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Basic question for somebody to help me with

Hey, I have never posted here before, But hopefully somebody can help me. I'm very amateur when it comes to electronics so any help is great. I am installing a soda pop can cooler in my car. To describe this most simply: I have a fan and a module. Two different things that need power. They both are set to run off of my 12V battery car power. I need to find some sort of a two-direction switch that both of them can be wired to so that the fan will run the same direction no matter what direction the switch is, but so that the module will switch according to the direction the switch is. (This is How the pop can can be either cooled or heated). But the fan needs to run the same direction. I hope this makes sense. Can anybody help with advise?

Reply to
jgwilliam
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Assuming that you'll want to turn things off, you could use either a
3PDT switch with CENTER-OFF position or a DPDT switch with a
CENTER-OFF position and a bridge rectifier:



    +-----+---------+--------------+-------+
    |     |         |              |       |
    |+    O--> |  |  |  |  |
Reply to
John Fields

Plain and simple: Peltier coolers are a scam. They do not work.

The switch is trivial. The key problem will be getting an aceptable heatsink delta-T.

With a typical Peltier cooler, you will have MORE delta-T across the heatsink than you gain cooling. Thus your switch (and the root beer) goes from WARM to HOT, not COOL to WARM.

The quality and amount of insulation needed are also totally ridiculous.

Precision heatsink machining and superb quality heatsink grease is also a must.

Most people end up throwing their Peltier coolers away after finding out how uselessly and maddengly infuriating they are.

The fundamental problems are that (A) at best your COP is 0.2, and that (B) your output heatsink has to handle SIX OR MORE TIMES the cooling watts transferred at a very low delta T.

Peltier is great to cool a microscope slide or for a dewpoint apparatus, but anything higher power simply does not happen.

Approaching ice temperatures of drink sized fluids is beyond the pale.

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Many thanks,

Don Lancaster
Synergetics   3860 West First Street  Box 809  Thatcher, AZ 85552
voice: (928)428-4073 email: don@tinaja.com   

Please visit my GURU's LAIR web site at http://www.tinaja.com
Reply to
Don Lancaster 

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Or a coupla diodes, a la Ken Smith:

    +----------------+-------+
    |                |       |
    |      O--> |  | |--+-|
Reply to
John Fields

Because they sure as hell ain't gonna cool the can with Peltier. See my other post and

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The two switch positions will be HOT and HOTTER.

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Many thanks,

Don Lancaster
Synergetics   3860 West First Street  Box 809  Thatcher, AZ 85552
voice: (928)428-4073 email: don@tinaja.com   

Please visit my GURU's LAIR web site at http://www.tinaja.com
Reply to
Don Lancaster

NOt using a peltier type module. At least I don't think so. I'm using the (UT) module in the (TEC) module section. surprisingly very powerful with only 12V feeding it! I've done tests with 100 degree water in a pop can, and timed the rate of temperature drop. Pretty impressive. entire can of water fromm 100 to 42 degrees in 24 minutes. thanks for your help. HOpefully I can get this thing hooked up.

Reply to
jgwilliam

How many luxury cars do you know that include Peltier coolers in them factory stock?

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Many thanks,

Don Lancaster
Synergetics   3860 West First Street  Box 809  Thatcher, AZ 85552
voice: (928)428-4073 email: don@tinaja.com   

Please visit my GURU's LAIR web site at http://www.tinaja.com
Reply to
Don Lancaster

Nobody has asked the obvious...Why do you want to heat a can of pop? If you don't need the heat function, things get MUCH simpler.

Dan

Reply to
Dan K

--- How about these guys?:

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They seem to be pretty up-front about it all...

-- John Fields

Reply to
John Fields 

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In Mexico the water faucets are labeled "C" and "F".  
"CALIENTE" and "FRIO"?  No, "COLD" and "FREEZING"! ;)
Reply to
John Fields

Yup.

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Many thanks,

Don Lancaster
Synergetics   3860 West First Street  Box 809  Thatcher, AZ 85552
voice: (928)428-4073 email: don@tinaja.com   

Please visit my GURU's LAIR web site at http://www.tinaja.com
Reply to
Don Lancaster

"At a temperature of 80 deg.F (27 deg.C.) the contents of the cooler can be maintained at approximately 38 deg.F (3 deg.C) (Normal household refrigerators are usually maintained at 45 to 48 deg.F. (7 to 9 deg.C)."

I've got a commercial capuccino maker that uses a thermoelectric module (with fan, I think it's a 40mm x 40mm unit) to keep the milk (for foaming) cold in a small refrigerator under the unit.

Best regards, Spehro Pefhany

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"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
Reply to
Spehro Pefhany

If it is not Peltier, what is it? Where did it come from? Who makes it? Is it a mechanical or a solid state cycle?

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Many thanks,

Don Lancaster
Synergetics   3860 West First Street  Box 809  Thatcher, AZ 85552
voice: (928)428-4073 email: don@tinaja.com   

Please visit my GURU's LAIR web site at http://www.tinaja.com
Reply to
Don Lancaster 

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Ummm... none.

Does that mean they don't work?^)
Reply to
John Fields

You need a double throw switch with center off.

You either need (a) a 3 pole switch or (B) a 2 pole and a couple of diodes.

+12V ------+--+-------------------+----------------------- ! ! ! ! ! O To O ---O ! !
Reply to
Ken Smith

I assume you can work out how to wire up the switch so that it applies alternate polarity, as required, to the module?

Look up "full wave rectifier" and put one of those to the fan.

Alternatively, use 2 switches, one to switch on and off the whole lot, the other just reverses the polarity across the module.

I'm assuming this is a peltier type module.

Gibbo

Reply to
ChrisGibboGibson

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Peltier coolers need not be a scam - they can work, if designed by competent engineers who understand their limitations, and can cope with their low efficiency and limited power-handling capacity.

You certainly can get more temperature rise at your heat-sink than you get temperature drop across the Peltier junction itself, but only if you put too much current through the Peltier junction - the heat transfered by the Peltier effect is linearly proportional to current, while the Ohmic heating is proportional to the square of the current.

There is a simple relationship between current and heat transfer which I worked out for myself back in 1993 and published in 1996 in Measurement Science and Technology (volume 7, pages 1653-64) and again in Review of Scientific Instruments this year (volume 75 pages 788-89) which includes the aggregate thermal resistance from the object being cooled through the Peltier junction and the heat sink to ambient. The Measurement Science and Technology paper includes the derivation (e-mail me - my e-mail addres is real - and I'll send you a reprint).

Once you've gone to the trouble of working out the parameters of your particular system, you can work out the maximum current you can usefully put through your Peltier junction, and the maximum temperature difference you can sustain.

Cook-book enginers who don't understand what they are doing can get frustrated, but advertising your frustration isn't good for your reputation.

------- Bill Sloman, Nijmegen

Reply to
bill.sloman

Why is there ice in my fridgelet then? Reminds me, time to make a cup of tea...

Paul Burke

Reply to
Paul Burke

I read in sci.electronics.design that John Fields wrote (in ) about 'Basic question for somebody to help me with', on Thu, 16 Dec 2004:

Relative to Mexican ambient temperatures or those conducive to human life?

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Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
Reply to
John Woodgate

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