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Speed controller for ceiling fans With summer now in full heat, ceiling fans will be in full swing to keep the household cool. This ceiling fan controller will provide better speed control than most standard controllers. By JOHN CLARKE While those large ceiling fans are very effective in moving large amounts of air, their speed controllers often leave a lot to be desired. Although they may have 4 or 5 speed settings, these can be generally summed up as moderately fast, fast, faster, very fast and terrifying. They don't let the fan run slowly which is what you need, most of the time. After all, you want a gentle cooling breeze not a freezing gale. To solve that problem, we have taken a typical ceiling fan and modified its controller to let it run over a wide speed range from slow to fast. To do this, we have added the Speedi-Watt Universal Dimmer as described in the December 1987 issue of SILICON CHIP. The SpeediWatt reduces the mains voltage fed to the fan motor and thereby controls its speed. It is a phase controlled Triac circuit with electromagnetic interference (EMI) sup_pression components and a snubber We removed the speed switch from our sample fan speed controller and wired a 3-way terminal block in its place. The Speedi-Watt controller was installed in a standard mains power point mounting block. to allow the Triac to safely control an inductive load. Tapped inductor So why aren't the existing fan speed controls effective? We put it down to skimping in the design. Fig.l(a) shows the circuit of a typical ceiling fan with a tapped inductor in series with the motor. For the slowest speed the whole inductor is in circuit while for faster speeds the inductor is progressively switched out. For the fastest speed, position 5 on the switch, the inductor is switched right out of circuit and the full 240V AC is applied to the motor. The reason why the inductor is ineffective is simply that it does not have sufficient inductance. Our modification to the circuit, as shown in Fig .1 (b ), is to wire the Speedi-Watt in series with part of the inductor so that the mains voltage to the motor can be substantially reduced. The inductor and 0. lµF 250VAC capacitor form a filter network which cuts out any buzzing sound in the fan motor caused by the switching action of the Speedi-Watt circuit. Note that our circuits of Fig.l(a) and (b) do not show the details of the fan motor wiring. If you have a look at a typical fan motor you will find that it has quite a bit of external wiring associated with it. This wiring includes a capacitor (generally around 3.5µF 250V AC) to feed the split phase winding and a DPDT slide switch which enables the fan to be reversed. Fig.2 shows the circuit for the fan controller and is identical to the circuit published in the December 1987 issue of SILICON CHIP. It functions in exactly the same way as a JANUARY 1990 63 PARTS LIST 2-WIRE CONTROL 1 Speedi-Watt dimmer (Jaycar KJ-6522) 1 knob 1 3-way insulated terminal block 1 0.1 µF 250VAC capacitor 1 HPM 1 40P standard mounting block 1 HPM 800 blank wall plate 1 metre of 250VAC insulated hookup wire (a) OFF 0 A N SPEED CONTROLLER TO MOTOR ACTIVE OUTPUT SPEEDI-WATT UNIVERSAL DIMMER I 0 0.1 250VAC ACTIVE INPUT Construction ACTIVE MOOIFIEO SPEED CONTROLLER (b) A Fig.1: the original speed control circuit is shown at (a) and used a tapped inductor in series with the motor. The speed of the fan was increased by progressively switching out the inductor. Much more effective speed control can be obtained by wiring the Speedi-Watt Universal Dimmer in series with part of the inductor as shown in Fig.l(b). conventional Triac-based light dimmer (which is exactly what it is). It reduces the AC voltage to the fan by switching on early or late in each AC half cycle. If the Triac switches on early in each AC half-cycle, the power delivered to the load is high; if it switches on late in each half-cycle, the power delivered to the load is low. Now let's discuss the circuit operation in a little more detail. The Active input connects to a single pole switch which is ganged with potentiometer VRl, the speed control. VRl controls the rate at which capacitors Cl and CZ are charged, during each AC half-cycle. CZ is charged to the point where it just exceeds the breakover voltage of the STZ Diac and this then dumps its charge into the gate of the Triac, turning it on. The Diac is a symmetrical device which means that it breaks over and delivers CZ 's charge into the gate of the Triac for