Controlling electric heater from computer

[Bratters]

Anyone have any experience of controlling an electric heater (smallish - say 1KW max) from a PC?

At least switching the whole thing on and off - better still would be any way of controlling the power going to it to allow "fine" control in, say, 100W increments, although I realise there may be major reasons why this wouldn't be possible...

Any ideas?

[toscal]

You could use this from Maplin http://www.maplin.co.uk/Module.aspx?...rface&doy=25m3
But you will then need a suitable mains rated relay connected as well.
Or here http://www.quasarelectronics.com/3074.htm
Or here http://www.controlanything.com

But if you want to maybe control something else in the future then why not use X10 its quite cheap and you can add to it as and when you feel the need.

[Karam]

To control power output you can 'pulse width modulate' the heater. That is you pick a regular time period over which you switch on for x% of the time and off for the rest. Depending on the system dynamics you may be able to get away with doing this using a mechanical relay. For example for room heating your cycle time period could be say 10 minutes (so switching on for 1 minute and off for 9 effectively gives you 100W average). But ideally you'd use a solid state switch such as a triac or power transistor. A suitable heatsinked triac driven by a zero crossing optisolator would probably be your best bet - low cost, minimal electrical switching noise, no mechanical wear/noise, and with an ability to PWM down to individual mains cycles. Only problem is sourcing such a circuit nicely packaged up to connect to your PC. No doubt some internet searching might yield a source. Tends to be called burst fire control but this will probably turn up lots of industrial or standalone units.

Karam

[Bratters]

Thanks for both those replies. The PC mounted boards look interesting and within my capabilities.

And the PWM idea is very interesting - especially if used with a triac so there's no noise.

I'll have a play with the heater in question, in the room in question, and determine how much "light flicker" there is going to be when the heater comes on and off (not sure of the wiring arrangement in this room yet) - then I'll see if that's going to be a viable option.

I'm especially interested seeing as you say it might be possible to PWM the supply down to quite fine resolution - no need to go to individual cycles, but going to - say - 6 seconds out of a minute to give 10%, rather than 1 minute out of 10 minutes, gives me a nice fine level of control.

Maybe I'll write back when I get this done and let you know how it went.

Thanks again both of you.

[melonpeach]

Hi,

I make these (www.tctec.net) relay boards.

However, wiring up Mains is a challenge and a risk, so you might want to do this:

www.emx.net.au/homeautomation.htm

What's especially good about these power boards (from jaycar) are they are solid state. (but the one shown is only 700 Watts).

Regarding PWM.
If you are controlling the temperature, you don't need PWM.

If the control is working like this:

If too warm, then turn off, if too cold then turn on.
And, ensure that the 'ON' time is no less than say 20 seconds so the heater can't turn on and off a thousand times a second....,

You should end up with the heater controlling the temperature accurately. .

[toscal]

Just had a thought.
Why not use a plug in thermostatic heater controller. Ok not quite what you are after but as it doesn't give you PC control.
Available from
http://www.gil-lec.co.uk/products/Co...tat/1809484596
or here
http://www.tlc-direct.co.uk/Manufact...guard/Therm_1/
Specs from manufacturer
http://www.timeguard.com/product/con...nic-thermostat
They are also reasonably priced at about 15 pounds.