Build a Full-Wave Motor Speed Control and Light Dimmer with New Triac Semiconductor and Four Other Components

By DON LANCASTER

Build a full-wave motor speed control and light dimmer with new Triac semiconductor and four other components

EET the "Dymwatt." It's a no-non- a half-range type of control, as be 1M sense light dimmer and power-tool tween half and full brightness. or be speed control that pro,·ides up to 600 tween zero and half brightness. To watts of 117-volt a.c. with a symmetri provide full-wave. full-range control, cal waveform and full-ra nge. variable you have to add parts-usually a sec power output. The circuit uses only five ond SCR. a single mechanically switched electronic parts and fits in the palm of diode, or a fu ll-wave bridge rectifier. your hand. The "Triac" is new semiconductor With the Dymwatt. you can get pre which makes possiblen full-wave control cise control of incandescent lights. photo without the need for all the extra com floods, soldering guns and irons, and ponents. Th e electrical equivalent of electric drills. It will also control any SCR's back to back. it operates equally motor rated up to horsepower and well in both current directions. and with eq uipped with brusheL�s- including most. either a positive negative gate pulse ! or but not all. sanders. fans. and electric Two of th e Triac's th ree leads (Tl mixers. The only things th is control and T2 ) are connected in series with the can't handle are fluorescent lights and load. The th ird connection is th e gate induction motors-but neither can most lead ( G). (The designations Tl and T2 of the ordinary power controls. simply mean terminal 1 and terminal 2. Th e two special parts in the circuit, Designations of anode and cathode, un QI and D l, price out at $6.98 and $2.25 fortunately, cannot apply in this case. respectively. This puts the Dymwatt's An equivalent set of components for the cost at less th an $10 if you've got a Triac would contain seven transistors volume control. a box, and two stock and several resistors. ) capacitors. A small signal pulse can trigger the The "Triac." Older control designs Triac so that it will fire just like a call for SCR's. A single SCR provides thyratron. and switch on full or partial

1965 71 May,

www ::imP.rir.;:mr::irliohisto m Dz .. power to the ioad. Conduction stops the value of : I controls the r.m.s. volt when the current through the load cir age. See B' ig. , 2. cuit drops to zero. This happens every If Rl is nearly zero in value. Cl time the a.c. voltage goes through zero. charges very rapidly, and nearly full It also happens when the load is re power reaches the load. If R 1 is very moved. or the circuit is opened. large in value. C 1 never reaches 30 volts How It Works. Current through po within the 60-cycle swing. With each tentiometer RI (see Fig. 1) charges alternation of voltage. C 1 starts to capacitor C 1 up to 30 volts. which is th e charge in the other direction. Under breakdown voltage of the special pulse this condition. gate pulses cannot be diode (DI ). At 30 volts. the pulse diode "snaps" on and delivers a pulse to the Triac gate. The Triac then turns on. allows full current flow through the load, and shorts out the Rl. Cl circuit. Finished Oymwatt can be Diode DI keeps conducting until C 1 is discharged. and then turns off. The plugged into one opening of a duplex receptacle Triac continues to conduct until the a.c. without obstructing the line voltage alternates and goes through other. You have a choice a zero. of using the controlled The larger is. the longer it takes or noncontrolled outlet. RI Cost of this full-wave to charge C 1 and the longer it takes to unit is less than that turn on the Triac. The fact that the of commercially available Triac shuts off at the end of each V� half·wave controllers. cycle of line voltage. plus th2 delayed start of conduction. reduces the conduc tion time and the effective voltage ( r.m.s. ) accordingly. Thus. it becomes apparent that increasing or decreasing

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Fig. 1. The Triac (Ql) will conduct in either di rec· The heat sink on the inside of the case and the dial tion. A positive or negative gate pulse can trig· plate on the outside are held in place by a rivet ger conduction and control r.m.s. output voltage. (hidden by the capacitor) and the potentiometer nut.

Fig. 2. When C 1 reaches 30 volts. 01 conducts and LARGE RESISTANCE MEDIUM RESISTANCE SMALL RESISTANCE triggers Ql. The sooner VOLTAGE ACROSS Cl the gate pulse is devel. MAXIMUM VAL UE: VOLTS oped with respect to the 30 60-cycle line voltage. the higher the effective TRIAC CONDUC TION - - + ON• - output voltage. With lit· I • • + - ··- I L . •- OFF•D tie or no resistance in the circuit, the output is maximum. As the re· , , ' LOAD VOLTAGE sistance increases. the ' LI NE VOLTAGE- --- output decreases. If the �" v resistance is made high ' ' LOW RMS VOLTAGE MEDIUM RMS VOLTAGE HIGH�--;,LJ RMSu--,'-----\,, VOLTAGEQ, vr- -. enough. th€ output is 0. v \

