Battery operated amp

Discussion in 'General Electronics Chat' started by brandongordon2002, Jan 4, 2010.

  1. brandongordon2002

    Thread Starter New Member

    Dec 28, 2009
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    Hey guys, greetings from Canada, im new to the forum and am not sure how to start a new post, my question is i have several 6v 7ah seald lead acid batteries, im going to be using 4 in series parallel to run my 300 watt kenwood amplifier. Im currently charging the batteries with a 12v 1amp power supply. I was wondering can i use a regular car battery charger to charge these batteries? or will a regular battery charger have too much power for such small batteries? I was looking at a Motomaster Eliminator Intelligent Battery Charger 12v - 6A/4A/2A battery charger. Would this work? Thanks for your help guys.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Welcome to the forums.

    That thread you hijacked was so unrelated that I won't include a link. Take a look at the button next to the "Post Reply" - that is the "New Thread" button.
     
  3. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    wouldn't be calling coytes would you?
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Your little batteries will total 12V at 14Ah. So they can supply 1.4A for 10 hours or 14A for about half an hour.

    A 13.6V 300W amplifier has a max supply current of about 36.8A which your little batteries might not be able to supply and a charge on your little batteries will not last long.
     
  5. brandongordon2002

    Thread Starter New Member

    Dec 28, 2009
    10
    0
    Ive been using them for a while, what kind of charger can i buy? a regular 12v charger for a car?
     
  6. Paulo540

    Member

    Nov 23, 2009
    188
    0
    I'd use a motorcycle battery charger, that should work ok, 1 or 2A charge would be safe.
     
  7. brandongordon2002

    Thread Starter New Member

    Dec 28, 2009
    10
    0
    So if i understand correctly, when charing sealed lead acid batteries all you need is a 6v or 12v charger that puts out low amperage? So charging my 6v batteries with a 6v charger at 1-2 amps will be safe? Id like to charge all 4 batteries in series parallel with a regular 12v car battery charger my only worry is there is im not sure how high of amperage is too much. If i was to charge them with a 25 amp charger would they charge quickly or is that a recipe for distruction? The batterys work great for my amplifier i just wish i could charge them quickly properly or if they would auto charge that would be cool to. Thanks for all your help guys
     
  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Don't try to charge them faster than 1/5th of their AH rating. You will cause too much internal heating, which may result in venting of the cell (spewing out the electrolyte).

    Since they are rated for 7AH, that's 1.4A. Charging efficiency for lead-acid batteries is not 100%; more like 70%-80%, so it'll really take more like 7 hours to charge them.

    But, that's basically just the "bulk charge", getting them up to around 90% charge. During bulk charge, the current to the battery is held at a constant rate until the voltage reaches a set level.

    The "absorption charge" phase takes longer. This is where the voltage across the battery is held constant until the charge current drops below a certain level.

    Then there is the float charge phase; the voltage is reduced to roughly 6.8v, depending on the battery internal temperature. Batteries can be left on float charge indefinitely, as long as the charge level is temperature compensated.

    The deeper you discharge them, the shorter their life will be. If you only discharge them about 20%, you'll get many times the charge/discharge cycles as you would if you discharged them to 50%. If you discharge them until they are dead, you will have a very short service life.
     
  9. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    If those little batteries power your "300W" amplifier properly then the amplifier is 300 Whats which is only 30 Watts.

    Maybe "300W" is actually the PMPO which is about 3 Watts.

    Cheap amplifiers use a very tiny decimal point on their power rating number that cannot be seen.
    So "300W' is really "3.00W".
     
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