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Topic: 1 HP AC motor speed control (Read 16110 times) previous topic - next topic


My Drill press got a new motor when my 50 year old DC varidrive motor died

The new motor is a  Baldor brake motor  # VBL3510T
1HP, 1725RPM, 1PH, 60HZ, 143TC, 3524L, TEFC, F1, Wired to run in 120 VAC
It's reversible too.

I would like to control the speed of the motor and also to reverse it.  I'd like a dial (just a friggin dial) to run the speed up or down.  I don't need feed-back or diagnostics,  I just want speed control.
Reversing can be done with a switch but speed control is another matter.
There's VFD and PWM.
VFD is the current norm for AC speed control
can the arduino serve this purpose?
And most especially: Has any one done it?    If you have would you be willing to share?


For easy speed control in an AC motor you are best off with a 'Universal Motor' - this is a brushed motor with both armature and field windings.  These can be speed-controlled with a triac circuit.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]



How about a VLT microdrive?

The 132F 0002 seems like a good option.

98 pound + 20% VAT for a VLT .... even though it's a small VLT it's cheap.



Usually a 3 phase motor is used with a VFD. There are some single phase motors that will run off a VFD but you would have to select the proper motor/drive combination.


Jun 02, 2011, 12:29 am Last Edit: Jun 02, 2011, 12:55 am by CR Reason: 1
I have a white paper by a student about  a DSP & microcontroller on an induction 1 PH motor
All of it  over my head.

I emailed Baldor and their Tech guy told me I couldn't get there from here as I need a 3 PH  motor and I only got one.
I just sent Sales at Danfloss a query to see if they say differently.

I got this motor for $80.00 shipped.  Factory MSRP is about $1200.  I  think the guy had tried selling it for more  but failed cuz he was eager to be rid of it.  It presented it's "issues" for consumer sales because of the shaft diameter ( 7/8") and mount type.  It was still in the Baldor factory packaging with that fresh whiff of factory air.    I built  a custom mount bracket  from 3/8" angle iron and welded tabs on  to extend it  because the motor has that  kind of mount where there are 4 bolt holes on the radial end of the motor and no base flange.  I have it on my DP and it's really a very nice motor, but in a perfect universe I could speed control it too.  

My old  DC motor was a brake motor and let me tell you once you get used to a brake motor there ain't no going back.
Being reversible and vari-drive it made for a superb tapping machine. I was kind of hoping to replicate that.


Jun 02, 2011, 07:47 am Last Edit: Jun 02, 2011, 07:50 am by Pokey Reason: 1
You need to look for a phase angle controller.

Something like this might work:

It can be controlled with DC PWM 0-10v.


Controlling the motor could be quite simple...this all depends on the wiring of the motor. If it uses a large capacitor to start up, things could be difficult, but if the motor uses brushes and has more than one winding, a simple 12-amp triac (in series with one of the 240/120 VAC wires to the motor) using the PWM output from your MCU board. The duty cycle of PWM  will control the motor using an optocoupler to trigger the TRIAC.  You only need to vary the PWM duty cycle to control the speed of the motor.  You must use a simple AC transformer and a 393 comparator to get a zero-crossing time reference for the PWM interval to start.   


Reversing the direction means reversing the connections to one of the two windings on the motor...either the two wires to the armature brush windings or to the field.  Changing direction is done with two SPST 12-amp relays to reverse the connections, and changing direction must be done with PWM modulation of the the two serial windings turned off while the relays are changing state.
For this control to work, the two windings must be wired in series to the TRIAC, with one of the windings being reversed in connection by the two relays.

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