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Old 04-02-2010, 03:47   #16
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[QUOTE=Woodsy;398486]
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Originally Posted by akio.kanemoto View Post

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.

Both of the alternator feet are bolted to the same base plate with the alternator boss through-bolted onto 8mm thick steel mounting points welded onto the base itself. The base plate is stupidly overengineered and if anything rotates here by bending anything, I will eat my hat. (famous last words. To give some further info - I designed and calculated the steel thicknesses etc for a 300kg cantilevered load and the alternators are only about 8kg all up. So the mounting itself weighs about 7-8kg, reinforced specifically for torque/loads. The only thing that I can vouch for in this application as an absolute is that the mounting won't bend/flex/break.

Unless you're referring to the alternators both leaning towards one side - but I don't think that will be possible with the belt of the opposite alternator pulling against the central crankshaft pulley and preventing movement in that direction (and visa versa).
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Old 04-02-2010, 03:50   #17
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Originally Posted by Tellie View Post
Like Chief says "A thing of beauty" Just one question. What off sets the side loading of the watermaker pump?
This is the only unbalanced load - so my theory is that since it is small, and the pulley groove on the crankshaft is almost at the face (not extended like the alternator grooves further out), the load should be insignificant - this one, I'm not worried about as it is closer than the standard alternator groove and will draw less HP than the stock alternator.

All theory of course.
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Old 04-02-2010, 04:08   #18
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Originally Posted by akio.kanemoto View Post
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.
To be able turn the alternator field off or 50% is great idea. Sometimes you need all the power you can get, but for normal motoring I would plan to run the alternators and watermaker if at all posssible. I dont meet many boats that claim to have too much power or water particuarly without a genset.
I have a Yanmar 4JH4AE and the sweet spot for engine operation whit my instalation is about 2300. Every boat is different but operation at 2800 when stationary or motoring sounds too high too me. I dont think it will damage the motor, but I think you would be more comfortable (less noise vibration) with a sligly lower target rev range.
Too get maximum fuel economy when running in the stationary mode (and only consuming a fraction of the available horsepower) the ideal revs would be low perhaps 1600 or so. An engine doesnt like to run at these revs for a long time (but lots of people do this when charging) another reason to make power and water when motoring, diesels like to run hard.
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Old 04-02-2010, 11:05   #19
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Me thinks you need to do a little more research. Your math is way off; a 100-amp high-output alternator will require up to four horsepower to operate. Can your boat's wiring handle the amps? What about the batteries; what do they need? What about the grounding (isolated or case)? What about frequency vibrations?
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Old 04-02-2010, 12:51   #20
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I like it This will remove the load off the water pump Since you are almost there try and lets un know how it works
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Old 04-02-2010, 13:46   #21
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Originally Posted by Seahunter View Post
Me thinks you need to do a little more research. Your math is way off; a 100-amp high-output alternator will require up to four horsepower to operate. Can your boat's wiring handle the amps? What about the batteries; what do they need? What about the grounding (isolated or case)? What about frequency vibrations?
Wiring is fine - 4/0 cabling to the batts about 50cm away. Batts are AGM. Grounding is fine. Vibrations have been included in calculations.

As for the math for the hp load - I believe the math is correct, if you can show me how you derive 4HP for a 100A alternator, with units, I would be very interested. If that is true, then the alternator that number refers to is pulling almost 3000W (which is 4HP expressed as Watts - using the conversion factor of 746) - yet is only delivering 100A at 14V, meaning 1400W of output. For something drawing 3KW and delivering only 1.4KW, that's a MASSIVE loss no matter how you look at it. While I've never measured/calculated loss on an alternator - I would be very suprized if it's that high.

Happy to be corrected/educated however if my derivation above is incorrect.
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Old 04-02-2010, 13:59   #22
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Originally Posted by noelex 77 View Post
To be able turn the alternator field off or 50% is great idea. Sometimes you need all the power you can get, but for normal motoring I would plan to run the alternators and watermaker if at all posssible. I dont meet many boats that claim to have too much power or water particuarly without a genset.
I have a Yanmar 4JH4AE and the sweet spot for engine operation whit my instalation is about 2300. Every boat is different but operation at 2800 when stationary or motoring sounds too high too me. I dont think it will damage the motor, but I think you would be more comfortable (less noise vibration) with a sligly lower target rev range.
Too get maximum fuel economy when running in the stationary mode (and only consuming a fraction of the available horsepower) the ideal revs would be low perhaps 1600 or so. An engine doesnt like to run at these revs for a long time (but lots of people do this when charging) another reason to make power and water when motoring, diesels like to run hard.
On the "meeting no boats who have too much power/water" note - unfortunately this is one of my design limitations... very depressing, but I have the world's smallest water tank and there's nothing I can do about it without seriously affecting the boat's trim. I have 200L, so if the WM is run for 1.5 hours, then I can't store it..

On the revs, I need them quite high otherwise I would have to have the crankshaft pulley significantly larger (or alternator/WM pulleys smaller) - if 2800 does indeed work out too high and it groans, I will have to consider getting new pulleys made and play with the ratios again. At least I don't have to throw away the lot though...
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Old 04-02-2010, 14:31   #23
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Dual Alternators

I'm contemplating adding a second alternator, too.

We currently run a 100 amp externally regulated (Balmar MC-612) with temp sensors feeding a bank of six 6v golf cart batteries.

Question - must the alternators be identical twins of the same brand & output?

