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Old 05-02-2010, 06:57   #31
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Akers.. : Sorry about this semi-thread drift but I have a what may be a stupid question.

Why don't we see toothed belt drives? These survive tens of thousands of miles pulling heavy Harleys, models of which, are appropriately named "Fat Boys".

Or even chain drives? (Motorcycle "O" ring chains are self lubricating)

Do these not minimize side loads on the bearings?

If this is the case, then it might have been easier for you to engineer a tooth belt or chain drive with a single large alternator.

Or have I, as usual, missed the point?
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Old 05-02-2010, 14:27   #32
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Originally Posted by neelie View Post
Akers.. : Sorry about this semi-thread drift but I have a what may be a stupid question.

Why don't we see toothed belt drives? These survive tens of thousands of miles pulling heavy Harleys, models of which, are appropriately named "Fat Boys".

Or even chain drives? (Motorcycle "O" ring chains are self lubricating)

Do these not minimize side loads on the bearings?

If this is the case, then it might have been easier for you to engineer a tooth belt or chain drive with a single large alternator.

Or have I, as usual, missed the point?
Toothed/synchronous belts require more precise engineering for a start - much closer tolerances which can't be engineered unless you have very good tooling and access. I.e. it's not really possible in a boat with an engine that you can barely access and have no official dimensions of except those which you measure yourself. Possible, but too darn hard. V-belts are much more forgiving.

As for chains, great for low rpm applications, however chains don't really want to spin at 6000 rpm (my alternator for example), and won't be too happy doing this on a small pulley either.

As for side-load - neither a toothed belt or a chain will address side load - you'd still need to balance the crankshaft.
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Old 05-02-2010, 14:37   #33
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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,
Nick.
Hi Nick, thanks for the reply - just out of curiosity - have you had an alternator belt "snap" before? Is it noticable/makes a sound?

On the HP - yep, I'm working on the assumption that it will be around 3 each, but then again, , since the loads are balanced, they in theory can be even higher (up to the point when the crankshaft itself starts groaning.
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Old 05-02-2010, 22:00   #34
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Akio,

In addition to the standard 55A alternator on my Yanmar 4LH-HTE I have two Lestec Brute210 alternators. Each is driven by a single (!) Napa plain vanilla V-belt. I put on new belts in April 2003 and now, 7 years of full time cruising later, these same belts are still on there with no sign that they are at their EOL. So I wouldn't worry too much.

I did have the belt snapping on my genset though. I noticed because it shut down with a high temperature safety so no, I heard nothing.

ciao!
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Old 05-02-2010, 22:27   #35
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would it not be better for each Alt to have its own belt and ajuster that way if one fails you still have the other to fall back on.

Dutch
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Old 06-02-2010, 00:17   #36
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Originally Posted by s/v Jedi View Post
Akio,

In addition to the standard 55A alternator on my Yanmar 4LH-HTE I have two Lestec Brute210 alternators. Each is driven by a single (!) Napa plain vanilla V-belt. I put on new belts in April 2003 and now, 7 years of full time cruising later, these same belts are still on there with no sign that they are at their EOL. So I wouldn't worry too much.

I did have the belt snapping on my genset though. I noticed because it shut down with a high temperature safety so no, I heard nothing.

ciao!
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Heh.. I won't hold my breath trying to listen for belts snapping then.
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Old 06-02-2010, 00:28   #37
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Originally Posted by johnar View Post
would it not be better for each Alt to have its own belt and ajuster that way if one fails you still have the other to fall back on.

Dutch
Each alternator has it's own belt but it's the tensioner that they share. I would want both to stop if one belt breaks because with these big alternators the side loads are too high with just one going, and it is not a crucial system so time enough to replace a belt when needed.

cheers,
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Old 06-02-2010, 10:22   #38
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Good engineering practice would require that for a power take off rotating clockwise when looking at the front of the power take off, a belt driven load be installed on the right of the power take off. It has to do with the sag of the belt.

Quote:
Originally Posted by akio.kanemoto View Post
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.
It seems to me that you are omitting the power required to build the magnetic field inside the alternator.
My experience is that 750W is required to produce 338 VA, which is in accordance with
Quote:
Originally Posted by Seahunter View Post
Alternator manufacturers industry standard is that a 100Amp alternator needs 4HP to run optimally
and some data produced by mighty Gord in an other thread in this forum. “Remember, the Alternator will use about 1 H.P. of engine power, for each 25 Amps of Output as produced “Gordmay post 4 Alternators, what’s the difference?”

Every engine is manufactured according to some specification. The one you should get from your engine manufacturer is the maximum power available at the front-end drive, better you should approach them with your idea and see if they approve it.

