Can I charge my car battery with 75 amps?

Discussion in 'General Electronics Chat' started by earthtodan, Nov 30, 2010.

  1. earthtodan

    Thread Starter Member

    Dec 3, 2008
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    I have my car in the garage while I do a pretty extensive stereo install, probably two weeks. I'd like to tend the battery, since once in a while I use some function or other. I have a 12V 75A power supply in the garage. Will it damage the battery to hook up a high current supply like this? How long should I leave it if I do?

    Thanks,

    Dan
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
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  3. timrobbins

    Active Member

    Aug 29, 2009
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    Does the power supply have a variable current limit? Does the power supply have a variable voltage limit limit? Does the power supply have a reverse current protection mechanism or circuit scheme to stop the battery discharging back in to the power supply?
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    12V psu is not enough to charge a lead-acid battery, you need about 14V.
     
  5. tom66

    Senior Member

    May 9, 2009
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    You could however try wiring the power supply in to the car and running it off the power supply. It should be fine to run the accessories. Remember to disconnect the actual battery. Do not try and start the engine though; you are likely to damage the supply due to the hundreds of amps pulled by the starter.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    You really do need a charger designed for automotive batteries. A plain 12v power supply won't do the job.

    Fully-charged automotive batteries will read 12.7v-12.8v when their internal temperature is 25°C/77°F. If they are allowed to discharge down to 12v, they will be over 50% discharged, and will have a very short service life.

    Get a decent automatic charger capable of between 5A and 12A output, and use it at least once a week to keep your auto batteries fully charged. The money you save will be your own.
     
  7. iONic

    AAC Fanatic!

    Nov 16, 2007
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    +1 Sgt.
    Despite 12V not being enough to charge the battery, using a 75A power supply will probably spell disaster for your battery, especially wilthout temperature monitoring...etc.

    iONic
     
  8. timrobbins

    Active Member

    Aug 29, 2009
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    I very much doubt that anything like 75A would flow though a discharged car battery at 12.0V, depending on battery chemistry, and if the SOC was high then you probably wouldn't get any charger current at all.

    Over-current damage is really only a concern if SOC is quite low (given that charge voltage is at manufacturer recommended level).
     
  9. iONic

    AAC Fanatic!

    Nov 16, 2007
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    The assumption would be if the voltage was higher, 14V - 15V. It may not reach 75A, but probably more than the reccomended charge current.
     
  10. earthtodan

    Thread Starter Member

    Dec 3, 2008
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    Thanks for the replies guys. I've been meaning to read up on Battery University but I haven't had time yet.

    The PS is a Cascade (made by Iota I believe), with reverse current protection but no variable voltage. It's nominally 12V but I measured it at 13V. The car's charging system is 13.8V. The battery is fine, it's not discharged, but I'm worried it will get drained over two weeks of working on the car, and opening and closing the doors, since can't find all the fuses that control the dash lights. So I'm not trying to charge it, I'm trying to tend it.
     
  11. iONic

    AAC Fanatic!

    Nov 16, 2007
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    I'd still rqther use a 12V+ wall wart at 500mA. Will you be removing the car battery or leaving it in the car?


    iONik
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    Disconnect the negative (ground) cable from the battery terminal until you are ready to test it.

    Your power supply was not designed to function as a battery charger. Don't try to use it as such.
     
  13. earthtodan

    Thread Starter Member

    Dec 3, 2008
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    That's advice I can take.
     
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