[time-nuts] Wine cooler as temperature chamber
kb8tq at n1k.org
Tue Oct 14 11:36:24 UTC 2014
On Oct 13, 2014, at 10:09 PM, Jim Lux <jimlux at earthlink.net> wrote:
> On 10/13/14, 4:17 PM, ed breya wrote:
>> I have this nice little thermoelectric "12-bottle" wine cooler (about
>> one cubic foot inside) that I've fixed twice already, and it just
>> crapped out again. It's always the same thing - bad caps in the
>> switching power supply - they're just too small to take the necessary
>> ripple current. So, I could replace them again and be good for a couple
>> of more years, cram bigger caps in there and maybe have a permanent fix,
>> or decommission it from beverage service and convert it to a chiller
>> cabinet for the lab.
>> I'm wondering if anyone has experimented with these things to see how
>> low in temperature they can go. In normal service, the minimum setpoint
>> is 50 deg F, so not all that cold, but I'm sure it can do better than
>> that with a good supply and running full blast. There's about one inch
>> of insulation on all sides, and the door is double-layered glass.
>> There's a circulator fan on each side of the TEC.
> The TEC probably has a maximum delta T of about 30-40F.
> They are usually about 10% efficient, so for every watt you suck out, you need to dissipate 11 watts from the hot side.
The efficiency varies quite a bit as the delta temperature increases. At “max T” they are 0% efficient. The point many miss is that the TEC is rated surface to surface. Your gizmo cares about heat sink to heat sink (or heat sink to air or air to air). If you have a 20 degree rise on your heat sink, you have thrown away half (or more) of the available delta T. YouTube has videos of people getting significant pumping with stacks of these gizmos. The one thing in common between the ones I have seen - they do not try to talk over the noise of the (likely 20A 220V) blower they are using to cool the heat sink.
You would *think* that being solid state devices, TEC’s would be very reliable in cycling setups. Oddly enough, thermal expansion / mismatch are a real issue on these parts. That can limit their lifespan.
This has all been hashed out before on the list and it’s all in the archives. The bottom line is that using them as a thermal resistor (heat mostly, cool rarely) is a better approach power wise than using them as a full time cooler. The heat of your target device works to your advantage in that mode.
> MELCOR (now part of Laird)
> has all the ap notes you might need.
>> I would put in a bigger supply and new control system, but it wouldn't
>> be worth it if it can't chill much better than original. I don't know
>> yet if the TEC is accessible for possibly upping the size and rating.
>> I have experimented with R-12 type mini-friges for this purpose - they
>> can typically reach minus 40 deg running continuously, but will be
>> oil-starved at the high vacuum, low flow conditions there, so may not
>> last long compared to normal service. They're kind of awkward and ugly
>> too - the best would be a nice small, glass-doored wine chiller, with a
>> normal refrigeration system built in, but maybe a TEC type would be OK
>> for some uses.
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