Opinions on digital temperature controllers?

I am planning on building two walk-in refrigerators. One will be at 68 degrees F, and the other will be at 36 degrees F. I am on a budget, so as long as it works well and is inexpensive, that would be great! This newer product called, Coolbot($300) seems like it works the same as a Johnson temperature controller($58), but is three times the price? Has anyone used either of these products? What kind of experience have you had?

I'm confused....you want cheap, but you're considering a three hundred dollar temp controller? I haven't used em, but the Johnson's and Rancos always have good reviews...

Wow! I ave no idea what's with the $300 controller, but there are MANY MANY digital and analog controllers much cheaper that work well for home brewers. The Johnson and Ranco controllers are simple and work well for most purposes.

You can also pick up a Love controller or one of the 'EBay' temperature (seach the threads for ebay controller) controllers and wire them in to control heating and cooling. I prefer this route because they mount nicely, but anything here will probably do the trick for a walk-in refrigerator.

Pay close attention to the Amp rating of the controller you choose and the refrigeration unit to pick. If the refrigeration runs over 10 or 15 amps, you might have to add a relay to run the cooling.

They are not the same and you will not get the same functionality from both out of the box.

The trick is that most AC units these days are digital and everytime you turn it off (as the Johnson and Rancos are normally wired to do) you have to re-set the controls. The other issue is that window AC units are not designed to cool that low (36 for example). They can, you just probably can't set it to '36.' So you need to 'trick' it into cooling lower.

The "CoolBoot" bypasses all these problems by putting a wire over the AC temp probe and senses the temp coming out of the vent and the room. Probably uses some PID control to set the room temp. So, if the room temp is right, it tells the AC it is at the right temp., if not, it tells it to keep running. (I am essentially deducing all this from the 'coolbot' website.)

If you want to use a Johnson or a Ranco, you are going to have to figure out how to keep the AC on all the time and essentially apply the control to the AC's on/off system internal to the AC. This can be tough if you are not electrically inclined. I am sure there are some guides on the web, but every AC is different.

EDIT: If it works as well as claimed the CoolBot would be indeed cool, but there is no way I would pay $300 for it.

Thank you for the quick responses, I was wondering why the Coolbot was so much more in price. If the only difference is the constant power to the AC unit, that is a huge cost?? I have seen some DIY videos on getting inside of an AC unit and hard wiring it, but I need more research?! Does anyone have any experience with the Coolbot? Let me know if it is worth the extra money? The difference between buying a 3-5 grand walk-in fridge or making one myself, would be around 2-4 grand cheaper, at that example, I can budget in this Coolbot, if it is more efficient?

I don't have direct experience with the Coolbot, but one of my friends has one and it's working very well for him. The Coolbot is much different than the common temperature controllers which are basically just a thermostat which over-rides the fridge or freezer thermostat. In a nut shell, the Coolbot is designed for use with a window type air condiitioner for a cold room. The main problem with using a window air conditioner for this purpose is that they tend to ice up and when that happens, they can't cool the air as the air flow is restricted. This causes a problem as the air never cools enough to trigger the thermostat to shut the AC unit off, so it remains iced up and the problem only gets worse while the room warms up. I've forgotten exactluy how it works excactly, but IIRC, it montiors the return air from the AC and shuts off the unit when the air flow temp approaches freezing. It lets the AC unit resume cooling once the air flow rises enough above freezing temps. A digital controoller (or analog also) simply montors the air temp and turns on and off at the chosen set points. This is all good unless the unit never reaches the shut off point before icing sets in. I think this is explained on the Coolbot site, but it's been awhile since I chedked it out. it does work and it works very well as desinged. I would get one if I were using a window type AC unit for a cold room.

The Coolbot is a Love controller and a heatstrip. Basically you add a heat strip to the existing AC units thermostat, which keeps it on all the time. Then you Love control the AC unit. Definitely can be done for way less than half the Coolbot price. The other, less expensive options require some expertise in wiring. Using those cheap fish tank controllers to directly control the AC compressor/fan would require some on-site wiring expertise.

Ricand said:

The Coolbot is a Love controller and a heatstrip. Basically you add a heat strip to the existing AC units thermostat, which keeps it on all the time. Then you Love control the AC unit. Definitely can be done for way less than half the Coolbot price. The other, less expensive options require some expertise in wiring. Using those cheap fish tank controllers to directly control the AC compressor/fan would require some on-site wiring expertise.

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That's completely different than how I thought they worked, but it makes sense. If that's all there is too it, you should be able to hack one together using a love controller and improvise something to heat the AC unit's thermostat thermocouple or thermistor probe thing. Seems like that would not be hard to do. So, I guess I was misinformed about the icing up issue and that's not a problem. I would guess that you could build a Coolbot clone for under $100 using a Love controller. Not bad considering you would need to buy a controller of some kind no matter how you set it up.

If you insulate the area well, the unit freezing up should not be a big deal. Of course, the first time you cool it down you will want to go slow. (Don't just set it to 36 and walk away.)

So, I guess I was misinformed about the icing up issue and that's not a problem.

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All air conditioners will freeze up under the right conditions. Normally it's due to a lack of air moving over the coils, particularly in humid conditions. Moist air always condenses on the coil, normally enough air moving over it keeps the condensate from freezing. If the air is restricted for some reason, then it freezes, ice on the fins blocks more air, causing more freezing and it cycles like that until the evaporator coils are a solid chunk of ice. Not changing your HVAC filters can do that as well. It would depend on the AC unit you chose, but stepping down the temp, as previously suggested, would probably avoid the icing problem.

I have been looking into this solution. It seems that there is also a sensor that checks for icing on the air conditioner. When it senses that things are icing up it turns the heater off so the air conditioner probe will get cold and shut the compressor down. The air conditioner does not plug into the coolbot like Johnson controllers. It is always plugged into the wall. The only connection to the coolbot is the heater to temp probe on the air conditioner. So no wiring involved and nothing that will void the warranty of the unit.

I am thinking about buying one of these for my cold room but I am open to ideas of building the same functionality cheaper if there is a proven DIY approach.