Controlling AC motor for PT camera

Hello!

I have been trawling the web looking for some help with this design but everything I come across is just that much different. I am designing and implementing the pan and tilt control of a camera. The camera unit uses two 24V AC motors to actuate pan and tilt (I have no choice in the camera unit). The motors are two-phase induction motors with instantaneous reverse. I am having a lot of trouble finding any resources that deal with these type of motors specifically. Any advice would be greatly appreciated!

  • Adam

You could use a random turn-on AC solid state relay. Most of the ones designed for 240V AC are specified down to 24V AC. Alternatively, build your own SSRs using an opto-triac and a normal triac, then you can reduce the value of the resistor feeding the opto triac to allow for the lower voltage. See fig 3 in http://www.farnell.com/datasheets/6532.pdf. You may need a snubber network across the triac to ensure that it turns off.

You will get around 1.6V voltage drop with either solution, but that is unlikely to matter.

Any progress on this Adam? I'm in the same predicament, planning to control a 24 V AC valve actuator for a home heating system. It has three terminals: forward, common and reverse. So to turn the valve in one direction you apply AC between forward and common. The power is low, max rating some 6 VA. I've been thinking of two options:

Two relays (one forward, the other reverse), supplying 24 V AC from a transformer. Not so elegant but will work. The actuator moves slowly so timing is not so critical, typically the controller would turn the valve with pulses of 1 s, moving the valve one degree or so each pulse. Solid state relays could make it slightly more elegant.

Far more elegant would be to generate the AC from the Arduino, but that would require drive voltages of at least -40 V to +40 V. Or generate the output at low voltage then step up with a transformer.

Has anyone else done anything similar?

Instead of using relays, you could consider using this opto triac: http://uk.farnell.com/vishay/vo2223-x001/phototriac-power-dip-8-0-9a/dp/1870800. It's rated at 0.9A, so it should handle your 24V 6VA valves easily.

Excellent, I will do that. Electronics have done some progress while I wasn't watching - a decade or two. Might use those devices also for controlling contactors (is that the word) later on, requiring 230 V control voltage. Also nice not having to consider backvoltage as from mechanical relays, only a simple LED to power.