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Topic: Arduino + Peltiers = refrigerator? (Read 1 time) previous topic - next topic

Stigern

Just got some cheap 130W peltier elements from eBay. Also got some weaker 50W ones.

Would like to make a refrigerator out of it, just a small plasticbox and some isolation and it should work?

Arduino would control the fans/peltiers and measure temperature with a temp sensor.

Anyone got some ideas or?
I'm from Norway!

Mike Mc

Yes it can be done. What do you mean by 'any ideas' ?

Stigern

I dunno, some inputs on how to do it. Or if anyone have done it before.
I'm from Norway!

RaygunGothic

#3
Aug 11, 2009, 01:56 pm Last Edit: Aug 11, 2009, 01:57 pm by RaygunGothic Reason: 1
I've not done this, but my immediate impression/guess would be that the temperature control loop (using Arduino) would be very simple, but the power electrics - mechanical build - and thermal efficiency would be the hard part and wouldn't necessarily be made any easier with Arduino control.

It might even make more sense to leave the Arduino out of the thermostat control loop altogether so you don't have to convert between the microcontroller voltages and 130w switching. Unless you have more complex behaviour in mind than "it's too warm, turn on the coolers!"?

Stigern

#4
Aug 11, 2009, 02:33 pm Last Edit: Aug 11, 2009, 02:36 pm by Stigern Reason: 1
Well, I was thinking about using a temp sensor combined with arduino to control the outside fan, on the hot side. When it reaches above 50C it would turn on.

Also when the "fridge" reaches it's set temperature(temp sensor inside too), the peltier and fans are turned off. And turned on again when needed.

Anyhow, might be enough to use the 50W peliter. I dunno how much 50W is, when cooling down a 50x30CM "box" with stuff inside.

Or maybe the 136W would make a freezer? :P

Or... ebay got a 400W peliter, but then again I might just need a watercooler to keep it alive :P
I'm from Norway!

TeamMCS

I was curious about this myself. Could make a decent aircon unit for a rack server.

ajb

#6
Aug 12, 2009, 07:18 am Last Edit: Aug 12, 2009, 07:19 am by ajb Reason: 1
Peltiers aren't very efficient; a phase-change heat pump system (like most household refrigerator/freezers and air conditioning systems) is 6-12 times as efficient, and on their own TECs can't move heat nearly as far as a phase-change system can.  They're really only good for very localized cooling (overclockers used to (still?) use them on CPUs to squeeze another hundred MHz or so out of their machines), or situations where you want heating and/or cooling (especially both) in a small, lightweight package.

If you want to get a sense of how much cooling power you have:

Total power * efficiency * time = energy

50W * 0.10 * 1hr = 5Whr

5Whr = 4.3 kilogram calories, so your 50W TEC refrigerator could cool a kilogram of water by up to 4.3°C in one hour, not accounting for losses due to imperfect insulation.  Of course that also assumes your specific TEC is 10% efficient, which it may not be.

One big advantage to peltier devices is that you change direction of heat flow with the direction of current flow.  There are commercially produced travel coolers that can run from a car or wall adapter with unpolarized DC plugs--mate the plugs one way and the container keeps your drinks cool, or mate them the other way and it'll keep your casserole warm on the way to grandma's house.  So if you really wanted to develop an arduino project, you could do something similar with both warm and cool temperature control.

Stigern

Got my 60W today, freezes quite nicely.:



But, now I've ordered a 230W :D That should pack a punch!
I'm from Norway!

Grumpy_Mike

Well done, but note there is a maximum temperature difference you can maintain across these devices. If you push it greater than this maximum the effect breaks down and it all heats up. So see the data sheet for how far you can push it.

I wouldn't bother controlling the fans, just keep them on all the time. The commercial one I had for keeping my son's injection medication below 8C when camping would flatten a car battery in about two hours if the engin was not on.

Stigern

#9
Aug 18, 2009, 12:48 am Last Edit: Aug 18, 2009, 12:52 am by Stigern Reason: 1
By that you mean like if the cold side is -19C and the hot side is +80C isn't good?

So far I've only had the cold side at -17C and hot-side at 27-34C.

To power my peltiers, I've also ordered a switch mode power supply from eBay. Gives out 12V and with a whopping 30A! They only cost 50$ with free shipping!  ;)
I'm from Norway!

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