# Generator speed selection



## solidwoods (Dec 23, 2005)

Howdy
I'm shopping for a 30kw, single phase, 2 bearing generator to install on an engine.
Anyone have pros/cons for the difference in 1800 vs 3600 rpm generator speed?

I notice the mfr. says 50hp required for the 3600rpm and the 1800rpm requires 60hp.
jim


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## TnAndy (Sep 15, 2005)

At 3600, an engine is screaming. These are used on most cheap gensets. Get the 1800 version, and your engine will last a LOT longer.

What in the world are you planning to run with that big a generator ?


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## solidwoods (Dec 23, 2005)

It's not the engine running 3600, the gen requires 3600 or 1800rpm depends on the model. 
The gen is a 2 bearing gen that will be run by an engine via pulley. So engine torque range or other pro's cons I'm guessing would be a factor.
I'm running a large property with a woodworking and dog grooming business for pwr requirements.
I don't think I should run 30kw from a 30kw gen so I figured less output continuous of about 20kw.
Thanks
jim


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## Jim-mi (May 15, 2002)

Even the 1800 rpm engine is going to be sucking a lot $$$$ of fuel to meet those requirements.

Have you done an audit as to what the wood shop could / would be drawing . .??


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## artificer (Feb 26, 2007)

A rough guesstimate for a diesel generator is about 0.08gal/kw-hr, or 1.6gal/hr running 20kws.

The probable reason for more hp needed at 1800rpm is that few engines are rated for that speed. When the engine is run at the slower speed, you have to de-rate the engine.

The main difference between the two speeds for the generator heads is the robustness of the unit. 3600 rpm units are 2 pole, and tend to be smaller/lighter. If you go with a 4 pole 1800 rpm head, they tend to be larger and better built. If you go with one of the Chinese ST heads, they're built like a tank, and weigh as much, but run for a long time. (if properly set up)

Michael


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## solidwoods (Dec 23, 2005)

Howdy
I'm setting up a gasifier to run the engine.
The engine has a pulley the 2 BEARING generator head will have a pulley, so I am in control of the engine speed that will run the generator head.
That is what I am trying to talk about.. Which rpm gen head rpm has what pros and cons.
I'm shopping generatorjoes.net for the gen,, the AR250 model .
I'm also looking for 2 bearing gens if anyone knows of a source.
I won't be able to make electric for all of the load I have (one machine has 6 motors total 50hp so it will be on the grid,,, etc)
jim


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## Fire-Man (Apr 30, 2005)

Posted before I seen you are using a gasifier---Deisel sure would be costly.


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## solidwoods (Dec 23, 2005)

I sawmill/kiln dry and make flooring to furniture so I produce allot of wood waste. I also allow tree trimming companies to dump their chips on our property.

My wood work tools, kiln heat, hotwater home heat system and my wifes dog grooming shop use allot of electricity so I'm not trying to fully gen our electric just a major amount.
Some of my tools are 3ph and I use a rotary phase converter for that.

I like the idea of a slower rpm gen head requirement but it costs allot more than the 3600rpm gen head.
So it will boil down to will an engine have the torque at the engines rpm of (?) to run the higher rpm gen head.
What engine rpm? I don't know. 

If the engine is run at 1800rpm and the gen head at 3600rpm will the engine have the proper torque/pwr ? That's what I have to figure out.

I'm also considering a PTO gen head 540rpm to be run from an engine 

Anyone know of other sources for 2 bearing gen heads besides generatorjoe ?
Thanks
jim


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## Johnny Dolittle (Nov 25, 2007)

I don't see that the increased torque to run the 1800 rpm unit is an issue if you have the hp you need and the right pulley sizes.

I do see a problem transferring that much HP with V-belts. You will need multi sheave pulley with a lot of matched belts.... I don't know how many belts but probably at least five !!!!

Also .... wood gas set up might work but you will lose about 40 % of your engine power so now you will need maybe 100 or more hp speed governed engine.

Finding a 2 bearing head that big might be impossible

Maybe talk to the Amish if you can


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## solidwoods (Dec 23, 2005)

Johnny
I'm not catching your first sentence.
I like the 3600rpm gen head because it's cheaper (at jenjoes).
I don't know if you are talking about the gen head or the engine.

Got the hp drop requirement covered.
And generatorjoes.net has 2 bearing generator heads up to 325kw.
The 3600rpm head is $1848 and the 1800 rpm head is $2975.
The spec for both those are 3 belt drive. I wouldnt mind a direct coupling but for right now I'll go with belt. The engine is a pwr unit with a hand operated clutch and a speed govener (couple of must haves).

From the specs of other 30kw gensets I see the engine is run at 1800rpm.
I've test run the gasifier all went well.
I'll post pics when I tidy up (looks like 2 Hillbilly trains collided :hohum::hysterical.

The gasifier is set up as- gasifier then water filter/ cooler which is submerged in a water tank,, the heat is sent to a greenhouse with an electric fan heat exchanger- then the gas goes to a water extraction condenser, then engine.

