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Topic: Wine Cooler hack? (Read 575 times) previous topic - next topic

mistergreen

May 20, 2018, 05:00 am Last Edit: May 20, 2018, 05:07 am by mistergreen
Hey,
My peltier wine cooler doesn't function as it should. I think it's the power/logic board the maintains cold temperatures shorted. So I was thinking of replacing it with an external power supply and an arduino as the controller.

I have a question about the temperature sensor that's attached to the Peltier device.


It's in the block below the peltier. I have no idea what make/model it is since it's inside the metal block. The temperature sensor changes in ohms depending on the temperature. How can I use input into the arduino? Send 5v through it and into the arduino analog input? I'll then have to figure out the temperature formula base on the voltage I get?

I could easily use a more arduino friendly temperature sensor if this is too much of a challenge.
thanks.

jremington

#1
May 20, 2018, 05:25 pm Last Edit: May 20, 2018, 05:27 pm by jremington
The sensor is probably a thermistor. Google "arduino thermistor" for thousands of tutorials.

The Peltier module could be burned out, so check that first. Use your multimeter to check the resistance, or power it up with any low voltage DC source, even flashlight batteries, to see if the module is pumping heat. The polarity does not matter.

And while you have that multimeter out, measure the resistance between the thermistor leads and report back.

mistergreen

Thanks for the thermo resistor id.
The thermo resistor reads at 16.8K ohm.
And the peltier reads at 14 ohm. I plugged it in a 9v battery to it and the cold side does drop slowly. I used an infrared thermometer to read it.


jremington

#3
May 21, 2018, 12:02 am Last Edit: May 21, 2018, 12:05 am by jremington
Quote
The thermo resistor reads at 16.8K ohm.
In that case, you would use the thermistor in a voltage divider with a resistor in the range of 10-22 K. Connect the center tap to an analog input, as described in the many thermistor tutorials.

To calibrate it, you need to measure the thermistor resistance at three or more accurately known temperatures in the range of roughly 0 - 30 C and use this web site (among several possibilities) to calculate the Steinhart-Hart coefficients.

If the Peltier will just be used for cooling, then a simple MOSFET driver will work to control it, similar to the drawing below (replace the motor with the Peltier module).

mistergreen

Hey, so I figured out all of the components power usage and figuring out a power supply and circuit.

1. Display -  10V 2A
2. 2 fans - 12V 1A
3. Peltier - 12V 5A

So a power supply of 12V 8A would suffice. I read that if the peltier exceeds the 5Amps, it will fail. How do I protect it from getting too much Amp? A fuse?


jremington

#5
May 22, 2018, 06:16 am Last Edit: May 22, 2018, 06:19 am by jremington
You regulate the Peltier power supply voltage to regulate the current. PWM will not work to regulate the current.

If  the Peltier is specified as 12V/5A, then it should draw 5A from your 12V power supply.

Best to check both with a multimeter, though, and check whether the power supply has a pot (possibly internal) to adjust the voltage.

Quote
1. Display -  10V 2A
What sort of display draws 20 Watts?

mistergreen

What sort of display draws 20 Watts?
It's an LED display on the door that possibly have another temperature sensor and controlled an light inside the cooler. I'll check again, maybe it draws 1 amp instead.

jremington

#7
May 22, 2018, 07:57 pm Last Edit: May 22, 2018, 08:13 pm by jremington
Even 1 A sounds high for an LED display.

I should add that you could also use a resistor (less than 1 Ohm) in series with the Peltier module to reduce the current, if you think it is too high. The resistor will get very hot, so choose the power rating accordingly (e.g. 0.5 Ohm, 25 Watt resistor).

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