positive and negative voltages. This enables it to trigger the Triac for positive and negative half-cycles and thus con64 SILICON CHIP trol the power to the load. So if VR 1 is set for a low resistance, capacitors Cl and CZ will charge quickly and the Triac will be triggered early in each AC half-cycle. VRZ is for fine adjustment and enables the minimum speed to be set for the fan. Rl and C3 form a snubber network across the Triac to protect it from back-EMF voltages generated by inductive loads each time the Triac turns off. 11, a 50µH choke, and C4, a .0lµF 250VAC capacitor, form a filter network to reduce EMI caused by switching of the Triac. S1 -- -- The complete kit of parts for the Speedi-Watt Universal Dimmer is available from Jaycar stores for $9.95. The kit takes the form of a small board which has most of the parts already soldered onto it. All you have to do is solder in the 500k0 switchpot (VRl) and three brass terminals. Solder these in, according to the wiring information provided with the kit and you're almost finished - well, not quite. The next step is to decide how to modify the existing inductive speed control. On some models, you may be able to remove the existing switch and install the Speedi-Watt controller in its place. Alternatively, you may find it easier to wire the Speedi-Watt in its own housing as we did. For this we used a standard 33mm deep mains power point mounting block and matching blank wall plate, as made by HPM or Clipsal. These are available from most hardware stores, Dick Smith Electronics and Altronics . The blank wall plate needs a 10mm hole drilled at its centre. This 1 I TRIAC ACOJF VR2 2M CJ .033 C1 250VAC .047 400V ACTIVE OUTPUT CEILING FAN CONTROLLER Fig.2: a conventional Triac-based light dimmer is used as the speed control circuit. It reduces the AC voltage to the fan by switching on early or late during each AC half-cycle, depending on the setting of VRl. accommodates the mounting bush of the switchpot which is then secured with its supplied nut. Before mounting the Speedi-Watt in this way though, it needs the input and output wires connected to it. These are shown in the wiring diagram of Fig.3. We removed the speed switch from our sample fan speed controller and wired a 3-way terminal block in its place. We then wired the existing speed control and the Speedi-Watt as shown in Fig.l(b) and Fig.3. When installing the Speedi-Watt board on the wall plate, some washers may be necessary behind the plate to prevent the pot shaft and bush assembly protruding too far. We fitted the shaft with a standard 21mm diameter aluminium knob. If you doing a new fan installation, you might consider installing the inductive controller in the ceiling so that it is out of sight. Alternatively, if you are modifying an existing installation, just install the Speedi-Watt next to the inductive controller. Note that when the Speedi-Watt is turned on, the fan will run at full speed. You then turn the knob clockwise to reduce the speed. This is opposite the normal operation for light dimmers but is quite standard for fan controllers and it ensures that the fan starts reliably. Finally, note that the Speedi- INOUCTOR ACTIVE ACTIVE TO SPEEOI-WATT INPUT--....j ACTIVE OUTPUT TO MOTOR Fig.3: here's how to re-wire the existing speed control to include the SpeediWatt. Use 240VAC cable for all wiring and don't forget to insulate the ends of the unused inductor tappings. Watt has an adjustment via trimpot VR2 to set the minimum speed of the fan. To check this, first wind the main control fully clockwise and let the speed of the fan settle down. If that is slow enough, don't worry about adjusting VR2. If you want it to run more slowly, then you will need to adjust VR2. When setting the minimum speed make sure that you don't try and run the fan too slowly otherwise it will tend to stall. The Speedi-Watt is supplied with most of the parts already mounted but you have to install the 500kfl switchpot and the three brass terminals yourself. 0.1 250VAC Warning: don't attempt to adjust VR2 while 240V AC mains power is applied to the circuit. The circuit operates at mains potential and is lethal. Note also that these fans will tend to buzz when operating at very low speed. This buzz is lamination rattle caused by the switching action of the Triac. By using part of the inductive controller as a filter, the tendency to buzz is reduced. ~ This Omega fan is very effective at moving air but runs much too fast in standard form. Our circuit allows it to be slowed right down. JANUARY 1990 65