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Layman's Question About Batteries

  1. Sep 5, 2015 #1
    Hello all,

    I really hope this isn't a super annoying question for a layman like me to post here, but I just bought an airpump that runs on 12V DC1, but I want to be able to run it from a portable battery pack. So, I found a 2000 mAh 12V DC battery2 and a female 12V DC car adapter3 to connect the air blower to the battery pack.

    Is there any reason why this rig will not work? Sorry if there is something obviously wrong with the set up. I really don't know much about electricity.

    Thanks in advance for any help!

    steiney

    1http://www.ebay.com/itm/281705671878
    2http://www.ebay.com/itm/171867425580
    3http://www.ebay.com/itm/12V-DC-3-5m...te-Lighter-Socket-Cable-Adapter-/321767199977
     
  2. jcsd
  3. Sep 6, 2015 #2

    NascentOxygen

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    Staff: Mentor

    That battery stores only 2 ampere-hours of juice, so won't be able to power anything much for many minutes, even if it were possible in the first instance.

    How many amps or watts does your air pump need? --- it's sure to be printed on it. For how many minutes do you want to run the pump, before needing to stop to recharge the battery? Not until we know this detail can anything much be decided.
     
  4. Sep 6, 2015 #3
    Hey there and thanks for the reply! The only specification I could fine on the internet was 5.5 Amps. Does that help? I need to be able to run that electric air blower for approximately 15 minutes per job.
     
  5. Sep 6, 2015 #4

    NascentOxygen

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    You need to be a bit more careful with your figures! The link points to a hefty 20000 mAh battery, not a puny 2000 mAh item.

    EDIT: on closer inspection, the description of that battery indicates it is good for supplying only 1-2 amps. This seems low for lipo cells, but it's apparently what you've bought. So I have to retract what I said. That battery does not have the ability to power a 5.5 A motor.
     
  6. Sep 6, 2015 #5
    Whoops! Haha. Thanks and sorry. Okay, cool. Is there a calculator or something I can use? Or could you show me the math so I can figure it out for other sizes?
     
  7. Sep 6, 2015 #6

    NascentOxygen

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    Perhaps you should be looking at a battery pack as sold by RC suppliers, because these use special high current cells for powering remote-controlled model cars and planes. You need a battery pack with a discharge rating of at least 8 amps, preferably 10 A or more to give a margin of safety and for starting the motor from standstill.
     
  8. Sep 6, 2015 #7
    Oh, okay. Thanks. I'll check into that.
     
  9. Sep 6, 2015 #8

    meBigGuy

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    Gold Member

    There is nothing to calculate. The battery is rated for 1-2 amps which is very weird for a 20AH battery. Maybe because the cells are not well matched?

    This style battery has high current ratings, but they are expensive.
    http://www.ebay.com/itm/Battery-Ten...ery-/321831962693?hash=item4aeeae0845&vxp=mtr

    Maybe a sealed lead acid system would be better?
    https://www.amazon.com/ExpertPower-...sr=8-15&keywords=12v+lithium+ion+battery+pack

    Or, there are some pretty neat high capacity car jumper systems (not sure about deep discharge though)
    https://www.amazon.com/RAVPower-Por..._4?s=automotive&ie=UTF8&qid=1441521982&sr=1-4
     
    Last edited by a moderator: May 7, 2017
  10. Sep 8, 2015 #9

    NascentOxygen

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    The "battery pack" here is probably not merely a battery, because the nominal 12v output is not a multiple of a LiPo cell's 3.7v. Most likely the power block comprises 1 or 2 LiPo cells feeding a low power boost switching regulator to step their potential up to 12v. So the 2A maximum would be related to the designer's choice of regulator components, rather than a limitation of the composite cells.

    Using LiPo cells without the electronics, the nearest the nominal battery voltage could be would be either 11.1v or 14.8v
     
  11. Sep 8, 2015 #10

    meBigGuy

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    The 12V battery pack is spec'ed as 10.8~12.6 volts which makes it three cells between 3.6 and 4.2 volts (3.7 is considered nominal, and it will be near that for most of the discharge period).
     
  12. Sep 22, 2015 #11
    Hey NascentOxygen and meBigGuy,

    Sorry for the delay responding back to this thread! After all that figuring, I discovered that I could buy a battery powered air pump for about the same price as the car battery powered version. The battery fits into the housing of the pump, so it is much less bulky than a pump with that big battery packed attached.

    Anyway, I really appreciate both of you helping me out!
     
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