3 phase motor upgrade

[Smiles79]

I recently picked up a 1973 Delta Rockwell 15-017, and the 3 phase motor and VFD conversion seems like a fun project.

I found a guy selling a 3hp 220v 3 phase Dayton motor for $30. Frame 145T. Is there any reason this won't work? Is there such thing as having too much power?

 

[cvairwerks]

Ah...that's 6 times the original horsepower it had. I would doubt that the bearings will handle that much extra power for very long. The quill most likely wouldn't either. Unless you are turning bits in the 1" or greater class, there's no need for that much hp on that size drill press.

 

[whateg01]

The biggest thing to look for is the number of poles or rated rpm. Unless you plan to change pulleys, you'll probably want to stick close to original, even with the vfd. Second thing is having enough HP. Too much HP isn't really a problem as long as you continue to limit what you are drilling to what the rest of them machine is capable of. It'll just be like driving a Corvette with a block of wood under the gas pedal.

 

[Smiles79]

Ah...that's 6 times the original horsepower it had. I would doubt that the bearings will handle that much extra power for very long. The quill most likely wouldn't either. Unless you are turning bits in the 1" or greater class, there's no need for that much hp on that size drill press.

Yeah I know it's way more than necessary, but the price is right.

The biggest thing to look for is the number of poles or rated rpm. Unless you plan to change pulleys, you'll probably want to stick close to original, even with the vfd. Second thing is having enough HP. Too much HP isn't really a problem as long as you continue to limit what you are drilling to what the rest of them machine is capable of. It'll just be like driving a Corvette with a block of wood under the gas pedal.

It's about 3450 rpm. I think the motor on it now is about 1750. What's the reason that this is an issue if I plan on controlling it with a VFD?

 

[Firebrick43]

I recently picked up a 1973 Delta Rockwell 15-017, and the 3 phase motor and VFD conversion seems like a fun project.

I found a guy selling a 3hp 220v 3 phase Dayton motor for $30. Frame 145T. Is there any reason this won't work? Is there such thing as having too much power?

The shaft size and foot mount/motor mount sizes are going to be wrong compared to the original 56c motor

Yeah I know it's way more than necessary, but the price is right.

It's about 3450 rpm. I think the motor on it now is about 1750. What's the reason that this is an issue if I plan on controlling it with a VFD?

A two pole motor (3600rpm) will have half the torque of a 4 pole motor (1750rpm) which is really what you’re after not full hp.

 

[Smiles79]

The shaft size and foot mount/motor mount sizes are going to be wrong compared to the original 56c motor

Ah, so it wouldn't be a quick and easy swap then? I could probably easily make an adapter plate but I wouldn't want to drill out the pulley ID.

 

[whateg01]

Yeah I know it's way more than necessary, but the price is right.

It's about 3450 rpm. I think the motor on it now is about 1750. What's the reason that this is an issue if I plan on controlling it with a VFD?

I get the price thing. I have a shelf full of motors I bought for that reason.

In general, an AC motor loses torque as you slow it down. You can slow it down quite a bit before it's a problem, but if you are spinning big tools, that's when you need the slow speeds and big torque. If you use pulleys, you can still probably get the spindle speed down anyway. I'm not sure how your machine is configured. If you are wanting to use the vfd just to slow the machine down for use drilling big holes in metal, you may need the bigger motor to keep enough torque to drill the hole. Another consideration when slowing a motor down like that is that it depends on air flowing through or around it for cooling. If you slow the motor, you slow the air.

 

[whateg01]

A two pole motor (3600rpm) will have half the torque of a 4 pole motor (1750rpm) which is really what you’re after not full hp.

Everybody points that out when these questions come up. If you are using pulleys to get the speed down, you get the torque back.

 

[Smiles79]

Thanks everyone. I think I'm still going to pick these up because of the price, but maybe I'll just hold on to them for something else.

 

[Firebrick43]

Everybody points that out when these questions come up. If you are using pulleys to get the speed down, you get the torque back.

That is a possibility for sure. I don’t know if that drill press has the center low speed pulley or not?

Also with a standard 3 phase motor you don’t want to drop hertz much below 20 percent. however it no issue to run a 3 phase motor, even a 4 pole one to 3600 rpm so with a 4 pole on the low speed pulley you can normally cover the full rpm to maintain proper speed for small or large drill bits. A two pole would need a belt change in there.

An inverter rated 3 phase 56c motor can typically be safely operated down to 2 hertz without issues and up to 4000 rpm. With a properly programmed vfd this makes power tapping in sub 3/8 taps very easy to do without belt changes.

 

[Smiles79]

That is a possibility for sure. I don’t know if that drill press has the center low speed pulley or not?

Also with a standard 3 phase motor you don’t want to drop hertz much below 20 percent. however it no issue to run a 3 phase motor, even a 4 pole one to 3600 rpm so with a 4 pole on the low speed pulley you can normally cover the full rpm to maintain proper speed for small or large drill bits. A two pole would need a belt change in there.

An inverter rated 3 phase 56c motor can typically be safely operated down to 2 hertz without issues and up to 4000 rpm. With a properly programmed vfd this makes power tapping in sub 3/8 taps very easy to do without belt changes.

I do not have the center pulley.

I think I'll just pick these up for some other project, and keep an eye out for one better suited for the drill press.

 

[whateg01]

I agree on overspeeding. I run the 6 pole motor in my lathe up to about 2500. It's hard to give generic advice on 3ph motors without just saying but a vectorless drive and inverter rated baldor. Lots of variables and for me cost is usually one of those.

 

[Maui]

Your motor may only be $30, but did you check to see how much a VFD that is capable of powering a 3 hp motor costs? I hope you are sitting down when you do.

 

[whateg01]

I use a cheap $100 vfd off eBay for one of my machines. No brake and it won't accelerate instantly but it does the job. Other machines have Fuji electric drives that were about $300.