I would like to use a k8004 to control a small AC induction motor. how can I modify the circuit to use a triac instead of the dc control device. Is there a better circuit already out there to do this. I need pulses to create enough torque so the motor will not stall. I need variable rate and width. That is why I thought the K8004 was perfect except it is made for DC motor control.
The K8004 is only for dc motors. You can’t PWM with a triac.
This type of motors can only be controlled with a frequency controller, which is an expensive and highly sophisticated device, not in our range of products.
there is a device used for controlling small ac motors. it uses a variable pulse circuit and an optp coupler to a triac. the idea is to get the motor to turn very slowly. about 6 rpm. I just dont want to copy someone else and go thru all the trouble of making a board for just a few. why couldnt the output of the 8004 be run into a optocoupler chip amd then a triac for this same purpose? if you think so could you provide a circuit diagram showing this. would I need a spike prevention device across the motor ortriac?
Sorry, this is not possible with a triac. The only way to adjust the speed of an induction motor is by means of an frequency converter like stated by VELxxx earlier.
If you want to make it yourself: make a study about IGBT’s etc.
well I know it exists because I have one. I would like to find a way to do it for myself. the circuit takes 120Hz feeds it into a 4017 and has dip switches to send pulses back into the reset line on the chip for different speeds. It sends about 6 pulses per second to the motor and the motor spins slow with lots of torque.
so why couldnt I take the output of the K8004 and feed it to a optocoupler and on to the triac. if the dc voltage pulses at 6hz into the opto coupler why wouldn’t the triac follow this perfectly and send 120 volts ac to the motor 6 times a second or whatever the pulse rate is adjusted to? The optocoupler and triac would act as a DC pulse to AC pulse converter. I just need a little help with the exact design concerning resistor values and the completed diagram. I am not enough of an engineer to do this alone.
Because a triac that has been fired, keeps conducting until the current becomes zero. You can start him but you never know when he will stop (inductive load, timing dependant on load of the motor, current speed of the motor, …). Besides that: to keep things a bit in sync, you will need to sync on the mains pulses. The K8004 does not do that + frequency of the K8004 is much higher. So your triggering will be quite random.
So will this circuit you have work? It could be. Is it a good way of regulating: absolutely not and your supplier of electric power certainly does not like it.