DIY Advanced fan setup (Electrical)

[bubblekarma]

Whats up AFN? I'm working on a better way to control my environment. I have a temp controller that independently controls heat/cool via relay switches. I've got the heating figured out. But I don't have the cooling figured out.

I've got a typical exhaust fan setup with carbon filter. The fan is (currently) wired to a fan controller that allows me to manually adjust the fan speed. I run it about 50% most of the time via the controller.

It would be really nice to allow the fan to run full speed through the temp controller relay, only when in cool mode, and back to the manual fan controller when not. In this way, say the environment gets to 85*, the cool relay would activate and run the exhaust fan at full speed (to draw more cool air in). Once it has cooled down, the fan would go back to operating via the fan controller (set at medium speed). However, AC fans use capacitance values to alter the phase on 1 coil and spin the rotor. So I cannot just dual input it like I've described. It would also back feed the line, which I also don't want.

I'm trying to figure out how to make this happen. I realize my electrical knowledge may be more than most on this site, I have lots of background in the field. But this one is boggling me so I figured I'd see if anyone else might have any ideas.

TL;DR I want to run my fan on HIGH only when the cooling relay is activated. Otherwise it should run at 50% or whatever speed I have set using the fan controller.

 

[Itisi]

Hello mate.

I may be over simplifying things here.

Assuming the fan speed controller is not an integral part of the fan, would a thermostat set to the desired temperature supplying the fan directly work?

You may need some sort of diode or other electronic trickery to stop a back feed from blowing your speed controller, but I think it would work.

I

 

[bubblekarma]

Hey man thanks for chiming in! You are exactly correct.. what you described is how I would typically handle this if I were working with DC - I could prevent the backflow. AC changes things a bit. I'm not sure of any device to directly prevent AC line backfeed because it's flow direction is always changing from + to -. I thought about additional relays to control this too, but there again AC makes that more difficult as well haha. I'm still looking into ideas though.

 

[Ozone69]

The electric jargon on what you're saying is a bit above my knowledge level, but could you use something like this and then set it to the same temps as the cooling to kick in? I think, though, to do what you're really looking for you'd have to have this feed into something like a relay to switch between full power and speed controller fed power.

http://www.homedepot.com/p/Ductstat-Plug-In-Thermostat-Temperature-Sensitive-Switch-DS100/100028788

 

[bubblekarma]

I think something like that could work, thanks for the input.

I was also just thinking about tearing the speed controller down and using my environment control output as the switch inside the controller that essentially would preform this way, however its much easier in theory haha.