[Noisebridge-discuss] N00b question - changing power supply voltage

[Corey McGuire]

http://www.sparkfun.com/commerce/product_info.php?products_id=527 times 18?
That sounds like a bit much.  Maybe there's a better regulator.

On Tue, Jul 6, 2010 at 10:14 AM, Corey McGuire <coreyfro at coreyfro.com>wrote:

> This is the best back-of-napkin application I've seen for TEJ's, ever and a
> 24v power supply is the perfect supply for it.
>
> There are two problems I see:
>
>    1. When you cycle them to maintain a temperature, the heat you moved to
>    one side will quickly conduct back to the other.
>    2. In this process, a charge will be created and sent down the wire.
>
> How you handle this is a mystery to me.
>
> Here's what I would do.  I would NOT wire them in series.  Instead, I would
> implement switching power supplies and use them to keep the TEJ's active at
> 16v when cooling or a lower voltage while maintaining the desired
> temperature.  Then I would switch them relative to how far below the desired
> temperature they are.  Any temp above desired, 16v; 1 degree below, 12v; 3
> degrees below, 8v... or whatever.
>
> I would NOT overdrive them because I imagine they just get even LESS
> efficient.
>
> 1 arduino
> 1 temperature probe
> a fist full of switching power supplies
> a capacitor just to keep power going to the TEJ to help resist the heat
> moving backward (I don't know if this is a problem, but it is a cheap
> solution.)
> whatever else (I am not even pretending to be an EE.)
>
> YMMV
>
>
>
>
>
>
> On Tue, Jul 6, 2010 at 9:35 AM, Sean Cusack <sean.p.cusack at gmail.com>wrote:
>
>> Oh yes...I know they are terrible at efficiency...but they are also the
>> only thing that I know of that can get you to sub-ambient temperatures
>> without using a (comparatively) giant refrigeration system.
>>
>> I'm planning on using these to cool a few pieces of lab equipment.
>> Typically, to get to sub ambient conditions, you have to use ice/water (gets
>> you to 0C), or dry ice/acetone (gets you to -78C), or full on Liquid N2
>> which gets you too cold for most practical applications. It would be
>> *awesome* to hit like -20 or -10 or even 5C repeatedly and controllably for
>> a million and one different chemical reactions.
>>
>> There is equipment that allows you to do this now, but pretty much its a
>> standalone refrigeration system that pumps cooled silicon based oil through
>> your reaction mixture. It takes up a ton of room on my bench, and since
>> those refrigerators are on the order of $7k a pop, its tough to convince my
>> boss to allow me to buy more than about 2 of them. In other words, longer
>> hours for Sean in the lab = teh sux.
>>
>> So, I'm trying to use these doodads as a way to run a bunch of reactions
>> at a controllably cold temperature. I agree there's problems, but given the
>> application, it may just work!
>>
>> Sean
>>
>>
>> On Tue, Jul 6, 2010 at 8:44 AM, Jonathan Foote <jtfoote at ieee.org> wrote:
>>
>>> On Tue, Jul 6, 2010 at 4:17 AM, Corey McGuire <coreyfro at coreyfro.com>
>>> wrote:
>>>
>>> > Messy, messy stuff.  TEJ's are not efficient.  This is fine by
>>> themselves.  When you stage them, their inefficiencies > become readily
>>> apparent as they begin to compound.
>>> >
>>> > May I ask what you intend to do with them?
>>>
>>> Yeah, also curious. Corey is absolutely right: TEJs have terrible
>>> Carnot efficiency --  way less than 10%. This means to move (not
>>> remove) 5 watts of heat you have to put in 50+ watts of power, which
>>> turns into heat you ALSO need to remove.
>>>
>>> So they are only useful in a few applications where the small temp
>>> difference over a tiny scale is worth the waste. If they really were
>>> the magic refrigerators people think they are, they would be in every
>>> PC and laptop. And note that if you are trying to keep things cool,
>>> there may be far better solutions.
>>>
>>> "In this house we obey the laws of thermodynamics!"
>>>
>>> -J
>>> _______________________________________________
>>> Noisebridge-discuss mailing list
>>> Noisebridge-discuss at lists.noisebridge.net
>>> https://www.noisebridge.net/mailman/listinfo/noisebridge-discuss
>>>
>>
>>
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>>
>
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