Computer-based temperature control question: USB relays

I'm thinking of building a computer controlled fermentation chamber, using USB temerature probes. What I'm wondering about is controlling the cooling (a mini-fridge I've got sitting around) via USB. I've found some USB relays on ebay that I think will do the job, but I have no experience with electrical work. I was wondering if someone who knows a little more about it could have a look and let me know if these would be safe/effective for controlling standard 110V household current to run a fridge or lightbulbs for heating? They are here and here.

Has anyone else ever done this kind of thing?

How about the BCS 460 or Brewtroller?

I'm guessing that if your pc powers off, that it will not longer work.

The hardware looks like it would work for that application, the wiring design is simple, but your PC has to be on and awake 24/7. Do you have programming skills?, if not then it would be better to look at a digital temperature controller or packaged system for this application as the software needed would take more time than the hardware installation.

Thanks Kladue. I have a CS degree, so the programming won't be a problem, and I run a personal home server that's on 24/7 that will host the application. I'm also planning to set it up to do logging/graphing of brew conditions and set up remote web-based monitoring (it's actually going to be relatively simple from a code perspective.)

The first link shows 12vdc relays.

the second link shows 12A 125vac relays.

Go with the second one, as long as your mini fridge is under 12 amps. I'm guessing it might be around 8 depending on the age of your fridge.

B

bad coffee, I think the 12v is the power supply for the relay itself. In the specs below it says: Relay specification - 12V / 30mA, 15A/24VDC (120VAC), 10A/250VAC. Would that work?

Yeah. I didn't read the specs, I just did a quick read.

It will work. But do you need all those relays? You'll need one for the fridge and one for the lightbulb. That's about it on this project. If you're looking at the same program controlling different things, then go for the bigger board. If not, you can keep cost and programming down and just go with the two relays.

B

Yeah, the bigger one would leave room for long-term expandability, but I might just go for the smaller one.

Good luck with the project, a suggestion that would preserve the compressor on the refrigerator would be to put in an off time duration of at least 5 minutes to prevent short cycle compressor overload. An electrical suggestion would be to use a snubber on the AC side of the relay to save it from the inductive kick from the compressor when the relay opens under load. I have went too far with Java and SQL tables and wish I could find a painless conversion to C# for my system control application.

I was thinking of using similar setup for the pump and heating element in the kettle/mash tun.
Besides SSR for the Heating element, what else do I be need?

Royi

Here is a USB input system http://www.bipom.com/products/us/2951617.html, add sensors, temp, level, etc and you should be good on he hardware side.

kladue said:

Good luck with the project, a suggestion that would preserve the compressor on the refrigerator would be to put in an off time duration of at least 5 minutes to prevent short cycle compressor overload. An electrical suggestion would be to use a snubber on the AC side of the relay to save it from the inductive kick from the compressor when the relay opens under load. I have went too far with Java and SQL tables and wish I could find a painless conversion to C# for my system control application.

Click to expand...

Don't want to get too off topic, and its been a long time since I've done any programming in Java, but I recall there being a few converters that could convert Java source code to C#. I've never used one so YMMV... your database should be fine, they generally don't care about the code accessing it so long as the query is passed the same way.

Here you go: http://www.electronickits.com/kit/complete/elec/ck1610.htm

You would just need a cheap USB/serial converter and you're good to go. That one will even directly switch 120V/15A, so you wouldn't need any additional relays.

another option
http://cgi.ebay.com/USB-Relay-Board...ltDomain_0&hash=item19bf57b1d4#ht_3424wt_1137