how to vary the cooling temperature in the peltier module.?

Thread Starter

muthuaiyan

Joined Aug 4, 2014
19
hii crutshow,

i want to vary the TEC input supply so that temperature should varies in the TEC,
which method is suitable for varying the input supply and how??
 

wayneh

Joined Sep 9, 2010
17,496
Control by voltage or by current gives a similar result. The apparent resistance of the TEC doesn't change much, in my experience. But controlled current would give more precise control and with a system at steady state, you could calibrate current flow to heat removal.

You should explain what your goal is. There might be some good ideas to reach that goal.
 

Thread Starter

muthuaiyan

Joined Aug 4, 2014
19
hii crutshow and wayneh,

this is the GOAL of my project

i want to vary only the input supply so that one side of the cooling temperature in TEC should vary.., (20c to 5c)

Which method is suitable for varying the cooling temperature in one side by varying the input supply and how??
 

wayneh

Joined Sep 9, 2010
17,496
Use a constant current supply with an adjustable current output. If there is no heat load on the TEC and you care only about its surface temperature, plan to run the TEC well below its rated maximum current. I would estimate that ~10% of maximum current would cause the face of the TEC to drop from ambient to 5°C or so. Experiment with different current levels to get the effect you want.

If you want CONTROL of temperature, you will need a way to measure the temperature. Your goal is still very unclear.
 
I designed one of these using op-amps and a thermistor many years ago to keep reagent tubes in an aluminum block at a 50 deg. F temperature. Nowadays, a PID controller using a microprocessor is the way to go. Even an I-pad app. may be available to do the job. Its to your advantage to do a thorough search for all applicable technologies to find the one that best fits your need within your budget. A Honeywell Programmable Thermostat immediately comes to mind ($30 US), AA battery powered and touchpad programmable. The negative Feedback approach to this problem is, I think a good fit. Relay (contactor) control of the Peltier Power (DC) is sufficient as the response is pretty slow.

Cheers, DPW [Everything has limitations...and I hate limitations.]
 

Thread Starter

muthuaiyan

Joined Aug 4, 2014
19
Hii wayneh,

if i use constant current supply,and the adjust the current supply..
which method is implemented to adjust the current supply and how?
can solar panel is able supply the constant current?or we can give another power supply?
 

Sensacell

Joined Jun 19, 2012
3,432
You control the cooling output by varying the average current flowing through the peltier junction.

Maintaining a specific temperature requires a feedback mechanism, a sensor of some kind that controls the current.

A PID controller is one way, a simple on-off thermostat will also work, with less accurate temperature control.

Control of the current can be accomplished using a PWM driver, or a linear current regulator, (far less efficient) a potentiometer is not a power handling device, it will not work for this application.
 

wayneh

Joined Sep 9, 2010
17,496
.. if i use constant current supply,and the adjust the current supply..
which method is implemented to adjust the current supply and how?
If you don't care about efficiency, the usual approach is to include a low ohms resistor in series with your load. You use an op-amp to watch the voltage across that shunt resistor, and use its output to control a power transistor that is also in series with the load. A voltage that is "too high" due to excessive current causes the op-amp to reduce the base voltage to the transistor, reducing current. If the voltage is too low, the base current is increased.

The problem with this approach is that it is "linear", causing a voltage drop across the transistor that must be burnt off as waste heat. That's why people use PWM instead, a technique where the transistor is always fully on or fully off.

can solar panel is able supply the constant current?or we can give another power supply?
Probably not, but that depends on the details, the specifications of the panel, supply, and TEC.
 
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