Thanks,

Kirk
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Old 04-02-2010, 14:49   #24
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Originally Posted by Gallivanters View Post
I'm contemplating adding a second alternator, too.

We currently run a 100 amp externally regulated (Balmar MC-612) with temp sensors feeding a bank of six 6v golf cart batteries.

Question - must the alternators be identical twins of the same brand & output?

Thanks,

Kirk
I believe that it's all a risk mitigation calculation as with my setup. I would suggest that yes, they should be identical and exactly 180 degrees apart, however I know that there is at least one other person on this forum who has been using my same engine, with totally unbalanced loads at odd angles, with even more load than mine... and has been doing this for ~10 years without any issues.

For me, I'm paranoid and like accuracy, hence my specifics (and I'm still hugely worried).. but you may find that having different brands/outputs may indeed still work. It all depends on your risk profile, as in the end, only running it for a few years will tell.
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Old 04-02-2010, 16:46   #25
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Quote:
"As for the math for the hp load - I believe the math is correct, if you can show me how you derive 4HP for a 100A alternator, with units, I would be very interested. If that is true, then the alternator that number refers to is pulling almost 3000W (which is 4HP expressed as Watts - using the conversion factor of 746) - yet is only delivering 100A at 14V, meaning 1400W of output. For something drawing 3KW and delivering only 1.4KW, that's a MASSIVE loss no matter how you look at it. While I've never measured/calculated loss on an alternator - I would be very suprized if it's that high."
I'm asking about the house wiring not the battery cables. When you supply high amp the product on the other end uses it and it has to go through the wiring to get there.
As for the HP, you can't go by an internet calculator to estimate conservation of energy. Alternators run on a curve dependent upon RPM, Temp, belt size/width, pulley diameter, slippage and friction (within bearings belt etc.) Alternator manufacturers industry standard is that a 100Amp alternator needs 4HP to run optimally; not that that they convert. As for the loss, welcome to the world of DC.
Why not just buy a genset and spend the rest of your money on solar panels and beer?
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Old 04-02-2010, 20:11   #26
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Originally Posted by Seahunter View Post
I'm asking about the house wiring not the battery cables. When you supply high amp the product on the other end uses it and it has to go through the wiring to get there.
As for the HP, you can't go by an internet calculator to estimate conservation of energy. Alternators run on a curve dependent upon RPM, Temp, belt size/width, pulley diameter, slippage and friction (within bearings belt etc.) Alternator manufacturers industry standard is that a 100Amp alternator needs 4HP to run optimally; not that that they convert. As for the loss, welcome to the world of DC.
Why not just buy a genset and spend the rest of your money on solar panels and beer?
Thank you for the reply, but let's agree to disagree here on our respective understandings of physics.

In any case, I'm not worried about the load/electrical calculations, just whether the tensioning threaded rod idea looks like a winner or not.
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Old 04-02-2010, 20:38   #27
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I think it will work but personally I would have independent tensioning for each alternator. Like someone already mentioned, if you lose the belts on one, you have no way to tension the other. Likewise, if the bearings go out on one and you want to take the belts off of it you have the same problem, or if a mounting bolt breaks, etc. I would go ahead and give it a try, but give some thought to how to rig it if you need to take one alternator offline for some reason. Seems like it wouldn't be too hard to figure something out. Innovative idea, I like it.
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Old 04-02-2010, 21:02   #28
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I think it will work but personally I would have independent tensioning for each alternator. Like someone already mentioned, if you lose the belts on one, you have no way to tension the other. Likewise, if the bearings go out on one and you want to take the belts off of it you have the same problem, or if a mounting bolt breaks, etc. I would go ahead and give it a try, but give some thought to how to rig it if you need to take one alternator offline for some reason. Seems like it wouldn't be too hard to figure something out. Innovative idea, I like it.
Thanks for that, appreciate it. Although I must admit that in my rush to get it done, I didn't think of the failure of bearings etc scenario... will think of a fallback (carry extra alternators???? )
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Old 04-02-2010, 23:41   #29
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I like the idea that both alternators stop when a belt problem occurs with one. You do not want to run on one alternator!

I also think it'll work fine and I am sure I've seen a similar setup before. The belts stabilize the construction with the exact equal opposing force of the tensioner and the power take-off in the middle stabilizes it against "turning".

About horsepower: I know for sure that a 210A 12V alternator uses up to 7 hp. That would put you at just over 3 hp for each and close to 7 for both.

Yes, you must use exact twins for alternators, both new or the same run-time. If they differ, only one will do the work (the one with highest voltage output wins.

cheers,
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Old 05-02-2010, 01:21   #30
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Quote:
Originally Posted by akio.kanemoto View Post
On the "meeting no boats who have too much power/water" note - unfortunately this is one of my design limitations... very depressing, but I have the world's smallest water tank and there's nothing I can do about it without seriously affecting the boat's trim. I have 200L, so if the WM is run for 1.5 hours, then I can't store it..

On the revs, I need them quite high otherwise I would have to have the crankshaft pulley significantly larger (or alternator/WM pulleys smaller) - if 2800 does indeed work out too high and it groans, I will have to consider getting new pulleys made and play with the ratios again. At least I don't have to throw away the lot though...
Good luck with it.
Gipsey moth 4 (Frances chichester yacht) was restored with a Yanmar 4JH4AE with a second large alternator mounted below the crancshaft. (although they removed it when the yacht went into day sailing duty) It might be worth a look. I think there should be lots on the web about it as it is a famous yacht restored with sponorhip money.
I am on my yacht with a very slow internet so will leave you to do the googling if interested.
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