Peltier Current

Discussion in 'General Electronics Chat' started by edgard_Peltier, Apr 5, 2015.

  1. edgard_Peltier

    Thread Starter New Member

    Apr 5, 2015
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    Hello,

    Peltier TEC have a name printed on one side like 12705, 12710, 12720.

    The last number indicated the maximum current.

    I bought a few elements and connected them to my bench power supply.
    I cooled the hot side [water cooling].
    But in all cases and at Vmax, the current that flows is about 50% of the Imax listed in the specs.

    So the 12710 when fed with 15.4 Volt, I get 11.3 Amp,

    Am I misunderstanding something here? I cannot imagine all unuts are faulty.

    How to reach the Imax current?

    Thanks

    Edgard
     
  2. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    Generally speaking supply current will increase with the 'inverse' temperature differential (in a manner [weakly] analogous inverse-paralleled DC power supplies)...

    Specifically, to see a rise in current drain; heat the 'cold' side while cooling the 'hot' side...

    Perhaps your comprehension will be augmented via observation of the fact that, from a technical/scientific standpoint, TECs are nothing more than series arrangements of (relatively) efficient thermocouples...

    Best regards
    HP:)
     
    Last edited: Apr 6, 2015
  3. edgard_Peltier

    Thread Starter New Member

    Apr 5, 2015
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    Thanks for your quick reply.



    What you say is correct but the effect is not that big.

    When applying Vmax I should measure Imax. At these max values the Temp delta plays not a big role anymore.

    I need to try another Peltier element but strange that the 2 units I have both only show about 1/2 the current at Vmax.

    [​IMG]
     
  4. edgard_Peltier

    Thread Starter New Member

    Apr 5, 2015
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  5. Hypatia's Protege

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    A disparity of 50% surprises me as well --- And, yes, I concur with your assertion that you should 'see' Imax at Vmax (even at ΔT=0) --- Even so, I can't help but wonder if said disparity owes to an error/ambiguity of specification (e.g. Imax may merely represent a guaranteed upper limit, etc...)

    I would advise speaking with a CS/Support Tech before drawing conclusions -- datasheets are not uncommonly (poorly) translated/interpolated -- with 'lamentable' results...

    Do the devices seem to function as expected from a qualitative POV?

    FWIW manufacturing defects often effect entire lots/runs -- but, again, I wouldn't draw any conclusions just yet:)

    Best regards and good luck!
    HP

    EDIT:
    Your OP (see excerpt below) appears to say that a 10 amp device draws a current of 11.3 Amps @ Vmax (Which would be well nigh consistent with Spec.) --- I assume I'm misinterpreting said post???:confused:

    ========================================================================
    PS please let us know how it turns out!
     
    Last edited: Apr 6, 2015
  6. Gibson486

    Member

    Jul 20, 2012
    199
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    Are you just running straight form the supply with no heat sinking? In my experience, this was a good way to kill the peltier, especially if you have no way of disconnecting power quickly. Also, from what I have seen with them, if you watch the current, it generally goes to that specified current upon power up, but as T increases with delta T decreasing over time, current goes down.
     
  7. edgard_Peltier

    Thread Starter New Member

    Apr 5, 2015
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    I appologise for my mistake.

    At Vmax on a 12710 I get just shy of 5amp.

    I just ordered another unit from a reputable vendor as my other units are from ebay.

    Will run a test tomorrow.

    I do not believe Imax is a rush in current but a constant current as the data sheet shows
     
  8. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    This is indeed curious! -- Doubly so inasmuch as both you and member 'larryc' are experiencing similar phenomena...

    How long did you leave the TECs connected? As per 'Gibson486' they thermally 'self-destruct' quite rapidly in the absence of adequate 'heat sinking' -- especially at EMFs approaching Vmax...

    Again, I urge you to contact the manufacturer's/distributor's customer service technician -- Sadly, misleading datasheets are not entirely unheard of...

    Good luck and please keep us posted! :)
    HP

    PS:
    Please be advised that, inasmuch as your TECs span different 'models' (i.e. power specifications), manufacturing defect productive of similar malfunction is extremely unlikely...
     
    Last edited: Apr 6, 2015
  9. edgard_Peltier

    Thread Starter New Member

    Apr 5, 2015
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    I have watercooled both sides. One to cool tbe hot side to reach about 45 celcius.

    Cold side is cooling a water bath to about 15 degrees.

    So well within the spec and below 'frying point'.

    I will run tests with a brand new element tomorrow and let you know.
     
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  10. Hypatia's Protege

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    Just an 'FYI'...

    I've tested several TECs, while I apologize that I ignore the model No. and specification, it should be possible to match or extrapolate same from the description (below).

    Plate dimension = 50mm square
    Module thickness = 4.45mm
    Number of couples = 256 (based upon an apparent 16*16 array)
    These devices are NOS purchased from Jameco Electronics many years ago...

    Upon application of 15v the devices draw ~14 Amps decreasing to:
    ~5 Amps within ~300ms --- Free air
    --Or--
    ~ 9 Amps within ~1s --- Plates 'mounted' to (100 square cm) Al heat sinks via silicone thermal conductive pads...

    A total of ten units were tested with similar results...

    Thus it seems that the current demand is lower than one would expect for devices of this size...?

