Help me adapt Peltier Mini Frigobar into an incubator

[yamato96]

hi there. im planing to adapt a china peltier mini frigobar to a incubator wlth a constant +35*Celcius inside.

the inside of the fridge consists off a smps 220/12v, a circuit board with switchs to hot/cold op. and 4 wires to the peltier element ....opened up the peltier and the RED/BLACK wires supply the peltier and the other two YELLOW wires are inside the heatsinck block. my first impression was that the thick yellow wires where to a ptc or ntc resistor, but the abcence of logic components in the switch circuit board and no ohm variation thru the wires during op. are poiting me to plated thermostat that switchs off at 60*C.

im i wrong? i need to sort this out to deploy a correct control circuit.

 

[davoud]

Re: peltier mini frigobar

Yes, you are right. this component find in two shape 2 wires usually, that 2 wires peltier just has RED/BLACK wires and 4 wire has a thermostat additionally because this component doesn't withstand on high temperature.

 

[tpetar]

Re: peltier mini frigobar

Better use hot air station heater to make warm air and force that hot air over some pipe inside, precise thermostat will regulate when heater should be on or off. You can se histeresis to minimal or give some higher tolerance on temperature inside, all depence from thermostat which you use. Peltier need more handwork on that fridge and its not elegant, plus you will get water-dew outside. Better save that peltier if you need to cooldown similar portable fridge.

or

If you whant to eliminate air turbulance inside, use heat pipe. Outside use heaters from standard soldering station, heat pipe will transfer heat inside, without any outside contact with inside air.

 

[yamato96]

Re: peltier mini frigobar

hot air station will increase costs exponentialy,but thanks for the input.

just stumbled on an magazine articule that describes the circuit of a popular solder station and the temperature control is achivied by a magnetic thermostat that works by the curie effect - temperature will demagnetize the magnet opening the circuit.

i intend to maintaing this switch as a fail safe in case my control circuit fails, protecting the peltier.

now to control the peltier im planing to use a mcu + ds18b20 + irfp250 fet . Advice in the way to control it? simple switch on and off like a the original circuit or proportional pwm/temp.?

 

[tpetar]

Re: peltier mini frigobar

hot air station will increase costs exponentialy,but thanks for the input.

Not hot air station, I mean on hot air heater element its not expensive :

just stumbled on an magazine articule that describes the circuit of a popular solder station and the temperature control is achivied by a magnetic thermostat that works by the curie effect - temperature will demagnetize the magnet opening the circuit.

i intend to maintaing this switch as a fail safe in case my control circuit fails, protecting the peltier.

You plan to protect peltier with curie effect temp point ? 8-O
Its possible if peltier survive that high temp, why not.

http://en.wikipedia.org/wiki/Curie_temperature
http://www.rmcybernetics.com/projects/experiments/experiments_curie_effect.htm

Do we know peltier temperatures on both sides (average range of temp) or given by manufacturer ?

What is max allowed temp of hot side ?

now to control the peltier im planing to use a mcu + ds18b20 + irfp250 fet . Advice in the way to control it? simple switch on and off like a the original circuit or proportional pwm/temp.?

Peltier cannot be controled by PWM, its not good. Control should be based on switch or supply lower voltage or limit current, or simple buy appropriate peltier element. You can use some fine uC driven thermostat circuit with LCD or LED displays.

You can see one example :

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