I've set the condenser up so I can add scrap steel to inside the condenser. I want to see how much oxidation results I can produce (non electrolysis first then maybe,,because that has complications) . Oxidation steals oxygen and adds hydrogen. Removing oxygen strengthens the gas concentration and adding more hydrogen adds more BOOM BOOM . At what rate is what I have to learn first.

And thanks everyone else for the input,, it all helps.
jim


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## Johnny Dolittle (Nov 25, 2007)

How effectively can you scrub out the contaminates ? Will using wood gas affect the longevity of the engine ?

Isn't most of the energy the result of oxidation of carbon monoxide to carbon dioxide (which uses oxygen) ..... So why do you have too much oxygen in the wood gas ?


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## solidwoods (Dec 23, 2005)

The gas must be just as clean as other fuels liquid or gas.
And it's easy to prove it to ones self with a cloth filter.
The start is at the gasifiers reactor. It must be able to be hot enough to crack the atoms of the fuel, then fly ash.

Gasifiers create hydrogen and when done properly (which it must be) the gas runs just as clean (some can prove cleaner) than LP/NG/LNG.

The energy comes from hydrogen mostly. 
Oxygen just tags along with the other gasses that the gasifier produces. If it could be removed the gas will be stronger.
The oxidation that I will experiment isn't required and it's not done with gasifiers.
The concept is it removes oxygen which will increase the strength of the gas making it more powerful to the engine and off gas one of the hydrogen sisters which will increase they ratio of hydrogen to the other gasses.




Johnny Dolittle said:


> How effectively can you scrub out the contaminates ? Will using wood gas affect the longevity of the engine ?
> 
> Isn't most of the energy the result of oxidation of carbon monoxide to carbon dioxide (which uses oxygen) ..... So why do you have too much oxygen in the wood gas ?


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## TnAndy (Sep 15, 2005)

Solidwoods,

Sent you a PM.


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## artificer (Feb 26, 2007)

If you want a cheap robust 2 bearing head, do a search on the chinese ST generator heads. Here's on on ebay for $1,095 plus $175 shipping. 30Kw, 4 pole 1800rpm, 585lbs.

Hp, torque, and RPM are all related. As long as the engine has enough hp, and the gen head is connected with belts, it doesn't really mater what rpm the engine runs. By this I mean that if you have an engine that has a rated hp at 3600 rpm, you run the engine at 3600rpm, and do a 2:1 reduction to the gen head. If you use that engine, but only run it at 3000 rpm to extend its life, the engine will need 20% more rated hp at 3600rpm.

One thing to remember is the engine will be derated to 1/4 -1/3 of hp compared to running on gas. If you had a honda civic engine with about 90hp at 3000 rpm, you would get no more than 30hp out of it using a gassifier. That 30hp would make about 18-20hp depending on gen head/drive train efficiency.

If you want to disconnect from the grid, you need a gen head. If you just want to slow down your power meter, you can overspeed an induction motor to produce power. It only works if you connect it to the grid, however.

Michael


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## solidwoods (Dec 23, 2005)

Artificer
So far my plan is to use the gen for as much of our pwr needs as I can. 
I will stay grid tied. I have multiple bldgs. My total elect need is greater than 30kw and some of my equipment is 3ph from 220 rotary gen.
So I will have to rewire a bit to have a gen/grid service via manual xfer switch. I'm starting to work the schematic now. Its complicated by the fact that my electric right off the xformer is split into two feed. 1 for the house and 1 for the shop bldg that uses 3ph gen. So basic goal is keep 3ph and some other circuits on grid and as much as possible gen/grid.

The gen head:
Thanks for the link. The gen in the link on ebay is a brush type.
Any other pros/cons besides brushes wear out and will have to be replaced v.s. brushless? Looks like brushless are a little lighter but that's not a benefit for me (after shipping).

I have the loss of pwr from gasification covered with a larger engine.

I've looked at gensets in the 20/30kw range and they run the engine at 1800 ,, the brochures don't say what model gen head it has but the brochures that mention the drive type they say direct coupling. So 1800rpm engine direct coupled = 1800rpm gen head. So maybe I should follow my rule of keep it as simple as possible and go with a 1800rpm head.
jim


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## artificer (Feb 26, 2007)

If you're staying grid tied, I'd just go with an overdriven 3phase induction motor. No speed control needed. Some of the larger wind turbine systems use this idea. You can google it to find out more.

http://en.wikipedia.org/wiki/Induction_generator

Direct drive a large induction motor with a V-8 running on the gassifier output, and it is self regulating. You need a few safety mechanisms to cut power when the engine if off, or not driving the generator, but that should be fairly easy to come up with.

