coupling 2 alternators to an engine, with out using belts

[Milton Mike]

Hi,   I am in need of a 210 amp 24 volt charger.  Does any one know of a simple way to couple 2 alternators ( at 105 amps each ) to a single shaft of an engine ?    I am hoping to skip the use of pulleys.

I was thinking of giving the idea of a out board motor a go...   I have heard that the reduction gear box ( 2 to 1 ) is right down the bottom near the propeller.  May be the cogs can be reversed,   but I would still have to raise it up to 1 to 3....

I  thought I would go for a 20 to 25 HP unit, so I could run it at a slow rpm,  and use Bobs ideas of an external regulator.  ( Thanks Bob )

One idea could be a small Diff....   but I don't know what the gearing is like, from the drive shaft to the wheels....

any ideas ?

Mike

[Milton Mike]

or should I say " Professor Bob " lol

[BioHazard]

Gears are a lot less efficient than belts. You'll lose something around 10% through a gear drive, while belts only use about 2%. You don't need anywhere near 25hp for 210 amps, I'd say more like 10-15 at the most.

If you really want 210 amps though, you should just get a single 210 amp alternator. That would be a lot easier and more efficient. If you're stuck on two alternators for one engine with no belts, I'd look for an engine where you can mount an alternator on both ends of the crankshaft.

Outboard and other marine motors are generally about as expensive a motor as you can find, and I wouldn't even think about a 2 stroke...

[Milton Mike]

That's interesting about the belts higher efficiency.  It's sort of counter intuitive, but I think your right about that being the best way to go.  Belts and pulleys will be easier to put together too, as the gearing is greatly simplified.

By my calculations,  210 amps is about 6200 watts which is around 8.3 horsepower.   I should have mentioned that I kind of like to run every thing at well withing their limits to get max life, for both the engine and the alternator.

Add to this, I have read you get a significant loss's due to running petrol engines on methane or wood gas,  so I thought I would max out the HP by around 3 fold.  I would like to hear if any one has any real world experience with this, as so far my plans are compiled from web info and lots of spread sheet calculations.

I would love to have to only fit one alternator.  I was hoping to over rate the alternator by 100 % as well.  That would mean I would need a 400 amp 12 Volt unit,  as per Mobile_bob's white paper.  I thought I would follow his advise, and go with 2 *  Prestolite Leece Neville 110 555jho alternators, but if there is a 300 plus amp 12 volt unit out there that I can afford without selling my home,  I should go for that.

I was hoping to find a 2nd hand 4 stroke outboard, and try it just to see if it works, but if I can find a 20 hp water cooled diesel, that would be nice too.     As yet I am still looking for an engine to make the job as easy as possible.

Thanks for your ideas, as its all very helpful.

[Ronmar]

For that much DC, I would be real tempted to find a small direct drive 3 phase generator and build the bridge to rectify it to DC.  It might also be a little more efficient than an automotive alternator... 

For 6200W, you are going to need at least 12HP for sustainable power generation.  This takes into account drive and generator efficiency losses.  2HP per KW of ELECTRICAL output...  This rule is followed pretty closely on just about every generator set I have worked on over the years IE: A 15KW generator has a 30HP engine...   

[mike90045]

By my calculations,  210 amps is about 6200 watts which is around 8.3 horsepower.   I should have mentioned that I kind of like to run every thing at well withing their limits to get max life, for both the engine and the alternator.

Charging a 24V battery, needs about 29 volts in practice.  And you will have a lot of windage lossage in the fan of an auto/truck style alternator.

[BioHazard]

2HP per KW of ELECTRICAL output...  This rule is followed pretty closely on just about every generator set I have worked on over the years IE: A 15KW generator has a 30HP engine...   

That's good for high voltage generators, not so much with alternators that aren't nearly as efficient.

I don't know how much you're looking to spend, but one of these Kawasaki water cooled engines have been begging me to be a generator...
http://www.surpluscenter.com/item.asp?item=28-1714&catname=engines

[Henry W]

They are very good engines. I have the air cooled version of that engine and it has not given any problems. I run it wide open loaded and with now over 2000 hours and is still does not use oil between oil changes. That water cooled engine is much quieter also. I ran my friends water cooled Kawasaki Z-turn mower and it was very nice. But he burned the engine up a month later by not cleaning out the radiator screen. He said he noticed a loss in power than RPM's dropped and than the engine stopped running abruptly. He said he was smelling some type of odor. Had it for a month and a half and he killed it.

They are a pretty smooth running V-twin and I don't think any of us will have problems with one of these engines for generating power. They should last for a very long time. Unless a person is a dumb @$$

Henry

[rcavictim]

I have a 400 amp, 50 volt DC generator (20 kW) for sale in the parts for sale section.  It will put out any voltage up to about 50-60 VDC that you wish depending on shaft RPM and excitation voltage.  24 VDC @ 400 amp would be easy at 1800 RPM with reduced excitation.  This is a large frame old school generator in very good condition.  Should last nearly a 2nd lifetime.

[LowGear]

That's good for high voltage generators, not so much with alternators that aren't nearly as efficient.

Talk about counter-intuitive.

The efficiency of belts over gears is a real brain warp - thanks.

Casey

[BioHazard]

Back on the subject of outboards - sometime in the early 80s they changed the horsepower ratings from "at the powerhead", to "at the prop shaft". The same 150hp outboard that's on my boat from 1974, became a 115hp outboard in the 80s when they started measuring the gear loss.

[rcavictim]

Back on the subject of outboards - sometime in the early 80s they changed the horsepower ratings from "at the powerhead", to "at the prop shaft". The same 150hp outboard that's on my boat from 1974, became a 115hp outboard in the 80s when they started measuring the gear loss.

35 HP lost in gears?  That's 35 X 746 = 26 kW of heat!!!  That seems a bit hard to believe, even for a really crappy design.

[BioHazard]

35 HP lost in gears?  That's 35 X 746 = 26 kW of heat!!!  That seems a bit hard to believe, even for a really crappy design.

Yeah, most people agree that they under-rated it at 115hp, most likely because they had just released a 150hp V6 outboard and they didn't want the 150hp Inline 6 to directly compete.

Works for me though, since my boat hull is only rated for 120hp and my stickers say 115, but I've got a 150hp powerhead. 

[DaveG]

I've been hovering around this forum for a while (learning from the experts) but I find myself wondering more and more why there is so much emphasis on low voltage systems.  For example, generating 210 amps at 24 volts is going to involve substantial I^2 R  losses however tightly the connectors are torqued up and transmitting it more than a few feet will require pretty thick cables.  Even 0.1% loss is still 60W or so and that's a lot of heat to lose safely.  Is there a reason (perhaps particular to the USA) that I'm not appreciating?

[Ronmar]

These losses have always been known and accepted, most likley because of market economics.  Or put another way, you can't buy it if no one builds it, and no one is going to develop and build it, unless they are sure someone is going to buy it...

Most of the available products were geared for the 12V automotive, RV and boating markets.  And to a smaller degree 24V systems on busses/RV's and boats...  Now in the interests of efficiency and the increase in alternative energy demands, you see a larger segment of the market shifting toward 48V systems.  Bit of a risk developing and marketing a 48V or higher rectifyer when there is not yet a market for it.  Have yet to see a vehicle with a 48V main buss, and probably not worth the effort to re-engineer a vehicle electrical system when the parts are already available for the existing electrical system. 

Unless the government gets involved to spur a development project for some military program or such, to which the company could also market it's products to the rest of us at little additional cost, the suppliers have to rely on the often slow buildup of market momentum...

My .02