Peltier dampening?

Discussion in 'The Projects Forum' started by trex66, Jan 18, 2011.

  1. trex66

    Thread Starter New Member

    Jan 3, 2011
    4
    0
    I am controlling a Peltier unit with a controller that turns the electricity on full and then cuts it off. I've read that Peltier modules need to be dampened, the electric needs to be slowly raised and lowered? Is this true and if it is how can I dampen the electrical load?

    12VDC 10A
    TEC1-12709


    One more question, If I have one 12VDC 20A circuit and split it in two, will I have two circuits of 12VDC 10A?
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,027
    I think, not 100% sure, that the issue is rate of temperature change and not voltage per se. If your supply is truly delivering 10A into the 12709, that could lead to a pretty rapid change. I'm using only about 4A, and I don't worry about it. I've used one 12709 for many hours with no evidence of damage.

    Can you give more detail about your second question, I don't get it.
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,344
  4. trex66

    Thread Starter New Member

    Jan 3, 2011
    4
    0
    I was told by a sales person that if I wanted to use a 12709 (9A) that I would have to deliver 9A or it would blow a fuse trying to get it?

    I have two 12709's that I want to run together. The power supply I have delivers two separate 12VDC 10A circuits, but the temperature controller can only handle one 10A circuit. So I can't wire them together. I originally wanted to replace the 10A Mosfet's with 20A ones, but I can't find any. So then I thought I could use the temp controller to trigger a switch to run the 20A circuit. Or split the circuits and use four Mosfets, then re-join the lines. BUT, if what you say is correct, and I don't have to deliver the full 9A to each of the the 12709's then I will be OK. I don't need the full 9A power.

    My major concern was if I needed to use some sort of dampening device or if it would it be OK to run them full on and off without causing any damage?


    Thanks Bertus, I've seen those pages, just can't find my answers there
     
    Last edited by a moderator: Jan 18, 2011
  5. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    I don't know how familiar you are with using peltier devices but it is important to recognize how critical it is to remove heat from the hot side rapid enough to keep the risk of damage to the device down.

    The application information to which Bertus has linked in his reply above stresses this and describes one solution.

    hgmjr
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,027
    I can't imagine what that means. The 12709 has a nominal resistance of ~1.2 ohms, and that's a reasonable way to predict what current it will draw at a given supply voltage, ie. 12V/1.2Ω = 10 amps.
    Do you mean in series with each other, actually linked to achieve a greater ∆T, or in parallel and independent?
    I use the IRF540, which are widely available and should have no problem with that current.
    Not sure where you're getting the 20A? You can't just attach the two supplies together.
    I'm absolutely sure that the TEC will work just great with less than max (10A) current. It will NOT achieve the max ∆T at lower current, but will actually be more efficient at lower currents.
    Like you, I haven't been able to find anything suggesting you cannot switch them on and off as you are planning. I think reversing their polarity from cooling to heating, at max current, would probably be stupid, but switching on/off, especially at lower current, is not a problem.
     
  7. trex66

    Thread Starter New Member

    Jan 3, 2011
    4
    0
    Wayneh: lots of info... thanks

    if anything, this is getting more confusing to me, Wayneh, you said

    "The 12709 has a nominal resistance of ~1.2 ohms, and that's a reasonable way to predict what current it will draw at a given supply voltage, ie. 12V/1.2Ω = 10 amps."

    and

    "I'm absolutely sure that the TEC will work just great with less than max (10A) current. It will NOT achieve the max ∆T at lower current, but will actually be more efficient at lower currents."

    Are you saying that if I run it at 12V it will pull 10A, but if I run it at a lower voltage it won't need 10A?

    Let me explain in more detail what I am doing:

    I have wine fridge with two TEC units, fans, heat sinks, and PSB. I want to convert this into an incubator. I have a temperature controller with two 10A circuits - one for heat and one for cooling. It would be easier if I used one TEC to heat and the other to cool, but I want them to both work together. I plan on using the temperature controller to switch relays to change the currents polarity. The PCB has two 12V, 10A circuits. The two TEC's that were in the unit were broken 12706's. So I want to control one 12V, 20A circuit with a 12V, 10A circuit to run both of the TEC's.

    Can someone tell me why I can't wire both the 12V, 10A circuits from the PCB together to get one 12V, 20A. I said I was using switches, what I have are relays, sorry. The relays I have are Songle SPDT 12VDC 10A.
     
  8. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,027
    Yes, exactly. I'm running mine from a 5v supply (old computer PSU) and the TEC 12709 draws ~4.5A.
    I can't, but it's just generally bad to connect power supply outputs together. I think anyone here would make the same recommendation unless more information comes along. Perhaps if you could post pictures or schematics, we'd have a higher comfort level. You would DEFINITELY want both circuits to control exactly the same, so that you never had one on with one off.
     
  9. trex66

    Thread Starter New Member

    Jan 3, 2011
    4
    0

    Thanks, I understand now. I don't want to have to work in another power supply. I'm just going to get two 12703- or 04's. That way I can run them both off of one 12v, 10A circuit.
     
Loading...