High-Low Switch

Two-level operation of small a-c le;ads can easily be achieved by using a silicon rectifier diode and a three-position switch. This is very handy for use as a:

- Lamp Dimmer: Off-Low-High

--Soldering Iron Life Extender and Economizer --Small Electric Oven Control

- Two-speed Control of Small Power Tools

A diode inserted into an a-c circuit in series with the load will block half, or one polarity, of ail the half-cycles available from the supply line. As a result the load (lamp, motor, etc) sees only the half-cycles of line frequency that are not blocked by the diode. This amounts to a reduction of the applied rms voltage of about 30 % (about 85 volts instead of the full 120 volts supplied). One must be sure, however, that the the load will take this type of voltage waveform which con-tains a d-c component. Because of the d-c component, this type of operation is all right for incandescent lamps, resistance heaters, d-c motors, and universal motors (commutator motors that work on both a-c or d-c). It is not to be used for transformer loads of any type, or fluorescent lamp ballasts.

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1 PROJECT Hl

Figure Hl.1 shows a simple high-low-off circuit that can be con-veniently assembled and wired in a small aluminum Minibox. The three-position switch is mounted on top with the line cord on one side and the output receptacle on the other. The diode is mounted between the proper switch terminal and the output receptacle as shown.

12OVAC

1 1 1 1 1

SI

FULL ON

0OFF REDUCED OUTPUT

~"°'"""

CRI _

OUTPUT RECEPTACLE 1 GE -Xl4

Parts List

CRl- G-E Type 1N1693 rectifier diode for 130 watts output

- GE-X4 rectifier diode for higher output

CR2- GE-X14 Thyrector diode (optional transient voltage sup-pressor)

S1- SPDT, 3-amp, 125-volt a-c switch with center "off" position

1

TO LAMP

=[)=:

MOTOR

Figure H 1 .1 High-low switch schematic diagram

Use a G-E type 1N1693 "top hat" diode for an output rating of up to 130 watts. This device is lead-mounted and has an overall length of about 3 inches. It can be wired directly between the switch and the receptacle-point to point. The GE-X4 should be used if a larger out-put rating is desired. Unlike the 1N1693, this is a stud-mounted device, but it has a higher rating. It should be mounted electrically insulated from the Minibox. One end of a fuse clip, or a similar clamp, taking the

¼" stud of the GE-X4 rectifier diode can be conveniently used.

It is recommended that a Thyrector diode be wired into the circuit as indicated in the schematic. It is shown dotted because its presence is not essential to the operation of the circuit. However, it is a good idea to use the Thyrector to protect the silicon diode against voltage transients that may be present on the supply line.

j

X-Line Night Light* .

While away on your vacation, the X-Line Night Light will auto-matically turn a lamp on when night falls, and turn it off again at dawn. Or if you just like to see a light burning in the window when you return home after dark, the night light will take car~ of it for ~ou.

Built around the GE "Experimenter Line" X-7 magnet1c reed sw1tch and X-6 photoconductive cell, it's both compact and inexpensive.

See'Figure H2.1.

Resistor R3 and coil Ll are wired in series, and both are in parallel with photocell PCl as shown in Figure H2.2. As night falls, the light striking the sensitive surface of PCl decreases, increasing the res~st-ance of the cell and thereby reducing its shunting effect on Ll, causmg more current to flow through it. When the light level is sufficiently low, the field generated by Ll becomes strong enough to cause switch S1 to close as the magnetic switch is mounted in the coil. When the switch operates, it closes the 117-volt circuit to the socket, turning on a small lamp. The lamp should be no larger than 15 watts.

* Reprinted by permission of Popular Electronics magazine.

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Conversely, an increase in ambient light will decrease the current drawn through coil Ll, deactivate the switch, and cause the circuit to open.

Cl 4µ.f.

200 V Parts List

SI

Cl- 4-8 mfd, 200-uolt electro-lytic capacitor (GE-QTl-2) Dl- GE-504 diode or equiualent Ll- 10000 turns of No. 39

enameled wire on ¼" form 2"

long or G-E reed switch coil C-2 PCl- Photoconductiue cell

(GE-X6 or equiualent)

Rl- 10-ohm, 1-watt carbon resis-tor

R2- i0000-ohm, 5-watt carbon resistor

R3- 3300-ohm, 1-watt carbon re-sistor

S1- Magnetic reed switch (GE-X7) or equiualent)

1-1%" x 2½ x 3¼" aluminum minibox

Misc-Line cord, a-c receptacle, terminal board, cable clamp, grommet, hardware, wire, solder

Figure H2. l Night light schematic diagram. Switch 51 is glass-encapsulated reed type

The power circuit is a simple half-wave rectifier that provides d-c voltage to the electromagnetic coil. The nominal value of capacitor Cl is 4 uf, although a greater value can be used if convenient. Less capacity might cause chattering of the switch.

The wiring is not at all critical, and all components are assembled on a terminal board, except the PCl. The photocell is mounted to the Minibox through a rubber grommet. As resistor R2 dissipates quite a bit of heat, it should be mounted away from PCl. Mount the ter-minal board securely inside the metal box, making certain that no connections touch the box.

1 PAGE 120

PROJECT H2 j

The coil is available from GE distributors as "GE Reed Switch Coil C-2." However, if you prefer, you can wind your own on the form supplied with the X-7 switch. You will have to wind on 10,000 turns of No. 39 magnet wire, with the aid of a small winding jig and a drill. The coil wire is very fine, however, and care should be taken to avoid kinks or breaks.

When the coil is completely wound, terminate the lead wires by soldering a length of hookup wire to each of the two coil wires, and carefully tape the entire body of the coil to prevent unraveling. Then place the reed switch inside the coil (use a heat sink when soldering te it), and mount the coil assembly in place, holding it firmly with a plastic cable clamp.

Check the wiring visually for errors, then plug the unit into a con-venient outlet. Plug a small lamp (not over 15 watts) into the socket; · with light falling on PCl, the lamp should go out. Cover the photocell with your finger to simulate darkness, and the lamp will go on. Now, place the unit in a window, and let night fall!

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