peltier circuit

Discussion in 'The Projects Forum' started by beanmed, Jan 9, 2008.

  1. beanmed

    Thread Starter New Member

    Jan 9, 2008
    1
    0
    Please help, I am trying to build a circuit that uses either 2 AAA Li batteries (4.5 A and 3.1 volts) or 4 AA (5.0 Volts and 8.0 amps) for a circuit to run a peltier chip with requirements of 0.5-1 volt and 1.5 amps. I am very new to electronics and have been trying to create this simple circuit with no luck. Any ideas including changing the power supply would be welcome, but is must be free standing

    Thanks

    to add further detail, I am trying to develop a device for biomedical research that is small ~50-75grams that is able to cool a biological sample about 0.5 Watt (415cal/hr?). The battery can be changed at regular intervals if required so if I can get an hour of work from a battery that would be great. The circuit will be controlled via a PMC with a thermocouple input for temperature measurement. The PMC will also communicate with a computer via RF for data collection.
    the peltier is from custom thermoelectric part#00711-5L31-03CA I max 3.0 A,Qmax 1.4 Watt,Vmax 0.9 Volts
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    1.5 amps is a lot of current for battery power. You won't be able to power your Peltier device for very long, even using four AA batteries.

    I think you're getting your amps and volts confused. When you wire four Li AA batteries in series, you will quadruple the rated voltage, but the current output stays the same as for 1 battery (about 1700mAh to 3000mAh). When you wire four of them in parallel, the voltage stays the same as for a single battery, but the current output quadruples.

    It would be much easier to construct something like a PWM circuit if you were using a 12v sealed lead-acid battery. Trying to run such a power-hungry device from such a small power source will be rather difficult, and even hazardous (Li batteries leak or explode if overheated, spreading caustic materials.)

    With the higher amount of power available, you could then construct a PWM circuit using a 555 timer and a power MOSFET to drive the Peltier device at a 1/24 to 1/12 duty cycle to maintain between 0.5v and 1v across the junction.
     
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    Where did you get your current levels: "2 AAA Li batteries (4.5 A and 3.1 volts) or 4 AA (5.0 Volts and 8.0 amps)" ? A quick check for Energizer AAA shows max continuous of 1.5A, and 2.0A if pulsed with a 2 sec on 8 sec off duty cycle. For Energizer AA's a max cont. of 2.0A and 3.0A if pulsed with a 2 sec on 8 sec off duty cycle. Even at that level the batteries are not going to last long. So...bigger batteries.

    How do you want to control the Peltier... temperature ?, time ?, a knob ?...?

    Maybe a little more elaboration...please.

    Ken
     
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