I'm familiar with simple dimmer circuit, now I want to build a more powerful triac unit to use with a high power heater.

The resistance of my heater is made of 9\$\Omega\$ 3mm diameter nichrome wire. On 240V(rms) voltage this makes 25A(rms) current. I have an access to a mains line capable of delivering 30A, so in theory I will be able to drive heater at full load. In reality I probably won't, but nevertheless, I want to build a unit that could do that in theory if needed.

My question is - what should I take into account when building a simple optotriac/triac/zerocrossing circuit when moving from 8A triac to 40A triac?

Triac i'm going to use is this: BTB41

My schematics looks like this:

enter image description here

up vote 3 down vote accepted

Two things I would check:

  • the trigger current, your triac requires 50 mA. If this is more than the triac your circuit was deisgned for you might need some changes

  • cooling! At 25A your triac seems to dissipate in the order of 25 .. 35 W. At a Tc of 75C and an assumed Tamb of 40C this means a heatsink of 1C/W. That's not a small one!

  • yesss, I already have the biggest heatsink i've seen for this. Good point about triggering -- (360+470)*50mA = 41.5V. This means, I can't fire in the first asin(41.5/340) = 7 degrees? – miceuz Apr 14 '13 at 17:10
  • This is not my specialty, but I think the C2 provides a phase shift of the trigger wrt. the power, to make triggering on the 0-crossing possible. Do you intend to DIM this load? IMH that is not needed for a heater. A simple and slwo on-off should be enough. – Wouter van Ooijen Apr 14 '13 at 17:22
  • 1
    IV quadrant requires 100mA according to the spec so don't skimp on this part of the circuit – Andy aka Apr 14 '13 at 17:22
  • In fact I want to dim it as I will want to limit the power when the mains line can't supply enough current. Now I've just realised that I don't get R6/C2 at all. I thought it's just a filter to cut off high frequency transients. – miceuz Apr 14 '13 at 18:48

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