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
or should I say " Professor Bob " lol
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...
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.
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...
Quote from: Milton Mike on August 16, 2011, 06:59:17 AM
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.
Quote from: Ronmar on August 16, 2011, 08:17:07 AM
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
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. :D 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 @$$ ;D
Henry
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.
QuoteThat'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
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.
Quote from: BioHazard on August 17, 2011, 01:50:23 PM
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.
Quote from: rcavictim on August 18, 2011, 12:09:23 AM
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. ;D
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?
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
Ron (among others) have it right, it is a market driven thing...
also it is fair to note that 48volt nominal is the upper limit of what the NEC (national electrical code) will allow for DC systems, although
there are work arounds to exceed that safely, however no one is going to develop higher voltage systems for a market that is so miniscule.
12volts dc was the defacto standard almost world wide because of the plethora of generators/alternators, and equipment made to run on that
voltage.
24 volts dc was the next logical step up, and the various appliance manufactures followed along supplying all sorts of goodies to run off that
voltage.
48 volts dc is more efficient in copper losses to be sure, however the oem appliance manufactures have been very slow to supply stuff that run off that voltage.
anything higher in voltage is likely never to have much available to run off of it.
so at least around here, if you want to run dc appliances, then the only logical choice is to operate at 24volts dc, perhaps that will change as more equipment comes on the market to run on 48volts dc?
even at 24 volts, using careful design losses can be quite low, however this means short fat cables in most cases.
bob g
Hi Guys:
BioHazard said: "Gears are a lot less efficient than belts. You'll lose something around 10% through a gear drive, while belts only use about 2%"
Wellll, only sort of - you have to be careful what kind of belts you are talking about here and what size pulleys they are running on and how good of fit/finsih the pulleys have.
When I was working at Ford, many long years ago, and we were using CHEAP stamped, small diameter sheetmetal pulleys to drive v-belts, we were told to use 15% for the power loss in the drive! It probably was more like 10%, but that, still, is a lot more than 2%!!!
Now if you're talking about a cogged-tooth belt, 2%-3% may be near the truth!!!
One size does not fit all, either - if you are using small diameter pulleys, and thus small contact area, you need to have higher belt tension to eliminate slipping and this causes the belt to ride down in the pulley further and thus generate more friction and losses. If you are using BIG pulleys on a generator that is turning 1800 rpm, you can use much less tension and friction losses will be a lot less!
Just a heads up! YMMV
Regardz,
Wayne Stayton
Quote from: WStayton on August 20, 2011, 10:47:28 AM
Hi Guys:
BioHazard said: "Gears are a lot less efficient than belts. You'll lose something around 10% through a gear drive, while belts only use about 2%"
Wellll, only sort of - you have to be careful what kind of belts you are talking about here and what size pulleys they are running on and how good of fit/finsih the pulleys have.
When I was working at Ford, many long years ago, and we were using CHEAP stamped, small diameter sheetmetal pulleys to drive v-belts, we were told to use 15% for the power loss in the drive! It probably was more like 10%, but that, still, is a lot more than 2%!!!
Now if you're talking about a cogged-tooth belt, 2%-3% may be near the truth!!!
One size does not fit all, either - if you are using small diameter pulleys, and thus small contact area, you need to have higher belt tension to eliminate slipping and this causes the belt to ride down in the pulley further and thus generate more friction and losses. If you are using BIG pulleys on a generator that is turning 1800 rpm, you can use much less tension and friction losses will be a lot less!
Just a heads up! YMMV
Regardz,
Wayne Stayton
Yes size matters! Large contact area on a V-belt and reduced interface pressure also leads to much extended belt life and reliability.
Back to Milton Mike's original premise of using two different alternators: this can be made to have many advantages.
The two alternators opposite each other greatly reduces and eliminates engine bearing wearing side pressure.
You now have some redundancy back-up now too. Better half output than nothing. Common spares. Or even a whole spare unit for true bolt on minimum triple redundancy.
ANY good millwright/farmer fabricator will put in some type of slip-able drive member inline for equipment and personnel safety.
No gear drive is this. They are all precision high quality lubricant dependent assemblies. VERY noisy with wear or improper set up.
