Author Topic: Mad Modder speed control for DC motors...  (Read 5823 times)

Offline John Hill

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Mad Modder speed control for DC motors...
« on: December 29, 2013, 02:40:07 PM »
Suppose I have a 230V DC motor of a horsepower or so that I want to control the speed of (and I am too skint to want to buy a  "real" DC speed control).

How about a lamp dimmer to a rectifier to the motor? :coffee:

Now the lamp dimmer operates by delaying the turn on at every phase reversal  i.e 100 times a second (or 120 in some parts of the world) then when that goes through a rectifier we have pulse width modulated DC (with round cornered pulses).

I think it would also work with a transformer before the rectifier for lower voltage motors? :scratch:

Now then, do lamp dimmers have any smoothing circuits, inductors for example, to smooth the output which would have the effect of reducing the peak voltage.  If so we would want to take those out so that the motor got full voltage peaks and hence better torque.
From the den of The Artful Bodger

Offline awemawson

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Re: Mad Modder speed control for DC motors...
« Reply #1 on: December 29, 2013, 03:29:00 PM »
The old 'drill speed controllers' were phase delay controllers, and most mains drills are 'universal' ie ac/dc so if you drive your 'dc' motor from an ac source it will work if it is indeed 'universal' ie series or parallel comutated

http://en.wikipedia.org/wiki/Universal_motor

Andrew
Andrew Mawson
East Sussex

Offline Pete.

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Re: Mad Modder speed control for DC motors...
« Reply #2 on: December 29, 2013, 03:44:41 PM »
John you need a phase angle device and a rectifier. I use this to control the field voltage on my 3hp DC motor. You'll only get about 190VDC though.

The CSR1004 is the phase angle chip and will output 0-240VAC at 10 amps. You feed 240v into the middle leg and the right leg into a 10A bridge rectifier, other side of the rectifier to ground. Hook a 250k 1w variable resistor between the left and middle leg and this will give you zero to full speed control. You don't need the three pots as shown on my drawing, that's just for limiting the output from 50-115v on my lathe. A single control pot will do.




Offline Dawai

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Re: Mad Modder speed control for DC motors...
« Reply #3 on: December 29, 2013, 04:56:24 PM »
  I bought a KB 2hp "jumper selectable"  drive off ebay for $16..plus shipping..  "Hard to compete with that home-made."  It's the one running the cnc'ed english wheel in one of my youtube videos.

Large DC motors new are expensive. I got a cheap 3/4hp one and gearbox that came from under a treadmill.. drive was a pulse-follower. as the belt turned it spun a encoder pulsing the motor drive.   you see them drives about too. ( free )

I Hung a 24 foot Ibeam this morning in the ceiling by myself, programmed a Arduino this afternoon for a solar project, Helped a buddy out with a electrical motor connection issue on the phone, then cut up a chicken for Hotwings. I'd say it has been a "blessed day" for myself and all those around me.

Offline BaronJ

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Re: Mad Modder speed control for DC motors...
« Reply #4 on: January 01, 2014, 05:46:42 PM »
Hi Guys,

One of the problems with universal motors is that they tend to accelerate to very high rpm's if not loaded.  Another is the torque produced fall off very rapidly as the phase angle and hence the applied voltage reduces.  One way of trying to overcome these problems is to separate the field winding and feed it from a dc source then by feeding the armature from a phase controller you have more influence over the torque and speed.  I used to have a good application note all about motor control.  Unfortunately I lost this and a lot of other useful data following a HDD failure.  If I can find it again I'll post a link to it.
Best Regards:
                     Baron

Offline Dawai

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Re: Mad Modder speed control for DC motors...
« Reply #5 on: January 02, 2014, 05:22:40 AM »
A H-bridge control with current feedback is what you need. I wasn't trying to be smart saying it is cheaper to buy a drive, but it really is..

with a H-bridge, you have 4 power transistors and a big heat sink to dissipate the "lost power" or braking heat.
it is a push pull arrangement with two transistors doing a forward current, and two doing a reverse flow.

A good universal transistor to learn & play with is a IR540 FET transistor. it takes logic voltage input and can source (bad memory) 27 amps or so. With the logic gate you can tie it directly into a output pin on something like a basic stamp or a arduino processor. From that point you PWM (pulse width modulate) the signal going out to vary the amount of power it passes. Last similar project I had about sixty - eighty dollars in parts.

Setting up a dc motor and drive, you turn the max pwr adjustment all the way down, back up just a tweak, put a pipe wrench on the motor shaft, put your dc current meter inline with the motor, turn on the drive and turn the drive up to "YOUR motor nameplate power out", this will take a minute or two, it will heat up pretty fast under full current, but not burst into flames.. a dc motor can stall out and still apply torque pretty well.  THIS way, the dc drive will not "over current" the motor and burn it out, but stall when it reaches the max load the motor can pull.

The current feedback circuitry inside a dc drive is basically a inline resistor with a voltage drop across it comparative to the amount of power being pushed through it, used to be all IC circuits, now days it is a micro-processor.  I installed one dc drive that I as there from 8pm to 4am trying to program it without a booklet telling how..

Last real big dc motor I had, I put on a water wheel in a creek, a old truck axle, tied it directly to a heater coil inside the house and a switch on the wall, it'd never really heat the heater up red, but it put out free heat.. and I like free.

Look to the HF router speed control.. cheap, sometimes on sale.. I have one here, it is tied into a pvc welder to control the heat. it has no true feedback thou. Motor speed would vary with load.
I Hung a 24 foot Ibeam this morning in the ceiling by myself, programmed a Arduino this afternoon for a solar project, Helped a buddy out with a electrical motor connection issue on the phone, then cut up a chicken for Hotwings. I'd say it has been a "blessed day" for myself and all those around me.

Offline BaronJ

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Re: Mad Modder speed control for DC motors...
« Reply #6 on: January 02, 2014, 02:40:11 PM »
Hi Guys,

These are links to useful application notes.  It deals with several motor configurations.

<https://www.fairchildsemi.com/an/AN/AN-7511.pdf>  and
<http://www.nxp.com/documents/application_note/APPCHP3.pdf>

Also see this thread: <http://madmodder.net/index.php/topic,8693.0.html>

HTH.

Best Regards:
                     Baron