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Peltier cooler circuitry

Discussion in 'General Electronics Discussion' started by ptxpet001, Sep 19, 2010.

  1. ptxpet001

    ptxpet001

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    Sep 19, 2010
    I'm building a portable peltier fridge and need help with the circuitry design. Im using 2 peltier modules which would ideally be drawing 2-3A each and 2 fans which will draw +- 0.5A together. I need to be able to run these off a 12V battery. I know Ill need some power transistors cooled by heatsinks but do not know which to select since Ive never something like this before. Any help will be appreciated. Thanks Pete
     
  2. Resqueline

    Resqueline

    2,848
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    Jul 31, 2009
    What's the Voltage rating of the modules, and do you figure you'll require temperature control? (I guess the need would depend on the size & the insulation of the fridge.)
     
  3. ptxpet001

    ptxpet001

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    Sep 19, 2010
    The peltier description is; I = 6A, Voltage = 15.4V, but the battery I am using only has 12 Ah so I cant run the peltiers at a very high current for too long. I am using a LM35 and opamp coupled to a microcontoller for temperature control. The fridge space is 160x160x100mm and will be well insulated.
     
  4. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Ok, with that space, insulation & power it's quite appropriate with a temperature control. Is your uC output linear, some fast PWM, or simply a slow on/off?
    I'll point out that Peltier's will be more efficient when driven with a constant voltage than if turned on & off. During the off period they'll "leak the cold out" of the fridge.
    On the other hand a simple linear drive will waste a lot of Ah's as heat, so a linear uC output driving a switch-mode "inverter" then driving the Peltier is by far the best option.
     
  5. ptxpet001

    ptxpet001

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    Sep 19, 2010
    Would I be able to build a switch-mode inverter myself, is it quite complicated? I say this since this project is for my final year thesis and I will need to design all the circuitry myself, and cannot simply purchase the item. I also have a limited budget, of which not much is left! Would you be able to assist me with the finer details of the circuitry?
     
  6. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    There are some quite simple power switcher IC's available. You need only the IC, maybe a transistor, an inductor, a diode, and a couple of capacitors & resistors.
    There are of course some design (& layout) rules to observe when it comes to high frequency, high power circuits, but it's not really too complicated to make it work.
    Is that 6A @ 15V for each of the two Peltier's, adding up to 12A max? Will you design & produce the PCB's yourself?
     
  7. ptxpet001

    ptxpet001

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    Sep 19, 2010
    Yes, the max current for each Peltier is 6A @ 15V but I probably wouldn't run them at that. I would need to design the PCB's myself. Could you help me with the layout please?
     
  8. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    You'd need to design the inverter for a hefty 12A anyway then.. Is it an important feature of the fridge design to have that much spare cooling capacity?
    Many of the IC manufacturers have an evaluation PCB layout for some of their IC's. They usually also state some basic layout rules in some of their documents.
    I can guide you if you don't find sufficient info there, but my capability to help will be quite limited from the weekend and two weeks forward as I'm away on vacation then.
     
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