"V" belts now get a bad reputation. Plenty efficient enough if you follow the design recommend and experienced learned pulley sizing. Cheaper more ready available for "V" belts and pulleys by far over noisy prone Gimmer/toothed/cogged belts - leave those for timing needed applications and street rodders. Serpentine/micro grooved are great for efficiency, but have far fewer pulley size options, and have virtually ZERO shock load tolerance. Without a dampend spring tensioning arm ( more $$) can shock hammer out unit ball bearings and micro chirp slip flat spotting the belt at the pulleys. Then they then run rough and the unit bearing hammering accelerates.
MM you mentioned methane and/or woodgas as fuels. You DO want an oversized, low to medium speed power capable, low stressed, four stroke, durable, easily repairable engine that is COMMON to your area. Preferably some thing with, or could be $$ bumped up to at least 11/1 compression ratio. More efficiency gain here than in belt fussing. No outboard engine is this. IF serious about woodgas as a fuel you DO WANT PUSH ROD operated valves as a bendable stuck valve easily repairable safety link.
Just stuff I have learned along the way with $$$ wasted, broken pieces, skin and blood, hearing losses and a few burns.
Regards Washington State Steve Unruh
following proper engineering tables, a good V drive can be very efficient
i have found them to be as high as 98% efficient
however it is doubtful that this can be attained using cheap stamped steel undersized pulley sets, single cheap belts
and short drive centers typical of the automotive applications.
a well engineered serp drive can be a bit better than a V drive, however it is likely there isn't any difference between one
or the other unless you use good drive components and a quality belt, and of course follow the engineering tables to
set it up with.
bob g
Thanks for the responses to my question. I still think that I must be missing something however as the technology has moved on immensely from the time when we had to use big lumps of iron and copper to handle large amounts of low voltage power.
For example
1) We now have very slick and extremely cheap Grid Tie Inverters available that will implement a conversion from a voltage wild input (anything from 10V to 55V for the units I've seen and used) to standard 110 or 220 AC outputs at your choice of frequency. In addition they will implement maximum power point tracking - great for getting the maximum out of an un-optimised alternator and even better because we don't need to worry about tightly governing the engine speed.
2) The GTI can be used off the grid if you wish by paralleling it with a small inverter so you don't need the hassle of making a deal with the power company.
3) You can use any size (voltage) stack of batteries you like with the appropriate charger but this means that we can trade higher battery voltage for lower cable current and hence far lower losses in the system. For example given a 0.01 ohm cable and terminal resistance and a 2.4kW load at 12V (200 amps) we get about 400W developed outside the load. With the same load at 48V (50 amps) we get 25W losses. That's a reduction from losing 16% of the energy to losing only 1%.
4) Copper isn't getting any cheaper - electronics is!
5) And, given that wiring together lumps of electronics is far easier than welding lumps of metal together and getting them to balance (even if not as much fun) I just wonder still why we would want to do that?
Sorry if this is slightly off topic but I can't find anywhere on the board that is addressing this.
Best regards Dave
Dave:
i haven't been able to be as active here as i once was, been very busy after relocating half way across the country with remodel
and now in the middle of getting my shop built.
i don't have any of my notes from testing handy and they are packed away, so from memory
the question you have posted has been addressed in various means, i along with several others have done some testing and come to
some conclusions which undoubtedly will result in further development and testing...
using a grid tie inverter to control and wild alternator is useful "if" you have no control over the alternator at all, such as with the PM units "and" if you wish not to take active control of the engine rpm via some sort of governor.
using one of the off the shelf oem alternators, and one of the various balmar et. al. controllers there is really no advantage to using the
grid tie inverter that i can see, except maybe the replacement of a battery bank to buffer against.
using a standard oem alternator and a controller, coupled to a battery bank of even a small size to buffer and a standard inverter can achieve
everything you are talking about and if done right can do some things that your wild alternator fed grid tie inverter cannot do.
overall efficiency can also be quite good in my experience.
bottom line, there is much written on the forum about this scheme, look for hybrid systems for instance will lead you to some interesting reading.
hopefully by this fall i will be at a place where i can contribute some more detailed information from my system that might be useful to others.
bob g
Steve, thank you for a very informative post.