Are people still using DC motors to power their machines?

Karl_T said:
which machine, what HP, what speed range?

I am rebuilding a Monarch 10EE from DC to 3 phase motor and VFD. Have a thread on it here.
www.hobby-machinist.com

Which VFD for 10 hp spindle

You don’t need the encoder. It is helpful for maintaining extremely low rpm or very precise rpm regardless of slip. You can always play with pulley size on the motor to get your ideal performance.
www.hobby-machinist.com www.hobby-machinist.com

For machines of say 3hp or more 3phase VFD is a pretty clear winner. small stuff depends. Keep in mind it nice to over size the 3 phase motor to give torque at low speeds.
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oh man, you're eliminating the crazy crystals? One is an old Delta 14" bandsaw and the other a van norman no. 0 mill...
 
markba633csi said:
I like DC drives, but then I've been lucky as far as finding motors. The one I'm using currently is a husky 4-brush EG&G servo motor with a KB scr controller. Buying surplus you can save a lot. Total outlay about 70$
The old technology scr speed controls are easy and cheap to fix (not that they need frequent fixing in my experience) something you can't do easily with VFDs for the most part
They are a bit hummy but I don't mind- I just hum louder :)
-Mark
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Mark,
I'm running my small metal lathe, ostensibly anyway, off a similar setup and that is kind of the impetus for this post. That works a treat and has for the past year or so and I have another DC motor just laying around so I figured I would try and do that again. However, this second motor is annoyingly bigger and I'm afraid that it would fry up most of the KB drives (the motor is a 90VDC 20A jobber that's rated for 2.5hp continuous so the KBIM and KBCC and KBPC and all of the other alphabet soup drives under $200 are rated for like half that draw or less...) so It spurred a little bit more in depth of a looksy at the other options and new 2-3hp 3phase motors with a new vfd can be had for like $300 so that seems like a no-brainer, unless I'm quite wrong, which seems to happen from time to time...what do you think?
 
Yep, once you get too big, the VFD 3 phase is the better option. it does pay to shop around for 3 phase motors - great deals can be found.
 
20 amps is about the limit from a 120 volt circuit and you are right most dc drives top out at about 1.5 to 2 HP. Personally if I was determined to use that motor I would modify a KB drive with bigger scrs, heatsink, and wind a custom "horsepower" resistor but that might be a bit out of your wheelhouse.
Also, anything above about 1.5 HP should really be run on 240 volts for efficiency's sake
-Mark
I believe in larger sizes you get smoother power delivery from 3-phase motors, from what owners of larger lathes have said on the forum
 
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most decent DC drives have overcurrent protection so if you use a more powerful motor and take a big heavy cut, the drive will either limit the current or shut itself down. No experience with KB drives, but I've had this happen with 2HP motors and MC60 drives. That's one big reason why I'm going through the learning curve to use a MC2100 drive with the lathe and then I'll probably add one to the mill to replace the MC60 it has.
 
I just scored another free treadmill off Craigslist. I'm planning to use the motor on the WT drill press I just acquired. It is hard to beat free. If it dies from shop dust, I wait for another treadmill to show up on CL.
 
markba633csi said:
20 amps is about the limit from a 120 volt circuit and you are right most dc drives top out at about 1.5 to 2 HP. Personally if I was determined to use that motor I would modify a KB drive with bigger scrs, heatsink, and wind a custom "horsepower" resistor but that might be a bit out of your wheelhouse.
Also, anything above about 1.5 HP should really be run on 240 volts for efficiency's sake
-Mark
I believe in larger sizes you get smoother power delivery from 3-phase motors, from what owners of larger lathes have said on the forum
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Mark, first off thank you, but secondly, how can I make that something I'm comfortable doing aside from taking some courses at the local tech school because that fundamental knowledge would seemingly be advantageous quite often. Anyhow, for the time being, I think I did something like that anyhow...I bought an SCR off eBay, had some full bridge rectifiers laying around, and made a little aluminum housing box, wired it all up and ran it slowly for a few minutes to listen and see what was what. The motor sounded fine and everything seemed ok so I ran it harder for a few minutes with a temp gun handy and everything stayed cool except the rectifier so I bolted that to a larger piece of aluminum and wired in a little computer fan and so far, everything seems good...
 
The thing you'll run into without some type of current/voltage sensing is the motor speed will vary depending on the load. The KB and others have circuitry to correct that, which is why they cost a bit more than a simple "light dimmer" or "router speed control"
May not be an issue for you- you may not ever load that motor enough to notice it
 
markba633csi said:
I like DC drives, but then I've been lucky as far as finding motors. The one I'm using currently is a husky 4-brush EG&G servo motor with a KB scr controller. Buying surplus you can save a lot. Total outlay about 70$
The old technology scr speed controls are easy and cheap to fix (not that they need frequent fixing in my experience) something you can't do easily with VFDs for the most part
They are a bit hummy but I don't mind- I just hum louder :)
-Mark
Click to expand...
Where might one find a KB SCR controller?

jack vines
 
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