Picked up half a megawatt worth of Caterpillar power, think I'll make a PTO generator

[4570Man]

Here’s what I came up with. You need to travel 7,040 feet a minute to go 80mph. A 24” tire should travel 6.28 feet per rotation. Actually less but I used 6.28 for the next calculation. 6.28x1800=11,304 feet per minute. Or 128 mph. I double checked my math but the possibility still exist for it to be wrong. In either case something doesn’t add up.

 

[pmsmechanic]

Ok so let me get a few people bent out of shape again. I'm seeing ideas here that make no sense to me at all. First of all lets talk about the chain drive. I think that idea is finished for obvious reasons. Personally who would want all that noise anyways.

So how come nobody has mentioned a serpentine belt? They are pretty efficient though I don't know the numbers. They are also available in sizes to handle 37.5 hp!

I found this formula on the internet some time ago.

D2 = D1 x N1 over N2.

D2 = Generator pulley diameter.
D1 = Engine pulley diameter.
N1 = Engine RPM
N2 = Generator RPM

So lets say we want to know the generator pulley diameter. In my case I have a flywheel off of a hay baler 23.5" dia. I want to use this for a pto setup so it would be the engine pulley diameter. Now for the math. 23.5 times pto rpm of 540 divided by 1800 generator rpm = 7.05" generator pulley diameter. This answer is close to what I come up with when I figured everything out with a tape measure before I found this formula so I'm ok with the math on this one.

Now if you are going to go with a pto the belt makes far more sense to me as you can engage your pto and then slowly tighten up the belt with some kind of an belt tightening or idler pulley setup if you are worried about your pto clutch with the inertia load. I don't think you need to worry about it but it seems to be an issue for some people.

Now lets talk about the Honda engine. I'll just be blunt and say that there's no way I would run the transmission. I haven't researched the numbers but if it's at all possible I would run it as a direct drive setup. Surely the Honda will put out 37.5 hp at 1800 rpm. If it doesn't then use a serpentine belt setup to get the RPM's up to where you need them. There are lots of 8 rib serpentine pulley's available at semi truck wreckers with close enough diameters. In my case with the 23.5" drive pulley there is enough friction to run the belt on the pulley with no groves cut into the flywheel.

 

[strantor]

Your math looks ok for engine speed vs axle RPM, but a 24" tire at 1800 RPM would travel 128.5 MPH so not sure where you came up with 80 MPH. Will a Civic go 128 MPH?

I also calculated 128mph @1800 axle RPM. But whether or not a civic can go 128mph (I doubt it can) isn't really relevant [*]. The HP required to push that car through the air @ 1800 axle RPM (128mph) likely exceeds what the car can put out. But we know the engine can spin 4700rpm and we know it has a 5th gear, so it should be capable of 1800 axle RPM.

80MPH was more of a sanity check to verify my math with the gear ratios. If I asked him "HEY, when you're going 128mph, your RPMs are about 4700, right?" - well, we know where that would go. So I did the math backwards from 80mph (typical TX highway cruising speed when the signs say 65mph) and arrived at 2700rpm. I asked him if that was correct and he said that, to his recollection, at 80mph it's closer to 4,000 RPM. So either my math, the gear ratios posted on the internet, or my brother's memory are wrong.

*Edit: I suppose it could actually be relevant if the car has a governed max speed. Some cars won't go above 99mph despite having plenty of power left.

 

[strantor]

Ok so let me get a few people bent out of shape again. I'm seeing ideas here that make no sense to me at all. First of all lets talk about the chain drive. I think that idea is finished for obvious reasons. Personally who would want all that noise anyways.

So how come nobody has mentioned a serpentine belt? They are pretty efficient though I don't know the numbers. They are also available in sizes to handle 37.5 hp!

I found this formula on the internet some time ago.

D2 = D1 x N1 over N2.

D2 = Generator pulley diameter.
D1 = Engine pulley diameter.
N1 = Engine RPM
N2 = Generator RPM

So lets say we want to know the generator pulley diameter. In my case I have a flywheel off of a hay baler 23.5" dia. I want to use this for a pto setup so it would be the engine pulley diameter. Now for the math. 23.5 times pto rpm of 540 divided by 1800 generator rpm = 7.05" generator pulley diameter. This answer is close to what I come up with when I figured everything out with a tape measure before I found this formula so I'm ok with the math on this one.

Now if you are going to go with a pto the belt makes far more sense to me as you can engage your pto and then slowly tighten up the belt with some kind of an belt tightening or idler pulley setup if you are worried about your pto clutch with the inertia load. I don't think you need to worry about it but it seems to be an issue for some people.

