Control of a 12v fan circuit - wifi, wired

Forums › Home Workshop DIY › Control of a 12v fan circuit - wifi, wired - home automation

davidcole

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#206132 11-Dec-2016 08:46

As part of this thread @richms and @sumnerboy talked about controlling a garagedoor via wifi.

http://www.geekzone.co.nz/forums.asp?forumid=141&topicid=198633&page_no=1#1593900

I have a fan circuit (2 x 12v 120mm fans) that I have just put in for cooling down my comms rack when it's a warm day. I don't think it needs to run 24x7 so I'd like to add some smarts to it.

In the same cupboard, but about a 3m ethernet cable away is a raspberry pi that I use for monitoring my UPS (usb connected) and it also has two gpio connected dht22 sensors (so it's pretty loaded up).

What I'd like to do is using the temperature sensors in that cupbaord (which are fed into openhab via mqtt) is to turn on those fans when the temp gets up above 25 degrees.

So the posts of @sumnerboy where talking about wemo d1 and relay shield, but as far as I can tell they are 5v. So I don't know enough how to make 5v devices control 12v ones.

I assume I could also wire something in to that existing raspberry pi (assuming it doesn't use any of the 6 GPIO posts I'm already using) and control it that way.

Preferably, I'd rather that whatever I end up doing is already powered, but either the current pi, or by the 12v circuit itself (ie I'd rather not has an independently powered device).

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frankv

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#1685953 11-Dec-2016 09:04

The relays are controlled by up to 5V (3.3V is OK), but can switch 12V DC (or 240V AC) no problem at all. Any GPIO pin that can be set to output can be used.

On my 3D printer, I have a RPi 3 switching 10A @ 12V via a 4-relay board. NB that relays consume a bit of current... I had to upgrade my RPi power supply because at boot all 4 relays turned on, which sucked all the power, which caused the RPi to reboot again. A single relay was OK.

You might want to think about a MOSFET instead of a relay... you would then be able to control the fan speed by PWM... this is common in 3D-printing.

timmmay

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#1685954 11-Dec-2016 09:10

Do you want a toy or do you want a solution? You can get a 12V thermostat with a relay from ebay for about $15.

davidcole

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#1685955 11-Dec-2016 09:16

frankv:

The relays are controlled by up to 5V (3.3V is OK), but can switch 12V DC (or 240V AC) no problem at all. Any GPIO pin that can be set to output can be used.

On my 3D printer, I have a RPi 3 switching 10A @ 12V via a 4-relay board. NB that relays consume a bit of current... I had to upgrade my RPi power supply because at boot all 4 relays turned on, which sucked all the power, which caused the RPi to reboot again. A single relay was OK.

You might want to think about a MOSFET instead of a relay... you would then be able to control the fan speed by PWM... this is common in 3D-printing.

I think that might all be above my skill level. I'm much better on software than I am on electronics. Pre-made components are more my bag, or the simple cobbling together of some parts.

davidcole

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#1685967 11-Dec-2016 10:02

timmmay:

Do you want a toy or do you want a solution? You can get a 12V thermostat with a relay from ebay for about $15.

ooooooh, so while not controllable, this is independent entirely and therefore if temp reaches xyz then activate fan.

t0ny

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#1685979 11-Dec-2016 11:07

while not as much fun as this project, i used the aeotec zwave garage door opener which works fine. Also tells me when door has been left open

SumnerBoy

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#1685982 11-Dec-2016 11:14

The Wemos relay shield is a mechanical relay so it can switch anything from 5vdc to 240vac, although you would want to limit the current. The relays say they can switch 10A but you would be mad to trust them with that!

Not sure off the top of my head but the Wemos might have an on board regulator so feeding 12VDC might work out of the box into VCC.

So you could power it with your 12VDC and have the relay switching your control signal.

davidcole

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#1685989 11-Dec-2016 12:13

t0ny:
while not as much fun as this project, i used the aeotec zwave garage door opener which works fine. Also tells me when door has been left open

I really want to play with zwave but the initial cost is a bit of a barrier. And all the cool stuff has eu frequencies (radiator valves anyone?)

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davidcole

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#1685990 11-Dec-2016 12:14

SumnerBoy: The Wemos relay shield is a mechanical relay so it can switch anything from 5vdc to 240vac, although you would want to limit the current. The relays say they can switch 10A but you would be mad to trust them with that!

Not sure off the top of my head but the Wemos might have an on board regulator so feeding 12VDC might work out of the box into VCC.

So you could power it with your 12VDC and have the relay switching your control signal.

So how would that look, wemos d1 with a relay shield ? Then how would it be wired?

RUKI

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#1685995 11-Dec-2016 12:43

Alternative solution could be - thermistor (e.g. 10kOhm, changes resistance with temperature) in the mosfet gate circuit. Mosfet in turn would control your fan directly or through relay.

davidcole

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#1686118 11-Dec-2016 17:04

Slight change of plan. I bought an chromecast audio today, so my raspberry pi that was volumio has just become free. And I've put it in the enclosure that the fan is cooling. It has a dht22 temp sensor (I put them on all my raspberry pi's for giggles). So it's now possible that it can do the detection and control of the fan.

To that end, would this work:

http://www.14core.com/wiring-mosfet-module-board-on-higher-loads-with-motor/

I get the impression it passes through the 12v power controlling the fan, and the raspberry pi just turns on a switch (of which it can be done via code from the dht22).

Am I right?

frankv

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#1686134 11-Dec-2016 18:10

SumnerBoy: The Wemos relay shield is a mechanical relay so it can switch anything from 5vdc to 240vac, although you would want to limit the current. The relays say they can switch 10A but you would be mad to trust them with that!

Not sure off the top of my head but the Wemos might have an on board regulator so feeding 12VDC might work out of the box into VCC.

So you could power it with your 12VDC and have the relay switching your control signal.

Wemos D1 mini is supplied by 5V DC, regulated down to 3.3V. 12V to 5V buck voltage converters are cheap as... I have several that I use for D1s.

davidcole: I think that might all be above my skill level. I'm much better on software than I am on electronics. Pre-made components are more my bag, or the simple cobbling together of some parts.

I'm more into software than electronics too. Relay boards for the RPi are available as pre-made components. Then you just need 3 jumpers for 5V, GND, and a GPIO pin. Google will find lots of sites which tell you how to do it.