I want to add a booster fan further down the ducts in my house. The heat exchanger ventilator has 3 selectable speeds; I would like to drive the booster off of the same command board.

I could probably drive the second motor directly in parallel with the first one by adding a heatsink on the TO220 triac but I am concerned with durability because of the LRA current draw at start.

The circuit is deceptively simple but I don't want to overload the board or alter the preset speeds in any significant way.

The motors are identical; 149W, 1.31 FLA, 120 VAC. The BTA06-600C triac gate (pin 3) is driven by pin 4 of a MOC3043M zero-cross opto diac through a 200Ω, ⅛W resistor. The load is directly connected across the main triac terminals, no snubber cap/resistor between them.

I'm thinking of adding a dedicated BTA06 for the second motor but I wonder if the gate draw will affect the turn-on timing of the existing one. I guess my question boils down to what to do with the gate resistor(s) or if I need to double-up the opto too.