Michael


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## solidwoods (Dec 23, 2005)

Artificer
I understand the principal of the induction motor way but what does a suitable size induction motor cost vs a 30kw gen?
Plus I'd have the ability go gen electric instead of just owning a large 
motor.
30kw gen is sold by a shop with $175 shipping anywhere in USA (shipping is a bit of a $ factor )
jim


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## Azrael (Jun 2, 2008)

I would recommend the 1800 RPM. I would also go out of my way to make this a direct coupled or driveshaft coupled unit, I forsee alignment issues trying to use belts and pulleys to run these offset from each other. Does GJ provide an alignment spec with the unit?

I do not find on the website what the generator duty is (Prime, Standby, or Continuous) this will have a significant impact on the actual KW output. I did see that the KW rating is at unity (1.0PF), I would derate this to .8PF which would bring you down to 24KW available, with a possible further derate depending on duty.

I also would want an accurate rating on the engine shaft HP, 60 gives a good amount of wiggle room, but if it is putting out 50 or below, it will not run that gen at full capacity.


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## solidwoods (Dec 23, 2005)

Howdy.
My pwr unit is set up with a pulley and clutch on the rear . My long term goal is to direct couple the gen to the engine. It, takes a bit of work to do that because the 2 must be on the same frame and the gen will need vibration dampeners so I'll go vee belts first.

Genjoe does provide the manufactures brochure for what the items they sell.

My electric need will be based on 20kw I use more than that but I'll limit the 30kw gen to 20kw.

Any one have any ideas on how many hrs brushes run in a 30kw Chinese St ?
I'll post pics when I clean up a little more
Thanks
jim





Azrael said:


> I would recommend the 1800 RPM. I would also go out of my way to make this a direct coupled or driveshaft coupled unit, I forsee alignment issues trying to use belts and pulleys to run these offset from each other. Does GJ provide an alignment spec with the unit?
> 
> I do not find on the website what the generator duty is (Prime, Standby, or Continuous) this will have a significant impact on the actual KW output. I did see that the KW rating is at unity (1.0PF), I would derate this to .8PF which would bring you down to 24KW available, with a possible further derate depending on duty.
> 
> I also would want an accurate rating on the engine shaft HP, 60 gives a good amount of wiggle room, but if it is putting out 50 or below, it will not run that gen at full capacity.


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## defenestrate (Aug 23, 2005)

The lower RPM engine will generally last longer. It's kind of like comparing a semi tractor with a Mustang (I can't remember where I'm taking this analogy from but it works) - you could do some frame and gearing mods to a Mustang and pull a good amount of cargo, but your engine would be running at high RPMs and wouldn't last long. The semi is designed to run for a very long time at modest RPMs (part of the reason for having so many gears, along with more efficient use of fuel) so it is clearly the better choice. As a general rule, other motors are like this - greater hours running before need for maintenance or failure possibilities. Some engines are designed to run higher but you aren't going to run your generator on an RC car motor or a 2-stroke from a weed whacker - engines used for the same function will generally be more reliable and efficient at lower RPMs, though as posted above there are many considerations to keep in mind before you invest in a good generator.


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## solidwoods (Dec 23, 2005)

Thanks defenstrate.
Looking into what other 30kw gens run their engines and gen heads gets me in to 1800rpm engine/gen head speed. I'm a big believer in kiss , don't try to re-invent the wheel, and use common off the shelf items. Specialized concepts and components can be hard to find Sometimes.
jim


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## farminghandyman (Mar 4, 2005)

I once saw a small power plant for a factory that used one belt driven generator, but they had two engines, one small unit for night time use and a larger unit for day use, each engine had a clutch on it and my guess is once started all they would do is clutch the off engine to start it, and then unclutch the other and shut it down, 

looked like a good way to do it to me, now taking it one step further use the hot water the engine creates and run it through a heat exchanger for heating your house, or building,

also if one engine goes down you have a back up to take over,


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## solidwoods (Dec 23, 2005)

One of the issues gasifiers have is the hearth diameter needs to be suited for the cfm or air passing by. Not enough air the burn isn't complete and you make tar too much air blows a hole and sends flyash.
So to use different size engines the hearth would need to be adjustable.
Which to me sounds fine on the drawing board but gasification needs allot more evolution.

I considered a dual gen set up with each gen head pulley sized for the engines rpm 1800 day big gen, slow as possible for the small gen. Respect for the small gens torque requirement would have be met.

I use hotwater to heat a 3ksf wood work shop/showroom/dog groom , heat a lumber kiln that holds 3ksf of 1" lumber. The hotwater lines are sent out of that bldg following the domestic water line (for no freeze help) through the well box (now now french fry heat lamp in the winter) then follows the water line to the house 1890 3ksf orginal windows (and staying that way).
I was expanding by building a 10ksf kiln but I'm on American economy hold right now.
I have added a 20x48 greenhouse which requires heat which will be hot water also.

For those considering hot water system- Do it. That will make the overall time in your life that you have to hang your head and say "why the heck didn't I do this years ago".
I'm lucky, my wife isn't a frying pan hitter so I don't get whacked at that pointound:

Your burner can be block and fire brick with black steel pipe inside for heat exchanger or a welded up underwater campfire like most commercial designs.
jim


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