240 vac thermostat project for SX ?
T&E Engineer
Posts: 1,396
Has anyone ever built anything like this? I added a backyard office/cabin for a larger workspace project area. I bought·a sears heater/cooling device kind of like an air conditioner.·However, it does not have a built in thermostat that I know of - just auto fan and·high and low settings for a·turn knob for cool going into heat (like you would see in your car).
I was thinking about a·240 vac timer but would rather have thermostat based control. Does this·exist (at Lowes?) or is it something I would have to·build - probably with either an SX28 or Basic Stamp 2.
If it has not been done, what kind of parts would I need for this to start with?
Thanks.
I was thinking about a·240 vac timer but would rather have thermostat based control. Does this·exist (at Lowes?) or is it something I would have to·build - probably with either an SX28 or Basic Stamp 2.
If it has not been done, what kind of parts would I need for this to start with?
Thanks.
Comments
http://www.lowes.com/lowes/lkn?action=productDetail&productId=30062-49285-FTA2AC
Would this do the job with or without an SX chip?
However, I will probably want to find a way to mount it to a small box that will plug into the external 240 vac outlet and then have the Sears unit plug into this small box. Does this sound right? Does the SX chip get used here?
Originally I thought that I might have to build something to handle 240vac at 20a. Then I found this Lowes part which looked like I may not need to but thought I would ask the group. It would be nice to add micro-controller support but perhaps as you stated, it is not necessary afterall.
Thanks
I've been successfully using solid state relays (SSRs) together with the SX. From the SX side, the SSR looks like a "regular" photo coupler (it actually is one). The Sharp S216S02, for example can switch up to 16 A, 600 V, and it operates as zero cross type for reduced EMI. The isolation between the input and output sides can stand up to 4 kV RMS.
There are many other SSRs avilable when you need to switch higher currents.
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Greetings from Germany,
G
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Chris Savage
Parallax Engineering
One note about the thermostat at Lowe's if it rate 22 amps and your unit has a compressor this will not last long
Keep in mind that all of what I am going to say here is how and what·I would do with this problem
One thing·I would first·get is·a 40 amp contractor· that·has a·coil was 24 volts this
I can help you with·
>>>> PM me for details
Second thing I would· get is a· solid-state relay
Why I would do it this way is unless you can find a solid-state relay that can handle at least ·80 amps to allow for in rush current for the compressor ·that solid-state relay will not last long· I have look for these and they cost some money
Then you can build a timer or thermostat for this unit
I hope this helps
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··Thanks for any·
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Sam
Post Edited (sam_sam_sam) : 12/9/2008 10:12:23 PM GMT
-Phil
BTW, I agree with Chris. Any connection to the SX here is tangential at best.
There are some unit on the market that for what ever reason they do not put a thermostat on them I have seen
this before and if it has a thermostat it not a very good
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··Thanks for any·
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Sam
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Chris Savage
Parallax Engineering
Most furnaces and AC units use a thermostat to activate a 24V relay coil, so all you need is a standard thermostat, a 24V transformer, and an AC relay. If you really wanted to use the SX to control it replace the thermostat with a temp sensor, SX, and an opto isolator to drive the relay coil.
If this is a heat pump you will also need to switch between heating and cooling which may require additional circuitry.
Just to chime in here. I adapted my "wall banger" AC unit from horribly inaccurate bi-metal thermostat to full Propeller control about 18 months ago now. It has a 3A compressor, so I used a 5A SSR off the shelf from futurlec.com. It has cycled in excess of 20,000 times since I first turned it on and is happily ticking away still. It keeps the temperature in the room at the desired setpoint +/- 2.5 degrees C (which is not bad for a cycling compressor style AC unit) and is completely controlled by a propeller (and monitored / graphed on my server over USB).
So if you do your homework and watch your inrush currents, you will probably be ok. Remember I'm on 240v, so I have less current to worry about. The entire unit draws about 3.5A on startup and runs at about 2.2-2.3A while cooling. (It's also only a small unit).
Oh.. and make sure your SSR is a zero-cross switching unit. Switching that sort of load at peak is certainly less kind to the semis.
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Cardinal Fang! Fetch the comfy chair.