I have a 480v, 33-A (single phase) heater to control. As provided by the vendor, the heater is simply 'on' or 'off.' I'd like to find a way to control the output. The heater is nothing more than a bit of sheet metal holding a resistance element. Think "big toaster."
The heater is the first of many, that will be permanently mounted at work stations. As currently planned, the heaters are WAY too close to the operators and the equipment. I want to warm folks - not sear them! Having the operator cycle the disconnect between 'on' and 'off' strikes me as a (forbidden words deleted) means of control. Vendor does not offer any controls.
I imagine the 'perfect' control to be a simple dial .... turn it more, you get more heat .... plus a timer to keep it from being forgotten.
Any thoughts? I'm open to anything from a readt-to-use product, to some specific component suggestions.
I use SSR (Solid state relays) to control the elements in large industrial dryers They can be cycled rapidly to regulate the elements controlled by a temperature controller or thermostat. Athena Controls as well as others make proportional control relays that can control the amount of current that passes. These are driven by a 4-20 ma controller. Thermocouple needed to send the temperature to a controller. Somewhat complicated for just a heater. I think a SSR with a standard thermostat would be better.
If there's no fan integral to it, I would want to phase control that much power in close proximity to people. Phase angle would be driven by the difference between ambient and setpoint temperatures. But surface temperature would limit the maximum phase angle. That's what I would want/build and I would use 120VAC or less for my control power. With no phase control, I would use a 2-pole 480VAC contactor with a 24VAC coil, small 24VAC control transformer, open-on-rise thermostat for the work space, and a fixed temperature, bi-metallic temperature switch for the heater enclosure surface. Joe
With no phase control, I would use a 2-pole 480VAC contactor with a 24VAC coil, small 24VAC control transformer, open-on-rise thermostat for the work space, and a fixed temperature, bi-metallic temperature switch for the heater enclosure surface.
With no phase control, that contactor will be banging on and off like crazy! 16 KW for bench heating seems to be a bit excessive. A PID temperature controller would make more sense for moderating versus a bang-bang control scheme. If it is grossly oversized, why not operate it on 277 or 240 if available? Less output, longer cycle times.
It just seems to me that someone is making you use the wrong heater(s) for your application. My latest crazy thought would help if they were being installed in 2's. You could use a dual diode module and drive each element from opposite half cycles. So you cut your power in half per unit and not even add any odd harmonics. A scope would be the only place where you might see a tad of crossover distortion. You could still add phase control upstream. Joe