Peltier cooler set up

Discussion in 'The Projects Forum' started by shezza, Jun 9, 2014.

  1. shezza

    Thread Starter Member

    Mar 19, 2014
    45
    0
    Hi all,

    I have a peltier tile 30mm x 30mm, a heatsink, cooling fan and metal plate. So basically a plate that will heat up or get cool depends the direction of polarity.
    I bought it with a USB end on it, but I want to install it in my car. So a couple of questions -

    Firstly, is it ok to put 12v to the fan and tile? Or do I need to get a regulator to bring it down to 5v? Would the voltage have to be limited for the fan and/or the tile?
    If Im not limited by the tile, does more voltage = a greater cooling effect?

    Thanks in advance!
     
  2. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,131
    267
    Does the Cooler come with a data sheet?

    And the fan?

    Without knowing the specifications of the devices you are wanting to power, all we can do is guess. Your new toys will be smoking wreckage for sure.
     
  3. paulktreg

    Distinguished Member

    Jun 2, 2008
    612
    120
    It's strange that it's got a USB connector because the peltiers that I've come across are normally a few amps?
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,447
    3,363
    1) A peltier cooler or themo-electric cooler (TEC) is a heat pump. It will get hot and cold at the same time, i.e. it pumps heat from one side to the other, one side gets hot while the other gets cold.

    2) It helps to know the max wattage of the TEC but this is not essential. You can estimate the wattage. The USB is designed to supply 0.5A @ 5V = 2.5W

    Here is an example of a 60W TEC:

    https://www.sparkfun.com/products/10080

    Your TEC is likely to be less than 40W based on physical dimensions.

    The TEC is a low-resistance device, i.e. the current is relatively high. The simple way to test a TEC is to use a variable DC power supply and gradually increase the voltage while monitoring the current and the cold and hot temperatures.

    The TEC does not require regulated 5VDC. Simply, the higher the voltage, the greater the current and hence the greater the wattage.

    3) A TEC is easily destroyed if the temperature of the hot side gets too hot. While testing for short periods make sure the hot side is mounted on a large heat sink.

    4) If you are thinking of cooling the compartment of your car with this, forget it. It would not work. You cannot cool your house by opening the refrigerator door. You have to vent the heat to the outside of the house or car. And you would need a TEC rated at minimum 1000W.
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,145
    3,055
    Not likely if the designer expected a USB connection, which is only 5V. In your car it might see 15V and go poof.
    I'd start with an old computer PSU and try supplying 5V from it to your device. See how much current is drawn and how the fan runs. If you don't have a meter to make these measurements, go get one. They can be had for under $5 and you'll find it useful for years. The fan can probably take 12 volts, though its life may be shorter if it wasn't designed for 12V. The TEC will be destroyed in a few seconds if it is specified at max 5V.
    Yes, cooling effect is proportional to the power supplied, and the power will go up with the square of the applied voltage. Double voltage equals ~4X power. But the cooling becomes less efficient as you increase the overall power, so your device might be intentionally designed to operate far below its rated maximum voltage.

    Specifications would answer all your questions.
     
    shezza likes this.
  6. shezza

    Thread Starter Member

    Mar 19, 2014
    45
    0
    Some really thorough replies! Appreciate it...

    The Fan was rated at 5v so I just purchased a 12v one to not mess around. I assume itll handle my 14v. If not, Ill have learnt a lesson. I also purchased a higher wattage Peltier tile rated for 12v to just opt on the safe side. They are fairly cheap anyway! Im looking at a kit ready to go and it not only has a fan and heatsink on the hot side of the element, but had one on the cool side... Any idea what that might be about?
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,145
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    The 12V fan will be fine and the peltier should be as well.

    The peltier works best when you can get the heat into the cold side and out the hot side, so that's why it has heat exchangers on both sides. Think of the flow of the heat. Anything you can do to increase the flow is a good thing.

    There is a lot more flow that needs to leave the hot side, since that's where all the power drawn by the peltier shows up. But the hot side is...hot. There's more driving force due to a larger ∆T versus ambient on the hot side. You want your cold chamber to be only a few degrees warmer than the peltier, so even though the flow of heat is much smaller on the cold side, you need a heat sink to make up for a lower ∆T.
     
  8. shezza

    Thread Starter Member

    Mar 19, 2014
    45
    0
    I have read that 3 times and its gone wayyyy over my head! Any way of simplifying it?

    Though I had a thought. What if I had a peltier cooler set up and on top of the hot side heatsink fan, I put another peltier cooler to assist in the cooling?
     
  9. wayneh

    Expert

    Sep 9, 2010
    12,145
    3,055
    Some basic thermodynamics: Energy (BTUs, calories, watt•hrs) is conserved at all times - you can only move it around or convert it to other forms. That means that for any system at equilibrium you can look at the energy coming in and know that there is an identical amount of energy leaving. If the in and out amounts are not in balance, the system is not at equilibrium and changes temperature.

    Heat moves by conduction, convection, or radiation. The temperature of a device relative to its surroundings is the driving force for all these processes. Larger ∆T leads to larger heat flux, all else being equal. Heat exchangers help move larger amounts of heat at a lower ∆T. They are often specified by the amount of heat they can move at a given ∆T, for instance watts/C°

    Peltiers: The small amount of heat being removed from the cold chamber enters the cold side of the peltier because its face is below the cold chamber temperature. A heat exchanger can help this. In the peltier, the power supplied as electricity is converted to heat, adds to the heat coming in from the cold side, and all ends up on the hot side. The hot side will get very hot, to the point of damage, if you don't use a heat exchanger to help dissipate all that heat.

    Your refrigerator or air conditioner can move ~10 BTUs for every 1 BTU you buy as electricity. So 10 BTUs are removed from the room, 1 BTU is consumed, and 11 BTUs are exhausted to the outdoors.

    A peltier, by contrast, consumes as much as 10 BTUs to move just 1 BTU from the cold to the hot side. This is why they are not widely used except where other cooling methods are impractical. They make a lot of heat and you need to use fans and such to get rid of it all.
     
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