DIY Fan Controller lights on/off speed changer

Hi everyone.
I've had many requests for this thread.

The circuit below is used to automatically change the fan speed in your grow depending on lights on or off.
If you do not know what G N H are on the circuit diagram, maybe have some else build it that does. This can be dangerous if wired incorrectly.



SC1 is a fan speed controller used when lights are out, generally this is set for a slower speed to reduce the fan speed to reduce noise when cooling isn't necessary but stink control is.
SC2 is the fan speed controller for when the lights are on. This can also be replaced by a thermostat if you wanna get fancy.

Some of you more electrically savy guys will ask why I bothered to switch the neutral. The reason behind that is when you modify this circuit to include a back up power source, you will want to switch the power completely. The inverter or back up power source may be in a different phase and switching both neutral and hot will decrease the likelyhood of the power jumping the gap in the relay and frying your inverter.

Nice work HideyourBud! So basically the DPDT relay just switches the power from 1 SC to the other depending on the depending on if power is going into the trigger side of the relay?

I've been wanting to see a SSSC that adjusts the speed according to the temps...is there any semi easy way to do that without buying multiple SC's? I've got a feeling it's gonna take some surface mount stuff to handle it, but there's always someone out there that has a trick up their sleeve

G=Ground=green wire
N=Nuetral=white wire
H=Hot=black wire

Thats what I make of it..........

MTF-Sandman said:

Nice work HideyourBud! So basically the DPDT relay just switches the power from 1 SC to the other depending on the depending on if power is going into the trigger side of the relay?

I've been wanting to see a SSSC that adjusts the speed according to the temps...is there any semi easy way to do that without buying multiple SC's? I've got a feeling it's gonna take some surface mount stuff to handle it, but there's always someone out there that has a trick up their sleeve

Click to expand...

An option would be to buy a Johnson Controls A419 digital thermostat from www.mcmaster.com (seems like they're the cheapest) in conjunction with a speed controller. It's a 15 amp SPDT unit that'll run you about $70 including tax and shipping.

While this only gives you 2 speeds, on and controlled, it may be enough.

Where can the speed controllers be obtained what is the namebrand/Make model #. Thanks for the diagram..

Redux said:

An option would be to buy a Johnson Controls A419 digital thermostat from www.mcmaster.com (seems like they're the cheapest) in conjunction with a speed controller. It's a 15 amp SPDT unit that'll run you about $70 including tax and shipping.

While this only gives you 2 speeds, on and controlled, it may be enough.

Click to expand...

Thanks I understand exactly how it works now..

Redux said:

An option would be to buy a Johnson Controls A419 digital thermostat from www.mcmaster.com (seems like they're the cheapest) in conjunction with a speed controller. It's a 15 amp SPDT unit that'll run you about $70 including tax and shipping.

While this only gives you 2 speeds, on and controlled, it may be enough.

Click to expand...

Yeah, I've seen that one before...I was hoping for an infinitely variable SC so that if temps got too low it would go to the point of shutting off and for points inbetween it would adjust accordingly to the temps thereby keeping ventilation noise to an absolute minimum. It's probably not really necessary to do it that way, but I've got some ideas floating around in my head that could benefit from it.

MTF-Sandman - I figured that's what you were really interested in. I use an A419 to run two fans on flip flop. One pulls in cold outside air and the other warm house air. Keeps my open air system in a 2 degree range without sacrificing air flow. Gonna wire up another with a speed controller for the mother room so I always have at least some air flowing through and kick the fan into high gear to control heat.

HIDEyourBUD - didn't mean to jack your thread. I like your design and am sure it'll come in handy for me somewhere down the road. Always good to see how people are dealing with issues .

Budweiser13 - I think one of the cheaper controllers is something like a KB Electronics KBWC-13 or -15. Search the net and am sure you'll find em.

this is exactly what i need. thanks for posting the info. where do i find a relay like that? home depot or radio shack?