I would like to use a solid state relay (25A) in a 230V max. 1400W environment which will switch in 10 second intervals for a few minutes and then remain idle for hours.
Will this type of switching produce any noticeable thermal output or even require a heat sink? I am intending to place the relay close to the inside wall within a warm box (coffee machine, ~80C) with limited air circulation.
Can SSRs be used for such use cases, or are additional measures required to prevent overheating?
Best Answer
Let's do some maths:
Consider this 40 A rated triac - BTA40.
Vto = Threshold voltage = 0.85V = Voltage drop across triac.
Rd = Dynamic resistance = 10 mohm
IT(RMS) = Current through the triac = 25 A
Power dissipation = [0.9Vto X IT(RMS)] + [Rd X {IT(RMS)} X {IT(RMS)}]
Where 0.9 = 2*sqrt(2) / pi
Putting the values, you get P = 25.375 Watts
This much power can't be dissipated by a small triac. You will definitely need a beefy heat sink (maybe a cooling fan too).
In my humble opinion, if you plan to use a triac without a heat sink and in closed spaces, you should limit yourself to 1A or so (for a continuous draw, it gives P = 0.775 watts). For the application you have mentioned, I'd suggest you to go for an electro-mechanical relay which will be cheaper and smaller as compared to triac + heat sink assembly.