversion kit in the US but its very expensive.

 

Does anyone know of a similar kit in the UK to make the crankshaft pulley larger and the alternator pulley smaller?  

 

(I think it might be preferable to fit a second pully over the crankshaft pully like that kit does rather than replace the pulley for a bigger one, as I believe the crankshaft oil seal is formed against the pulley, not the crankshaft so I'd rather not disturb it if I can.

 

 

[Tony Brooks]

That link suggests its to allow you to fit a larger alternator the likes of which are sold by - guess who - Balmar, the kit makers, not to drive an existing alternator faster.

 

I don't know the shaft size of the pulley size of your alternator but it may be worth talking to @Sir Nibble to see if a smaller alternator pulley is available as a direct replacement.

 

You should NEVER charge at idle, always at the seed that gives maximum charge (amps) unless you are moving so the prop helps load the engine. It sounds to me as if your prop might be changed to a "smaller" one with advantage. It would give a higher engine speed for the same boat seed. You may be over propped. What is your flat out RPM when under way?

[BEngo]

Replacing a pulley with a larger or smaller one (according to which end of the drive you are at) has the big advantage that the Alternator stays lined up. Adding a DIY pulley means that you usually have to move the alternator to get the belt right.  You then often need new brackets and have to be careful about alignment.

Alignment in two planes is important, or you will use up belts in short order and everywhere will be covered in rubber dust.

When shrinking an alternator pulley you also need to watch that you get enough belt contact to drive the alternator without excessive belt slip at lower revs and high charge current.  The wrap angle needs to be at least 90 degrees to cope with typical small frame alternator loads and much more is better.    Poly V belts are also more tolerant than V or Wedge belts.  Making a bespoke pulley is quite easy and your local model engineers will probably help if you don't have the kit yourself.

 

N

[Tony Brooks]

and if its a V belt then if you are not already using a cogged/notched belt you should do so. They wrap a smaller pulley easier.

[malp]

Try here or Google "vee belts and pulleys"

 

I don't know the make of your alternator, but back in the day when I had to do this Lucas would supply a data sheet with a diagram plotting rpm against output, from which you can work out the pulley sizes needed.   Try the alternator maunfacturer's website, or get a phone number for technical support to request this info as a starting point.

[Sir Nibble]

2 minutes ago, malp said:

Try here or Google "vee belts and pulleys"

 

I don't know the make of your alternator, but back in the day when I had to do this Lucas would supply a data sheet with a diagram plotting rpm against output, from which you can work out the pulley sizes needed.   Try the alternator maunfacturer's website, or get a phone number for technical support to request this info as a starting point.

Good luck with that.

[wetfoot]

Yes, the company confirmed their fit doesn't change the ratio.

 

The alternator is a unipoint ALT 4036 which is the same as a Lucus A127, default pulley size is 66mm OD. engine speed is about 600rpm at idle and about 1,000 rpm flat out (whether prop engaged or not. Engine is a Yanmar 4JH4AE

 

@Patron: I don't understand why I shouldn't charge at idle, cars do it because their engines typically run faster.

Charging at idle would also load the engine nicely even if the prop isn't engaged.

 

The Lucas A127 needs about 3000 rpm to generate 60A  From memory the crankshaft pully is about 150mm diameter, so with a 66mm alternator pulley I'm getting about 1:2.3 ratio meaning the alternator is going at between roughly 1,360 rpm at idle to about 2,500 rpm when the engine is flat out, that would explain why I've getting little charge unless the engine is going fast.

 

By changing the alternator pulley to 45mm OD I would get alternator speeds of 2000rpm at idle to 3,666 rpm with the engine flat out at 1,1000 rpm so potentially getting a charge of between 45A and 65A. That would load the engine at idle to about 0.85 HP and 1,25 HP when flat out

 

The wrap would be about the same

 

Trouble is I can't find anywhere to get a 45mm OD V pully with a 17mm shaft bore.

 

 

Edited December 9, 2020 by wetfoot

[ditchcrawler]

33 minutes ago, wetfoot said:

 

 

@Patron: I don't understand why I shouldn't charge at idle, cars do it because their engines typically run faster.

Charging at idle would also load the engine nicely even if the prop isn't engaged.

 

  

In our car there is a definite brightening of the headlights if the engine is reved a bit above tickover, this is apparent when the car is on the drive facing the garage doors so I don't know how well it would be charging on tickover

[BEngo]

You have to make them.  Ordinary turning job, if you start with a bit of round bar.   IIRC  The included angle of the V is 39 degrees for all belt sizes and it wants to be 10mm wide at the outside for the normal Z section. Belt  section dimensions are easily found  online.  Try talking to the chaps at the local model engineering society. They will probably be happy to make one and always appreciate beer tokens!?

The job is well within a  Myford 7 series capacity.

The belt wrap on a 45 mm Z section pulley is not enough for a 70 A A127 without squealing and rapid wear at lower speeds.  Even with a cogged belt. Trust me, I have tried it. 

 

I think your power required expectations are a bit low.  You are right about the electrical demand but need to add in the mechanical and windage losses in the Alternator and a good dollop of power for the fan.  Something like 2 hp is nearer the mark at 3500 rpm and say 60 to 65 A at  13 V.

 

It will just work with a 6J poly V belt, but that means a new crank pulley too.  The smallest alternator  pulley I could get by with is 55mm  for a poly V belt.

 

N

[BWM]

Anyone reconditioning alternators will probably have a load of pulleys laying around, would be worth asking if you have one locally. 

[Oddjob]

On 06/12/2020 at 09:52, wetfoot said:

My sons boat has a Yanmar 4JH4AE engine and a ALT 4036 70A Unipoint alternator. 

As a expected, there is almost no output from the alternator at idle and only at a relatively fast idle , or slow boating speed, is there any charging of the battery.

 

I'm investigating changing pulley sizes to increase the alternator speed so that it charges at idle.

I found this conversion kit in the US but its very expensive.

 

Does anyone know of a similar kit in the UK to make the crankshaft pulley larger and the alternator pulley smaller?  

 

(I think it might be preferable to fit a second pully over the crankshaft pully like that kit does rather than replace the pulley for a bigger one, as I believe the crankshaft oil seal is formed against the pulley, not the crankshaft so I'd rather not disturb it if I can.

 

Speak with “4 countries marine services" he did an upgrade for me 90 amp alt with smaller pulley and it works like a dream. I have a Barrus engine with a travel pack he also replaced the bearings in it and fitted a free wheeling pulley that also was a first rate job.