Cheap Coolbot DIY Concept - am I crazy?

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foodplusbeer

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I like the idea of the coolbot (http://storeitcold.com/), but the price is ridiculous. It's $315 for a device that essentially turns an A/C unit on and off. The way I understand it, this device tricks your A/C unit to thinking it's hotter than it really is, to essentially bypass the the lower limit to cooling.

Given that, do you think this concept would work?

$25 - Willhi Wh1436 Ac 110v - 240v Digital Temperature Controller: http://www.amazon.com/dp/B00V4TJR00...&ascsubtag=87001489fffdaaf4c40fbbd5a9994f84_S

$4 - simply outlet spitter like:
http://www.amazon.com/Globe-Electri...d=1461783516&sr=1-12&keywords=outlet+splitter

$4 - low volt heating pad like:
https://www.sparkfun.com/products/1...D7H4v8m8zK_Ey-_yMDSOAJffcwyh0vT6EnBoCXcfw_wcB

You would plug the splitter into the Temp Controller, then plug both the A/C unit and the heating pad into the splitter. Tape the heater to A/C units temperature sensor and voila! The Temp Controller turns the A/C and the heating pad on at the same time, heating pad will warm up the A/C temp sensor to make it think it's really hot, and then the A/C will kick on and cool. Both the A/C and the heating pad will turn off at the same time once the temperature set by the controller is reached.

Am I over simplifying this? $32, no special handiwork required.
 

jtratcliff

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Looks like only thing you're missing is the sensor in the fins to detect icing up...

You could probably throw a raspberry pi into the mix to to handle the de-icing logic.
You want:
- AC on when "room" is warmer than set point AND fins aren't iced up
- AC off when room is cooler than set point OR when fins are too cold/iced (coolbot uses 0F, I think)
- heater on when room is less than 60F
- heater off when room is greater than 60F

If you're not worried about icing up, your simple solution would do the trick, I would think.
 

laredo7mm

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Not my original idea, I think I saw it in the DIY Coolbot thread somewhere on here, but why not use two STC-1000's in series? The first one is set to the room temp you want. When it turns the cooling on it turns on the second STC-1000. The second STC-1000 has its temp probe in/on the AC fins and is set to 30° (or whatever). The second STC is connected to the AC unit power. If the fins get close to freezing, the second controller turns off the AC so the fins can warm up. The first STC is still on and calling for cool so when the fins warm up the second STC again calls for cooling and turns the AC back on.

You would have to move the AC temp probe and maybe also add a small heat source to fake out the AC's control logic. I have seen people tape the AC's temp sensor to a small light bulb and have it turn on with the first STC controller.
 
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foodplusbeer

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Agree with all of you.

So we've got:

2 Temp Controllers
1 Outlet Splitter
1 Heating Pad

Plug Controller 1 into wall
Plug Controller 2 into Controller 1.
Plug Splitter into controller 2.
Plug Heating Pad and A/C Unit into Splitter

Controller 1 sensor goes to AC Fins
Heating Pad goes to AC temp sensor
Controller 2 sensor goes to room/fermenter/whatever

Set Controller 1 to Cool to 0
Set Controller 2 to Cool to "set temp"
Set A/C to 60

Controller 1 ON if fins are > 0 (not frozen)
controller 2 ON if fins are > 0 AND room is > set temp
Heating Pad turns on when Controller 2 is on.
A/C turns on when its temp sensor reads > 60

Up to 58 bucks, but still not bad for plug and play. Could get a cheaper STC controller if you're up for some minor wiring work.
 

laredo7mm

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What size AC unit do you have? I checked on that controller link you posted and it looks like it is good for 8 amps. STC is good for 10 amps. If you have a decent sized AC unit you might have to go with solid state relays controlled by the STC.
 

MaryB

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Solid state relays are a good idea with ANY inductive load like a motor. Otherwise you will see relay contact pitting/welding because start up currents can be double the nameplate rating.
 
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