RPC question .....

[mmcmdl]

What is needed to " start " , not actually operate a 7.5 HP lathe motor ? Would a 10 horse do it ? The difference between a 10 vs 15 is about $500 . I do not plan on keeping the lathe , just showing it to interested parties wanting to see it run . The 10 would run anything and everything else planned for the small shop . TIA .

 

[rabler]

Dave,
If the lathe has a clutch, for your limited demo use, I think you'd be fine. Clutch means the motor isn't starting under load. If you're dealing with a clutchless lathe where the motor starts under load, I'd be wary of going with less than 15hp idler.

 

[mmcmdl]

Thanks Rab , the lathe has a clutch .

 

[rabler]

Just a note, you risk the RPC tripping if you engage the clutch more than gingerly. But, I think you can explain that to a perspective customer to the tune of $500 for the bigger RPC. I wouldn't recommend this if it was for regular use.

 

[Eddyde]

I have a 5 HP clutched lathe that I start and run off a 7.5 HP RPC-Motor. I never have any issues with it tripping a breaker or overheating, etc.

 

[mmcmdl]

This would be a 2 speed on the Republic lathe . It has 2 ratings , one at 7.5 , the other at half that . Not sure how this works into the equation .

 

[rabler]

I have a 5 HP clutched lathe that I start and run off a 7.5 HP RPC-Motor. I never have any issues with it tripping a breaker or overheating, etc.

I'd be curious if you ever measured the voltage drop on the generated leg while starting the lathe and closing the clutch? That's a pretty good indicator of how well the RPC is doing in keeping the motor well fed. Roughly speaking, less than 10% is ideal, although quite a bit more is not a show stopper if brief (say less than 5 seconds). The issue is that a voltage drop heats up the lathe motor more, and stresses the motor bearings more as the torque is not continuous full circle. That is really only an issue if the clutch is cycled frequently

 

[GeneT45]

I have a 7.5HP (clutched) lathe and a 10HP GWM RPC. That was the sizing recommended by GWM ~20 years ago and it has served me well. I do not have to be ginger with the clutch nor take any other special precautions.

GsT

 

[rabler]

This would be a 2 speed on the Republic lathe . It has 2 ratings , one at 7.5 , the other at half that . Not sure how this works into the equation .

If at all, problems would only manifest on the 7.5 HP rating.
likely it will not be a problem at all, but the oddities of the motor, mass of the pulleys and clutch, and even the shop wiring, etc, make is hard to guarantee.

 

[mmcmdl]

My mistake . The motor is a 5 hp and 2.5 hp . I misread the manual . The 16" has the larger motor , so a 10HP converter would definately power it up .