Adding Duct Fan

[Thomv]

I just purchased a 10" diameter Tjernlund duct fan that I want to install at the end of a teed off main blower duct work. It is a 110 volt fan. I have already run a 12-2 line from where the fan will be mounted all the way back to my Payne 4 ton air handler. I thought this would be the way to go so that the booster fan would be controlled only when the main air handler fan would cycle on and off. When I started to look at how the main blower fan was wired I then realized that the motor is a 230 volt unit. I now need to know if there is a way to find a 120 volt connection that is activated when the fan comes on. What I have found is that the black wire from the main blower motor goes to a relay mounted onto a PC board. I believe this is the high speed connection.The other yellow wire goes to a transformer which I believe is the common leg. There are two other wires. red and blue, that are capped off. I believe these two capped off wires are the low and medium speed connections of the 3 speed motor. So is there a way to hook up this booster fan to the main motor?

[HayZee518]

what is the voltage on the main blower? 120 or 240?

[Thomv]

what is the voltage on the main blower? 120 or 240?

The main blower motor is 240 Volts

[HayZee518]

then there should be no problem. just parallel the new wiring with the existing blower motor. when it kicks in the aux will also start. the relay should handle the slight increase in amperage.

[Thomv]

then there should be no problem. just parallel the new wiring with the existing blower motor. when it kicks in the aux will also start. the relay should handle the slight increase in amperage.

If I do this would I be supplying 230 volts to the aux motor which is only rated for 120 volts?

[HayZee518]

ok, I didn't read your complete posting. Yeah, slight problem.
you'll need a 240 volt to 120 volt step down transformer. Now to figure out the size of the xfmr.
How many watts or amps does the fan draw? Once I have this info I can figure out the size [in Kva] for the transformer.

[Thomv]

ok, I didn't read your complete posting. Yeah, slight problem.
you'll need a 240 volt to 120 volt step down transformer. Now to figure out the size of the xfmr.
How many watts or amps does the fan draw? Once I have this info I can figure out the size [in Kva] for the transformer.

The fan motor is 1.8 amps or about 220 watts.
Thanks

[HayZee518]

go to an electrical supply house [not a big box store] and ask for a dry type distribution transformer 50 va, 240 volt to 120 volt. the primary is annotated as H1 - H2, the secondary is X1 - X2. Your 240 volt will go in on H1-H2, your load will come off on X1-X2.

[Thomv]

go to an electrical supply house [not a big box store] and ask for a dry type distribution transformer 50 va, 240 volt to 120 volt. the primary is annotated as H1 - H2, the secondary is X1 - X2. Your 240 volt will go in on H1-H2, your load will come off on X1-X2.

Thanks again for all your help. To keep the transformer out of the air handler, when it finally goes and needs to be replaced, I was thinking of mounting the transformer into a utility box away from the air handler and just then run the 240 volt wires from the handler into the utility box which I would also add two ventilation round openings for air flow around the transformer. I don't want an AC installer to start telling me more money for the install because he would have to remount the transformer into the new air handler.

[HayZee518]

the other alternative would be to run an additional 120 volt line to your furnace to a relay, rated at 240 volts on the coil and use the common to normally open contact to switch the 120 volt hot to the motor. I priced a few transformers and they are out of this world! the relay coil would be in parallel with the blower motor to close when [IT] turned on. the relay's common to normally open contacts would close feeding 120 volts to the aux blower.

[Thomv]

the other alternative would be to run an additional 120 volt line to your furnace to a relay, rated at 240 volts on the coil and use the common to normally open contact to switch the 120 volt hot to the motor. I priced a few transformers and they are out of this world! the relay coil would be in parallel with the blower motor to close when [IT] turned on. the relay's common to normally open contacts would close feeding 120 volts to the aux blower.

I did find one on ebay as new for $34.00 with free shipping that I just purchased.
Thanks

[HayZee518]

blower

here you'll find a drawing for the relay. its cheaper than a transformer and does essentially the same thing BUT with the addition of another 120 volt circuit.

[Thomv]

here you'll find a drawing for the relay. its cheaper than a transformer and does essentially the same thing BUT with the addition of another 120 volt circuit.[ATTACH=CONFIG]2628[/ATTACH]

Let me try that out. If my relay has different tabs than what you displayed I will get back to you.
Thanks

[HayZee518]

which relay did you get from eBay? I looked and there's a bunch of different ones. I hope the one you got has a 240 volt coil and not just the contacts rated at 240 volt!

[Thomv]

which relay did you get from eBay? I looked and there's a bunch of different ones. I hope the one you got has a 240 volt coil and not just the contacts rated at 240 volt!

I did not order a relay. It was a transformer 240 down to 120 at 50 VA.