# Are people still using DC motors to power their machines?



## sdy5001 (Apr 8, 2021)

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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## Karl_T (Apr 8, 2021)

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.


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## Ulma Doctor (Apr 8, 2021)

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


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## martik777 (Apr 8, 2021)

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
					

Smarter Shopping, Better Living!  Aliexpress.com




					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.


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## epanzella (Apr 8, 2021)

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


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## Superburban (Apr 8, 2021)

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.


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## savarin (Apr 8, 2021)

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.


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## Bi11Hudson (Apr 8, 2021)

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.

.


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## mattthemuppet2 (Apr 8, 2021)

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


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## markba633csi (Apr 8, 2021)

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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## sdy5001 (Apr 9, 2021)

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.
> 
> ...


oh man, you're eliminating the crazy crystals? One is an old Delta 14" bandsaw and the other a van norman no. 0 mill...


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## sdy5001 (Apr 9, 2021)

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


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?


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## Karl_T (Apr 9, 2021)

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.


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## markba633csi (Apr 9, 2021)

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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## mattthemuppet2 (Apr 12, 2021)

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.


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## Shotgun (Apr 12, 2021)

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.


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## sdy5001 (May 2, 2021)

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


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...


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## markba633csi (May 2, 2021)

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


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## Packard V8 (May 2, 2021)

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


Where might one find a KB SCR controller?

jack vines


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## markba633csi (May 2, 2021)

Ebay has them, here's one that's been tested:  price is reasonable at 40$. Some of the prices are outrageously high IMO








						KBLC-120 120VAC Input DC Motor Speed Control, Used, Tested  | eBay
					

KBLC-120 120VAC Input DC Motor Speed Control, Used, Tested. Condition is "Used". Shipped with USPS Priority Mail.



					www.ebay.com


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## Joe in Oz (May 3, 2021)

... 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....


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## Nigel123 (May 3, 2021)

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...


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


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## Shotgun (May 3, 2021)

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


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.


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## GrahamT (May 3, 2021)

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...


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.


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## Nigel123 (May 3, 2021)

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.


Most of the motors I use are old iron Reliance and Baldor yes they are big but barely get warm when running


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## Nigel123 (May 3, 2021)

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.


Thanks for the comparison the current limit on the DC drive is a nice option saves on fuses or worse


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## Shotgun (May 3, 2021)

Nigel123 said:


> Thanks for the comparison the current limit on the DC drive is a nice option saves on fuses or worse


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.


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## RJSakowski (May 3, 2021)

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.


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## brino (May 3, 2021)

RJSakowski said:


> When the project is completed, I will be writing up a full article in a separate thread.



Excellent! I am looking forward to it.
-brino


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## epanzella (May 3, 2021)

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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## sdy5001 (May 3, 2021)

markba633csi said:


> Ebay has them, here's one that's been tested:  price is reasonable at 40$. Some of the prices are outrageously high IMO
> 
> 
> 
> ...


Thank you so much. Over the past 2 months I have talked to innumerable reps from KB themselves, Galco, and whatever other big reputable manufacturer or distributor and not one has suggested the KBLC120, yet it appears to be the exact controller that I described as ideally looking for (and at $85 new, also 1/3 the price of what was often suggested...which is so frustrating and disheartening...) Anyhow, I just read the provided manual with that drive and it appears to be pretty close to spot on and if wired up in a decent enclosure with a heat sink and fan, appropriate resistor, and some fuse, that it should perform quite well for quite some time. Thank you very much for sharing that, and this goes to everyone, thank you very very much for sharing your knowledge and time in general!


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## sdy5001 (May 3, 2021)

epanzella said:


> 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.


Can you share which VFD you are using?


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## sdy5001 (May 3, 2021)

Ulma Doctor said:


> 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
> ...


Is there a 'cheap vfd' you recommend for something single phase in the 2hp range? That is the tentative plan for my upcoming mill project, which I expect to get underway in about 2 weeks so I'll be ordering a setup quite soon....


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## epanzella (May 3, 2021)

sdy5001 said:


> Can you share which VFD you are using?