    Hope you find this somewhat useful:)

    Best regards
    HP
     
    Last edited: Apr 6, 2015
  11. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I had the same problem..My peltiers does not draw the stated current. All 7 pcs is them. Figured it might be poor Peltiers to begin with.
     
  12. wayneh

    Expert

    Sep 9, 2010
    12,090
    3,027
    This rash of misbehaving Peltiers is interesting. For what it's worth, I got two modules some years ago that matched up very well with the specs. I think they were 12710, and they draw about 4A on a 5V supply.

    One more thing falling to Chinese counterfeiters?
     
  13. Hypatia's Protege

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    I doubt mine are Chinese counterfeits inasmuch as I purchased them about 15 years back -- Jameco had a very good (too good?) price on them (Ca. $45.00 [USD] apiece) so I 'snapped up' 20 of them with the intent of applying them to a pre-cooler design (for a Gifford-McMahon cryo-refrigeration unit) -- Yet another project I've yet to get 'round to:rolleyes:

    Anyway, it is my hypothesis that the Spec./performance disparity seen with the TECs owes to ambiguous specification. --- Specifically, that 'Imax', as specified, indicates the current drain @ 'Emax' under such condition that ΔT truly equals zero -- A condition which can exist only momentarily at power-up despite heat sinking (baring application of significant, external 'inverse' heating/cooling) --- Such tends to explain the 'inrush like' excursion upon application of power...
    Inasmuch as the forgoing is not wholly consistent with the presentation of data in the attached document, I can only conclude that said specification is 'flawed' and that the 'good behavior' of your TECs is accounted for by perspicacious documentation...:)

    It will certainly be interesting to learn of the OPs results...:D

    Very best regards
    HP
     
  14. Austin Clark

    Member

    Dec 28, 2011
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    The greater the different in temperature across the peltier, the greater the voltage drop across the two terminals. This is because a temperature differential creates it's own voltage/potential in the opposite polarity as the voltage source you're using to power the peltier. Remember, peltiers can be used to generate electrical power from temperature differentials as well. The principles is the same as reverse emf from electrical motors.

    The reason you're not reaching the rating current is because the temperature difference is too great between the cold side and the hot side. You need to dissipate the heat on the hot side better and/or allow the cold side to pull heat from the environment more efficiently. Beings that you're water cooling the hot side, I think it's staying plenty cool. Your best option is to add a heat sink to the cold side, so allow it to pull more heat from the ambient air.

    You could probably get away with applying a higher voltage from your power source, because the voltage actually working across the peltier is going to be lower than that (due to the previously mentioned voltage drop/reverse polarity voltage being generated). Try removing your power source and immediately measuring the reverse voltage being generated. That'll give you an idea how much higher you can go on the power source voltage. You could also measure the temperature of both sides and check the datasheet.

    Hopefully that all makes sense.
     
  15. edgard_Peltier

    Thread Starter New Member

    Apr 5, 2015
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    1
    First of all thanks for having this discussion.
    I just finished the test with a brand new element and which I bought from a RS Singapore. It is rated at Imax = 8.5 Amp.
    At Vmax I reach 7.5 Amp and which is very close.
    So I can conclude that the eBay element is under specced since I only can get 11.3 Amp at Vmax for a 12720 element.

    But what Austin is saying is definitely very valid and he raised another element from the wonderful world of Peltier elements [and often misunderstood].

    I cannot get the hot side colder than ambient and which is 30 Celcius in Singapore.

    But I will definitely try to measure the voltage generated by the element just after power off and curious to compare this among the different TEC models I have.

    So are you saying that if Vmax is 15 Volt and in my setup I measure 5 volts [just a guess] self generated, then I should apply 20 Volt to compensate?

    Seems a bit on the edge since these thermodynamic setups are constantly changing and I might go over the red line.

    Edgard
     
  16. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    Or re/mis-labeled:rolleyes:

    Actually, as regards semiconductor Peltier devices (i.e. TECs), Emax is, within reason, determined by Imax --- Which is to say I agree with your assertion however be warned that it is imperative Emax is not exceeded at the moment of power-up -- lest the 'ΔT=0 inrush' result in damaging over-curent!

    Best regards
    HP:)
     
  17. edgard_Peltier

    Thread Starter New Member

    Apr 5, 2015
    8
    1
    I agree that living on the edge is dangerous...:)

    In any case a Peltier element is not at is best at these Max values. This is illustrated when using the excellent tool on:

    http://www.tecpeltier.com/viewtopic.php?f=4&t=19

    People always say not to bother with TECs to cool stuff as they are very inefficient but when they are driven the right way they can reach very high efficiency levels with positive COPs.

    But that is not to say that the TEC you buy [on eBay or elsewhere] needs to deliver the Pmax values as stated so that then you can apply the right voltage to achieve your goals in the most efficient way.

    Edgard
     
  18. Hypatia's Protege

    Distinguished Member

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    Indeed efficiency isn't always paramount -- often the prime consideration is 'getting the job done' with the resources at hand:) My major 'gripe' in regards to TECs is their (seeming) inability to reach sufficiently low temps for my purposes (To wit: ≤ 73 Deg K [-200 Deg C]) --- If I had a penny for every failed cascade I attempted...... I'd have a lot of pennies --- A point is reached where the plate-to-plate thermal reflux is irreducible despite ample sinking by the preceding stages...

    Best regards
    HP
     
    Last edited: Apr 7, 2015
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