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Thread: Peltier Load

  1. #1 Peltier Load 
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    Hi all, I am building a system that uses a Peltier to control air temperatures in a small box. I am wondering how I have to work with it - what I mean by this for example is that when working with motors you need to account for the stall currents, is there anything equivalent with a Peltier unit?

    Also, if a unit is rated at say 60w cooling (12V@5A DC) and I feed it 12V@3A DC (from a power supply of that rating) will I risk damaging my circuits or the power supply? ...will it want to keep drawing more power?

    It will also be cycling on and off and I am sure this will cause wear and lead to eventual failure...any hints how this can be avoided from happening prematurely?


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    my electronic knowledge is severely rusted..
    but why can't you just make a power supply that would meet your needs?


    as far as your cycling..get a new seat,that will help keep your end from wearing out...


    The term 'Free' in Free thinking, does not imply control....
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  4. #3  
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    Quote Originally Posted by NMSquirrel View Post
    my electronic knowledge is severely rusted..
    but why can't you just make a power supply that would meet your needs?


    as far as your cycling..get a new seat,that will help keep your end from wearing out...
    funny, thanks...I will try the new seat idea...of course thermal cycling was what I meant...

    I am only asking to learn how to work with these devices...
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    This might give you some ideas. I haven't played with them myself.
    Tellurex - Introduction to Temperature Control Of Thermoelectric Systems
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    Quote Originally Posted by fatman57 View Post
    Hi all, I am building a system that uses a Peltier to control air temperatures in a small box. I am wondering how I have to work with it - what I mean by this for example is that when working with motors you need to account for the stall currents, is there anything equivalent with a Peltier unit?
    No. There are no moving parts, first of all, so there can be no "stall." A Peltier device just draws the current that it draws for a given applied voltage.

    Also, if a unit is rated at say 60w cooling (12V@5A DC) and I feed it 12V@3A DC (from a power supply of that rating) will I risk damaging my circuits or the power supply? ...will it want to keep drawing more power?
    That's not how electricity works. Imagine that a graph of current vs. voltage fully characterizes a Peltier's electrical behavior (it's a good enough approximation here, and I want to keep the explanation simple). As soon as you specify either the voltage OR current, the other quantity is automatically determined. A supply rated at 12V, 5A simply means that it is capable of maintaining 12V output all the way up to 5A. It does not mean that it will magically enforce both 12V across the element and also force 5A through the element simultaneously. The relationship between V and I is determined by the load (here, the Peltier device), not the source.

    Use of a 12V 3A supply means that you run the risk of not being able to maintain 12V across the device, if the Peltier attempts to draw more than 3A.

    It will also be cycling on and off and I am sure this will cause wear and lead to eventual failure...any hints how this can be avoided from happening prematurely?
    What "it" do you mean? A properly designed power supply isn't bothered by such cycling. A Peltier device has no moving parts, so it wouldn't care, either. The only issue is that temperature cycling can cause mechanical movement (and hence, related stress-induced wear). But other than that, on-off cycling is no problem for solid-state devices.
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    If you control your cooler with a thermostat, the thermostat switch will be a potential area of wear and pitting. If you use a proportional controller that will not be the case, but that would probably make it more complicated than you need.
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    thanks all!

    tk421 - by 'it' I meant the Peltier and wear due to thermal cycling...but learnt more when you mentioned how the power pack will perform

    Quote Originally Posted by tk421 View Post
    Use of a 12V 3A supply means that you run the risk of not being able to maintain 12V across the device, if the Peltier attempts to draw more than 3A.
    I understand it will not be able to maintain 12V across the whole device. But if the Peltier attempts to draw more than 3A (which I suppose it will as in this example it is a 60W device) that will mean the power supply will be constantly running at full output, is this correct? If yes then will this strain the power supply?


