Best method of controlling a resistive heater

Hey all, 

I'm creating a resistive heating system (I don't have a choice on that, the resistors are already provided), and I'm looking for the best method of being able to control this. 

Resistors are 50W 4 Ohm Panel Mount Units, of which I've got about 32, but I'll likely need more going forward. 

Currently it uses 4 zones, each of which use a custom MOSFET PCB which is PWM pulsed by an Arduino which is all fed from 4 24V DC power supplies. 

This has worked OK thus far, but it's not the most reliable and I was wondering if there's something COTS which would suit this better that provides a better method of control to be able to vary the temperature of the panel, as the current ones have no sense feedback, so they're unable to temperature compensate. 

I was wondering if an inverter could sort something like this? 

I know I'm limited by the supply of the room (which is just 230V, there's no 415V supply etc.), but I'm curious to see what people recommend in terms of whether to look at motor controllers as off the shelf PWM units, current stabilised sources etc. 

  • Hey Mike, 

    Yeah PWM as you say may be a bit long. I was reading a technical paper on here about using PWM for resistive heading and having the frequency at around 0.1 of mains frequency or thereabouts (basically keep the switching SLOW). 

    Yeah I can do any of that in the arduino, it's between that and what roger mentioned about using a eurotherm temperature PID controller  (which could be nice as it allows for analogue and digital IO input for sensor inputs. 

    We've got thermistors at the ready so that's no issue, I can use them as preference. 

    We have got two pumps going to maintain the vacuum, one roots pump and a turbomolecular pump. 

    Plasma, no not really, we're using this for the outgassing of materials, so the idea is to remove atmosphere from the inside of the chamber and keep pulling for a few weeks until the outgassing process is 'complete' 

    Thermal fuse is a good shout. 

    I'd not got an idea of how much power to throw at this to be completely honest as the previous setup was never documented, so it's all been done on the fly previously. 

    I've been doing some number calcs and I was thinking if I use 6 resistors in series, with 2 parallel strings, that gives me just over 2.2kw per panel. 

    Or I could lower it to 1.6-1.9 kw by changing to 8x2 or 7x2. 

    I'm tempted to play it safe and suggest the 1.9kw which uses 14 out of the 16 positions by using two parallel strings of 7 resistors.