72 POPULAR ELECTRONICS

::imP.rir.;:inr;:irliohistorv r.om IMMN produced and the Triac remains cut off. Construction. The Triac should be By making Rl variable, it is possible to mounted on an aluminum heat sink. A adjust for maximum or minimum power 1/i;;"-thick piece of aluminum will do the output. trick. Bend it in a vise or small brake Capacitor C2 is directly across the and then drill the holes. Use insulated line to prevent any high-frequency pulse, mounting hardware and silicone grease which might be set up by the fast to mount the Triac, as shown in Fig. 3. switching action of the Triac, from radi The Triac rnust be electrically insulated ating down the power line and becom from the heat sink. Test the setup with ing a source of radio interference. (Continued on page 95 )

PARTS LIST

Cl- -0. 1 -µj .. 600-,•o// ((IParilor C?-0.05-µj .. MIU-t•oll caparilor /JJ-(;,.,,,.,.,,/ F.lfflric tliorle. 30-vo// Zl-:!JS "''a l1111r/1 (' lri,.;i;tr for Tn111silro11 EN.-IJUU,or T1'.ras lmtn1111 1·11ts Tl--13) l'l-11 .c. plug (.l111phf'llol or c1111i<.•alc11t} nl-.11 (JJ---!:c111"ra/ Efrclric i'.l-?57 Trillc IU -:!50,VOO-o/1111 corbou p11tr11lio111clcr, li111'ar TO taper SOI SO J-..t .c. socktl (..l 111phru11/ 151-For cquh• almt} 1-! ��"x.2�'..t "x·I" and rasc. kuob.CO' 'i.'!�"t'r .. Pop" rhHls, Jlisr.-Silico1u' f!.rnHr. spag!tctti. sofrfrr, -;cirt, uamrpfo.lr, aud !-4" Fig. 3. Silicone grease, two mica washers, and a ny soldrrfrss l ' m 11 1 . !}'� " }� " pito· of i r i t / .r JU" .r lon bushing are used to mount Triac on heat sink alu111i1111m, I'/(. to get thermal conduction without electrical contact.

Fig. 4. Terminal lug at tached to T2 (it should not touch heat sink or case) provides easy connection to R 1 and SO 1. The end terminal of Rl can be left disconnected as shown in the schematic. but for smoother operation the center and end terminals should be connected to . gether as shown here.

May, 1965 73

www ::imP.rir.;:mr::irliohistorv r.om axial cable as the <1own lea J. Coax is completely unaffected b�· its surround ings. The only th ing you must not do to coax is to crush it. Crush ing changes the spacing between the conductors. thus changing impedance. In order to use coax. howeYer. �·ou must match it to 300-oh rn antennas ri nd TV sets. Both an outdoor mritching trrins former. used to match the antenna to 75 ohm coax. rind an indoor unit mounted on a TV set are illustrated in this article. Some TV ri ntennas ri re nlready matched to 75 ohms. and eliminate the need for an outdoor matching transformer. Coax is very easy to You can tape nm. VERBA-MATIX REVERBERATION it to the mast or run it through a metal America·s Prestige Reverb Systeni conduit. If you have any left over. you The onty system with • 4 Transistors • Heavy 7 oz. Ceramic ran coil it and hang it up beh ind the TV Magnet Speaker • Complete Control set

Area 312 - 666·0066 PE-s i CIRCLE NO. ON READER SERVICE PAGE The Dymwatt C3!t ��;,, '!::.34 ?3.�E�;"� (Continued fro'/11 pa ye 73 ) I � 1 an ohmmeter to be sure there is no elec trical connection. An aluminum case will help the heri t sink do its work. Do not use n smaller box than the one specified-it might get too hot to touch and could damage the Triac. The case used b,v the author re mains relatively cool for all but the heaviest power loads : above 400 watts it becomes notieeably warm. See Fig. 4 for parts layout. The heat sink on th e inside and a dial plate on th e outside of th e case are held in place with a "Pop·· rivet and the mounting nut of the potentiometer. A \"Oid oYer heating either Ql or DI when you are soldering. If you wish. a �E-83 neon lamp can be substituted for D 7 to re duce cost. but it will also red uce the MUL Tl.ELMAC COMPANY control range. As long as the Dymwn tt is used \\"i th 11470 COC-llDGE HIGHWAY OAI< ll'AAI< 37, MICH. in its ra tings and only for its intended Name types of loads. it !s capable of Jong life AddreB trouble-free service. - - and ]) _ ..... _ ...... C•ty ·-·· ...... ········· Zone ...... State ON READER SIERVICE PAGE .. May, 1965 95 CIRCLE 1'10. 22