How much power can these spur gears handle?

strantor

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I pulled these out of a scrap bin at a place I used to work 10 years ago. They are brand new. I don't know what their intended purpose was. They have 7/8" keyed shaft and are 7/8" thick. All of them Stamped MP02877, I get no results googling that. No brand stamped on them. They come in teeth of 39, 37, 33, 31, and 25. I believe They're steel, not cast, as I get a high pitched "ping" when I tap them together.

I'm considering using them in my tractor PTO generator project. Ultimately (extra long term goal, years down the road when I upgrade my tractor to 55hp) I will need to turn 540ft×lbs @ 540rpm into 160ft×lbs @ 1800rpm. For now the max PTO HP my tractor can put out is 32hp, so (shorter, this year) long term goal is turning 310ft×lbs @ 540rpm into 94 ft×lbs @ 1800 rpm. But before I do any of that, I just need to test my generator, make sure it puts out the proper voltage if I can manage to get it up to 1800rpm. I SWAG that will take 5hp max, so say 50 ft×lbs @ 540 rpm into 15ft×lbs @ 1800 rpm.

Will these gears help me accomplish any of those goals? Or are they too weak to even handle 5hp? I just want to know if I'm wasting my time before I go putting a hurt on my brain calculating if the RPM change will work out given the gears I have and the ratios I can create.

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According to that calculator:
39t @ 1800rpm = 17.5hp
39t @ 540rpm = 11hp
25t @ 1800rpm = 14hp
25t @ 540rpm = 7.87hp
So I could use these for testing, to get it up to speed. However, the tooth counts are not in my favor. I could only use 4 of the 5 gears for speed change, and the max ratio I could achieve would be 1:1.862. The math was way easier than I thought it would be, and took less time than asking this question.
 
Check the gears for hardness.....this will give a good clue to suitability...........they should not scratch with a hacksaw teeth across the pressure face.....if the saw cuts easily,they are no good for what you want.............In any case ,the setup will depend on the accuracy of the machining you do to the case.............If it were me,I would use an old truck gearbox thats already suitable for ratio,and remove the unwanted gears...........You should also note,there is going to be a big power loss in gearup and down ,so your setup wont be fuel efficient,but ok for ocassional use.
 
That job should be done with multiple vee belts, not spur gears. I suspect that those gears were intended for change gears on a lathe..
 
So now that the gears are put to bed, what solution would you gents consider, for stepping the speed up by a factor of 3.333? I would prefer to skip the intermediate steps and design around the 55hp goal as I'm feeling pretty good about this generator and I want to believe it will work.

The rotor has a ton of inertia (it's actually a 275kW Caterpillar generator head meant to power an oil rig) and my tractor has an electric clutch that's either ON or OFF. I can't feather the PTO clutch to get the rotor up to speed. I have a bad feeling about engaging the PTO while connected to this thing as I suspect it will stall the engine or destroy the PTO clutch/drivetrain. For that reason I like the solution of V-belts because I could engage the PTO with the belts slack, and then slowly increase belt tension as a sort of secondary clutch. The problem with belts, is that at these power levels (according to the formulae in belt MFG whitepapers) I would need a combination of large pulleys (expensive) and several pulleys/belts in parallel (expensive × n).

It's the same story for chains, but actually even worse, because achieving that ratio with a single set of sprockets would require me to derate the setup to the point of uselessness due to the tiny sprocket. So I would need multiple stages of multiple sprockets with multiple chains (again, according to whitepapers - not sure about real life).

The option I like best, is a manual automotive transmission with a manual clutch, but that would be heck of an endeavor to build.

Any other thoughts?
 
Another option on the table is toothed synchronous belts (timing belts) but I can't for the life of me find any reference for how much power these things can transfer. I know it's "more than a regular v-belt" and that's it. If anyone has a good reference for those things, please pass it along. So far all I'm getting from the MFG websites is "schedule an appoint with one of our applications Engineers to determine the requirements of your OEM design. "

EDIT:
oh, and multiple groove flat belts (automotive serpentine belts)... same story there. Any reference appreciated.
 
Belts can be slipped to slowly engage, similar to a clutch. Its done that way on many riding mowers for the blades. You could use an idler pulley, pulled to tension the drive belt, and give the slip needed.

Is that 275KW right? My 3KW generator has a 6 HP engine, my 1.5KW, has a 3HP. Going by that same ratio, you are looking at needing 550 HP.
 
Superburban - In the 50HP range, you can likely achieve a better efficiency for generating. What limits your gasoline engine is low end torque in bringing a loaded generator up to speed. You probably don't put a load on it until you have it running at speed well. A large load can more easily stall out a gasoline or diesel engine. The small engines are also generally overrated.

Your point is good though - with 100 percent efficiency, 55 HP at 746 W/HP is around 37kW. Fortunately, he doesn't have to draw the whole 275 kW from the generator. I expect his tractor isn't going to net much more than 20kW though. after the speed conversion. The gear box is going to get very warm though. IMHO, belts are the way to go. Machinery Handbook or the Mechanical Engineering Handbook probably has the definitive answer.
 
Until I saw that the gen was 275kw, I was going to suggest a hydraulic drive setup. Oh well back to thinking!
 
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