Are people still using DC motors to power their machines?

... i'm waiting for the day someone puts a Tesla motor on a big old horizontal mill and makes chips 3/4" x 1/4" thick....
 
sdy5001 said:
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...
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I converted most of the shop machines to DC about 20 years ago using motor and drives that had been scavenged from obsolete machines over 30 years in the industry
They range from 2.5 hp to fractional hp about 20 in total
Most are SCR drives Dart Multidrive or Minirac
4 are Variac (autotransformer) with a Bridge rectifier
All setups have worked very well over the years no motors have failed I clean the carbon out with a vacuum about every 5 years or so
Lost a couple of drives but these were all well used when installed
Not a big fan of PWM drives have replaced some with SCR drives for some people with wood lathes
Worked with VFD drives about 30 years ago they were crappy back then just like DC drives were when they first came out
Back in the early 70's the cost for a drive was about $1200
Now Vfd's have improved with time just like DC drives did and the price came down
Would like to hear more on VFD setups how people like there torque range over the speed range
load to no load situations
 
Nigel123 said:
Would like to hear more on VFD setups how people like there torque range over the speed range
load to no load situations
Click to expand...
I have an Atlas/Craftsman driven by a 3-ph on a VFD through a 110->220 step-up transformer, and a RF-30 clone mill using a 1.75Hp treadmill motor controlled by the MC-2100LTS circuit board.

I put both on a watt meter, and they pull about the same power. One kilowatt. I don't have any other empirical measures, but my "feel" is that they both bog down about the same under load, except that the mill will switch itself off if I bog it down too much for too long. Of course, that may just be a suggestion from the mill that I shouldn't be taking a .020" DOC with a 4" facemill on A36 steel.
 
sdy5001 said:
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...
Click to expand...
I am still running my old Drummond lathe using a GE 1HP DC motor that I bought second hand twenty years ago. I designed and constructed a motor speed control based on a simple triac phase control with feedback, works well and has been reliable. The motor is BIG for 1HP, and with thoughts of saving space, I bought a brushless 750 watt motor, 1 HP, and speed controller from a sewing machine supply company used to retrofit to industrial sewing machines. Unfortunately it did not live upto expectations. Main problem was resonance points at certain speeds, very similar to stepper motor resonance when the input supply to the motor, a complex pulse proportioned waveform interacts with the mechanical characteristics of the motor to produce vibrations that were transmitted to the lathe spindle. Try as I might to reduce this effect using damping pads and different sized pulleys and belt types the problem persisted. The other problem was at low speeds, the motor, being very compact, weighing only a couple of pounds, would quickly overheat, even lightly loaded due to the fan not spinning fast enough. The old GE beast would run all day at a hundred revs a minute and remain just warm, big fan paddles, large thermal mass and large surface area to dissipate heat, plus generous amounts of copper conductor and magnetics to reduce resistance and eddy current losses which produce the heat!
Just my experiences for what they're worth.
 
GrahamT said:
I am still running my old Drummond lathe using a GE 1HP DC motor that I bought second hand twenty years ago. I designed and constructed a motor speed control based on a simple triac phase control with feedback, works well and has been reliable. The motor is BIG for 1HP, and with thoughts of saving space, I bought a brushless 750 watt motor, 1 HP, and speed controller from a sewing machine supply company used to retrofit to industrial sewing machines. Unfortunately it did not live upto expectations. Main problem was resonance points at certain speeds, very similar to stepper motor resonance when the input supply to the motor, a complex pulse proportioned waveform interacts with the mechanical characteristics of the motor to produce vibrations that were transmitted to the lathe spindle. Try as I might to reduce this effect using damping pads and different sized pulleys and belt types the problem persisted. The other problem was at low speeds, the motor, being very compact, weighing only a couple of pounds, would quickly overheat, even lightly loaded due to the fan not spinning fast enough. The old GE beast would run all day at a hundred revs a minute and remain just warm, big fan paddles, large thermal mass and large surface area to dissipate heat, plus generous amounts of copper conductor and magnetics to reduce resistance and eddy current losses which produce the heat!
Just my experiences for what they're worth.
Click to expand...
Most of the motors I use are old iron Reliance and Baldor yes they are big but barely get warm when running
 
Shotgun said:
I have an Atlas/Craftsman driven by a 3-ph on a VFD through a 110->220 step-up transformer, and a RF-30 clone mill using a 1.75Hp treadmill motor controlled by the MC-2100LTS circuit board.

I put both on a watt meter, and they pull about the same power. One kilowatt. I don't have any other empirical measures, but my "feel" is that they both bog down about the same under load, except that the mill will switch itself off if I bog it down too much for too long. Of course, that may just be a suggestion from the mill that I shouldn't be taking a .020" DOC with a 4" facemill on A36 steel.
Click to expand...
Thanks for the comparison the current limit on the DC drive is a nice option saves on fuses or worse
 
Nigel123 said:
Thanks for the comparison the current limit on the DC drive is a nice option saves on fuses or worse
Click to expand...
The "worse" in this case being me having to walk all the way around the house to flip a breaker. The 2hp single phase motor the mill came with did not have this "feature". Just running it with belts arranged for the highest spindle speed would pull enough current to trip the breaker.
 
I am in the final stages of converting my G0602 with a 1hp single phase motor to a 2.5 hp variable speed dc motor. I kept the OEM pulleys and will have variable speed control from 15 rpm to 6,000 rpm depending upon pulley selection. In any single pulley selection, the speed can be varied between 6% to 100%. I added an encoder to provide feedback to counter low speed torque dropoff. It hasn't optimized yet but holds speed to within 5% regardless of load. Other features include onrush current limiting and protection against accidentally switching direction at speed.

The control uses a MOSFET transistor drive rather than an SCR to minimize any EMI generation as I also have a TouchDRO and Clough42 ELS on the lathe. The lathe has been operating with the breadboard circuit for about a month now with no issues. The current status is the final assembly of the circuit boards and integration on the final package.

When the project is completed, I will be writing up a full article in a separate thread.
 
I put a 2hp BALDOR with VFD on my mill. Very impressed with low speed torque especially when power tapping. I limited my bottom end at 30hz although the documentation says 15 hz can be used safely. I kept the standard stepped pulley setup so my speed range went from 120 - 2500 to 60 - 5000. The only slight snafu I've encountered is my brake setting. I keep the brake force high so I get instant reverse when power tapping which is awesome BUT the VFD will trip due to overcurrent if I shut the mill down suddenly from speeds above 3000 rpm as the electronic brake tries to overcome the inertia of all those pullies and belts in just a few seconds. I can avoid this by increasing the brake interval but I prefer to just wind it down a bit with the HZ dial before stopping from high RPM.
 
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