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Thread: PWM for Peltier

  1. #1
    Now with added Ruffus Dog Tattysnuc's Avatar
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    PWM for Peltier

    Hi,

    I don;t know if this is even advisable as I know very little about electronics, - I never liked electronics when I was at school, but somehow managed to pass all the modules at Uni. None of them actually involved making anything though!

    I think I'm after a PWM unit to control the amount of power supplied to 4x125W peltier units so that I can control how much cooling is performed by them

    I have 8 water blocks, 4 in a loop

    res -> Pump -> Y split -> 4 x 125W (cold side of) Peltiers (2 sets of 2 in series, in parallel) -> Y joint -> res

    The opposite side of the heat blocks go to a second loop

    Res -> pump -> Y split -> 4 x 125W (Hot side of) Peltiers (2 sets of 2 in series, in parallel) -> Y Joint -> res

    The idea is that I can run the system under water cooling, or when desired, fire up additional cooling to lower the temps in the main loop without having to plumb in/out loops each time I want to make the change

    Now, the problem I have is that I was going to use a variable resistance in order to change the voltage drop across the peltiers, but I've been advised/reminded that Peltiers don;t follow ohms law in the traditional sense as they are semiconductors, and cannot be treated as a resistive source. The advise was to use PWM to regulate the amount of power available to/dissipated by the Peltiers.

    Can anyone offer any advice? I'm struggling due to the high power requirements. I'm very rusty on my electronics, so please forgive my ignorance.


    Many thanks

    Tatty
    Last edited by Tattysnuc; 17-01-2011 at 01:54 PM.
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    Now with added Ruffus Dog Tattysnuc's Avatar
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    Re: PWM for Peltier

    Thought I'd re-write the job just to better explain what I'm trying to accomplish...
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    Now with added Ruffus Dog Tattysnuc's Avatar
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    Re: PWM for Peltier

    It would seem that modding is alive and well over on Bit-tech...

    http://forums.bit-tech.net/showthrea...=1#post2548195

    In case anyone's interested...
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    Senior Member Pob255's Avatar
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    Re: PWM for Peltier

    I didn't answer because I just don't have much knowledge on peltiers and little in the way of understanding how to make a PWM circuit or even if you'll get much out of chilling the water in a loop with a peltier cooled by 2nd loop.

    I can see that using a peltier to cool the water in a loop that's going to multiple blocks makes sense rather than multiple peltiers.
    However if you're just cooling one component using the peltier directly would be far simpler and less messy.

    If you do go ahead with this please let us know how it turns out.

    (at one point I was considering using a peltier and a couple of cpu coolers to make a sort of case air con, where the main air intake had a cooler attached to the cold side on the peltier to chill the air coming in, then I realised the heat pipes carry heat not cold solid copper rods would carry cold better than heatpipes. )

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    Tattysnuc (19-01-2011)

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    Now with added Ruffus Dog Tattysnuc's Avatar
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    Re: PWM for Peltier

    Thanks Pob. Was very surprised not to hear back from one of the resident "hardies". I'm going to build the concept without any PWM controls initially so each Peltier will be on or off, and then see if it's even necessary to regulate them, or whether what I've got is even big enough. Should be, but I've not factored in inefficiencies. IF there's a need to regulate, I'll see if I can do it via a relay or a switch, and then go more hi-tech as required. I'd like to have the temperature regulated in software ultimately and maybe design a commercial unit but first things first I've got to determine if the concept works.

    I think by building a single copper block/heat exchanger I'll be able to condense the size right down, and have it be able to plumb into any water cooling setup.
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    Re: PWM for Peltier

    It's an interesting project Tatty - I've not chimed in with a comment previously because - like Pob - I've not got any real knowledge on the subject - although I have actually been looking into Peltier cooling myself recently as I find it a very interesting concept.

    I think running a second loop to take the heat from the Peltier should work: it's a concept I considered myself. In simple terms the temperature of that second loop won't matter as long as you keep it below boiling: it doesn't matter if your water temperature stays up around 90 degrees as it's only cooling a hot Peltier block not any of your components.

    The most recent concept I played with was having a Peltier-cooled res: basically the Peltier sits in the body of the res, cooling an array of fins that the water runs over, and heating an array of fins on the outside of the res that duct the heat away: you could then blow some large fans across those fins to cool them. If that makes sense? it would replace a conventional rad and res. You might need to house it outside the case though: not necessarily convenient.

    EDIT: Oh, and Pob...?
    I realised the heat pipes carry heat not cold solid copper rods would carry cold better
    As any good physics teacher will tell you, you can't carry cold! Cold is simply an absence of heat, and doesn't move!
    Last edited by scaryjim; 19-01-2011 at 12:56 PM.

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