Now lets talk about the Honda engine. I'll just be blunt and say that there's no way I would run the transmission. I haven't researched the numbers but if it's at all possible I would run it as a direct drive setup. Surely the Honda will put out 37.5 hp at 1800 rpm. If it doesn't then use a serpentine belt setup to get the RPM's up to where you need them. There are lots of 8 rib serpentine pulley's available at semi truck wreckers with close enough diameters. In my case with the 23.5" drive pulley there is enough friction to run the belt on the pulley with no groves cut into the flywheel.

Good points. I hadn't considered coming off the serpentine belt on the Honda engine. That deserves more investigation. I'll get in it tomorrow, thanks for the suggestion. 5000rpm wasn't "all that loud" but it was still audible in the house. I bet 1800rpm wouldn't be noticeable at all and would probably save a LOT of fuel.

I did consider belts for the PTO drive because of the clutching action you mentioned, and being to drive the tensioner in to get it up to speed. But I abandoned it because similar to the multi-strand chain requirement, to transmit that much power with V-belts would have required like 8-10 parallel pulleys and would have had terrible efficiency. I never considered a serpentine belt though. Honestly I didn't think they were capable of that much power. I learn something new every day!

Thanks again.

 

[4570Man]

I’m not sure you don’t have your gear ratio table reversed. The transmission output shaft should turn less than the engine in low gear and more than the engine in high gear. I’ve never seen a transmission that turned slower than the engine in 5th gear.

 

[pmsmechanic]

Good points. I hadn't considered coming off the serpentine belt on the Honda engine. That deserves more investigation. I'll get in it tomorrow, thanks for the suggestion. 5000rpm wasn't "all that loud" but it was still audible in the house. I bet 1800rpm wouldn't be noticeable at all and would probably save a LOT of fuel.

I did consider belts for the PTO drive because of the clutching action you mentioned, and being to drive the tensioner in to get it up to speed. But I abandoned it because similar to the multi-strand chain requirement, to transmit that much power with V-belts would have required like 8-10 parallel pulleys and would have had terrible efficiency. I never considered a serpentine belt though. Honestly I didn't think they were capable of that much power. I learn something new every day!

Thanks again.

The only time I've seen 8-10 v-belts is on a pto pump for irrigation. The belts were rather narrow and the setup was designed to handle about 80 hp. I think that you are thinking of fractional hp belts or automotive ones. There are also B,C and D sizes. A double C belt easily handled 60 hp when the above pump was run on an engine pulley setup.

Harley Davidson and other manufacturers are using toothed belts instead of chains for the final drive on their motorcycles. They have for years already. Toothed belts and serpentine belts have similar construction. I wonder what the torque is going through a Harley drive belt at full throttle in first gear?

Automotive applications went to serpentine belts for several reasons. One belt could do the same job as two or three and they are more efficient. They also take up less space for the same power requirements.

 

[strantor]

Gee, I still like the idea of a Ford inline 6 direct drive.

Hey, I looked, did not find. I forgot to mention that, sorry; i didn't ignore the suggestion. If you can point me toward one within 200mi of zip code 77534 I'll check it out.

 

[strantor]

I haven't researched the numbers but if it's at all possible I would run it as a direct drive setup. Surely the Honda will put out 37.5 hp at 1800 rpm. If it doesn't then use a serpentine belt setup to get the RPM's up to where you need them. .

I've spent a little time looking into direct drive with the Honda and I think we can rule that out. I've attached several dyno charts that I was able to find of various Hondas, stock or close to stock, around the 1997 year model. They're all different engines but one thing they have in common is sub-go-cart power levels below 3000rpm. Still investigating serpentine drive...

 

[strantor]

I’m not sure you don’t have your gear ratio table reversed. The transmission output shaft should turn less than the engine in low gear and more than the engine in high gear. I’ve never seen a transmission that turned slower than the engine in 5th gear.

I looked up gear ratios for other transmissions and the ratios I posted seem pretty normal. I think the ratio is engine turns to transmission turns. I think I wrote it wrong previously. I put (ex: 1:3.25) when I should have put 3.25:1. So a in 1st gear the transmission output is 1rev for every 3.25 engine revs. And in 5th gear (0.702:1) the trans turns 1 rev for every 0.702 revs of engine; in terms of engine revs, that would be 1.425 transmission revs per engine rev. Sorry for the confusion.

 

[radios1]

I looked up gear ratios for other transmissions and the ratios I posted seem pretty normal. I think the ratio is engine turns to transmission turns. I think I wrote it wrong previously. I put (ex: 1:3.25) when I should have put 3.25:1. So a in 1st gear the transmission output is 1rev for every 3.25 engine revs. And in 5th gear (0.702:1) the trans turns 1 rev for every 0.702 revs of engine; in terms of engine revs, that would be 1.425 transmission revs per engine rev. Sorry for the confusion.

keep in mind that if you multiply the speed by 3.33 times by gears or chain, or belts, you will see an increase of 3.33 times the amount of torque needed from the motor.. the HP requirement will remain the same.. so, direct drive is best..