Ebay PTO generators

[Jim_in_Omaha]

I have been watching these listings for someone putting together a PTO driven generator for several weeks now. They use a Harbor Freight gen-head which I happen to own. The thing that has been bothering me is that they use a Grove Gear brand gear box reducer that is 5:1 ratio and drive the thing backwards. I have seen those gear boxes and they are a worm drive. I even have a Grove Gear catalog. They are turning the driven gear to turn the worm gear. Which is backwards of what it was designed to do. I keep thinking that there is a huge loss of power taken to move that worm gear. And to get 18hp on that generator it would be an incredible amount of side load stress on the worm gear/shaft.

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What do you think?
Jim

 

[shaley]

Wouldn't that gearbox have to be rated at 10 HP to run the gen set? I'd check with grove as to weather it can be reversed.

 

[srjones]

It states,

"IT'S WAS DESIGNED TO RUN FOR 1 HOUR OR LESS THEN OFF FOR 20 MIN THEN BACK ON. IF FACT THAT'S THE CORRECT WAY TO RUN ANY GENERATOR IN MY OPINION. THAT WAY THE SYSTEM LAST FOR A LONG LONG TIME."

Huh? You gotta be kidding me. The HF generator head (which this is) doesn't say anything about running for an hour or less and then letting it rest for 20 minutes. I can only conclude that it's a limitation of the gear increaser.

For $279 (list from HF) you could probably get that and build something yourself that you'll be happier with.

 

[California]

What do you think?

Looks like he is still in Beta test. (Build one prototype, let the customer see if it works).

His 'click to enlarge picture' goes to an earlier auction with a different gearbox that was pulley-coupled to the generator, at a pulley ratio of 2:1 after the gearbox's step up.

20 minutes rest after an hour use, and a recommendation to not run it at full output? If he's running the worm gear backward I'm surprised it will stand up to even that.

One of his auctions has a note saying the one shown was sold, and he has to build another to fulfill the auction.

I think he still has a few bugs to work out. I wouldn't buy one.

 

[Tom_Veatch]

...
What do you think?
Jim

"Custom Built system ,operates on a standard PTO drive or ANY POWER DEVICE WITH 16 HP.
Operates smoothly with a 16 PTO horse power or greater DRIVE.
Uses 56% less PTO RPM than others because it ONLYNEEDS 240 PTO RPM !!!!!!!!!!!!!!!!!!!!"

Let's see now. We've got a 10KW generator that's going to require (at 100% efficiency) 13.40 HP input from the PTO. He says 16 HP, so he's assuming an 84% efficiency through his gearbox and generator head. I think he's being insanely optimistic, but, let's accept his numbers for argument's sake.

Now, we're going to run the tractor at an RPM to develop 240 PTO RPM. Assume the "standard" engine rpm for 540 PTO is about 2200 RPM. That means the tractor engine will be running at about 980 RPM. So, we're requiring the tractor to produce 16 HP at the PTO output shaft while it's running at not much more than a fast idle.

Anybody want to take a guess at what the "rated" HP for the tractor engine will have to be? Remember, the engine will be turning much slower than it's "Rated/Maximum Power RPM" and will be driving through the PTO transmission gearing with significantly less than 100% efficiency. And it still has to produce 16HP at the PTO output shaft.

I'd say you probably won't have to go up to the big 4WD articulated machines but my guess is that you're outside the CUT category of tractors.

Now, finally, to answer your question, I think it's a crock of malodorous fecal matter.

 

[Jim_in_Omaha]

I have the HF gen head. Its rated at something like 7.2kw continuous, 10kw max. I looked through the manual and there is nothing in there about time constraints (not unless I missed it).

I guessing the gear box gets really hot from the friction loss driving that thing backwards.
Jim

 

[Tom_Veatch]

I have the HF gen head. Its rated at something like 7.2kw continuous, 10kw max. I looked through the manual and there is nothing in there about time constraints (not unless I missed it).

I guessing the gear box gets really hot from the friction loss driving that thing backwards.
Jim

Well, that makes his overall efficiency a little more reasonable at 59% instead of 84%. And I suspect you are right about the gearbox temperature. Most of that 6.35 HP lost to mechanical and electrical inefficiencies is going to reappear as heat in the gearbox.

But it's still going to take a respectable machine to develop 16 PTO HP at 240 RPM. That's about 350 Ft-Lb of torque at the PTO output shaft. Depending on the mechanical efficiency of the transmission and PTO gearing, you're looking at considerably more than 86 Ft-Lb of torque from the engine at little more than idle RPM.

[Torque in Ft-Lb = 5252 * HP / RPM]

I still detect traces of a very pungent odor in that eBay listing.

 

[Ray2210]

Generally the only worm drives cut to be run by the straight cut gear are in Torsen style differentials and are highly specialized. Previous to Torsen's involvement it was believed impossible to do. I highly doubt it is being driven from the output side of the gear box if its a worm drive gear box.

 

[sandman2234]

I purchased the same basic thing, for my Steiner lawn tractor. It is run off the front pto of the Steiner and was build using a HF head just like that. The Steiner has 23 hp, diesel, and has no problems running it. The one I bought was copied from the one Steiner makes, only using cheaper parts.
I would think that if I wanted to run it from the pto of my JD, I would mount it on a plate and mount a pulley to fit the pto shaft so that I could control the speed of the motor. Doing something similar to what he has, except with a pulley having 3-5 belts and over driving the generator. I would think slowing the tractor down from pto rated speed of a couple thousand to maybe 1600 would reduce fuel consumption, and still have enough hp to pull the generator. (My tractor is almost 70hp).
The reason I haven't done it is simple enough, I haven't needed it and have the steiner to run it if I do need it.
My suggestion is to find the hp/torque curve spec's of your tractor and buy a head from HF and build your own, custom to fit your tractor and it's hp.
David from jax