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Old 27-01-2010, 21:52   #1
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Dual Alternator Tensioning with Turnbuckle ?

Greetings Gentlefolk,

I'm not sure whether this question belongs in this forum since it's actually about the mechanical aspects of alternators as opposed to their electrical aspects, so apologies in advance..

After reading through a bunch of posts about how many people are running 4 trillion amp alternators completely lopsided off their small engines, I decided to bite the bullet and follow suit...

After doing some research on this topic, it appears that the biggest problem is indeed side load, and stalling the little engines at idle etc.

So to solve both of these problems, I decided to go for TWO industrial alternators which don't put anything out below about 2000 (alternator) rpm, and to have a new crankshaft pulley fabricated such that I can have 2 x 1/2" belts on each alternator, and mount them in front of the engine backwards, on either side of the crankshaft pulley such that they are exactly opposite each other.... voila! no side load (theoretically).

(the alternators are mounted on a big hunk of steel that is bolted to the engine mounts - on the engine - not the bed - so the engine and alternators move together)

Now, my question here is - since I have two alternators directly opposite each other, on a common base, with the crankshaft pulley in the middle - can I use a large turnbuckle or threaded rod between the upper alternator mounting holes to tension both alternators at the same time? My theory here is that by using a central common tensioner and pushing the alternators away from each other this way, the load on the crankshaft pulley will always be balanced.

Am I missing something or is this OK?

Photo attached showing the mounting base for the alternators and pulley (without the alternators mounted yet though although the two alternators are Bosch BXU12121A's (120A),) and the brand spanking crankshaft pulley has three pitches: 70mm for water pump">raw water pump per original pulley, 110mm for watermaker (1725 rpm at high pressure pump at 2800 engine rpm - yanmar manual states that this is ideal cruising rpm for this engine - highest power for lowest fuel consumption), and finally 155mm for the alternators.

Pulley is machined from K1045 high carbon steel, which I'm hoping will be strong enough to deal with the short shaft and long overhang, despite the loads being well balanced).
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Old 27-01-2010, 22:40   #2
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That seems like a lot of overhang, but I'm no pro.

I'm also very curious about others' real world experience using turnbuckles to maintain proper tension for second/duo alternators. It seems a lot of the aftermarket alternator mounts use turnbuckles, is engine vibration an issue on maintaining correct tension?
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Old 03-02-2010, 19:25   #3
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Last summer, we had a bolt head shear off from the belt tensioner bracket. Looking around for a better idea, we saw the engine set-up in a small trawler which used bronze turnbuckles, in tension. The turn buckles were kept tight by nice bronze cotter pins...looked like a nice set-up.
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Old 03-02-2010, 20:12   #4
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That looks like it could generate excessive side load.

Have you looked at AltMount.com - Welcome - Mount a second alternator to your Yanmar 4JH4 marine engine?

I have one with a 140amp @24v alternator. It is one fine piece of equipment.
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Old 03-02-2010, 20:17   #5
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Originally Posted by CAELESTIS View Post
That looks like it could generate excessive side load.

Have you looked at AltMount.com - Welcome - Mount a second alternator to your Yanmar 4JH4 marine engine?

I have one with a 140amp @24v alternator. It is one fine piece of equipment.
Howdy,

Unfortunately I've had the mounts fabricated for the alternators already, however there will be zero side loan on this as there will be one alternator on each side of the big pulley - exactly 180 degrees apart (I've removed the stock alternator + mounting too, so the only other "unbalanced load" will be the raw water pump which is tiny).

Anyway, this is all theoretical, until I fire it up.
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Old 03-02-2010, 20:54   #6
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An interesting idea, the only thing I could think of is once the tension is set the pivot bolts on the alternators are tightened to prevent any clattering or movement. This limits any movement. Should one of the alternator output be higher for whatever reason than the other then that set of belts will wear a little more than the other.
Have no clue as to how much of an imbalance in loading if any, probably very very minor.
In any event after a short run in period you may want to readjust the balance and tension of the belts.
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Old 03-02-2010, 22:40   #7
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Years ago, when I worked in a boatyard, a customer wanted to do this. He was going to cruise the world

He had a similar pulley made (a thing of beauty)
The Loads were, two alternators, water pump, and jabsco fire pump (with a manual clutch).....and a refrigeration pump

I was asked my opinion and said for the size boat, she will smoke like a bandit and not get out of it's own way......I was voted down......

It was slow and smoky

The boat has never left the harbor other than day sails
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Old 04-02-2010, 00:30   #8
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Quote:
Originally Posted by akio.kanemoto View Post
BXU12121A's (120A),) and the brand spanking crankshaft pulley has three pitches: 70mm for raw water pump per original pulley, 110mm for watermaker (1725 rpm at high pressure pump at 2800 engine rpm - yanmar manual states that this is ideal cruising rpm for this engine - highest power for lowest fuel consumption), and finally 155mm for the alternators.
Looks like a great set up good luck with it, making electricity water and speed at the same time is attractive. My only comment is 2800 is high. Diesels like to be run hard, but you are likely to find that the ideal crusing revs, balancing noise. speed fuel consumption and engine life is a few hundred revs lower. I hope this does not throw out the watermaker speed to much. 2800 may be the "highest power for lowest fuel consumption" for the engine , but when coupled to the boat the results will be different
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Old 04-02-2010, 02:16   #9
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Looks like a great set up good luck with it, making electricity water and speed at the same time is attractive. My only comment is 2800 is high. Diesels like to be run hard, but you are likely to find that the ideal crusing revs, balancing noise. speed fuel consumption and engine life is a few hundred revs lower. I hope this does not throw out the watermaker speed to much. 2800 may be the "highest power for lowest fuel consumption" for the engine , but when coupled to the boat the results will be different
Do you mean when driving a prop? Or you mean due to mounting vibration etc?