This is the one I got from from AMAZON. It's a MYSWEETY



			https://www.amazon.com/Variable-Frequency-Drive%EF%BC%8CMYSWEETY-Converter-VFD-2-2KW/dp/B07D76365G/ref=sr_1_6?dchild=1&keywords=vfd&qid=1620087796&sr=8-6


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## epanzella (May 3, 2021)

sdy5001 said:


> Is there a 'cheap vfd' you recommend for something single phase in the 2hp range? That is the tentative plan for my upcoming mill project, which I expect to get underway in about 2 weeks so I'll be ordering a setup quite soon....


VFDs only work with 3 phase motors.


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## Ulma Doctor (May 4, 2021)

sdy5001 said:


> Is there a 'cheap vfd' you recommend for something single phase in the 2hp range? That is the tentative plan for my upcoming mill project, which I expect to get underway in about 2 weeks so I'll be ordering a setup quite soon....


i have this model on my Shenwai 1236 lathe
it performs flawlessly









						Variable Frequency Drive / Inverter 3kW  4HP  220v  3 Phase  | eBay
					

3KW 220V 4HP 3 Phase 13A VFD Variable Frequency Drive Inverter. Frequency Drive 220 Volt, 3KW (4HP), Three Phase. Input ： 1 or 3 phase 220V/ Output ： 3 phase 220v. Frequency ： 0-50hz/60hz.



					www.ebay.com


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## Ulma Doctor (May 4, 2021)

epanzella said:


> VFDs only work with 3 phase motors.


not exactly.
folks have successfully hooked VFD's up to single phase motors
some motors are not good candidates without modification, namely capacitor start and capacitor run motors


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## epanzella (May 4, 2021)

Ulma Doctor said:


> not exactly.
> folks have successfully hooked VFD's up to single phase motors
> some motors are not good candidates without modification, namely capacitor start and capacitor run motors


I stand corrected, never heard of that before.


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## Ulma Doctor (May 4, 2021)

epanzella said:


> I stand corrected, never heard of that before.


i didn't think it was possible either, until i saw a working motor/vfd set up


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## RJSakowski (May 5, 2021)

The VFD's for single phase motors that I have seen have largely been used to control things like fan motors.  Fans have a low torque requirement at low rpm.  As I recall,  the torque required is proportional to air flow velocity cubed and  by extension, roughly to rpm cubed.

Ac induction motors have a speed determined by line frequency.  This is true whether the motor is  single phase or a split phase.  In theory, changing the line frequency should change the motor speed and this should apply to both single or three phase motors.  The rub occurs with capacitor start motors  because as the speed drops, the start circuit kicks in.  The start circuit is designed for short cycle times and will quickly overheat with prolonged operation.  Thus, VFD's have been considered unusable for single phase capacitor start motor.

There are a couple of options available for VFD operation on single phase  capacitor start motors.  One would be to change the centrifugal  switch characteristics.  Anyone who has dealt with a bad capacitor, switch, or start winding is aware that you can start the motor by turning the motor by hand in the desired direction.  Ir only takes a few rpm to activate the motor.  If the switch were modified by either adding weight to the centrigugal weight or decreasing the spring force, the start switch will cut out at a lower rpm.  If that rpm is below the typical operating range, the motor should behave well.  

Another way to use a VFD on a single phase capacitor is to remove the capacitor  and switch.  The start winding is then treated as a second leg of a three phase motor.  The VFD modifies the current in the second leg to prevent overheating and the motor runss.  I expect that VFFD's specifically designed to operate single phase motors are capable of varying the phase relationship from the typical 120º difference to optimize operation.

This is a theoretical discussion.  I haven't actually attempted this myself and modern VFD's are sophosticate devices capable of controlling a multitude of parameters. My original interest was to use the OEM single phase motor on my G0602 lathe as the assigned space requirements are strict.  My hesitancy was largely based on low end torque specifications and I couldn't find performance curves.  My p4rimary desire was not to increase high end rpm but to decrease low end  rpm.   The low end of the operating range on the OEM lathe was 150 rpm.  There are times when I would like to drop that to more like 50 rpm.  With now guarantee of adequate operation, I was hesitant to invest several hundred dollars in an experiment.


