I am still trying to deside to go with 3/4hp brushless dc motor or the 3 phase. My air compressor is the only thing on 220v right now. My G0704 is 110. and my lathe that has died was 110 dot shure of size as it is oooold and big. No lable but it has an external start compasiter mounted in a box with an open air relay with fowered and reverse switch. If I stay with a single phase motor I would need to get a drum switch. so the cost would end up the same.This is the motor I am looking at. Thay are out of 3/4hp.
http://dealerselectric.com/default.asp
I don't have much experience with DC motors in terms of powering shop machines. I have used VFD for a long time. The only problem I ever had with a VFD is reading the manual and getting the initial setup working. Most of the manuals are poorly translated. Aside from that, they've all been reliable.
A few random thoughts and questions that others will hopefully comment on:
DC motors produce more torque at low speed and it drops off at higher speeds. I'm curious about how that effects your machining operations. With the old VFDs, they didn't control torque at low speed too well but, newer units do a pretty good job of pumping current at low speed and keeping the motor strong.
Most everyone I know who has a DC motor, has had electrical problems with the DC controller. Various different problems experienced by several people I know or work with. They're always blowing fuses on the board or replacing resistors etc... What's up with that? Is that common or just problems due to junky controllers?
Is it my imagination or, do DC controllers cost WAY more than VFDs? (Maybe the expensive ones don't screw up as much).
DC motors seem to be 10 times heavier than equivalent single or three phase units. I presume the magnets are pretty heavy.
Depending on the DC voltage range, the connecting wire becomes substantial when you get out of fractional horsepower range. Hookup wire is usually a minimum of 8 gauge for lower voltage units.
Q: What's the tradeoff with higher voltage DC units vs lower voltage DC units? Yes, I know Ohm's law... What I'm after is the practical difference in terms of performance and application.
I guess I've stayed away from DC motors because of all these things. Maybe someone can enlighten me. All I can say, is that all my 3 phase motors and VFDs have done nothing but give me rock solid performance.
Ray