Request: fimware to make on/off switch work for 2-speed attic fan


A lot of houses (including mine) have a central exhaust fan. This is a large (2-3’ diameter) fan that blows air out of the living area either to outside or to the attic.

In general these use two-speed motors which have four wires- high, low, neutral, and ground. Applying 120v power to either high or low energizes one of two completely different sets of windings within the motor, resulting in the two speeds. You NEVER power both sets of windings at once, that will burn out the motor fairly quickly. The typical way to wire this is with a DPDT or SPDT switch.

To automate this, you either use a standard on/off smart switch and a separate speed control switch, or two on/off switches with the second one feeding a relay to switch speeds (so one is on/off and the other is low/high) or you could in theory use two on/off smart switches and some logic to prevent them both being on at once.
A normal fan speed switch (IE Windy City) won’t work here as those just add capacitance / reduce voltage to the one output terminal, which won’t work on this sort of motor.

From reading docs on the Red series on/off switch, it’ll work with a 3-way setup where the load is on the remote side. That means it has a relay to send power down the traveler wire or the load wire.

I’d like a firmware that would turn this into a high/low switch. IE tap up on the paddle once = low (power applied to load wire), tap again up on the paddle = high (power applied to traveler wire). Internal firmware logic would ensure that both load and traveler (high and low) are not powered at the same time.

Doesn’t have to be a separate SKU, although it could be.

This would also be the only product like this on the market…

I was under the impression that the relay on the on/off switch simply switched the output between the load and relay terminals.

Switch state Load Terminal Traveler Terminal
On Active Off
Off Off Active

I dont think there is a 3rd state (although I havent tested this) where both the Load terminal and Traveler terminal are “off” at the same time.

You might be able use the switch to toggle between low and high with the existing firmware, but you would have no way to actually turn the fan off since one of the output terminals is always active.

For a 3way with a dumb switch maybe, but what about when using add-on remote switches like HomeSeer or GE? Presumably the ‘off’ state isn’t dumping 120v into the add-on switch (or if the addon switch needs 120v, then it’d always be sending power, no?)
And what about for a dimmer? A dimmer would need to control power flow no matter whether the lamp is on the load or traveler terminal.
Thus it seems to make most sense that there are two relays in the LZW30- one for on/off, and one for load/traveler switch.

That’s a good point about the add-on switch. It would make sense to have two relays. I don’t have any compatible add-ons, and I haven’t been able to find any information about how they actually work.

I am curious now. How does the switch know what is connected to the traveler terminal (dumb switch vs add-on)? From pictures of compatible add-ons, it looks like there are only 2 wires (traveler and neutral). They have to receive power somehow.

I figured there has to be some kind of current sensor on the traveler wire. I don’t know for sure how the add-on switches operate, but if I were to guess, I’d assume the add-on switch is just a resistor and two diodes. So pushing up or down allows a little bit of current to flow through the addon switch to neutral in one direction or the other. If the switch detects bidirectional unresisted current flow, it assumes the 3way switch has been turned on, so it turns on the load relay, clicks the load/traveler relay to traveler, and the light is on.
At least that’s my guess.