What battery should I use for this project?

Discussion in 'General Electronics Chat' started by simonthedigger, Apr 18, 2012.

  1. simonthedigger

    Thread Starter New Member

    Apr 18, 2012
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    I am trying to make a new project that might revolutionize a certain field of work. The unit is designed as a cooling system for a mobile vest. However, I need to configure the power for it. It will be using this Peltier unit to cool it, but I need to find a battery that can keep this running for around 3 hours and then be recharged. Any suggestions?

    *Edit* this is a mobile suit so this needs to be fairly reasonable for portability reasons.
     
  2. #12

    Expert

    Nov 30, 2010
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    I max is 6 amps. Therefore 3 hours times 6 amps is 18 amp-hours. A 12 volt, 18 amp-hour battery is indicated.
     
  3. paulktreg

    Distinguished Member

    Jun 2, 2008
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    Therefore you need a 12V 18Ah battery. It shouldn't be too difficult to do the research and find the lightest/most cost effective charger?
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    A battery "AHr rating" is based on a current draw of AHr/10Hr. An 18AHr battery is rated at that based on a 1.8A continuous draw for 10Hr. You would need a much larger battery to continuously draw 6A for 3Hr and have many charge cycles. Probably something more like a 50-100AHr deep discharge marine battery.

    Ken
     
  5. evilclem

    Member

    Dec 20, 2011
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    You are aware how much heat you must dissipate from a Peltier device compared to the cooling power right?
     
  6. #12

    Expert

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    Better give the guy wearing the personal cooler vest a wheel barrow to carry that 100 amp-hour deep discharge marine battery and 60 pounds of aluminum heat sink.
     
  7. MrChips

    Moderator

    Oct 2, 2009
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    If you build the 100 Ah into the vest don't jump into the water thinking it is a life jacket.
     
  8. P-MONKE

    Member

    Mar 14, 2012
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    Ahhhh - the laws of physics: completely irrelevant to those who don't understand them.
     
  9. simonthedigger

    Thread Starter New Member

    Apr 18, 2012
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    Well this sucks, honestly I just need a portable power supply that can work for this unit for a few hours. It seems like a cell system would not be enough. And yes I am highly aware of the heat peltiers give off, I use one as a cooling system for my terrarium. But with that I have an old PSU system from a computer to power it. Remember I need for this to be portable and discreet. If need be I can sacrifice an hour of run time down to just 2 hours. But can any of you direct me to a cell unit that could be concealed and not heavily burden someone down?
     
  10. KMoffett

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    simonthedigger likes this.
  11. ssnyde

    New Member

    Apr 4, 2012
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    Hi,

    Is it fair to assume for the application that you need to crank this thing at full throttle the whole time. You only need to apply enough power to the peltier cooler to account for the delta T you want to achieve (taking into account the terrible efficiency). Last time I used this was to cool a radiation detector, where leakage current increases with heat and effectively raises the noise floor of your detector. We used a variable voltage supply and a temperature sensor with a MCU to make a simple PI feedback controller. This is one of the easier controllers to make because the system cools so slowly.

    You might need a lot less power if you fully characterized your cooling requirements.
     
  12. simonthedigger

    Thread Starter New Member

    Apr 18, 2012
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    Ok this works, thank you ken I will look over this. If any of you are curious I am building a vest that will be designed to circulate chilled fluid via a peltier unit and pump, then have the heat dissipated via a heatsink. The parts to make all this and house it is not the real issue but the power supply, I can make this device work and make it light enough to wear. But if I need to have a car battery to run it, then it will be far too impractical. It's a shame the heat side of the peltier can't be used for something more productive, what a waste of energy.
     
  13. #12

    Expert

    Nov 30, 2010
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    Remember, Ken said you need a HUGE battery if you want long life and many deep cycles. If you're willing to find out how fast a 12 to 18 amp-hour battery lasts under full discharge cycles, that's the lightest weight. (I think some lithium batteries have better watt-hours per pound.) That's what Battery University is for.
     
  14. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Maybe a bunch thermopiles on the hot side of the heatsink to recharge the battery.
    http://www.tegpower.com/
    But that's starting to sound a little like perpetual motion. ;)

    Ken
     
  15. #12

    Expert

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    It's not perpetual motion, but it could give 10% or 20% more run time. I say, "It's worth doing the math, Simon".
     
  16. simonthedigger

    Thread Starter New Member

    Apr 18, 2012
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    Oh this is awesome, perhaps this can give me some more options. I know I will need to discuss this in further details as time progresses and I will need some help with circuitry too, luckily I feel that I am in the right place for all this. Now to find a lithium cell that will do the job that I need it to do. Please give me some more suggestions while I am out at work. Will be back at 8pm EST -5
     
  17. Audioguru

    New Member

    Dec 20, 2007
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    Electric model airplanes use Li-po batteries because they are powerful and lightweight.
    I saw an airplane on its first flight and its $600.00 battery caught on fire.
    The battery cost $600.00 for the airplane to fly for about 20 minutes. Larger more expensive batteries will do what you want. Maybe a battery that costs $4000.00.
     
    strantor likes this.
  18. #12

    Expert

    Nov 30, 2010
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    Fat, sweaty, guys in personal coolant vests wouldn't like that result. ;)
     
  19. simonthedigger

    Thread Starter New Member

    Apr 18, 2012
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    This is actually for Fursuits :D
     
  20. simonthedigger

    Thread Starter New Member

    Apr 18, 2012
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    Hey look what I found. I think this might help provide a solution. This cooler uses a peltier and a Li-Po battery system. Only question is if the same parts could be used to cool down the fluid enough to make someone feel comfortable. I am not sure, any input guys?
     
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