How do it fit a second alternator?

[Puggy]

Hello all,

I have been puzzling this for a while as I have no experience of this and am not sure how to start. I apologise if this seems a elementary problem...

In my boat i have a 90hp Ford 2722 Dover 4 pot normally aspirated diesel of 1984 vintage. I has a single 75amp (i think) alternator charging a combined battery capacity of nearly 900ah... So, I have some expert help with the electrical bits and have amassed a second 110ah alternator and intelligent regulator and charge splitter relay system, ready for the big rewire next winter. The plan is to keep the existing alternator to charge the bow thruster batteries only, and the second alternator to charge the engine and domestics.

What i am struggling with is to understand how to mount a second alternator on my engine. Various manuals refer to the fact that you can fit one to the forward end left hand side as you look at it, but how do I actually do this? Are kits available? Do I get a bracket fabricated, and if so, does anyone have any drawings or description of what this should look like? I assume that alternator RPM is important: any advice on how to get this right. If anyone could offer any helpful advice or point me at any useful information, I would be very grateful.

Thanks in advance

 

[wooslehunter]

I have two fitted & am considering removing the one that's bodged on. The one that's intended to be there is attached to the engine. The other is attached to a bracket on the engine mount & is not free to move with the engine vibration. There's a pulley welded to one of the pulleys on the front of the engine & it runs from that. I'm not convinced that this is a good idea since it restricts the movement of the engine on its mounts. It's been there for years though & I would have expected the bearings in the alternator to have given up by now if it was a problem.

But, if you are mounting a second one, do as you seem to be doing & mount it on the engine.

 

[Puggy]

Yes I agree. I will make sure it is mounted on the engine...

 

[Tranona]

Unless there is a twin alternator option on the engine (doubtful) you are on your own designing and making attachments and the double pulley you will need. You may be better looking at replacing the current alternator with a higher output one such as a Balmar. Fully charging a bank of you capacity just with an engine driven alternator will be a challenge whichever way you do it.

 

[mitiempo]

A custom bracket is common. Make sure the second ald is on the opposite side to balance crankshaft loads.

The thruster should never be in need of enough amps to dedicate an alternator to it. I think you would be better off using a device like an Echo Charge for the thruster battery and using both alternators for the large bank - that will make a lot more difference to charge times than your plan will.

 

[gordmac]

Fitting the 110ah one in place of the 75ah one would give significantly more charging capacity, would that not be enough on it's own? Other than that you need to mount the second one on the opposite side of the engine and get another pulley on the crankshaft to drive it, if they are available off the shelf (Lancing?) wouldn't be too bad a job to do.

 

[pvb]

The plan is to keep the existing alternator to charge the bow thruster batteries only, and the second alternator to charge the engine and domestics.

This is not a good plan. Despite high current consumption, bowthrusters are used for very short periods, so Ah consumption is relatively low and can easily be replaced from normal charging sources, ie there's no need for a dedicated alternator.

You mention 900Ah of "combined battery capacity", and as you've mentioned "bow thruster batteries", I'd imagine you have around 150-200Ah of thruster batteries, 100Ah of starter battery and some 600Ah of domestic batteries.

On this basis, replacing your existing 75A alternator with the 110A alternator and its smart regulator will probably achieve improved results with minimum cost.

If you want to fit the 110A alternator as a second alternator, you'll need to get a suitable bracket fabricated and fit a second crankshaft pulley. It's not necessarily difficult, but don't underestimate the vibration and other forces on an alternator bracket - it needs to be substantial. The second alternator bracket on my Volvo Penta engine is very robustly engineered. As for alternator RPM, if your second crankshaft pulley is the same size as the original, the revs should be OK. But if you do fit both alternators, then ensure that both are controlled by the smart regulator, and combine their outputs so that you have optimum charging.

 

[outtametree]

My bukh has 2 alternators fitted, you're welcome to come & have a look, different motor, but may give you some ideas. Boats in Southampton.

 

[Talulah]

I fitted a second alternator to our Yanmar 4JH4E.
Yanmar do a kit but it didn't fit properly and was incredibly expensive.
In the end the only part of the kit I used was the additional pulley wheel that bolts to the face of the existing pulley wheel. The alternator mounting bracket and adjustment arm I had made up.
It took a couple of goes before I was happy with it but now it's all done and dusted without problems.
The alternators are Bulmar with external regulators. Both domestic and engine battery banks are now fully independent of each other. Each having their own alternator. There is still the 1,2,Both, Off switch.

