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AC Motor Speed Controller

AC Motor Speed Controller

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

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
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
U1 1 DIAC Opto-Isolator
BR1, BR2 2 5A 50V Bridge Rectifier
T1 1 Transformer
MISC 1 PC Board, Case, Line Cord, Socket For U1, Heatsinks

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