Slow running engine/alternator ideas

[Doodlebug]

Hi all, I am hoping someone who is better at problem solving than me might have some ideas.

The engine in the boat has a lowest tickover speed of 200rpm, a generally acceptable speed of 300-500rpm and then its absolute top speed is 1030rpm.

The problem is that the alternator that came with it is a 10inch to 2.5inch pulley system…

 

This means at tickover it runs at 800rpm and at full whack it runs at 4060rpm. This is clearly no good for generating usable power. The 120a alternator I would like needs at least 5000rpm to give its full output.

 

The 10 inch pulley can not be increased in size because it hits the water pump and the oil cooler. I can change the alternator to 2in but that only marginally helps.

 

Does anyone know of a system that could help? Ideas so far include using a secondary pulley to increase the speed (but how to mount this to the engine). I could use a planetary gearbox on the alternator (has this ever been done). I could use a marine gearbox in reverse to speed up the rpm and then use a pulley as normal.

 

Does anyone have any other ideas that could work?!

 

Many thanks

 

[MtB]

What engine is this?

 

 

(And why the strange tineeee writing!)

[Doodlebug]

1 minute ago, MtB said:

What engine is this?

 

 

It’s a Ruston Hornsby 35hp 3ydz 

 

I measured the speeds yesterday - I know it can go faster but not with the set up I’ve got 

[Tracy D'arth]

Had to change my glasses to read your post.

 

What engine?  Does it have a flywheel that you could put a link belt on? 

[MtB]

3 minutes ago, Doodlebug said:

It’s a Ruston Hornsby 35hp 3ydz 

 

I measured the speeds yesterday - I know it can go faster but not with the set up I’ve got 

 

Nice! 

 

Does it have an exposed flywheel? If yes, you can use this as a pulley simply by wrapping a vee belt around it. They do stay in place despite the absence of a vee groove. If it works ok, you can then get a groove machined in the flywheel.

 

[Tracy D'arth]

Just now, Tracy D'arth said:

Had to change my glasses to read your post.

 

What engine?  Does it have a flywheel that you could put a link belt on? 

A bit slow answering.

 

So it has a flywheel.  Many vintage engines use a vee belt running on the flywheel without a groove perfectly well.

You could even mount the alternator on the floor as your engine is probably ridgid mounted and doesn't move.

Alternators will run happily in reverse with the right fan on if need be, so it could be fitted facing backwards instead of normal.

Link belts mean that you can fit a belt without taking the drive shaft and/or gearbox off.

[David Mack]

18 minutes ago, MtB said:

Does it have an exposed flywheel? If yes, you can use this as a pulley simply by wrapping a vee belt around it.

 

Or fit a polyvee pulley to the alternator and run a polyvee belt on the flywheel rim. 

[Doodlebug]

Unfortunately the flywheel is totally enclosed! Please see the below picture

 

 

[Eeyore]

Picture of existing setup please.

 

[Tracy D'arth]

Two holes cut into the cover would allow  a link belt to be fitted. There is an access panel to aid fitting.

[Doodlebug]

13 minutes ago, Tracy D'arth said:

Two holes cut into the cover would allow  a link belt to be fitted. There is an access panel to aid fitting.

I think that the flywheel is about a 5mm gap between the case and the flywheel so not enough space for this to be fitted. I guess it could be totally taken out and cut but thats a major job. 

 

What do you all think of the gearbox (or use of a spur gear set up or chain and sprocket?)

 

Thanks

[MtB]

26 minutes ago, Eeyore said:

Picture of existing setup please.

 

 

Seconded. A View of the crankshaft pulley and existing alternator and drive belt please.

 

Moving the water pump and oil cooler to fit a bigger pulley is beginning to look like the most viable. Or extending the crankshaft nose so a bigger pulley clears them.

 

[David Mack]

What is the origin of the engine? Marine versions usually had an open flywheel on the front. If it's a converted industrial, then the gearbox isn't the PRM one would normally find.

I think your best solution is going to be to fit a secondary shaft at the front end, probably mounted direct to the engine beds (or a suitable bracket attached thereto). The existing 10" pulley would drive a small pulley on the secondary shaft, with a large pulley to then drive the alternator, also fixed directly to the engine beds/hull. As suggested above, it may fit in better with the alternator mounted the other way round.

[Doodlebug]

I don’t have very good pictures on my phone and not with the boat right now. 
 

You can just make out the oil cooler and the water pump in the picture. 

23 minutes ago, David Mack said:

What is the origin of the engine? Marine versions usually had an open flywheel on the front. If it's a converted industrial, then the gearbox isn't the PRM one would normally find.

I think your best solution is going to be to fit a secondary shaft at the front end, probably mounted direct to the engine beds (or a suitable bracket attached thereto). The existing 10" pulley would drive a small pulley on the secondary shaft, with a large pulley to then drive the alternator, also fixed directly to the engine beds/hull. As suggested above, it may fit in better with the alternator mounted the other way round.

 

It is off a generator off of a ship so would have been the industrial type I believe. 

[Eeyore]

Is there much clearance at the back of the alternator?

What is the direction of rotation? red or yellow arrow?

Which 120amp alternator are you thinking of?

