Are people still using DC motors to power their machines?

[sdy5001]

I have two machine restorations going on that I'm unsure what route to take so I guess I'm trying to lean on the community for input, but unfortunately I think the questions have a little bit of the chicken and the egg quandary inherently built in, but what route should one take when breathing new life into beautiful old flat belt driven machines?: single phase AC motors that use belts and pulleys for limited clumsy speed control, gamble with the longevity of repurposing DC motors, or having to alter the budget and break the bank with a VFD/3 phase setup?

Maybe 2 or 3 years ago, there seemed to be this surge of people of re-purposing treadmilll motors to run all sorts of machines and apparatuses in the home shop. Some had seemingly done it with more success than others, with the primary reasons for the ones that weren't successful coming from all angles (with both the PWM and SCR drives themselves burning up...usually because of poor import quality components, these drives frying brushes and armatures and windings in the motors, etc, and then with the more successful systems failing because the motors aren't sealed so they're trying to cool themselves with abrasive chips and shop dust) so by the time all of these issues are sorted, you've invested the same as if having bought an import VFD and 3 phase AC motor, I think, anyway. What are people doing on here now with machines that they plan on keeping for themselves for quite a while? If running DC motors, what drive/motor combos are you using? If going with the 3 phase route, what motor/VFD combos there? It seems that powering these machines is harder than engineering their construction in the first place, ha...

 

[Karl_T]

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.

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

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.

 

[Ulma Doctor]

MC40,MC60,MC80 boards are great for driving DC motors
KBC drives are proven assets
Dart drives are great DC drives
treadmill motors work very well

I work with higher end VFD's equipped on the machines i work on, but i use very inexpensive VFD's in my shop
My philosophy is that i can buy 3 or 4 inexpensive drives for the cost of a high end drive
the high end drives don't really power the machines any better than the low end drives in my experience
i have not had a single failure or experienced any of the horror stories others will lead you to believe.
this is on heavily used equipment- milling machines, lathes, surface grinders, pedestal grinders, tool and cutter grinders
for this experiment of 8 years on varying equipment and many cheap VFD's , i'll give the inexpensive VFD's a nod of confidence.
i figure if i do ever loose a VFD, i'll spend only a few $$$ and be up and running again
instead of spending for several hundred or up to thousands on a drive, i have been stocking my toolboxes with the money i have saved
the best motors to use with VFD's are inverter rated, but don't let that stop you
most motors can safely be operated for short periods of time out of the 60Hz envelope
a safe zone is 30 to 90 Hz for normal induction motors
for inverter rated motors the envelope can be very low 5hz or so up to 400Hz

 

[martik777]

Converted my mill and lathe to 3 phase (~ 1HP) with VFD. Motors on craigslist for < $50, VFD was ~ $50 but $90 now:

63.36US $ 55% OFF|VFD Inverter VFD 1.5KW /2.2KW Frequency Inverter XSY AT1 3P 220V Output Frequency Converter Variable Frequency Drive|Inverters & Converters| - AliExpress

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www.aliexpress.com

I use a treadmill motor with the SCR 10,000w controller, bridge rectifier and reversing switch for variable power feed on one of my lathes.
They have all been working for years without an issue.

 

[epanzella]

I went the VFD route. Low speed torque is great.

 

[Superburban]

I have a drill press that I repowered to DC, with a simple controller. It is a normal size motor, That was on an engraver that I picked up. I think it is a 120 Volt DC. Its been quite awhile since I looked at it. Works great for the drill press.

The controller is mounted to the left of the starter, and the motor is in the second pic. Yes, this is not a drill press. they were the only pics I could find on my computer. I took them off the engraver, and added them to the drill press. The controller is simple, just a few soldered components, and the rheostat.

 

[savarin]

Just finished converting my lathe to DC.
Total cost:-
Used treadmill motor, 180 VDC, 5000 rpm $0.00
simple cheap chinese controller $24
240VAC computer fan $0.00
I am wrapped in its smoothness and variable speed to the point where I will be converting my drill press to DC in the same manner.
We will see how long the controller works for.

 

[Bi11Hudson]

I am NOT a machinist, I am a model builder that uses machine tools to help build those models. Most of my machines are "fractional horsepower", with the exception of a compressor of 5HP. All are single phase A-C machines. There are advantages and disadvantages to any drive system. For my application, and mine alone, the single phase motors are the best bet.

D-C Drive Advantages are many, not the least of which is speed. D-C motors have been around longer than A-C motors, will run on 1 phase AC(with a rectifier) or DC, are easily reversed by swapping the "A1-A2" leads. They are excellent for low speed, bone crushing torque and are still used for hoisting equipment. There is a technique for increasing motor speed above base speed that is seldom used in smaller applications. It is called "field weakening" and is not usable on motors with permanant magnet fields.
Disadvantages: Heat in the controlling apparatus. Several winding techniques; Series has good torque, Shunt has fair speed regulation, Compound has a little of both but isn't really good at either. High maintenance, both brushes and cleanliness. Speed control is dependant on the type of contron. Pulse width modulation is good, but expensive.

PolyPhase AC(3 or 6 phase): Advantages are no moving parts beyond the rotor. easily reversable(swap any two leads), low maintenance(just bearings), strong(but not as strong as DC), essentially maintenance free. I have seen 3 phase motors that were in place before I was born.
Disadvantages: Speed control. AC motor speed is a function of power line frequency. To regulate speed, one must use a VFD, which can cost as much as the motor. An AC motor can be run above or below base speed by manipulating the synthetic frequency of the power line.

Single Phase AC Advantages: Cost, generally cheaper than the other options. Speed regulation is very good, either poly phase or single phase. Will run on single phase (household) power.
Disadvantages: Speed control. AC motor speed is a function of power line frequency. Single phase cannot be used with commercial 3 phase VFDs. Frequency can be regulated with synthetic power, but it is usually a "one off" design and fairly expensive. There is a "lope" in single phase power that can cause undesirable surface finish for beginners. That can be easily remedied with a flywheel for continuous running. But is a pain in the wazoo for frequent stops and starts.

Now that I have thoroughly confused you, let's introduce http://www.hudsontelcom.com/uploads/ShopElex.pdf to further the confusion. It only "touches" on motor theory, a generally deep subject. Motors are but one branch of electrical theory and take up many volumes of text. There is no universal one size fits all answer.

Now for my opinion(like a$$#0!es, everybody has one and most of them stink) Go with the cheapest solution you have, but leave some room to change in the future as your own needs mature. An example being that should you decide to make the machine(s) portable, as in truck or trailer mounted, DC becomes the default by necessity. Single phase with a low end generator becomes the fall back. Should you opt for a commercial shop where 3 phase is available, the answer is obvious. If you're like me and want to get old with as simple a power need as possible, single phase is the best.

.

 

[mattthemuppet2]

still using DC motors, just working up a drive for my new-to-me South Bend 9. They work really well, variable speed is fantastic and it's hard to argue with the price

 

[markba633csi]

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