Rearranging alternator belt setup?

[nigelmercier]

My boat has two alternators: a 50A 24V one (on the left in this picture) and a 120A 12V one which works quite hard.

The 12V alternator has a 9mm belt (I know), and as a result it often slips. I think that the 24V is also 9mm.

I've been considering various ways to upgrade the 12V belt: single or dual 12mm, or serpentine etc. However, yesterday I suddenly had a thought: drive the 24V and the water pump from the same belt, and drive the 12V on its own.

Thoughts?

 

[Talulah]

The 24V alternator protrudes this way slightly further than the water pump and the 12V alternator.
The belts wouldn't line up properley if you did what you propose.
You could add another pulley on the front of the existing water pump pulley to get the alignment right.
This would leave the rear water pump pulley empty. Not a problem other than that.

Alternatively swap over the 24V and 12V alternators and change the cables to match.

 

[Lakesailor]

Unless you swap the alternators over (alternator pulleys need swapping as well) and the wiring needs altering.

Or put a bigger drive pulley on the 12v alternator.
Two advantages. It will spin more slowly so won't have such resistance and the belt wrap around the pulley will be greater.
Disadvantage. The alternator will charge more slowly.

Funny. I didn't see Talulah's edit until after I had posted.

 

[old_salt]

Quote:-The alternator will charge more slowly.

Yes but if the RPM is sufficient then the 12v alternator will have kicked in and be OK
A bigger pulley on the 12v alternator would be my suggestion as well.

I am fiddling with a 24v Bosch alternator on the horsey box as The grandson call it the ignition light keeps coming on/off when we where out this last W/E. striped and freed the brushes, cleaned all the dust out of the brush holder checked the slip rings a bit worn but OK so will see what happens when I put it back on after lunch oops it's turned 2 already how time go's.
A new 24v Bosch alternator full price £400+ "ouch"

 

[nigelmercier]

OK, so assuming I have move them fore and aft (which I had considered) any reason not to do this?

 

[pvb]

OK, so assuming I have move them fore and aft (which I had considered) any reason not to do this?

None at all. Without changing the pulley on the 12v alternator, you'll still achieve more wrap for a better drive. It also means you'll be able to tension the belt more on the 12v alternator without putting undue load on the water pump bearings.

 

[old_salt]

There is another way you really need to keep the water pump driven by it's existing pulley so if the two alternators have the same shaft size and the pulleys will swap over leave the alternators where they are swap the pulleys and drive the 24v and water pump from the larger back crank pulley and the 12v from the the smaller dia front pulley as just driving by the larger back pulley would maybe over speed the 24v alternator I think the 12v will cope with the small difference in rpm with the drive pulley off the 24v it should be a better balance there might be a bit of engineering to the alternator brackets to get the belts all lined up.

 

[rogerthebodger]

I had a very similar arrangement to yours and I changed it to separate belts.

I replaced the single outer pulley with a double groove pulley and changed the belt to Fenner alpha belts which have a greater drive capacity to 'A' section belts.

The down side was that I had to fit a tensioning jockey pulley for the water pump belt as the pulleys are fixed centres where as the alternators centres are adjustable.

If you do consider the fenner alpha belts do check the depth of the grooves so the belt has the required side contact area.

 

[Marsupial]

My boat has two alternators: a 50A 24V one (on the left in this picture) and a 120A 12V one which works quite hard.

The 12V alternator has a 9mm belt (I know), and as a result it often slips. I think that the 24V is also 9mm.

I've been considering various ways to upgrade the 12V belt: single or dual 12mm, or serpentine etc. However, yesterday I suddenly had a thought: drive the 24V and the water pump from the same belt, and drive the 12V on its own.

Thoughts?

Its a tough call, ideally you want the lightest load on the one that uses the water pump pulley to reduce the load on the water pump bearings - but both alternators are pretty similar in power so little point in swapping them over. Toothed belts would be my choice as they don't slip and are self aligning.

 

[pvb]

Its a tough call, ideally you want the lightest load on the one that uses the water pump pulley to reduce the load on the water pump bearings - but both alternators are pretty similar in power so little point in swapping them over.