Edited March 4 by Eeyore

[Doodlebug]

3 minutes ago, Eeyore said:

Is there much clearance at the back of the alternator?

What is the direction of rotation? red or yellow arrow?

I believe the red arrow but does it make a difference? 
 

it’s quite hectic behind. Here is another photo and pipe might need moving but that’s not impossible. Why what were you thinking? 
 

pulleys on a pillow block might might work? 
 

 

[IanD]

The other alternative is to fit an alternator with higher output current at lower rpm than the one you've got -- which doesn't always mean the highest current rating one, sometimes this only kicks in at even higher rpm.

 

What model alternator do you have, and do you know how its current varies with rpm?

 

 

[Eeyore]

2 minutes ago, Doodlebug said:

I believe the red arrow but does it make a difference? 
 

it’s quite hectic behind. Here is another photo and pipe might need moving but that’s not impossible. Why what were you thinking? 
 

pulleys on a pillow block might might work? 
 

 

Yes, I think David Macks idea will fit below the alternator. The intermediate shaft mounted on two bearing (on a suitable bracket). Both pulleys at one end for a forward facing alternator, or one each end for an aft facing alternator. Depends which gives the clockwise rotation required by most modern integral fan alternators.

[magnetman]

Maybe don't use the engine as a charging set. 

 

When I had a RN DM2 it used to put a little bit in via the alternator when Boating and if I was stopped for a few days I just ran a small Honda genny for charging. 

 

It depends on your usage pattern but I tend to think when people start asking questions about alternators they might be using the engine when stationary to charge batteries which in my opinion is not appropriate. 

 

 

 

8 minutes ago, IanD said:

The other alternative is to fit an alternator with higher output current at lower rpm than the one you've got -- which doesn't always mean the highest current rating one, sometimes this only kicks in at even higher rpm.

 

What model alternator do you have, and do you know how its current varies with rpm?

 

 

Leece Neville large frame alternators are quite popular for this. Buses, large marine engines, trucks etc. 

 

 

[Doodlebug]

1 minute ago, magnetman said:

Maybe don't use the engine as a charging set. 

 

When I had a RN DM2 it used to put a little bit in via the alternator when Boating and if I was stopped for a few days I just ran a small Honda genny for charging. 

 

It depends on your usage pattern but I tend to think when people start asking questions about alternators they might be using the engine when stationary to charge batteries which in my opinion is not appropriate. 

 

 

 

I agree that running an engine for hot water and trickle charging is not suited but putting a 120a load on it to charge lithiums is going to be good load on the engine - which after all was built for generating power? 

8 minutes ago, Eeyore said:

Yes, I think David Macks idea will fit below the alternator. The intermediate shaft mounted on two bearing (on a suitable bracket). Both pulleys at one end for a forward facing alternator, or one each end for an aft facing alternator. Depends which gives the clockwise rotation required by most modern integral fan alternators.

This could work - I will investigate how the engine is mounted because if I can bolt to the floor it would be ideal! 
 

I wonder how I would tension the pulley though. 

[magnetman]

12 minutes ago, Doodlebug said:

I agree that running an engine for hot water and trickle charging is not suited but putting a 120a load on it to charge lithiums is going to be good load on the engine - which after all was built for generating power? 

 

When it was a generator it would have been on a direct drive not a side loading belt drive. 

 

 

belt drives can be a problem unless a lay shaft is used. This has been suggested and is a good approach but quite complex to execute. 

[Eeyore]

14 minutes ago, Doodlebug said:

I agree that running an engine for hot water and trickle charging is not suited but putting a 120a load on it to charge lithiums is going to be good load on the engine - which after all was built for generating power? 

This could work - I will investigate how the engine is mounted because if I can bolt to the floor it would be ideal! 
 

I wonder how I would tension the pulley though. 

A sliding mount for the secondary shaft bracket will work with the existing (primary) belts.

A polyvee 6PK belt with a tensioner pulley running on the back of the belt will allow for a fixed relationship between the secondary drive pulley and alternator, and will provide additional wrap (belt contact) on the smaller alternator pulley.

Edited March 4 by Eeyore

[magnetman]

 

No idea what the rating is but side loads with heavy power use go straight to the pulley so this part needs to be well sorted. Beta marine had problems with pulleys and big alternators at one time. I wonder if it might be worth putting two alternators on opposite each other. 

[IanD]

https://www.sp-shop.co.uk/Sterling-Power-Hi-Perfomance-12v-140A-Alternator-PN-AL12140.html

 

130A at 4000rpm, 95A at 2000rpm

 

 

[Doodlebug]

6 hours ago, IanD said:

The other alternative is to fit an alternator with higher output current at lower rpm than the one you've got -- which doesn't always mean the highest current rating one, sometimes this only kicks in at even higher rpm.

 

What model alternator do you have, and do you know how its current varies with rpm?

 

 

Unfortunately the alternator has been painted but is only 40a and I want to avoid buying a generator for this use. The engine should be able to deliver the power and with a trad stern using a generator would be a pain. 
 

5 hours ago, IanD said:

https://www.sp-shop.co.uk/Sterling-Power-Hi-Perfomance-12v-140A-Alternator-PN-AL12140.html

 

130A at 4000rpm, 95A at 2000rpm

 

 

It looks like they might have discontinued these as they are all out of stock 😔