Homebuilt Generator

vwgtiman · Post by **vwgtiman** » Fri. Oct. 23, 2009 11:33 pm

I am looking to build a genset using an ST type head w/4 pole 1800rpm and am wondering if the HP requirements are halved if I am going double the RPMs and having it to 1800 RPM via a belt.

SMITTY · Post by **SMITTY** » Sat. Oct. 24, 2009 1:08 am

Doesn't it need to spin at 3600rpm in order to achieve 60Hz?

I would have to say a 50% gear/pulley reduction should half the horsepower requirements - makes sense to me. I'd get a 2nd opinion from someone smarter than I though....just to make sure.

oros35 · Post by **oros35** » Sat. Oct. 24, 2009 2:05 am

SMITTY wrote:Doesn't it need to spin at 3600rpm in order to achieve 60Hz?

Nope, with the right number of poles you can make it go slower.

Looking at it this way, Horsepower is equavlent to watts through a conversion. 1HP=745watts

So say you want 5000watts of output you would need about 6.7HP. You will require a different torque though. Through conservation of energy you only get out what you put in.

Freddy · Post by **Freddy** » Sat. Oct. 24, 2009 7:12 am

vwgtiman wrote:am wondering if the HP requirements are halved if I...

If you want to plow a foot deep the horse remains the same size regardless of how fast or slow you ask him to walk.

gaw · Post by **gaw** » Sat. Oct. 24, 2009 7:24 am

Usually a 4 pole generator is powered by a diesel engine running 1800 rpm. Larger generators are usually 4 pole and smaller ones are 2 pole, my guess for the reasoning is to better match them to the engines driving them. A 4 pole may be a bit more durable because it turns slower but I do not know if in fact it is more durable.

As “oros35” posted watts and horsepower are directly related. When buying tractor PTO powered generators the rule of thumb is 2 horsepower per thousand watts. The most common tractor PTO shaft turns at 540 RPM and has to be geared up to 1800 or 3600 RPM. This has no effect on the power required; the output of the generator determines that.

Short answer; no magic to be found in speed reduction, buy enough engine to match the generator output.

wlape3 · Post by **wlape3** » Sat. Oct. 24, 2009 8:19 am

Makes sense to me. Power in equals power out plus efficiency losses. Looking at buying/rigging up a generator myself.

SMITTY · Post by **SMITTY** » Sat. Oct. 24, 2009 1:32 pm

Freddy wrote:If you want to plow a foot deep the horse remains the same size regardless of how fast or slow you ask him to walk.

Great analogy Freddy! Now I understand completely. If school was taught that way I'd have been a straight-A student!

gaw wrote:Usually a 4 pole generator is powered by a diesel engine running 1800 rpm. Larger generators are usually 4 pole and smaller ones are 2 pole...........

Now I understand. Double the poles & you can halve the RPM & still get 60 cycles. Never thought of that! Learn something new every day.

Not to hijack, but I just got a smokin deal last week on a Yamaha EF6300iSDE inverter generator. Was a bit of coin, but at 40% off the out-the-door price of a local dealer - AND SHIPPED TO DOORSTEP - , I HAD to jump on it! My old gen is already gone! But the whole point of posting this, is that the engine is 32cc's smaller & has 4 LESS horsepower than my old gen - goes against the 2hp rule that I've always gone by - but is rated for the same 5500W nominal power. That's some kick-ass efficiency right there!!

This one has a 6300W max vs. the 6500W. http://www.yamaha-motor.com/outdoor/products/mode ... /home.aspx

Can even order an optional remote start for it!

009to090 · Post by **009to090** » Sat. Oct. 24, 2009 1:40 pm

SMITTY wrote: I just got a smokin deal last week on a Yamaha EF6300iSDE inverter generator. Was a bit of coin, but at 40% off the out-the-door price of a local dealer - AND SHIPPED TO DOORSTEP - http://www.yamaha-motor.com/outdoor/products/mode ... /home.aspx

Smitty, Thats a nice gen! What was your final cost?

cArNaGe · Post by **cArNaGe** » Sat. Oct. 24, 2009 1:55 pm

Sooooo talking about generators here. How are those PTO driven ones? I know the tractor takes alot of fuel and all but price vs output looks pretty good.

SMITTY · Post by **SMITTY** » Sat. Oct. 24, 2009 2:25 pm

Chris you have mail...

If I had a tractor with a PTO, I would have went that way in a second. You can get a 10,000W gen for a tenth of what I paid for the 6300W Yamaha. I always wanted to build my own out of an old dirtbike engine or find a way to rig it to my G110 with the 25hp Kohler v-twin. This Yammie is sweet though - would be tough to part with it now.

Yanche · Post by **Yanche** » Sat. Oct. 24, 2009 10:11 pm

In my opinion the ideal generator is 6-pole. 1200 RPM operation gives you 60 Hz power. Nice quite operation especially with a water cooled engine. Barely above an idle.

vwgtiman · Post by **vwgtiman** » Sat. Oct. 24, 2009 11:00 pm

I was toying the idea of a low speed lister (800 RPM) but the shipping on one is out of this world. I have 2 Yanmar L100's and figured I would try to run them at 1800 instead of 3600 and save wear, noise, and fuel by running a 4 pole ST 5 or 8kva head.

Freddy · Post by **Freddy** » Sun. Oct. 25, 2009 6:10 am

Just recently I was given a 15 thousand watt PTO generator. I hooked it up to my little Kubota & it seems fine. Other than testing I've not used it. I love the idea of having a generator and not having another engine to maintain. I think the diesel will be about as efficient as anything. Yup, the PTO is 540, generator 3,600 RPM.

I've never heard of the "2HP per 1,000 watts", but it seems close. I know my 16 hp Kubota won't drive the generator to full capacity, so with the 2 to 1 rule I guess I might get 8,000 watts. I was figuring 10k, but 8k will be plenty.

009to090 · Post by **009to090** » Sun. Oct. 25, 2009 8:28 am

Freddy wrote: I've never heard of the "2HP per 1,000 watts", but it seems close. I know my 16 hp Kubota won't drive the generator to full capacity, so with the 2 to 1 rule I guess I might get 8,000 watts. I was figuring 10k, but 8k will be plenty.

Freddy, your kubota probably has closer to 14 PTO-HP. Theres a loss to the PTO.

Post by **coaledsweat** » Sun. Oct. 25, 2009 9:21 am

Freddy wrote: I've never heard of the "2HP per 1,000 watts", but it seems close. I know my 16 hp Kubota won't drive the generator to full capacity, so with the 2 to 1 rule I guess I might get 8,000 watts. I was figuring 10k, but 8k will be plenty.

My 16 HP GENRAC puts out 9000 watts at surge, I think about 8000 continuous. It will run the arc and mig welders, more than enough to keep the coven of witches here in WII, TV, coffee, hair dryers and curling irons. Not to mention warm and watered.