Extend temp sensor on digital A/C unit

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ThreeTaps

ThreeTaps

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Hi all,

I have a digital window A/C unit that works great, however it doesn't have a knob to turn that will make the unit turn on as soon as it has power. This sort of takes away the possibility of having a temperature controller for my soon-to-be fermentation chamber...unless of course I can extend the temperature sensor on the A/C unit itself.

Any of you ever done this? Is there a specific gauge wire that is typically used? Any advice is appreciated.
 
What is the existing temp sensor made out of? Is it a copper bulb with copper tubing attaching it or a wire with an electronic sensor? Post a link to a schematic and someone should be able to tell you what you could do.
 
chances are it's a bi-metal strip type thermostat, not really a sensor per se. if it is, you'll have to relocate the whole assembly, not too fun. or just disconnect it and reconnect the circuit to a cheap house thermostat.
EDIT: i'm an idiot. just read that it's a digital AC. the sensor is probably a thermistor. I relocated one by attaching it to the end of a phone cord I had lying around. just be sure not to thermally abuse it when de-soldering and re-soldering it.
 
PintOfBitter said:
chances are it's a bi-metal strip type thermostat, not really a sensor per se. if it is, you'll have to relocate the whole assembly, not too fun. or just disconnect it and reconnect the circuit to a cheap house thermostat.
EDIT: i'm an idiot. just read that it's a digital AC. the sensor is probably a thermistor. I relocated one by attaching it to the end of a phone cord I had lying around. just be sure not to thermally abuse it when de-soldering and re-soldering it.
Click to expand...

Thanks, I'll check it out whether it's a thermistor or not.
 
I recently updated my son of fermentation chiller with a remote temp sensor (instructions are somewhere online close to the mother of fermenation chiller info). Obviously, it's not an AC unit, but the spirit is the same. I located the thermistor, de-soldered it from the circuit board, soldered on nice long wires, added some heat shrink tubing over the thermistor, and now I can remotely read temps. My problem was that the unmodified thermostat was controlling air temps inside the chiller, while I need to control wort temperature. I have a california common fermenting there now and the sensor reads the same as the fermometer (yea!).

Here's the link to the thermostat mod:

http://www.wortomatic.com/articles/Remote-Sensing-DIY-Controller-for-Less-Than-$25


As for wire gauge, I used what I had laying around. I think it was 22 gauge (i.e. pretty skinny).
 
Just took the front of the unit off, here's what's behind. Looks good! I should be able to just snip the wire, splice in a longer lead and be done with it, yes?

IMG00113-20090929-0827.jpg


IMG00112-20090929-0827.jpg
 
shortyjacobs said:
Looks great, should be easy to move since it isn't even on a circuit board!
Click to expand...

When I opened it up, I smiled at how simple it would be.

I've heard that extending the wire for these sensors sometimes don't work out well, but I can't imagine why. It should be fine right?
 
ThreeTaps said:
When I opened it up, I smiled at how simple it would be.

I've heard that extending the wire for these sensors sometimes don't work out well, but I can't imagine why. It should be fine right?
Click to expand...

I know people can eff up the thermistors with the desoldering and resoldering, but you aren't doing that, so you're ok there.

Those are typically 5-15 kohm thermistors -- a thermistor is a resistor with a temperature dependent resistance....so you put a set voltage or amperage into it, and measure the amperage or voltage respectively to see how the resistance changes....then there's a calibration curve built into the controller to know how much resistance corresponds to what temperature. The only problem I could see is that the wire you add would increase the resistance of the circuit. This would have the effect of throwing your temp control off by a bit up or down, (depending on if you have a NTC or PTC thermistor...one that increases in resistance either as it cools or heats up). Again though, these are in the range of 10,000 ohm resistance, so I doubt your wire will add an appreciable amount to that, (unless you use 5 miles of wire, or use SUPER thin wire).

Basically, your temp control could be off by a degree or two...but it will ALWAYS be off by a degree or two, since thermistors have linear responses. Although I doubt it will be off at all, the way to check would be just with a thermometer. If the thermometer always reads 62 when your AC says 64, just know that your AC reads 2 degrees high and set it accordingly. Sure beats buying a 60 dollar controller.
 
shortyjacobs said:
I know people can eff up the thermistors with the desoldering and resoldering, but you aren't doing that, so you're ok there.

