I have a lot of experience driving DC motors but I've never worked with AC or triac's. I'm retired now but I've been asked by a friend to design a compact hydroponic system. The electric's consist of a control unit connected to a power bar. The power bar has 4 outlets controlled by 4 triacs. So my question is 1) is the circuit correct (see attached jpg) 2) how much of an inductive load can it handle. One inductive load will be a fan < 3A the other might be someone using an old ballast driving a MH or HPS light up to 600w. Can I avoid adding a snubber circuit?
Also the power bar will be rated for 15A max. from what I've read on the net I will need to dissipate about 12w of heat and need about 75 sq.cm. (12 sq.in.) of heat sink? I will be mounting the triacs on a 2mm thick rectangular (about 2.5:1) aluminum plate wall mounted on 1" spacers. One side of the plate will have the outlet enclosure over the triacs with limited ventilation I will consider this area as only 1/2 as effective. Does this sound about right? Also when a plate or a fin has both sides exposed to the air are both sides counted as surface area?

 

hi Colin,
It is advisable to fit some form of transient suppression, especially on inductive circuits.
This link offers alternatives to the resistive/cap snubber.
https://www.electronics-tutorials.ws/power/transient-suppression.html

Also this heat sink PDF will be useful.

E

 

I'm no expert on heatsinking, but given that a 6W CFL bulb in a well-ventilated shade gets too hot to keep a finger on, I suspect 12 sq in of non-finned plate inside an enclosure with only limited ventilation would be inadequate for a plastics enclosure.

 

Take a glance at this application note from ST.

http://www.elec.canterbury.ac.nz/in...r_electronics/snubber_circuits_and_triacs.pdf