The alternators may be similar in terms of maximum power capability, but I'd guess that the 24v one isn't loaded very heavily, whereas the OP has said that the 12v one "works quite hard".

 

[nigelmercier]

... you really need to keep the water pump driven by it's existing pulley so ... leave the alternators where they are ... and drive the 24v and water pump from the larger back crank pulley and the 12v from the the smaller dia front pulley ...

That's what I meant.

 

[superheat6k]

If this were me I would see if I could swap the fore and aft alignment, then make the 24v part of the triple set, but I would also swap the two alternator driven pulleys, this will keep ratios about the same, and will provide increased drive area for the 24v.

You could then also investigate availability of double pulleys for the 12v driver and driven. I would keep the notched belts as these grip better and run cooler.

There are formulas for working out belt circumference length, or just use some 10 mm rope with the alternators mid position to gauge the new circumference ranges.

Found this double pulley on eBay for the alternator 221277614203 £18.50. Still looking for the crank mounted pulley, but would likely need the PCD of the mount bolts.

 

[Marsupial]

The alternators may be similar in terms of maximum power capability, but I'd guess that the 24v one isn't loaded very heavily, whereas the OP has said that the 12v one "works quite hard".

Yes but the 12v one will work quite hard where ever you put it. Swapping the alternators from one side to the other will involve changing the wiring and I am not sure the benefits will justify that. The 120A 12v alternator is on the ragged edge as far as driving it from a single v belt is concerned, and the 24v machine is not far behind it. Let's assume the ratios for each device are reasonably correct (but see below) all we have to do is improve the drive system for the 12v alternator without increasing the bearing side loading, a toothed belt will do that. The belt wrap on the 24v maybe its saving grace but while you are re-engineering the 12v side you might as well do the other one. You COULD put a double thickness toothed pulley on the crankshaft and drive both from the same diameter with two belts of course (this would improve the output of the 24v machine) - and its self aligning.

 

[macnorton]

Fit another pulley and drive the 12v off that, fit a tensioner to drive the water pump.
3 belts.
You could then use a flat belt dive on the 12v if you wanted.

 

[pvb]

Yes but the 12v one will work quite hard where ever you put it. Swapping the alternators from one side to the other will involve changing the wiring and I am not sure the benefits will justify that. The 120A 12v alternator is on the ragged edge as far as driving it from a single v belt is concerned, and the 24v machine is not far behind it. Let's assume the ratios for each device are reasonably correct (but see below) all we have to do is improve the drive system for the 12v alternator without increasing the bearing side loading, a toothed belt will do that. The belt wrap on the 24v maybe its saving grace but while you are re-engineering the 12v side you might as well do the other one. You COULD put a double thickness toothed pulley on the crankshaft and drive both from the same diameter with two belts of course (this would improve the output of the 24v machine) - and its self aligning.

Too complicated. The 12v alternator run on a direct belt would be fine. It's unlikely ever to put out much more than 90-100A, which is OK with a single belt, given sufficient wrap and tension.

 

[William_H]

I think the 24 v alternator should be moved to the other side and run from the water pump crank pulley. This will be the lightly loaded alt. charging engine start battery only.
The 12v alternator can then be run off the existing crank shaft additional pulley or better still increase the size of both alt. and crank pulleys to reduce load by increasing belt speed or go for double pulleys or flat belt type.
A competely different approach might be to laeve as is but fit an alternator to battery charger running off the 24v system. ie a 24v to 12v converter as a battery charger running via a VSR. You will have redundancy for 12v systems charging or share charging of 12v batteries between 2 alternators by separating 12v batteries. good luck olewill

 

[Marsupial]

Too complicated. The 12v alternator run on a direct belt would be fine. It's unlikely ever to put out much more than 90-100A, which is OK with a single belt, given sufficient wrap and tension.

No its LESS complicated - fewer components and no alignment issues

 

[nigelmercier]

Thanks for the replies.

I certainly don't want to move the alternators from one side to the other, and I don't see the point. My plan was meant to be simple, and assuming I can move them fore-aft I think it will be. The 12V alternator is a Balmar, and is quite happy at lower RPM.