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Battery charger

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JOHN TIPTON

Joined: 17 Sep 2006
Posts: 239
Location: Torquay - England

Posted: Thu Aug 05, 2010 7:23 am Post subject: Battery charger

Hi Guys



The charger for my cordless drill (12v) has expired, can I connect my 

automobile charger to the battery?



Best regards: John (RV9a-wings)

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longg(at)pjm.com
Guest

Posted: Thu Aug 05, 2010 7:48 am Post subject: Battery charger

John,



How many cold cranking amps does your cordless drill require? Spoil

yourself - take a trip to Harbor Freight



Glenn



--

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nuckolls.bob(at)aeroelect
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Posted: Thu Aug 05, 2010 8:19 am Post subject: Battery charger

At 10:20 AM 8/5/2010, you wrote:

 	  Quote: 	
		  

<jmtipton(at)btopenworld.com>



Hi Guys



The charger for my cordless drill (12v) has expired, can I connect 

my automobile charger to the battery?


	


    Cordless products using Ni-Cad or NiMh batteries

    use chargers as current sources as opposed to

    voltage sources. While the wall-wart that comes

    with it puts out some name-plate voltage, the current

    fed to the cells during charging is generally limited

    by some resistor in series. The trick is to know where

    the resistor was installed. If inside the drill, then

    yes, you can hook the drill to 12v car battery and

    recharge the cells. If it's inside the expired wall-wart,

    then direct connection to the drill will probably produce

    some unhappy if not spectacular results.



    You can put a milliammeter in series with an experimental

    hookup to see. Put a 3A fuse in series with the whole

    mess just to be safe. Hook it up and see how much charging

    current flows into the drill . . . if under 200 mA or so,

    you're good to go. Most drills have c-cells that like to

    charge at 150 mA for 10-15 hours. If the current is too

    high, add resistance in series to bring it down.



    I have some tools where the wall-warts have died or gone

    AWOL. I charge them from my electronics bench supplies set

    to run in a 150 mA constant current mode.



    But as suggested, unless you really delight in solving

    such problems and want to take the $time$ to understand

    and implement a solution, a trip to HF is the quick-n-

    dirty solution. Let us know what you discover.

   Bob . . .

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