Can you help with some math?

[IAfarmguy]

I am needing to rebuild a tractor-drawn, PTO powered Harsh 190 feed wagon into an electric motor powered stationary unit. Suppose the PTO input runs at say 250-300 rpm. The electric motor turns at 1760ish rpm and has a double groove pulley diameter of say 4.5 inches. The question is what size double groove pulley do I need on the wagon input shaft (in place of the PTO yoke)? Or would this require a two step reduction to get there? I thought I knew how to calculate this but I guess my brain took the day off. Thanks.

 

[Powered By IH]

I am needing to rebuild a tractor-drawn, PTO powered Harsh 190 feed wagon into an electric motor powered stationary unit. Suppose the PTO input runs at say 250-300 rpm. The electric motor turns at 1760ish rpm and has a double groove pulley diameter of say 4.5 inches. The question is what size double groove pulley do I need on the wagon input shaft (in place of the PTO yoke)? Or would this require a two step reduction to get there? I thought I knew how to calculate this but I guess my brain took the day off. Thanks.

Easy math. Don't worry, we've all had those moments
1760 motor RPM / 275 wagon RPM = 6.4 to 1 ratio. 6.4x4.5= rougly 28 in.
With a single reduction you would need a wheel approx. 28 inches in diameter for the PTO.
If you have numbers for a double reduction I can calculate that out too.

 

[MarkB_MI]

I think you'd want to run a double reduction using a jackshaft and secondary chain reduction. If the second pulley is, say 9 inches in diameter, that gets you down to 880 rpm. To get on down to 300 rpm you need a 3:1 reduction, so have the 9 inch pulley drive a jackshaft that has a 3 inch sprocket and put a 9 inch sprocket on the input shaft of the feed wagon. The chain reduction will be able to handle the torque better than a belt drive, while the belt drive is better suited for the motor speed.

 

[Welding man]

I am needing to rebuild a tractor-drawn, PTO powered Harsh 190 feed wagon into an electric motor powered stationary unit. Suppose the PTO input runs at say 250-300 rpm. The electric motor turns at 1760ish rpm and has a double groove pulley diameter of say 4.5 inches. The question is what size double groove pulley do I need on the wagon input shaft (in place of the PTO yoke)? Or would this require a two step reduction to get there? I thought I knew how to calculate this but I guess my brain took the day off. Thanks.

I would use an electric motor with the proper gear reduction unit already on it and eliminate all the sprockets, chains belts etc. Just a thought.

 

[Tramway Guy]

Better find out what level of power needed to run it before you get too far into it.

 

[IAfarmguy]

Easy math. Don't worry, we've all had those moments
1760 motor RPM / 275 wagon RPM = 6.4 to 1 ratio. 6.4x4.5= rougly 28 in.
With a single reduction you would need a wheel approx. 28 inches in diameter for the PTO.
If you have numbers for a double reduction I can calculate that out too.

Thanks for your help on this. Your comments are appreciated. Stay tuned for coming developments on this project.

 

[joeysmith]

I second the double reduction or gear reduction motor
Especially if its going to be started loaded

 

[DanielW]

How much jam do you think it takes to run that feedwagon? And how much HP is your motor? An alternative option would be a smaller single reduction (maybe go to a 12" to 16" pulley) to slow it down to 500-600 RPM at 60 Hz, but then use a VFD or similar variable-speed control to adjust the motor RPM. This would be especially beneficial if you're running a three-phase motor (which most 5 HP or larger motors are) and you only have single-phase power. The VFD will let you run a three-phase motor on single-phase, and also allow you to play around with the speed at-will. You can get VFD phase converters for AC motors uber cheap these days (less than $300) and they work great. I suspect by the time you buy the bearings, keyed shafting, sheaves, and belts necessary for a two-stage reduction, it would have been cheaper and easier to just do a single reduction and run a VFD. And this also gives you the option to find and run a higher-HP three-phase motor: It's almost impossible to find single-phase motors larger than 3 HP (and if you find them, they're stupidly expensive). But there are oodles of larger HP three-phase motors available used, and they typically cost peanuts.

As you drop below 60 Hz with a VFD or similar speed control, you're in the constant torque region of motor performance, so for a feedwagon application I think the same size motor would work, as long as you don't slow it down to less than half the synchronous speed (30 Hz). Any slower and you might have some cooling concerns with that low RPM. But even if you do drop less than 30 Hz. to slow it down to a crawl, for a feedwagon application that's probably only running a couple hours a week, the motor would still probably last years.