Just to clarify - the alternators will only charge at anchor, while not driving the prop at all, during the daily charge cycle. When driving the prop, the alternator regulator (and hence fields) will be off, or field will be driven at only 50% duty if really really required for some reason (while moving).

There will be a solar panel in the equation as well, so the start batt should always be happy.

My theory here is that the engine will operate in two modes - one as a DC genset, and the other, as an engine. Not both at the same time.

I will mount the alternators in the next couple of days and will take some pics when done and post.
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Old 04-02-2010, 02:19   #10
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Originally Posted by Chief Engineer View Post
Years ago, when I worked in a boatyard, a customer wanted to do this. He was going to cruise the world

He had a similar pulley made (a thing of beauty)
The Loads were, two alternators, water pump, and jabsco fire pump (with a manual clutch).....and a refrigeration pump

I was asked my opinion and said for the size boat, she will smoke like a bandit and not get out of it's own way......I was voted down......

It was slow and smoky

The boat has never left the harbor other than day sails
Just out of curiosity - did he drive the prop at the same time or did he turn off the fields of the alternators when he wanted to go somewhere?

I'm hoping that when driving the prop (and the alternator field current is off), there will be little to no load on the front pulley at all so all the usable output will go to the prop - do you think that just having the pulley spin the unloaded alternators would cause too much load in terms of friction etc?
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Old 04-02-2010, 02:29   #11
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An interesting idea, the only thing I could think of is once the tension is set the pivot bolts on the alternators are tightened to prevent any clattering or movement. This limits any movement. Should one of the alternator output be higher for whatever reason than the other then that set of belts will wear a little more than the other.
Have no clue as to how much of an imbalance in loading if any, probably very very minor.
In any event after a short run in period you may want to readjust the balance and tension of the belts.

Thanks for that - I will definitely crank down on the foot - although one thing that's not apparent with the pic above (yet!) is that the turnbuckle (threaded rod actually) will go directly between the alternator bolts (the one opposite the pivot point/foot). So the alternators will always be pulling against each other and the theory is that by cranking up the tension on the threaded rod (i.e. moving the nuts/locknuts apart from each other on either or both ends against the alternators) - then both sets of belts will be tensioned at the same time and both sides will be at exactly the same tension.

I must say though that I didn't think of the situation wherein one alternator works harder than the other.. I'm hoping (doing a lot of that recently... ahem..) that since my regulator (SAR V3) will be driving the fields in parallel (off the same circuit/wires) - that the load will be the same... Which I'm hoping (here I go again..) leaves just manufacturing issues for variances in loading.. and I'm hoping (... uh oh..) that Bosch has at least this part worked out for me.
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Old 04-02-2010, 02:43   #12
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When we installed our second alt. I put it opposite the direction of the existing belt.
The thought was this would negate the original side pull....and actually make things better.
The only concern I see with a single turn buckle, holding both alts. is if you loose a belt on one side it will cause both sides to go slack.

You still have the issue of how much load you're going to put on the engine...but thatís something else.
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Old 04-02-2010, 03:19   #13
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When we installed our second alt. I put it opposite the direction of the existing belt.
The thought was this would negate the original side pull....and actually make things better.
The only concern I see with a single turn buckle, holding both alts. is if you loose a belt on one side it will cause both sides to go slack.

You still have the issue of how much load you're going to put on the engine...but thatís something else.

Very good point. although I'd have to lose a set of belts on one side (two belts per alternator) before losing tension completely, I wonder if one belt breaks, whether it will make noises or something that will warn me?

On the load issue - total load per alt is 120A x 14V = 1680W. 1680W/746 = 2.25HP. Add in a huge fudge factor for inefficiencies/friction etc and call it 3HP per alternator. So theoretically, together it will be maximum 6 HP, balanced.
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Old 04-02-2010, 03:36   #14
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[QUOTE=akio.kanemoto;394877]

Now, my question here is - since I have two alternators directly opposite each other, on a common base, with the crankshaft pulley in the middle - can I use a large turnbuckle or threaded rod between the upper alternator mounting holes to tension both alternators at the same time? My theory here is that by using a central common tensioner and pushing the alternators away from each other this way, the load on the crankshaft pulley will always be balanced.

If I understand what you are trying to do, no it will not work.
I tried this in a different setting, they wanted to walk.
The lower bolts where not dependable in holding against the combined torque. If one is fastened in place you can tension the other against it. It did work, in the short haul, it was not dependable, they as a unit wanted to rotate until one found something to lean on. YMMV.
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Old 04-02-2010, 03:41   #15
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Like Chief says "A thing of beauty" Just one question. What off sets the side loading of the watermaker pump?
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