Looking for options to control AC unit for glcol cooling

Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum

Help Support Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

homebrewdude76

Well-Known Member
Joined
Jan 29, 2012
Messages
640
Reaction score
70
Location
Chesterton
I have been reading about various options to control the AC unit.

It seems to me the full start/restart on the AC unit could be hard on a simple STC-1000 unit.
Or will this be ok to fully bypass all AC controls and use an STC-1000 to turn it off/on?

Or can I run the AC unit on its own power and have the STC-1000 somehow act as the thermostat?

Or would I need an STC with relay or contactor?

I am planning on having pumps to circulate, those should all be ok on STC-1000 units?
 
What is the power rating of the AC unit? STC-1000's, to my knowledge, can handle 10A on their relay contact. That should be robust enough to wire directly to the AC unit power cord but check how much amperage the unit draw just to be sure. I control an AC unit similarly with an Arduino and relay where I fully bypass the original controls. Just be careful when manually wiring things with that much power obviously.
 
I'm using one stc-1000 to control the temperature of a drawer full of water in a small freezer by powering switching the freezer unit directly. I use another stc-1000 to control the fermenter temperature by switching the jacket circulation pump. Regarding amps, we use 230V mains here, so our current is naturally lower than yours. Regarding the controls; the controller is too simple but I am able to reduce overshoot by keeping the cooling water only slightly lower than my desired fermenter temperature.

Is your modified ac even capable of regulating itself (i.e. the cold bath)? I'm not sure, but I doubt it. Key question is then if your stc-1000 can handle the load. If not you need a relay.
 
I used an stc in place of the humistat on a dehumidifier. You can do the same for an ac temperature control. If you use it to turn the unit on/off, you will need to bypass the control anyways, you could just wire the in and out. Posting a wire diagram would help as there is using fan settings that you would need to wire up to. The typical ac has high/low cool, which are the same, just different fan settings, then a fan only mode. You would need to wire the line to the load of one fan and the compressor.
 
I have a diagram, and I think I understand how to wire it. Just concerned about the STC switching the unit considering the amp draw
 
I can ignore white - that is low fan.

Tie Red and Red together, that is Cool+High fan

I leave all the wires from the capacitor to the compressor/fan as they are.
Blue/White to the cap is my neutral.

So I have Red+Red hot from my STC
White/Blue neutral from mt STC.
 
I think I want RTD sensors since they will be in liquid.

So will three of these work?
http://www.ebay.com/itm/New-Digital-PID-Temperature-Controller-Control-RNR-1-Alarm-Relay-Output-TC-RTD-/401245453541?hash=item5d6c17bce5:m:mtByIhcdh_MNe4yLNBcBoaQ

I can use the PID to switch a standard relay/contactor?

To switch a relay/contactor you need a PID with relay outputs, instead of (or in addition to) SSR outputs. You could easily control the contactor with something like an STC-1000. Not sure you even want the fast cycling capability of a PID when controlling a heat pump (they don't like fast cycling.)

Brew on :mug:
 
I already did this, and it works as expected.
Power to the AC unit causes the fan high+compressor to kick in.

Currently have it plugged into an Inkbird fridge controller.
AC coil is a solid block of ice at 32F.
Testing at 35F now.



I can ignore white - that is low fan.

Tie Red and Red together, that is Cool+High fan

I leave all the wires from the capacitor to the compressor/fan as they are.
Blue/White to the cap is my neutral.

So I have Red+Red hot from my STC
White/Blue neutral from mt STC.
 
I really want the ability to use RTD sensor.
STC-1000 can't do this.

Is there something like a STC-1000 that can work with RTD?

RTD in the conical will sense beer temp, and the "controller" will turn on/off pump(s) in the glycol solution.



To switch a relay/contactor you need a PID with relay outputs, instead of (or in addition to) SSR outputs. You could easily control the contactor with something like an STC-1000. Not sure you even want the fast cycling capability of a PID when controlling a heat pump (they don't like fast cycling.)

Brew on :mug:
 
The link to the PID from Ebay has relay output and uses RTD.
It is $6 more than a STC-1000.

I really don't trust the STC-1000 to switch the AC compressor startup amp draw.
 
The link to the PID from Ebay has relay output and uses RTD.
It is $6 more than a STC-1000.

I really don't trust the STC-1000 to switch the AC compressor startup amp draw.
The PID you link has a relay output that can switch 3A. The STC-1000 relays are rated for 10A. The PID cannot handle the AC unit's current draw by itself. You need to drive a contactor with the PID output. Also, in a quick read of the PID manual, I did not find anything that indicated you could set a compressor turn on delay time (minimum compressor off time.) Nor does there appear to be any way to set the on/off cycle time of this PID. This thing could kill your compressor in very short order.

Brew on :mug:
 
I ordered 3 STC1000 from inkbird. I will need to see what options to upgrade the probe to SS for the conical.

A simple thermowell might do the trick. The thermal mass of a fermenter is pretty high, so the temp changes slowly anyway. The added time delay from a thermowell is not likely to affect the overall system response significantly.

Brew on :mug:
 
Back
Top