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60 watts to 50 watts

Discussion in 'General Electronics Discussion' started by CW55, May 31, 2015.

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  1. CW55

    CW55

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    May 31, 2015
    I have a thermoelectric cooler, it is the common TEC1-12706. For my project I just need to turn my 12v 5amp (60 watts) DC transformer into 50 watts of power at the end of the circuit without changing the voltage.
    I would also like to integrate some safety features into the circuit like a voltage regulator and capacitor(s) to help with pulsing and variances of current.
    So the question is what do I do to build this? I am trying to wrap my head around the whole "how big to make your capacitor" thing and how much voltage/amps is lost with voltage regulators.

    Also is there any program where I can virtually test my board to see if it will work?

    Thanks,
    Charles
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Welcome to electronicspoint.
    Your supposed problem probably isn't one at all.

    The rated power of a transformer (or any power supply) is the max. power (or current) the power supply can deliver while stil maintaining a stable output voltage (12V in your example).
    The power drawn by a load (cooler´in your case) is defined by the current the load draws at the rated voltage.
    Therefore it is perfectly o.k. to attach a 12V / 50W load to a 12V / 60W power source. The power source is simply not fully loaded which in turn means you can attach a second load up to 10W (which makes 60W in total).
     
  3. CW55

    CW55

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    May 31, 2015
    Thanks

    That is a very good point.
    Here is the reason I need to get it down to 50 watts. The thermoelectric device will take up to 70 watts max. The more watts you give it the colder (or hotter) it will get. I need to get it to go down to a specific temp and 50 watts give it that perfect amount of cooling without blasting frigid air.
     
  4. poor mystic

    poor mystic

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    Harald is trying to say that the 12V device will only draw the power it "wants".
    You could use a million watt battery without damaging your 12V device, because it is designed to work with a 12V supply.
     
  5. davenn

    davenn Moderator

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    CW55
    you haven't told us .... what is the current rating written on your cooling device ?

    OK found the datasheet

    when supplied with 12VDC it will draw 4.5 Amps = 50W
    if you increase the voltage, the current will increase and obviously so will the wattage
    see this from the datasheet
    peltier.GIF


    Dave
     
    Last edited: May 31, 2015
  6. CW55

    CW55

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    May 31, 2015
    Awesome. Thanks davenn, I guess that answers how to get it to 50 watts. Or if I wanted to get it lower just follow the chart for voltage and just use a voltage regulator. Thanks again guys.
     
  7. Colin Mitchell

    Colin Mitchell

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    Aug 31, 2014
    There is one slight problem that no-one has addressed.
    The 12v transformer will deliver more than 12v on NO LOAD and also more than 12v on a load less than less than 60VA.
    The input to your cooler is DC. The output of your transformer is AC. When 12v AC is converted to DC via a bridge and electrolytic it will be about 17v. But on no load or reduced load, the output will be higher than 17v.
    Now your problem starts.
     
  8. hevans1944

    hevans1944 Hop - AC8NS

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    This sounds like an ideal application for a pulse-width modulated (PWM) power source, with negative feedback from a temperature sensor (thermistor, RTD, or thermocouple) to control the final cooler temperature. Hang your bridge rectifier and filter capacitor on the transformer and build on from there. Pay attention to @Colin Mitchell advice on voltage regulation (or the lack thereof) when choosing components.

    There are lots of PWM circuits on the Internet, and most do not require voltage regulation to produce a constant-current drive for your Peltier device. If I were building this, I would assemble an Arduino Uno along with a power MOSFET, a thermistor, and a few resistors and diodes to create a proportional power controller in software. You can add integral and derivative feedback too, but that is generally not necessary for static applications where the external variables don't change rapidly. A simple correction for "droop," which is the difference between set-point and actual temperature that is a characteristic of a proportional-only controller, can be provided with a potentiometer to allow adjustment of the final temperature, as visually read out on a simple numeric display. IIRC. PWM offers automatic integral action when implemented in software. Total cost I estimate to be less than fifty bucks American, maybe less if you have a well-stocked "junke box" of parts you can re-cycle from other projects.

    As for simulation... Linear Technology has a free pSPICE program (LTspice IV) with schematic-capture that you can download. Draw the schematic and run the simulation from it. Play "what if" scenarios with the component values. Tons of fun! This will help you design the PWM constant-current Peltier driver, which is an analog circuit. They also have an extensive library of application notes, oriented toward their products of course, but of general usefulness no matter whose products you use. But remember simulation is not reality. You have to actually build something with real parts and "let the smoke out" once in a while to learn anything.

    Ummm... what is your experience and desire for the sort of thing I have outlined above? Off-the-shelf solutions are possible of course, but that's not generally what we are here for.
     
  9. Colin Mitchell

    Colin Mitchell

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    Aug 31, 2014
  10. hevans1944

    hevans1944 Hop - AC8NS

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    And it could probably be hacked to provide closed-loop temperature control too, since the output is adjustable with the trimpot on the board. Multilayer PCB construction with plated-through holes, appears to be quality assembly... what's not to like at that price? Just add your transformer, bridge rectifier, an electrolytic capacitor, and the PID temperature control.
     
  11. CW55

    CW55

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    May 31, 2015
    Hmmm. This is getting good. This project seems more complicated and more fun than I thought it would be.

    I can put all of this together. I have messed and tinkered with electronics all my life. I haven't done any build from scratch circuit boards, so this I guess is my first. I am researching it and really needed a place to start, which you guys gave me more than I hoped for.
    I expected to be doing some testing and adjusting to get it to work perfect.
    I have heard of Arduino but I haven't really looked into it, I'll be sure to do that.

    Thanks for the simulation info. It's like flying an RC heli, you don't get good until you fly in real life, but the the simulator sure save a lot of time and parts.

    Just in case I don't get back online for a couple of days.
    Thanks hevans1944, Colin Mitchel, you have been of great service. ;)
     
  12. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Thank you for the kind words. IMHO Colin can sometimes be a little cryptic, but his comments are usually spot-on if you put forth some thought and effort.
     
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