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## jwmay (May 6, 2021)

While this topic seemed to develop into something more technical than i could hope to keep up with, I have a small warning regarding the treadmill motor idea.  When buying a donor treadmill, you don't always know what's inside it. I bought one, and the motor ended up being completely open with no protection from swarf, and it's variable speed came by way of a plastic reeves type pulley. Completely unusable for machine tools. So in the end I ended up with a destroyed treadmill to dispose of, fifty dollars less in my pocket, and 6 hours of wasted time. In the future, I will pay more money for parts I know are useable.


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## Shotgun (May 6, 2021)

jwmay said:


> When buying a donor treadmill, you don't always know what's inside it. .  . So in the end I ended up with a destroyed treadmill to dispose of, fifty dollars less in my pocket, and 6 hours of wasted time. In the future, I will pay more money for parts I know are useable.



In the future, watch the free section of Craigslist and be patient, and keep your wallet in your pocket. 

I've got the motor from a free one sitting on a shelf, another in shop ready to take apart, and two have popped up since I dragged that one home.  There is currently one available about an hour from me that I refuse to look at anymore, because I might go get it.

That said, you're $50 doesn't have to be completely lost:
-Save the walking board, and put it down in front of your mill or lathe with the plastic sheath on it.  It makes for a nicely padded place to stand, and swarf sweeps off the plastic easily.  I expect it to get ratty in a few months.  I'll rip the plastic off, use the MDF for trial cuts, and replace it with another freebie. 
-Those two rollers at the ends of the tread are nice for making a work support system for cutting long boards.  There is plenty of square tube in the treadmill for making the support frame.
-The lift motor (if the treadmill has it) is bi-directional and slow.  It would make a nice power feed for a mill table or lathe.
-Did it have a power lift spring for the walking surface to flip up.  Those can be quite useful in a number of projects.
-I keep all nuts and bolt that aren't mangled, and those treadmills are full of 'em.  Good quality, too.
-That walking tread is some really tough material.  Nice for anything you want to protect from swarf.  Cut it and roll it up.  Keep it on a shelf.

Even the motor:  It's open, but a little sheet metal can fix that.  That treadmill should have some.  I just left mine open.  If swarf destroys it, I'll be willing to pay double for its replacement.  I turned down the pulley it had, and fitted the pully stack that came with my RF-30 mill onto the stub.  I use the smallest one of the stack. And have a low-medium-high selection using the intermediate-to-spindle pulley setup. It shouldn't be hard to make an aluminum adapter.


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## jwmay (May 7, 2021)

You know I just knew somebody would have a million ideas for that old treadmill. Haha.  I've since learned a little bit, and agree that there was plenty of usability in what I had. But that ship..err treadmill sailed away on a scrap boat many years ago now.

I can't even remember what I was trying to run with it now. The only thing I had back then was a treadle sewing machine base with a grinding arbor mounted to the table and hand tools.

Glad those days are behind me! Ha!


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## rwm (May 7, 2021)

I know this thread is a little stale but y'all might be interested in this:









						275.0US $ 20% OFF|1000W Brushless DC Motor / Main Control Board / WM210V Lathe Power Drive Board&Motor Kit|Power Tool Accessories|   - AliExpress
					

Smarter Shopping, Better Living!  Aliexpress.com




					www.aliexpress.com
				




1.3 HP with a wide RPM range available.

Robert


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## Shotgun (May 28, 2021)

rwm said:


> I know this thread is a little stale but y'all might be interested in this:
> 
> 
> 
> ...


Still prefer the treadmill motor, if you can find it.  If you can find one with a working MC-60 or MC-2100 controller, it has several power takeoffs that are useful.  I've pulled power for LED work lights and to power a $5 Walmart USB fan.  It's all automatically tied into the switch that powers the mill.

There is also a power takeoff that controls the treadmill incline motor that runs at a good speed for power feed.  I was working that into the project, but went with a purposed designed power feed instead.  I got in a hurry for a solution.

Even if you have to get the control board on the aftermarket, there is just so much more utility there in the treadmill.   I'm posting a good diagram to follow below.  Using this, I figured out where to get the 8v to 12V to power a flexible-arm, LED desk lamp.  Cut off the wall wart, and spliced it straight into the connector.  You'll also see the power take-off for the incline motor, and the connector to tie into to control it with low power switches.



			https://dl.dropboxusercontent.com/s/3try02vjpvf8jur/Treadmill%20Schematic.jpg


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