    Harold14370 - I will be controlling the Peltier with a transistor and Arduino setup...thanks for the tip though!
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    Quote Originally Posted by fatman57 View Post
    I understand it will not be able to maintain 12V across the whole device. But if the Peltier attempts to draw more than 3A (which I suppose it will as in this example it is a 60W device) that will mean the power supply will be constantly running at full output, is this correct? If yes then will this strain the power supply?
    The power supply will then operate in a current-limited mode. Some supplies will simply output the maximum current (at which the Peltier device will work, but not as well as it could), or go into "foldback" limiting at a current value well below the maximum. Most modern supplies are designed to tolerate over-currents indefinitely, but Murphy always seems to guarantee that the ones I buy commit suicide spectacularly when overloaded by even a tiny amount. It's best to use a supply that has enough oomph to get the job done without complaint. But if you're impatient, and all you have is a 3A supply handy and don't mind the possibility of killing it, I suppose you could go ahead and try it.
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    ooo..flashback of my electric cord with aligator clips at the end of them..snap,crackle,BOOM! (smell that?)
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    Quote Originally Posted by tk421 View Post
    Quote Originally Posted by fatman57 View Post
    I understand it will not be able to maintain 12V across the whole device. But if the Peltier attempts to draw more than 3A (which I suppose it will as in this example it is a 60W device) that will mean the power supply will be constantly running at full output, is this correct? If yes then will this strain the power supply?
    The power supply will then operate in a current-limited mode. Some supplies will simply output the maximum current (at which the Peltier device will work, but not as well as it could), or go into "foldback" limiting at a current value well below the maximum. Most modern supplies are designed to tolerate over-currents indefinitely, but Murphy always seems to guarantee that the ones I buy commit suicide spectacularly when overloaded by even a tiny amount. It's best to use a supply that has enough oomph to get the job done without complaint. But if you're impatient, and all you have is a 3A supply handy and don't mind the possibility of killing it, I suppose you could go ahead and try it.
    thanks! you have been a great help!

    Just to confirm, will the peltier continue to demand power if it has a higher rater power rating than the power supply?

    Related question to save time, does the same theory apply to resistor heaters (electric heating) than what we have been discussing around the Peltier?
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    Quote Originally Posted by fatman57 View Post
    Just to confirm, will the peltier continue to demand power if it has a higher rater power rating than the power supply?
    If the load -- Peltier or otherwise -- tries to draw more than the supply, the supply will either go into some protective mode, or expire.

    Related question to save time, does the same theory apply to resistor heaters (electric heating) than what we have been discussing around the Peltier?
    Yes.
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  13. #12  
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    Well...Tk and others did a good job explaining things for real....so:

    Peltier Load
    Peltier's have long been prized for their luxurious pelts...so when hunting them, it is essential to use the right load, in order to minimize damage to the hide. While single and double-ought buck shotgun loads are effective against the wiley beast, they generally leave the pelt unusable. I prefer a 220 grain 30-06 full metal jacket. It has stopping power to drop the little devils in their tracks, without too much damage to the hide.

    I hope this helps.

    What's the application for the Peltier? If you need a 12 volt power supply, and don't want to build one, the 12 volt rail on a computer power supply could easily handle 5amps...and way more.
    Fixin' shit that ain't broke.
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  14. #13  
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    For any lurkers who don't know what a Peltier thermoelectric device is:

    It's a little pad, that when dc current is applied to it, gets hot on one side and cold on the other


    They can also be used to generate current. If you place the pad on something that's hot or cold it will generate a small amount of dc current. Pretty cool. (need to recharge your cell phone battery with a campfire? Do it the "Macgyver" way: http://www.youtube.com/watch?v=Zl_AvKkCFQk)

    Last edited by MacGyver1968; February 19th, 2013 at 08:42 AM.
    Fixin' shit that ain't broke.
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  15. #14  
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    Thanks tk421!

    MacGyver1968 - good choice on the full metal jacket, wouldn't the MacGyver way of had been to make a peltier out of some sticks, two stones and the knob from a transistor radio?
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