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

Parts

Part	Total Qty.	Description	Substitutions
R1	1	27K 1W Resistor
R2	1	10K 1/4W Resistor
R3	1	100K 1/4W Resistor
R4	1	33K 1/4W Resistor
R5	1	2.2K 1/4W Resistor
R6	1	1K 1/4W Resistor
R7	1	60K Ohm 1/4W Resistor
R8	1	3K Linear Taper Trim Pot
R9	1	5K Linear Taper Pot
R10	1	4.7K Linear Taper Trim Pot
R11	1	3.3K 1/4W Resistor
R12	1	100 Ohm 1/4W Resistor
R13	1	47 Ohm 1W Resistor (See Notes)
C1, C3	2	0.1uF Ceramic Disc Capacitor
C2	1	100uF 50V Electrolytic Capacitor
D1	1	6V Zener Diode
Q1	1	2N2222 NPN Transistor	2N3904
SCR1	1	ECG5400
TR1	1	TRIAC (See Notes)
U1	1	DIAC Opto-Isolator (See Notes)
BR1, BR2	2	5A 50V Bridge Rectifier
T1	1	Transformer (See Notes)
MISC	1	PC Board, Case, Line Cord, Socket For U1, Heatsinks

Notes

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.

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.

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.

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.

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

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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wind tech from Pine Ridge AC Motor Speed Controller Saturday, July 31, 2010 11:54:57 PM

About the diac used in the speed controller( to the person looking for a match to the triac) Diacs are not much different depending on the part # they only severe to allow the triac to trigger symetrically in both polarities of gate signal. They will not pass current until the gate trigger signal rises above the mid twenty volt range in either +/- voltage.

madhu AC Motor Speed Controller Tuesday, March 02, 2010 8:26:13 AM

this site is very useful for all the persons not only for techno grads but also for every one who are interested in electrical machines which is one of the challenging subject it also helps in improving knowledge

Walter C. Van Choate AC Motor Speed Controller Saturday, January 30, 2010 2:38:39 AM

I was reffered to your site. I wanted to please ask if you could show me how to add the AC motor controller to a vacuum cleaner that is way to fast to clean floor rugs, blinds, and counter tops.... Please be sure that your help with this matter willl be very much appreciated for sure. Willl be looking in the email for your reply. Yours Respectfully, WC

angel AC Motor Speed Controller Wednesday, November 25, 2009 12:08:06 AM

Very impressive design! but i want a circuit like this to operate in 220V AC. What should i do? i need your immediate response. Thanks..

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

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wind tech from Pine Ridge	AC Motor Speed Controller	Saturday, July 31, 2010 11:54:57 PM
About the diac used in the speed controller( to the person looking for a match to the triac) Diacs are not much different depending on the part # they only severe to allow the triac to trigger symetrically in both polarities of gate signal. They will not pass current until the gate trigger signal rises above the mid twenty volt range in either +/- voltage.
madhu	AC Motor Speed Controller	Tuesday, March 02, 2010 8:26:13 AM
this site is very useful for all the persons not only for techno grads but also for every one who are interested in electrical machines which is one of the challenging subject it also helps in improving knowledge
Walter C. Van Choate	AC Motor Speed Controller	Saturday, January 30, 2010 2:38:39 AM
I was reffered to your site. I wanted to please ask if you could show me how to add the AC motor controller to a vacuum cleaner that is way to fast to clean floor rugs, blinds, and counter tops.... Please be sure that your help with this matter willl be very much appreciated for sure. Willl be looking in the email for your reply. Yours Respectfully, WC
angel	AC Motor Speed Controller	Wednesday, November 25, 2009 12:08:06 AM
Very impressive design! but i want a circuit like this to operate in 220V AC. What should i do? i need your immediate response. Thanks..
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