Those are typically 5-15 kohm thermistors -- a thermistor is a resistor with a temperature dependent resistance....so you put a set voltage or amperage into it, and measure the amperage or voltage respectively to see how the resistance changes....then there's a calibration curve built into the controller to know how much resistance corresponds to what temperature. The only problem I could see is that the wire you add would increase the resistance of the circuit. This would have the effect of throwing your temp control off by a bit up or down, (depending on if you have a NTC or PTC thermistor...one that increases in resistance either as it cools or heats up). Again though, these are in the range of 10,000 ohm resistance, so I doubt your wire will add an appreciable amount to that, (unless you use 5 miles of wire, or use SUPER thin wire).

Basically, your temp control could be off by a degree or two...but it will ALWAYS be off by a degree or two, since thermistors have linear responses. Although I doubt it will be off at all, the way to check would be just with a thermometer. If the thermometer always reads 62 when your AC says 64, just know that your AC reads 2 degrees high and set it accordingly. Sure beats buying a 60 dollar controller.
Click to expand...

Thanks a lot, shorty!

I was able to read all the numbers and specifications from the wire itself, so I'll be getting an exact spool of wire at the hardware shop today.
 
Bobby_M said:
Why not just unclip it from it's little bracket there and move the business end around the side of the unit into the non conditioned space?
Click to expand...

That is exactly what I did with mine (not digital a/c) - took all of 5 minutes to unscrew cover, bend sensor tube to outside of cabinet, put cover back on. Since yours is just wire it should take you 4.3 minutes as you don't have to be careful of kinking copper.
 
samc said:
That is exactly what I did with mine (not digital a/c) - took all of 5 minutes to unscrew cover, bend sensor tube to outside of cabinet, put cover back on. Since yours is just wire it should take you 4.3 minutes as you don't have to be careful of kinking copper.
Click to expand...

Correct me if I'm wrong, but this essentially would be reading the temperatures outside of the chamber, not inside...which would mean the A/C unit would always be on here in San Diego since temps stay between 65 and 70 ambient in the winter, and closer to 80 in the summer. I want the A/C to only turn on when the temperature inside the chamber gets 70 or higher, so why would I want to read the temperatures outside of the chamber to achieve this?
 
ThreeTaps said:
Correct me if I'm wrong, but this essentially would be reading the temperatures outside of the chamber, not inside...which would mean the A/C unit would always be on here in San Diego since temps stay between 65 and 70 ambient in the winter, and closer to 80 in the summer. I want the A/C to only turn on when the temperature inside the chamber gets 70 or higher, so why would I want to read the temperatures outside of the chamber to achieve this?
Click to expand...

Justin, if I understand right, you're doing this right?
PRfVQ.jpg


Green = ferm chamber
yellow triangle = hood around cold side of AC
blue box = cold side of AC (the part that would face IN normally)
red box = hot side of AC
Blue arrows = movement of cold air
red arrows = movement of hot air

If this is the case, Do you even need to move the thermostat? The AC is sucking in air FROM the chamber, and barfing it back INTO the chamber. So the air it's sucking in will be passing over the thermocouple, like it should.

If you do want to move it lower, (which I think would be a good idea), what he was suggesting is just bend it into the chamber a bit, (I think he meant outside of the AC cabinet, not ferm cabinet), instead of cutting and reattaching it. Personally, I'd cut, and reattach in the center of the chamber, so you get an average of the hot top of the chamber and cold bottom of the chamber.
 
The reason you put the temp probe outside the chamber is so that you can use a ranco or other controller to get the cold room down below the A/C's stock thermostat range. This for people trying to ferment lagers, cold condition or hold kegs at serving temps. For ales, the stock thermostat is fine and no mods are necessary.
 
Bobby_M said:
The reason you put the temp probe outside the chamber is so that you can use a ranco or other controller to get the cold room down below the A/C's stock thermostat range. This for people trying to ferment lagers, cold condition or hold kegs at serving temps. For ales, the stock thermostat is fine and no mods are necessary.
Click to expand...

