Will a Triac withstand a Live feed from both sides

[forster388]

I have built a dimmer circuit that is adjusted by the level of light falling onto a LDR.
The circuit reduces power to a 3kW immersion heated proportional to the light falling on a solar PV array. In bright sun up to 2kW is feed to the heater, but on a dull day only about 200W. In the dark the circuit still seems to allow about 100W to the heater. On a dull day the water may not get hot enough and I would like to be able to top the temperature up by using cheap rate energy overnight.
My question relates to the following scenario. If the Triac is permanently fed at the hot side with 230V and the gate input allows slight current to flow during a fraction of the cycle to the immersion heater over night. What would happen if I used a time switch to provide a second live feed to the heater, effectively providing a full waveform on the other side of the Triac? There is also a snubber across the triac, is this likely to present any problems?

[bobcroft]

I am not sure exactly what would happen, however the full AC waveform does appear across the MT1 and MT2 triac terminals in normal use. To be absolutely safe and certain of what was happening I would add a relay to disable the triac feed when using the time switch.

If the triac is supplying a small current during darkness then the gate must be receiving a sufficient trigger level to turn it on so maybe you could adjust that level to ensure it turns off. Either way I would add the relay since there is no detrimental effect as far as I can see.

I hope this helps

Bob