 

[Gumpy]

I have a similar engine D6 and have a second alternator mounted on the engine beds, this is not a problem as the engine is hard mounted on wooden blocks so very little movement.
I have one alternator charging the domestics that runs off a second 11 inch drive pulley bolted in front of the original pulley , the original alternator charges the starter and navigation system batteries. You will have to fabricate it all yourself although Lancing marine made the pulley for me.
Its been running well for ten years but my only regret is that I didn't go for a multi V belt and the single belt sometimes struggles with 75amps at 24v

 

[LadyInBed]

I have a 12v and a 24v alternator, the 24v one is driven off a 2nd pulley on the 12v alternator.
This isn't a great arrangement as when the 12v Alt belt is retensioned the 24v belt also has to be done, and it puts extra strain on the 12v belt.
I have a spare pulley on the fly wheel but to use it I would have to move the 24v Alt as I can't find a long enough belt for its current position.
I will get round to doing it one day

If you don't actually need a 2nd alternator stick with one.

 

[Monique]

Unless there is a twin alternator option on the engine (doubtful) you are on your own designing and making attachments and the double pulley you will need. You may be better looking at replacing the current alternator with a higher output one such as a Balmar. Fully charging a bank of you capacity just with an engine driven alternator will be a challenge whichever way you do it.

I have 2 generators on my engine; received from the PO. I agree with Tranona, it is inevitable the system will be a "Rube Goldberg". It is on my boat.

Also, I do not understand why you would want to have one alternator charging the Bow thruster and not the rest of the system. You can also isolate your engine start battery with a simple switch.

A single large genny would be my choice. GL and keep us posted.

 

[TrueBlue]

First, my tale of challenges.
I bought a custom power plant from Beta, who are well known for "specials". I consisted of 1 24v 175 amp alternator and a 5KW 240 SeaPower generator. The alternators were mounted off the engine bearers via a very impressive cross-your-heart-bra arrangement of struts mainly to get the geometry right for the upper belt tensioning mounts. Very solid, very well made.
Over a period of time (six years before any problems), some bits have fractured and so on. The belts were double "A" and "B" driven by two huge double row 10" pulleys on the crankshaft. Last year these sheared the drive shaft and fell in the bilge.

Now the system is redesigned, much lighter and working well.

My point is this:-
Even an industrial type engine is beefed up for added bits of power take-off, but most of this is intended to be at the rear end. The front end is weaker in this respect.
You may do the calculations: and think, well a couple of HP is not much of an extra load. However folks ignore the shock loading (my engine runs stop / start in short running periods - river / canal working), and that puts a large torque load where it's not expected.

Two suggestions:-

Beef up the current single alternator to a larger size - you suggest 110 amps. BUT only up to the maximum that the drive pulley and belt section can accommodate.
Fit a toothed belt (BearingBoys have these available, by post at good prices). My standard belts lasted a season with luck and there was always a burning smell... Toothed belts lasted for at least two seasons before the bits fell in the bilge.

If you MUST fit an extra alternator:-
Investigate the possibility of fitting Poly-V belt to both as they can transmit more power and the drive pulleys will be alloy, reducing the torque load. Beta do a two generator pulley kit which MIGHT be adaptable.

To do the two alternator solution should really need an "engine out". It's horrendous to take measurements and later fit brackets in a cramped engine room. OK if you're mechanically competent and have a tame engineer / blacksmith / workshop near to hand.

Been there, done it, got the fuel bills and bleeding knuckles to show for it.

Electric wires and electronics don't require muscle to fit..

 

[Ludd]

If you do fit a second alternator,try to get one with the same mounting points a s the current one. Then if the main one(which will be driven by the same belt that drives the waterpump) has a bearing failure ,you can swap them.
I had to do a cobble up on someone elses engine because of different mounts----no use producing amps if the coolant ain't circulating!

 

[Puggy]

Thank you all very much for input. My conclusions are that a second alternator may not be worth the engineering and reliability aggravation it entails. Reading all the posts, I am coming to the conclusion that a single high output alternator intelligently split between the batteries might be a better solution in terms of reliability and efficiency. I think i will look into this. I already have an additional alternator, but it may not be big enough on its own, so might be putting it on eBay.

Sorry about delay in replying. Been upside down in my engine room trying to work out why my elderly Paguro genny would run for 10 mins and then overheat - jamming thermostat I think (hope...) - trying to source a replacement.

Shame about Beaulieu Boat Jumble being cancelled - the highlight of my year (I must get out more..)

Piers

 

[pvb]

...I am coming to the conclusion that a single high output alternator intelligently split between the batteries might be a better solution in terms of reliability and efficiency. I think i will look into this. I already have an additional alternator, but it may not be big enough on its own...

Remember that an ordinary single V-belt will struggle to drive much more than a 90A 12v alternator. If you're considering much bigger than your existing 110A alternator, you'll need to engineer a twin belt drive system, or a different type of belt.

 

[Puggy]

Remember that an ordinary single V-belt will struggle to drive much more than a 90A 12v alternator. If you're considering much bigger than your existing 110A alternator, you'll need to engineer a twin belt drive system, or a different type of belt.

Ok will do thanks. I have a single belt at the moment so will look at this.