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Author Topic: 35A 24v Dc motor control  (Read 1483 times)
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Hi all,

So I have a universal brushed DC motor that I want to use to power my metal working lathe,

I have just bought a 35A 24V power supply at a bargain price on ebay.

Now I have some optical encoder wheels and sensors lying around from an old inkjet printer and the motor I have has built in hall sensor.

So I would like to use one of those to provide feedback to regulate the RPM but I would also like to adjust the RPM manually.

What is the best way to configure these?

I know I will need to buy either some chinese motor board for arduino or build one myself with some high current transistors but I don't know how I go about controlling the RPM so that eventually I can have a nice LCD display with RPM and some buttons up and down to adjust, Then I would like the software /arduino to lock in the RPM with the inputs it is getting from the hall or encoder wheel. I don't need reverse at the moment braking would be nice, Maybe in the future I will want it reversable so I can make my whole lathe CNC which would be the ultimate goal.

P.S my universal motor is actually a replacement washing machine motor rated at (average) 300w and with an rpm of 12,000! I found that when powering it with a 19v Dc laptop power supply it has a nice slow speed and good torque, which is perfect, and means I won't risk electrocuting myself when the controller is inevitably in pieces being tinkered with in the messy garage.
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This encode library will help you with the programming... http://www.pjrc.com/teensy/td_libs_Encoder.html

Also some a el cheap o motor drive will not stand up to a high power motor like that! I have posted links to reputable place to get one
http://www.trossenrobotics.com
http://robotmarketplace.com/store.html

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What motor? is there some data about it?  Universal motors for mains use are not necessarily OK on DC as
the inductance of the field windings limits the current at mains frequencies - so some further testing to
ensure it isn't overheating on DC would be wise.

You'll probably want to disconnect the field windings from the armature circuit and provide constant
voltage to the field and only PWM the armature, should keep the torque reasonable at lower speeds.
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Quote
I have a universal brushed DC motor
I didn't know there was such a thing. LOL

Is this a DC motor, AC motor ?
Do you have a URL for it?
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Good luck, Jack

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What motor? is there some data about it?  Universal motors for mains use are not necessarily OK on DC as
the inductance of the field windings limits the current at mains frequencies - so some further testing to
ensure it isn't overheating on DC would be wise.

You'll probably want to disconnect the field windings from the armature circuit and provide constant
voltage to the field and only PWM the armature, should keep the torque reasonable at lower speeds.

thanks for your input, what is the difference / benifit or using pwm over voltage regulation, Can I use an adjustable voltage boost, and put that thru the armature for speed control or maybe use it along with pwm in the same driver circuit?

What is the benifit of pwm? what I'm saying here is that I've got it in my head that:

Current = Torque & Voltage = Speed (within limits).

Is this right or am I thinking wrong?


I can't find the manufacturers website or a schematic for it anywhere but it is very similar to this: http://www.ukanfixit.co.uk/content/indesit-washing-machine-motor-mca-6164-148ad1-c00143307

It seems the field and armature are not connected as I just continuity tested them, for the motor to work the armature cables have to be either connected together (series) or in parallel, there is no continuity between any one of the 2 armiture cables and the field windings.

The box it came in says universal motor and alternator, Had a big picture of a car alternator on the box.
And I read on a forum a post from a guy that fixes washing machines he said they would run at 12v + so I tried it and it worked, there is much more torque and slower speeds when the armiture is wired in parallel.



« Last Edit: August 17, 2013, 09:43:07 pm by charlie_smith87 » Logged

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I'm going to post random stuff now here because I have too many tabs open,

Power supply:

http://www.ebay.co.uk/itm/251312682419




Motor Driver Circuit Requirements,

Must have

Robust Design with High current capabilities and over-current / Over-heat protection.

Accept 20-36V DC input @ 35amps, (unregulated? dirty? Mains > fuse > Bridge Rect > Torrdial Transfrmr> out)

Output 24-72V Dc variable Voltage and PWM?

Soft start.

Adjustable output for motor speed controlled by input from arduino (5v logic, or pwm output pins), Will add LCD display later for RPM, etc will be handled by Arduino.


Wish list

DC brake and reverse expandable in future.

