Post by thread:[EE]: Using a Triac to control Fan Speed

Using a 16F628 and two triacs (600V 10A), I have designed a circuit to control the brightness of a lamp (240V 60W) and the speed of a fan (240V 80W) through remote control. I have used the Timer0 and Timer1 to independently control the two devices. The code checks for the zero crossings and fires the triac/s after a delay that determines the brightness / speed. A 7-segment display shows the brightness / speed in 16 steps - Zero to "F". If I connect two 60W bulbs to the triacs, the circuit works flawlessly. The brightness of one lamp can be controlled without in any way affecting the other. My problem is: If I connect a fan to the second triac, it doesn't work. How do I control the fan speed using the triac? I know that the fan is an inductive load and the circuit for controlling it with a triac is different from that of an incandescent lamp. Can I solve the problem by adding a snubber circuit to the triac that controls the fan? I guess, it is not as simple as that. I would highly appreciate suggestions / pointers / guidance on the topic. Thanks & Regards, Bala -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

It sounds like you - like many others have once again discovered reasons why a seemingly simple, low-cost project isn't out there already being mass-marketed - it's not a simple low cost deal unless you specify exactly the right motor for the control scheme. In that case, you'll have a device that will function in only a limited number of applications. If that's OK for your project,the following may help. Triacs are generally used to control either universal motors, where the greatest control range can be achieved, or shaded pole motors, where only a limited control range will result. You didn't say wat kind of fan motor you are using, but it's my guess that it's not a universal motor. If it's a shaded-pole motor, try running it with your control at full or near full power and see if it starts. Also, be sure to snub the triac's main terminals with something like 100 ohm & .22uF if you want the motor to turn off every time it's supposed to. If you can't change the motor, and the control range you get with it isn't good enough, you will then need to control it via frequency. This will then be a bit more complicated, but can be done. Chris > {Original Message removed}

You'll find that you will get poor (if any) results trying to 'dim' an AC motor such as those used in fans (not all AC motors work this way, but most AC fan motors do). Those fans that have speed controls are simply switching cpacitors in series with the fan motor. What little success you may get from 'dimming' the fan will result in an annoying hum. An example of one person's quest to obtain such a system is here: http://www.edcheung.com/automa/nohum.htm And you can find additional information here: http://repairfaq.cis.upenn.edu/REPAIR/F_appfaq7.html#APPFAQ_019 -Adam Bala Chandar wrote: {Quote hidden}>Using a 16F628 and two triacs (600V 10A), I have designed a circuit to >control the brightness of a lamp (240V 60W) and the speed of a fan (240V >80W) through remote control. I have used the Timer0 and Timer1 to >independently control the two devices. The code checks for the zero >crossings and fires the triac/s after a delay that determines the brightness >/ speed. A 7-segment display shows the brightness / speed in 16 steps - Zero >to "F". If I connect two 60W bulbs to the triacs, the circuit works >flawlessly. The brightness of one lamp can be controlled without in any way >affecting the other. > >My problem is: If I connect a fan to the second triac, it doesn't work. How >do I control the fan speed using the triac? I know that the fan is an >inductive load and the circuit for controlling it with a triac is different >from that of an incandescent lamp. > >Can I solve the problem by adding a snubber circuit to the triac that >controls the fan? I guess, it is not as simple as that. > >I would highly appreciate suggestions / pointers / guidance on the topic. > >Thanks & Regards, >Bala > >-- >http://www.piclist.com#nomail Going offline? Don't AutoReply us! >email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body > > > > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Thanks a lot, Chris, Adam and Peter for your comments and suggestions. It might be of interest to you to know of one method I tried some 7 years ago for speed control of ceiling fan through remote control with a fair degree of success. It's working satisfactorily even today. Using discrete parts, 4000 series ICs and a solid state electronic fan speed controller costing around $2, I designed a circuit to convert the closing of the only PB switch on the (RF) transmitter to cycle through 16 possibilities. A counter keeps track of the number of pulses received and closes three relays for speed control and a fourth one for controlling the on/off operation of a lamp. The resistance of the pot can be varied between zero ohms and 408K (in 7 steps of 68K each) for maximum and minimum speed respectively. This is accomplished by switching the three relays which short the resistors whose value range from 68K to 204K. When all the relays are open, the resistance is 408K and the speed is the minimum. When all three relays are energized, resistance is zero and the fan runs at full speed. Of the 16 possibilities, the first 8 are 0 to 7 fan speed with the lamp off and the second 8 with the lamp on. Peter's idea of firing the triac only during certain half cycles to control the fan speed sounds interesting. I will try it out one of these days. Regards, Bala > {Original Message removed}

On Mon, 27 May 2002, Bala Chandar wrote: >Peter's idea of firing the triac only during certain half cycles to control >the fan speed sounds interesting. I will try it out one of these days. Actually during certain *full* cycles. The idea is tried but this is the first implementation using a PIC that I know of (mine). Peter -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads