Let's talk dc motor control

[ScubaSteve]

I've been looking at what it might take to power some of these awesome old-school power tools I keep seeing pop up. They're definitely old and rusty, but a little TLC goes a long way. I'm researching what it will take to install a large DC motor to drive some of these beasts. I've never really worked much with DC....I do have a background in electronics...just not building/application of drive motors and/or machine tools.

What I know:

1. I need a DC motor with >1 horsepower, especially for a metal lathe or milling machine.

2. I need some type of motor controller for speed control.

3. I need some way to convert AC to DC...might be a feature of the speed controller.

4. I need to mount the motor appropriately, hopefully using the belts or gears that were designed to work with the machine.


What I don't know:

1. What kind of contoller/converter to look for. I see plenty of 0-90VDC controllers, but I think I'll need something bigger than a 100W PWM to run a 3HP motor, right?

2. LOTS of other things.

 

[CodeRage]

Does it need to be DC?

If so you're looking at large DC servos and servo controllers.

If these are for Mills and Lathes, look into some small 3 phase motors.
3phase motors
and you can find single phase in three phase out drives like these
VFD

 

[ScubaSteve]

No, it doesn't have to be DC, but it seems that they are more readily available and more powerful. Another thing I know very little about: 3-Phase. But what I do know....there is some AWESOME equipment to be had if you have 3 phase. I've walked away from several bulletproof welders because of this. The VFD drives are effing expensive.

There was a dude on here who powered his mill with some kind of fangled speed/frequency/voltage converter. You could pretty much dial in whatever you wanted. It was delicious overkill.

 

[CodeRage]

yeah, three phase is preferred because there is virtually no slip in the motor, tons of torque. With the VFD you can change the frequency of the AC wave form wich translates to spindle speed. That and you get nearly 100% power even at the lower speeds.

There's a dozen ways to skin this cat though. Good luck

 

[Catt22]

IIRC, three-phase power is rather rare for residential services and costly to have installed.

 

[Wberry]

FYI - You can MAKE 3 phase power for your house using a 3 phase motor and a cap start single phase motor ... that sould be enough info to get you into trouble on google.

For cheap DC drives look up fincore on ebay. For easy AC - look at stuff from automation direct.
If you can better describe what you are trying to accomplish there are enough electrical/industrial engineers here ... I am sure we can get you sorted out.

 

[ScubaSteve]

Really what I'd like to do is get an old metal lathe or mill and bring it back to life. I've seen several of them around; the older ones are about all I can afford, but they're also very well built.....most just need a lube and tune; maybe some paint. These units are often pulley driven; some are underpowered or lack adequate controls. seems like a cool project if I could nail down an affordable machine!

 

[Wberry]

Well, IF you can find one that is reasonably priced and actually has a straight, still threaded collet shaft then I would buy a Bridgeport. You can upgrade over time to digital readouts (DRO) and there are some after market servo packages for table control. The biggest problem that used machines tend to have is the deck is no longer square to the head and that the y-axis (toward and way from the operator) gets loose on its guides and can rack/twist. Though an EXCELLENT machinist can compensate for this with shimming and deep understanding of the behavior - it would be best as a beginner to start with a machine that is good/great shape. Guys that repair electrical motors tend to keep their vertical mills and lathes in very good shape, as opposed to a facility that used the machines 24/7 for 30 years - so try to find one that is going out of business.

A vertical mill would be my preference unless you see needing to turn a lot of stuff and even then I would lean toward careful jigging and a rotary table add-on for the mill (you just wont be able to easily thread stuff).

I would think in IL you could pick up one for $3500-$5500 that is in GREAT shape.

The other nice thing about a vertical mill with an automated table is that with a crafty jig you could hook up an oxy-actylene torch and have an automated cnc cutter!!!

Lastly, we will full circle to power ... I don't want to get into any trouble with direct recommendation; but, I can tell you I have seen a shop where my aforementioned 3 phase motor trick was used to run a lathe, cnc mill, horizontal mill, punch press, cnc plasma cutter and a sliding deck band saw from standard 200A single phase 220 ...

Post back if you have any specific questions!