Extra channels for Leadscrew & Top slide for full CNC.
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That power supply will produce an output as rough as a badgers bum.  I also doubt very much if it could deliver 35A for any length of time (10 amps might be nearer the mark)

As to why PWM is better than variable voltage.  Firstly for a DC operated field excited motor you need a fixed field voltage to maximise torque output. The ask yourself how you intend to vary the armature voltage.  Assuming you want to produce an output of say 5 volts at the full rated current of 35A you'd have to "lose" 19 volts across the regulator.  That means a heat dissipation of some 700watts.  By using PWM you can get down to virtually zero drive at full current with virtually no heat loss.

You stated that the field in parallel gives the slower speed and more torque.  You have learned one of the fundamentals of DC motors.  May I suggest you read up on DC motors and their control as this will then guide you towards achieving what you want.
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This is a "universal" motor and you should be using a "router speed control" with it.

The dark blue and light blue wires connect to the brushes, the red wires appear to be a tach output, and that leaves the brown, orange, and black wires for, likely, two ranges of speeds. You could guess that the black connects to the AC neutral line and the brown / orange allow to ranges of speeds, but without documentation it would be dangerous for anyone to make a straight up recommendation.
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That power supply will produce an output as rough as a badgers bum.  I also doubt very much if it could deliver 35A for any length of time (10 amps might be nearer the mark)

As to why PWM is better than variable voltage.  Firstly for a DC operated field excited motor you need a fixed field voltage to maximise torque output. The ask yourself how you intend to vary the armature voltage.  Assuming you want to produce an output of say 5 volts at the full rated current of 35A you'd have to "lose" 19 volts across the regulator.  That means a heat dissipation of some 700watts.  By using PWM you can get down to virtually zero drive at full current with virtually no heat loss.

You stated that the field in parallel gives the slower speed and more torque.  You have learned one of the fundamentals of DC motors.  May I suggest you read up on DC motors and their control as this will then guide you towards achieving what you want.


These torrodial core transformers seem to be much more efficient than traditional transformers, However you might be right about continuos current, I will find out when I get it.

Thanks for the clarification on pwm I will have to experiment with that power supply with my motor, I'm doing all of this because I want a solution to power my lathe that requires less gearing in the form pulleys, they annoy me, left exposed they are dangerous in a messy workshop and In 2013 we should be able to come up with a direct drive motor and control for something like this.
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Below are some motor controllers that might be of interest.

http://store.qkits.com/category.cfm/DCMOTOR
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This is a "universal" motor and you should be using a "router speed control" with it.

The dark blue and light blue wires connect to the brushes, the red wires appear to be a tach output, and that leaves the brown, orange, and black wires for, likely, two ranges of speeds. You could guess that the black connects to the AC neutral line and the brown / orange allow to ranges of speeds, but without documentation it would be dangerous for anyone to make a straight up recommendation.


Mine is slightly different, ( MCA 61/64-148/CY ) it has the 2 red Tachos wires in the middle and the brushes are one blue and one pinkish orange, there are 3 field windings, I think one is a tap for starting or speed control.

Are those router controls using a Triac or pwm? I have one of these:
 http://www.ebay.co.uk/itm/390600205094

I suspect it is the same thing as the router control, Based on a Triac, I have actually tried this with the motor and it seems to work for half a second, it blows my trip from the current draw ( I have a very weak RCD on this particular socket even starting a hoover will trip it, its fine for lighting and other stuff I normally plug in there) I will try it with another circuit today.

I could forget the DC power supply and maybe control the motor with this using my arduino to to trigger the gate of the Triac with pwm pin, but will need to isolate it properly.  
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Below are some motor controllers that might be of interest.

http://store.qkits.com/category.cfm/DCMOTOR



Thanks some of them look good :-)
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I know it's not exactly in the make-do-and-mend philosophy but I drive my lathe and milling machine with variable frequency inverters powering 3-phase motors.

Small (relatively inexpensive) VF inverters are readily available that are powered from 240v single phase and they produce a pseudo 3-phase 240 volts at frequency from a few Hz up to 100Hz.  This frequency variation is what controls the speed of the motor.  The drive voltage is controlled by the inverter to provide the full torque.  Many will say the motor doesn't get adequately cooled but that, as far as I'm concerned is an urban myth.  I've never had problems with motor cooling.

OK they aren't as cheap as a scrap washing machine motor but they are excellent at machine control.

You might want to browse over this site for typical info  http://www.newton-tesla.co.uk/
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