Solution for "loud" relays?

Discussion in 'General Electronics Chat' started by BackyardBrains, Sep 15, 2010.

  1. BackyardBrains

    Thread Starter Member

    Aug 26, 2010
    33
    0
    A friend has a neat project (DIY PCR Machine) that uses relays that are really loud (there's a lot of switching that goes on). I am wondering if he could use transistors instead, and what their limitations are.

    Currently he is using an ATX power supply for its 5v and 12v power. And uses peltiers that can go up to 9 amps, the more power the better in this case because it means faster heating and cooling times in his application. I would like to know if transistors are an option, or if he has to stick with relays, because of the amount of he's using.

    Here are some photos of what he's got going on if you want to check it out.

    Thanks for your help.
     
  2. AlexR

    Well-Known Member

    Jan 16, 2008
    735
    54
    If we knew what a PCR machine is we might be able to give some sensible advice. A quick search for PCR brought up the following but how any item relates to relays is beyond me.

    pedal-crank rates
    pellicle cleaning ratio
    Penile circumference responses
    per cent regurgitation
    peripheral chemoreceptor response
    Philips Computed Radiography
    Philips Computed Radiology
    photosynthetic carbon reduction
    photosynthetic carbon-reduction
    Pickled Cabbage Railway

    If you must use acronyms in your posts please give definitions so that others have some idea of what you are taking about.
     
  3. BackyardBrains

    Thread Starter Member

    Aug 26, 2010
    33
    0
    Sorry for the acronym. PCR in this case stands for a "polymerase chain reaction". It is used by molecular scientists to amplify a piece of DNA across several orders of magnitude. These devices are very expensive to purchase. The idea behind this project is to make it cheap enough to have in high schools.

    There is a picture of the machine (and the relays) are in the link above.
     
  4. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Switching 10A at 12V is not particularly difficult with MOSFET. However, a simple circuit diagram of how these peltier devices are connected in the existing project is needed.

    How many independent current paths? Where does the control signal comes from and its level?

    I would think the current need to be ON/OFF/REVERSE with current up to 9A for each path.
     
  5. hobby16

    Active Member

    Aug 30, 2010
    30
    4
    [​IMG]

    More seriously, mostfet H bridges can easily commute several dozen amps for Peltier modules. You have half H bridges in SO-8 (by Siliconix, Fairchild...) that would fit the job.

    But a too silent machine is so boring !
     
  6. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,789
    945
    If you feel more comfortable with relays than transistors, look into the solid state switching variety. They are very quite, if you listen real hard, you can almost imagine some sound.... :)
     
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