Consideration must be given to the following.
Some alternators when switched on will give full power, it is like dropping a car clutch, the engine may stall, the rubber may burnt out, something may crack or bend, yours power take off is pretty long.

Alternators may not be equally loaded with consequence that belt load will be different and load will shift if using only one shared tensioner.

Belt breaking in multiple belt arrangement is better avoided because a broken belt can jam the remaining running belts with disastrous consequence.

On a boat and mostly on a light displacement one, every piece of machinery added will be an added weight to the original design.

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Originally Posted by akio.kanemoto View Post
I have 200L, so if the WM is run for 1.5 hours, then I can't store it.
This is a very interesting statement. “then I can't store it”. How low would you go with your water? And how much more fuel would you have to carry to make this water? And what will happen if your machinery or your WM fails. I know some people who nearly died of thirst when their RO failed.
May be you could start another very interesting thread on the logistic of water making.
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Old 06-02-2010, 14:31   #39
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Good engineering practice would require that for a power take off rotating clockwise when looking at the front of the power take off, a belt driven load be installed on the right of the power take off. It has to do with the sag of the belt.
I'm not sure I agree with this one. It should make no difference as mounting on opposite side will just "pull" on the top of the pulley, and the bottom will sag upwards due to the flex modulus of the belt anyway - so if there's any difference here, we're talking really small numbers.


Quote:
It seems to me that you are omitting the power required to build the magnetic field inside the alternator.
My experience is that 750W is required to produce 338 VA, which is in accordance with

and some data produced by mighty Gord in an other thread in this forum. “Remember, the Alternator will use about 1 H.P. of engine power, for each 25 Amps of Output as produced “Gordmay post 4 Alternators, what’s the difference?”
While I understand conceptually that there's potentially more loss involved than the basic derivation - it shouldn't be the magnetic field as I understand that that energy is provided externally by the regulator/field current and isn't a direct load.

I'd be very interested if anybody has a link to an official explanation though, because empirically, there is clearly more load than just the standard calcs... but where?

Quote:
Every engine is manufactured according to some specification. The one you should get from your engine manufacturer is the maximum power available at the front-end drive, better you should approach them with your idea and see if they approve it.
Engine spec shows that max power take off is roughly within spec and officially that monstrous pulley in the pic I posted is actually within spec as well believe it or not. Yanmar allows 66mm overhang to the centre of effort of the load, from front of crankshaft pulley.. unbalanced. So my scenario is way within spec theoretically - especially since the load is fully balanced.


Quote:
Consideration must be given to the following.
Some alternators when switched on will give full power, it is like dropping a car clutch, the engine may stall, the rubber may burnt out, something may crack or bend, yours power take off is pretty long.
Good point, however these alternators will impose zero load until field current is provided, and field current will ramp up over 30 seconds per the regulator's control. No issue here.

Quote:
Alternators may not be equally loaded with consequence that belt load will be different and load will shift if using only one shared tensioner.
The assumption here is that the alternators are identical, brand new, same field current etc etc - so they should be close enough hopefully.

Quote:
On a boat and mostly on a light displacement one, every piece of machinery added will be an added weight to the original design.
In which case I may as well scuttle the boat now.

Quote:
This is a very interesting statement. “then I can't store it”. How low would you go with your water? And how much more fuel would you have to carry to make this water? And what will happen if your machinery or your WM fails. I know some people who nearly died of thirst when their RO failed.
May be you could start another very interesting thread on the logistic of water making.
Original boat had 120L diesel, 120L water - and another 100L water tank right at the bow to gravity-feed a small basin in the head, which again was right at the bow. There was no ground tackle of any sort.

I've taken out the original 120L tanks, replaced them with custom made HDPE tanks - and now have ~250L of diesel.

I've removed some weight elsewhere and have added the 200L water tank (on CL, below WL). The weight savings from the tank right at the bow will be replaced with ground tackle (plus a bit more...)

But all in all, my theory here while digressing from the original intent of this thread is that I can make water from diesel, but not diesel from water. Firstly, if frugal, 200L will go a long way anyway (crew of 2), and during passage, I'll take 2 jerry cans along as well "just in case". When just coastal cruising - the theory is that we will impose no official restriction on water usage and guzzle up to 150L/day (so always have about 50L in the tank + two full jerry cans). (I don't think we can guzzle 150L/day, but that's another story) - which means that while coastal cruising, tank water will be replenished daily, during the daily charge cycle.

