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-   -   need a DC fan signal for a WH Humidifier (

forresth 02-19-2010 01:49 PM

need a 24v fan signal for a WH Humidifier
I'm installing a Whole House Humidifyer into a wood heat forced air furnace, and I'm running into a problem getting a 24 volt fan signal for the humidifier.
I already tied into the 24volt system (used to controle the damper and backup gas burner) to power the humidifier's computer

The furnace uses a regular 120volt Honeywell Limit switch to turn on the fan when it is hot. The therostat just controles the combustion air damper.

The Humidifier Instructionssaid not to hook up the transformer to the switched power for the fan. Is this just to keep the computer from getting cycled off and on, so would be safe for me? or is it something to do with the capaciters spiking current or something?

The only other option I see would be to install an AC triggered rellay to controle the low voltage signal. That seams a bit backwards and overly complicated, not to mention finding and buying one.

humidifier is a Aprolaore 600a and furnace is a Yukon Eagle Husky1 (I think)

beenthere 02-19-2010 03:39 PM

The spike from the fan motor starting will overload the transformer.
Thats why you can't connect it to the fan power supply.

Houston204 02-19-2010 06:19 PM

A current sensing relay is available at Johnstone supply.
I'm not sure that they sell to the general public though...

forresth 02-19-2010 08:58 PM

boy, the correct search term sure helps. I found what I need on amazon.


forresth 03-05-2010 12:11 AM

OK, picked up a current sensing relay, I tried to bech test it.

It never shows an open circut. I hooked it up to the power feed for the furnace, and it shows no difference in resistance weather or not there was current flowing. I hooked a 24v tool batt, to see if for some reason it needs a 24 volt power suply to work properly, no difference, I get no change in voltage through the test circut (batt, current sensing relay, multimeter). I figured the relay was bad, after no real response from the online seller, I picked up another one (differnt brand) locally. Exact same results! I cant imagine I'd get 2 bad current sensing relay out of the box.

What am I doing wrong? does it HAVE to be right on the motor ground for some reason? it is a pain to get to, and I like to test everything as I go along, so I'd like to bench test the parts first.

beenthere 03-05-2010 02:19 AM

Should measure as an open circuit, until it senses inductive current flow.

forresth 03-05-2010 06:56 AM

Thats what I though, its just hard to believe I got 0 for 2 useing 2 different companies parts.

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