It's a fully digital A/C unit, so there's no knob to turn that will automatically allow the unit to turn on with a temp controller. Also, the unit will allow temperature setting of as low as 41F, so lagering with it is just fine. I went to Home Depot today and got some supplies, and already did the slice job which works great. I gave it a 6 foot lead so that it can reach down into the center of the chamber and attach to the wall. I've tested it in my fridge and it works like a charm...now the only problem is there's no way to turn the fan off on the A/C unit. The A/C compressor turns on when the temp passes the threshold and shuts off when it reaches target temp or below, but the fan stays on 24/7. Not a huge issue utility bill wise, as long as my following math is correct:

Unit: 500W (model dwc-058RL)

kWh Usage: 0.5kWh
SDG&E kWh cost: 0.10684

I assume the unit only consumes 500W during A/C usage, which means it most likely consumes closer to 200W (.2kWh) for the fan only (or lower). With that in mind:

For Ales
During A/C:
(.5kWh x .10684) x 1 (one hour each day, roughly)= 0.05342

During Fan Only:
(.2kWh x .10684) x 23 (remaining 23 hours of day) = 0.49146

Add them both up and it equals just about $0.55 / day.


Does that sound about right for a 61"w x 77"h x 20"d chamber?
 
ThreeTaps said:
Hi all,

I have a digital window A/C unit that works great, however it doesn't have a knob to turn that will make the unit turn on as soon as it has power. This sort of takes away the possibility of having a temperature controller for my soon-to-be fermentation chamber...unless of course I can extend the temperature sensor on the A/C unit itself.
...
Click to expand...

This was your first post. The solution I posted was in answer to this problem. You repeated the bold statement in your last post too which made me believe you want to add a temp controller. I guess I just didn't get what you were trying to accomplish.
 
Bobby_M said:
This was your first post. The solution I posted was in answer to this problem. You repeated the bold statement in your last post too which made me believe you want to add a temp controller. I guess I just didn't get what you were trying to accomplish.
Click to expand...

Sorry for the misunderstanding. I was open to getting a temp controller until I realized I could just lengthen the sensor's lead, which is much cheaper. I'm still not sure I understand how putting the sensor outside the chamber would allow a temp controller to be used, since when the A/C unit first receives power (just like when a temp controller would pass through the electricity on thermal event) it doesn't actually turn the A/C unit on, it just puts it in a stand-by mode.

In any case, I've got the top area measured and marked out for when I can borrow a sawzall, and have drilled the two corner holes to start from. Also gave it a thorough bleach solution wash since there were a good amount of mold spores on the top shelf and throughout.
 
ThreeTaps said:
It's a fully digital A/C unit, so there's no knob to turn that will automatically allow the unit to turn on with a temp controller. Also, the unit will allow temperature setting of as low as 41F, so lagering with it is just fine. I went to Home Depot today and got some supplies, and already did the slice job which works great. I gave it a 6 foot lead so that it can reach down into the center of the chamber and attach to the wall. I've tested it in my fridge and it works like a charm...now the only problem is there's no way to turn the fan off on the A/C unit. The A/C compressor turns on when the temp passes the threshold and shuts off when it reaches target temp or below, but the fan stays on 24/7. Not a huge issue utility bill wise, as long as my following math is correct:

Unit: 500W (model dwc-058RL)

kWh Usage: 0.5kWh
SDG&E kWh cost: 0.10684

I assume the unit only consumes 500W during A/C usage, which means it most likely consumes closer to 200W (.2kWh) for the fan only (or lower). With that in mind:

For Ales
During A/C:
(.5kWh x .10684) x 1 (one hour each day, roughly)= 0.05342

During Fan Only:
(.2kWh x .10684) x 23 (remaining 23 hours of day) = 0.49146

Add them both up and it equals just about $0.55 / day.


Does that sound about right for a 61"w x 77"h x 20"d chamber?
Click to expand...

If you are really picky, I bet you could wire a relay up to trigger the fan when the compressor kicks in, and kill the fan when it shuts off. You'd need a relay that takes 120V on both the coil side and the switch side, and that can handle a minimum of 5 amps coil side, and I'm guessing 2 amps switch side....
 
I get it. You were open to any options. Since the stock controller goes to 41, you're all set. I wasn't thinking about the fact that the AC keeps defaulting to standby. My in laws have a similar electronic unit and now I remember how it doesn't do anything until you press the "cool" button. If the thermostat didn't have the range you needed, I believe you would have been looking for a new unit.
 
Bobby_M said:
I get it. You were open to any options. Since the stock controller goes to 41, you're all set. I wasn't thinking about the fact that the AC keeps defaulting to standby. My in laws have a similar electronic unit and now I remember how it doesn't do anything until you press the "cool" button. If the thermostat didn't have the range you needed, I believe you would have been looking for a new unit.
Click to expand...

Before I took the front of the unit off, I actually looked on Craigslist this morning. Found some basic ones for $50, but this is better since the extra wire lead was only $1.76 :)

Thanks for the help, bobby!
 

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