My calculations so far have been that - just looking at fuel as a charging/water ingredient - at 2800 rpm, fully loaded, the Yanmar 3gm30 will drink 4.5L of diesel, meaning ~50 days before a refuel is required.

Unfortunately, what another poster has made me realize (can't scroll up now, but the fellow who recommended 1600rpm) - is that I was just looking at the fuel consumption curve and took the optimal point for max output, not required HP. So realistically, since I only need about ~11HP (using the larger lossy alternator loads, not mine + WM) - I can run at 2200 rpm, and only consume 2.3L/hour... meaning about 100 days until refuel.... a very depressing oversight, since I will need to have the pulleys redone to make the ratios work again. But I'll leave this for later.
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Old 06-02-2010, 23:36   #40
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Might it not be easier to build a power takeoff that doesn't apply any side loads of any kind as per sketch.
The coupling isolates any side loads and the 2 pillow blocks supports any amount of side loads.
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Old 07-02-2010, 01:20   #41
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Might it not be easier to build a power takeoff that doesn't apply any side loads of any kind as per sketch.
The coupling isolates any side loads and the 2 pillow blocks supports any amount of side loads.
Thanks, that's a good idea as well, which I will borrow actually if this one doesn't work.

The reason I didn't use pillow blocks originally etc is that they require more parts. I'm quite good with wood/glass, but have no metalwork tools - so I draw everything on CAD and get somebody else to do lathe the pulleys etc - and pillow blocks etc all contribute to complexity.

It's also very hard to source parts in Australia and there isn't a McMaster-Carr here, and even if you find a bearing catalogue somehow - it won't have any pricing info on it.. which means more calling around. So quite simply, ease-of-fabrication. In my design, although inferior, I have nothing complex to buy - meaning that I can draw a pulley and a mounting on Autocad, and just buy the metal from a steel store (even that has no pricing online, you have to call!), then take it to a welder, haggle a bit, and I'm done... whereas with bearings and couplings, it adds weeks to the project trying to source the right bearings/couplings etc...

But I really like the idea, I even have the room in front of the engine for it.
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Old 07-02-2010, 07:45   #42
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Originally Posted by akio.kanemoto View Post
and the bottom will sag upwards due to the flex modulus of the belt anyway
In practice it will sag downward reducing surface contact on both pulley.

Quote:
Originally Posted by akio.kanemoto View Post
I understand that that energy is provided externally by the regulator/field current and isn't a direct load.
And where that energy would come from?

Quote:
Originally Posted by akio.kanemoto View Post
Engine spec shows that max power take off is roughly within spec and officially that monstrous pulley in the pic I posted is actually within spec as well believe it or not. Yanmar allows 66mm overhang to the centre of effort of the load, from front of crankshaft pulley.. unbalanced. So my scenario is way within spec theoretically - especially since the load is fully balanced.
By comparison Perkins Marines engines Perama m30 or 103-10, engines similar to Yanmar 3gm30 but may be not as robust, supply as a part a PTO adaptor pulley that allow the use of no more than one SPZ belt.

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In which case I may as well scuttle the boat now.
Normally not done but just a serious trimming of what is not necessary.
All the best.
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Old 08-02-2010, 06:43   #43
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But I really like the idea, I even have the room in front of the engine for it.
AKIO
Take into consideration that any weight placed in the front of the engine will change the center of gravity of the engine, adding more weight on the front foots and less on the back foots.
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Old 08-02-2010, 12:19   #44
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Turnbuckle or Otherwise

Chala's got it; something is going to bend, break, snap, or fold. However, if you want the formula here they are:
Amps when
Horsepower is Known
(reverse as needed):
HP x 746
E x Eff

Horsepower
(output):
I x E x Eff
746

To find Efficiency:
746 x HP
E x I x PF

E = volts I = amps W = watts PF = power factor Eff = efficiency HP = horsepower


Based on these formula here is the general rule of thumb:

A 100 amp alternator at full load:
12 Volts x 100 Amps = 1200 Watts
1200 Watts / 746 = 1.6 HP

1.6 HP x Factor of 1.5 = 2.4 HP min. required
1.6 HP x Factor of 5 = 8 HP max. required



Keep in mind this calculation is at 12VDC. If you're using AGMs the float can be as high as 16.2 VDC.
Note: The PF can be found for each engine and alternator from the manufacturer and are usually 85% or the rated amount.
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Old 08-02-2010, 20:49   #45
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…something is going to bend, break, snap, or fold
Hum
"something is going to bend, break, snap, or fold". Not necessarily
HP x 746 imperial
HP x 736 metric
E x I x PF = W
E x I = VA
PF = power factor. see Power factor - Wikipedia, the free encyclopedia
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