coupling 2 alternators to an engine, with out using belts

[mobile_bob]

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

[WStayton]

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

[rcavictim]

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.

[SteveU.]

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

[mobile_bob]

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

[DaveG]

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

[mobile_bob]

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

[Mad_Labs]

Steve, thank you for a very informative post.