AC Motor Speed Controller

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This AC motor speed controller can handle most universal type (brushed) AC motors and other loads up to about 250W. It works in much the same was a light dimmer circuit; by chopping part of the AC waveform off to effectively control voltage. Because of this functionality, the circuit will work for a wide variety of loads including incandescent light bulbs, heating elements, brushed AC motors and some transformers. The circuit tries to maintain a constant motor speed regardless of load so it is also ideal for power tools. Note that the circuit can only control brushed AC motors. Inductive motors require a variable frequency control.

Schematic

Schematic of the AC Motor Controller

Parts
Part
Total Qty.
Description
Substitutions
R1127K 1W Resistor
R2110K 1/4W Resistor
R31100K 1/4W Resistor
R4133K 1/4W Resistor
R512.2K 1/4W Resistor
R611K 1/4W Resistor
R7160K Ohm 1/4W Resistor
R813K Linear Taper Trim Pot
R915K Linear Taper Pot
R1014.7K Linear Taper Trim Pot
R1113.3K 1/4W Resistor
R121100 Ohm 1/4W Resistor
R13147 Ohm 1W Resistor (See Notes)
C1, C320.1uF Ceramic Disc Capacitor
C21100uF 50V Electrolytic Capacitor
D116V Zener Diode
Q112N2222 NPN Transistor2N3904
SCR11ECG5400
TR11TRIAC (See Notes)
U11DIAC Opto-Isolator (See Notes)
BR1, BR225A 50V Bridge Rectifier
T11Transformer (See Notes)
MISC1PC Board, Case, Line Cord, Socket For U1, Heatsinks

Notes

  1. TR1 must be chosen to match the requirements of the load. Most generic TRIACs with ratings to support your load will work fine in this circuit. If you find a TRIAC that works well, feel free to leave a comment.

  2. U1 must be chosen to match the ratings of TR1. Most generic DIAC based opto-isolators will work fine. If you have success with a specific part, feel free to leave a comment.

  3. T1 is any small transformer with a 1:10 turns ratio. The circuit is designed to run on 120V so a 120V to 12V transformer will work. Alternately, you can wind T1 on a transformer core using a primary of 25 turns, a secondary of 200 turns, and 26 gauge magnet wire.

  4. R9 is used to adjust motor speed. R10 is a trim pot used to fine tune the governing action of the circuit. R8 fine tunes the feedback circuit to adjust for proper voltage at the gate of SCR1. It should be adjusted to just past the minimum point at which the circuit begins to operate.

  5. R13 must be chosen to match the load. Generally, larger loads will require a smaller value.

  6. Since this circuit is not isolated from mains, it must be built in an insulated case.

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Comments
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S P Naik
AC Motor Speed Controller
Tuesday, June 30, 2009 10:35:55 AM
its a very informative site. Thank you to the persons who made this possible its really helping
vijay
AC Motor Speed Controller
Tuesday, June 30, 2009 7:39:04 AM
hi sir i choosen this ac motorn speed controller as my project details of this project is very less so please kindly send to a mail to me about all details and cost and another my main doubt is ratings motor so please mentioned the ratings of motor
Bent Ears Audio Laboratories
AC Motor Speed Controller
Wednesday, June 24, 2009 4:14:25 PM
Great design! Took me about 2 hours to assemble and tweak. Works just as I wanted it to; took my studio exhaust fan down to a nice slow rotation - just enough to pull a gentle draft out of the room. Tom
fieroboom
AC Motor Speed Controller
Tuesday, June 09, 2009 2:27:34 AM
Hey all, I just stumbled on this schematic, and headed off to eBay... I found a BTA12-600B (600V, 12A max) TRIAC 2-pack for $2.50 shipped... The only problem is I'm not finding any DIACS that are anywhere near my needs (120V, 300W motor), much less being anywhere close to matching the TRIACS as mentioned in the notes. Anyone have any suggestions? Thanks.
farhan elahi
AC Motor Speed Controller
Monday, May 25, 2009 6:04:31 AM
i studeid the controll system and i found it more sute able for all technitions.Thnk you for this.
vimal
AC Motor Speed Controller
Wednesday, April 22, 2009 6:20:52 AM
sir plz tell me what should i do to made the model of ACmotor speed controler
RAYMOND EUGENE SIEGLER,PART TIME MAD SCIENTIST
AC Motor Speed Controller AND OTHER CIRCUT DIAGRAMS
Sunday, February 22, 2009 3:45:47 AM
THANK-YOU;ITS SO NICE TO SEE SITES ON INTERNET THAT ARE FREELY SHARING INFORMATION(AS IT SHOULD BE)SO MANY SITES "ARE IN IT FOR A QUICK BUCK".........KNOWLEDGE IS POWER....I HOPE SOMEDAY(HOPEFULLY SOON);I WILL BE ABLE TO SHARE SOME OF THIS"POWER"WITH OTHERS SO I MAY BE ABLE TO ENRICH OTHERS AS YOU HAVE FOR ME.KEEP UP THE GOOD WORK!
JACK
AC Motor Speed Controller
Thursday, October 16, 2008 4:46:46 PM
Well im busy with this project and i kinda have a problem its not running as it should. Ive used a BT139 triac do you think this might be a problem, anybody please.
Asumadu Seth Sarfo
AC Motor Speed Controller
Wednesday, September 24, 2008 10:37:30 AM
Mr. Aaron I like youe AC Motor Speed Controller and I want to build it for my project work. Sir my problem is, the power I wuold like to use is 220 volt but you said the circuit works with 120 volt. please tell me what to do. My exams is very close.help me
anonymous
AC Motor Speed Controller
Tuesday, September 16, 2008 3:56:21 AM
This circuit is radical!
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