Potentiometer Wiring Help Required

[hadj]

I'm trying to find help with a home brewing problem for a heating source.

I saw a kit online (which is now no longer available) where a potentiometer was used to regulate amp from a 240V power source passed through a 25 Amp SSR to control a 3kW immersion heater element.

I have all the parts, however I am unsure how to wire this correctly so that I can control this manually through the potentiometer. This will allow me to keep control at a boil, rather than the traditional controls which lose the boil and then rebuild back to temperature.

Can anyone shed any light on to how this should be wired?

Many thanks in advance.

[piratepaul]

The potentiomter should have 3 wires or terminals... one goes to - (negative) another to+ (pos) thats 240VAC accross them, the third is a center tap which goes to the heater+ ... the heater also has a neg- terminal or wire.

Up load a pic ... I will see if I can tell you which is which.

Tar&stuff.

[hadj]

Thanks for the reply Piratepaul, but where does the ssr go? ps is there a wiring diagram any where that could help?

[piratepaul]

Hi, Sorry I spoke, I know what the potentiometer is but what is an SSR? Perhaps the potentiometer is not designed for 240VAC... Any black smoke yet?... Keep your left hand in your pocket and stand on your right leg...
What about some pics.

Tar&stuff.

[Pauldf]

I'm not sure you have enough components to make it work, a SSR (solid state relay) will just switch on and off but can do this more rapidly than a normal relay, also common with optical isolation between the load and switching supply.

You'll probably need some sort of sensing mechanism such as a PRT100 or thermistor, a comparator circuit such as an op amp and a set point which can be a potentiometer. If you are needing fine control then some sort of PWM circuit to fire pulses to the heater may work well - how essential is it? You can buy controllers that switch on and off with temperature relatively cheaply.

[piratepaul]

A variable resistor from the oven circuit on an electric cooker would work.

[Pauldf]

I think there's more to them than just a plain rheostat, they have to dissipate a fair chunk of energy. Anything undersized will go up in smoke.
I'm wondering if it would be possible to use the ss relay using a potentiometer to adjust the sin wave entering it hence only switching it on during part of the cycle, similar to how a dimmer switch works?
You'd need to invert the lower part of the sin wave so it only went positive but may work as a crude device.
I remember buying a device for not a lot of money a while back that has a potentiometer on it and did pulse width modulation, I used it to control lighting but don't see why it wouldn't work with a resistive load such as a heater, I'll see if I can find it.