What is the torque at the input shaft to the machine and what is the desired RPM? Start there and THEN decide on motor and gearbox.
I think I would consider another motor type
UNLESS you need positioning accuracy. If so stepper is one of several ways to go.
See what Dick DV had to say on similar situation. Copied here for convenience.
http://www.plctalk.net/qanda/showthread.php?p=441535#post441535
When changing from DC to AC technology, the same basic rule applies and that is to size the drive and motor based on torque, rather than hp. And, that is two different torques: continuous torque and short term torque (less than one minute for accel and sudden load changes).
It is often thought that somehow DC motor/drive systems automatically develop large slow and stall torques but, if the DC drive is sized for only 10% or 50% short term overload current, that's all the short term overload torque you're going to get too regardless of how much torque the motor COULD develop with an infinite current source.
My approach is to mostly ignore the old drive system and use load data only. Design the new system on what the load needs, not what the old drive/motor could have developed.
Of course, there are always applications out there that seem to have no load data of any sort and, for those nasty rascals, the old DC drive can be a handy source of data. Keeping in mind that amps and torque are in direct relationship to each other in DC motors, you can monitor the fluctuation of amps over the whole range of short term and continuous operation and get the torque data you need from the old system. It's necessary that the old system still be operational, of course!
As to braking, it surely is true that it is easier and more cheaply done in DC but not all DC applications require braking. Again, it comes down to understanding your load, this time from a braking rather than from a motoring perspective.
The question of resistor braking, regen braking, common busing, or DC injection braking are application specific and often are chosen based on the VALUE of the recovered energy. It takes large amounts of recovered energy to justify a regen system. (Actually, this also comes down to understanding your load)
I do DC to AC conversions alot and almost never have to increase the hp. Using AC overspeed wisely usually takes care of the low speed and starting torque issues for free and improves the motor cooling too. Incidently, just because the DC motor has an auxiliary blower does NOT mean that the AC motor needs one. It could be, for example, that the DC blower was needed to keep the DC motor field cool while the motor was stationary.
Bottom line, no generalizations. These conversions require study and economic analysis before proceeding. None of us can do this on a BBS for you. If you aren't sure how to proceed, hire a consultant that does.
Dan Bentler
