Charge pump/voltage boost?

Discussion in 'The Projects Forum' started by GibbyG, Sep 3, 2014.

  1. GibbyG

    Thread Starter New Member

    Sep 3, 2014
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    I have a 12v 16A power supply.
    The load pulls 6A @12v to 10A @ 16v.
    Is there a way to boost the voltage and current capability to around 15v?
    Any close examples to learn from?
     
  2. b1u3sf4n09

    Member

    May 23, 2014
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    Hmm, is this load a motor? It's not often you'll find a load that pulls higher current at higher voltage.

    For the power supply, it would depend on the topology it employs. It is capable of 192W, so it is large enough for the load, but increasing the voltage may not be an easy task. For instance, it may use a transformer with a 12V output, which means you would have to use a regulated voltage doubler to achieve 15V, or buy another transformer and put the transformer outputs in series.

    Any info on the supply would be useful. Does it have a part number? Is it switched-mode or linear? Is it possible to put the power supply output in series (if it has more than one output)?
     
    Last edited: Sep 3, 2014
  3. GibbyG

    Thread Starter New Member

    Sep 3, 2014
    9
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    The power supply is a phihong PSM204-120
    The load is a 12710 thermoelectric cooler chip.
    The project is increasing the transferred BTUs without increasing the package size.
    At 12 volts the TEC is only pulling about 6 amps.
    I'd like to take the TEC to about 90% of it's max rating.

    Sometime last year there was a posting I read (not here) the showed how swapping one of the resistors on the PSU tricked it into outputting 13.5 volts while giving some derating values. The posting has since disappeared but it made reference to R1 that I found on the back of the motherboard but I thought I remember is mentioning one of the two daughterboards. While the above might be irrelevant, its another option or at least worth testing to see if we can move more BTUs.

    Would a voltage multiplier be able to handle the current the TEC will want?
    Can this be achieved with minimal additional components?
     
  4. wayneh

    Expert

    Sep 9, 2010
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    Not sure what you mean by that, as every resistive load will do exactly that.
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,151
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    Something may be wrong with your TEC or your measurements. A 12710 should draw ~10A at 12V, and those are its max ratings.
     
  6. b1u3sf4n09

    Member

    May 23, 2014
    115
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    [​IMG]

    Voltage and current share an inverse relationship. As your voltage increases, your current decreases, assuming a constant resistance. If you want to account for temperature in relation to your resistance:

    [​IMG]

    Resistance changes in relation to the change in temperature multiplied by the first order temperature coefficient. In most resistive loads, k is made to be as close to 0 as possible, thereby keeping your resistance stable over a wide range of temperatures. The main exception would be thermal devices like thermistors, hence why they are divided between PTC, positive temperature coefficient, and NTC, negative temperature coefficient.
     
    Last edited: Sep 4, 2014
  7. wayneh

    Expert

    Sep 9, 2010
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    Try it again. Suppose all the values are initially 1; 1 amp, 1 volt, 1 ohm. Now V is increased by 10% to 1.1. What happens to I ?

    Or in practice, imagine doubling the voltage on a light bulb. Do you predict the current - and thus brightness - will decrease?
     
  8. b1u3sf4n09

    Member

    May 23, 2014
    115
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    I apologize, you are right. I should have actually done the math before slinging it around.
     
    wayneh likes this.
  9. b1u3sf4n09

    Member

    May 23, 2014
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    I was thinking power, not resistance. To maintain static power, current decreases with increased voltage. I knew that thought came from somewhere.
     
  10. GibbyG

    Thread Starter New Member

    Sep 3, 2014
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    1
    Most TEC chips have their max amp draw listed at the max voltage rating.
    The 12710 pulls 10A @16v
    At 12v these pull between 6 and 8

    12710 Datasheet
     
  11. wayneh

    Expert

    Sep 9, 2010
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    My bad. I shouldn't have relied on memory, and read the data sheet. FWIW, my 12709 draws just over 4A with a 5V supply, consistent with its quoted 1.2Ω resistance.
     
  12. GibbyG

    Thread Starter New Member

    Sep 3, 2014
    9
    1
    Not having a good understanding of charge pumps I found this calculator online.
    Says I would be pulling 26 amps from the power supply to get results I want.
    Seems pumping that many amps from the 12 volts is too much.
     
  13. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Can you just get a 15V 10A supply? The parts for a DIY boost converter are likely to cost about the same...
     
  14. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Any chance that there is a trim pot on the PCB? On a 3.3 V, 9 A, PS, I was able to extend output V out to 4 V with pot in center range by add ing a resistor.
     
  15. #12

    Expert

    Nov 30, 2010
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    I've done that trick, too. Raised a 6V power supply to 6.3V for some vacuum tube filaments, but a 20% increase makes me worry that the 12V power supply won't cope that far out of its design parameters. Still, you can try. If it works, fine. If it doesn't you've lost a 10 cent resistor and some time.

    ps, I think there's something wrong with that calculator in post #12 because it predicts 38% efficiency.
     
  16. ronv

    AAC Fanatic!

    Nov 12, 2008
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