On Wednesday, November 26, 2014 11:27:34 AM UTC-5, Tony Hwang wrote:
wrote:
Are you aware that he said he had a variable speed blower, which
today is likely ECM?

right.

and even with an old fashion multi speed blower there are complications.. If you connect the humdifier directly to the blower motor, the humidifer will be fed with different voltages when the blower operates at different speeds.

The best way to deal with this is to add another relay to power the humidifer. A not so bad way to deal with it is to connect the humidifier to the HIGH speed tap. Then the humidifier will see full line voltage when the blower is on high and it will see LOWER line voltage when the blower is on low. This is not too bad usually. The worst thing you can do is connect the humidifer to a low speed tap. Then the voltage to the humdifier may get above 120 when the blower is on high speed, which can be very bad for the humidifer.

Bottom line, use a relay or be sure to connect to a the high speed tap and use a meter to check the voltage at the humidifer over all modes of operation.
Nothing is ever easy. :-)

Mark

Hi,
ECM or X13 type motor draws power from main AC, Humidifier connection
should be there. ECM is servorized DC motor ans X13 is also DC motor
with speed taps. Rectifiers produce DC for them for main 120V AC input.
Look at the control board schematics and trace the AC input to blower
circuit. No relay or hard thinking needed.

I don't know about your furnace or blower. But mine and I think most modern
ones of the type we're talking about,
the AC comes into the main furnace control board on a pair of wires that
gets connected to the house 120V AC.
The ECM blower motor is driven by a wiring harness connected between the blower
motor and that main control board. Between the incoming AC and the
ECM blower is the guts of the control board including CPU and power control
electonics to drive the ECM motor. IDK how exactly one figures
out what is going on in there and simply taps into a PC board. And even
if you do, what's there surely isn't just 120V, because the controller
can make the motor spin at whatever continously variable speed it wants and can somehow even sense the load on the motor to gauge the airflow.

If it's done the way you say, I'd like to see an example of an
install manual for a humidifier that says so.