Cordless drill rated to 7.2V on 12V (car battery)

Discussion in 'The Projects Forum' started by alan1975, Sep 16, 2012.

  1. alan1975

    Thread Starter Member

    Jan 1, 2012
    Hello friends,

    I'm looking for way to hook up my cordless drill with is rated to 7.2V to my car battery with have 12V.

    I'm afraid of connecting it directly, i'm pretty sure when i will do this for test, i will burn the engine..

    I'm also sure that ANY of linear converter won't be suitable...

    Also switching power supplies won't be able to carry so high current.
    I don't do any checkup because my drill battery is dead, but im sure that power can be over 10A peak, when drill stuck in something hard.

    Do You have guys have any idea what can i do, maybe PWR?

  2. akis02


    Apr 30, 2011
    Buy a 12V drill?

    12V drills must be very cheap these days as the most modern ones are 18V and 24V.

    It is probably less expensive than trying to build some sort of voltage converter with peaks of 10A and you will get a brand new drill + battery at the same time. :)
  3. alan1975

    Thread Starter Member

    Jan 1, 2012
    Hihihi it will be to easy!

    What do You think about putting 8 * 10Amps rectifier diodes in series ?

    8 * 0,6V voltage drop will be -> 4,8V
    So in theory should work ?

  4. bertus


    Apr 5, 2008

    Yes, in theory.
    If you want to use diodes to drop the voltage, the voltage will change with the drawn current.
    The voltage drop will not be the same for all currents.
    Also the diodes would need cooling, as each diode will dissipate 0.6 * 10 = 6 Watts.

    You could use a Buck converter, wich also is more efficient.

  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    A different approach would be to use (2) 6 volt batteries.
    You mentioned a car, so these batteries could be charged in series by the 12 volt car system and utilized one at a time or in parallel for the drill.
    vs buy a 7.2 volt battery pack for the drill.
    vs buy a 12 volt drill.

    If you have something nearby like a pawn-shop, or a flea-market, the last two should be available.
  6. alan1975

    Thread Starter Member

    Jan 1, 2012

    But please remember that 10A, i said as a peak... i think it draw much less...

    I got idea, i will try to get few integrated rectifier bridges...
    Easier to mount on heatsink, greater heat dissipation .

    After few days i will tell You guys what's the verdict.

    I will also plug that drill into variable power supply, and check how it react when i will slowly over-voltage her.

    I power all my devices from 12V power box.

    I got 2 of them, first build using 12V gel battery, second one build using 4x (10AA nimh eneloop battery in series).

    It's both working extremely well.

    I use it for: lighting,bosh electric drill for screw mounting, bosh hamer drill for drilling in concrete , soldering station (for small work cheappy car plug) for bigger normal soldering station using power inverter.

    All my equipment operate on 12V.

    This equipment save me a lot of nerves, allow me to work x times longer than using normal batteries included with equipment. I also charge one device not 10, and then asking myself is it really full charged. I use this set from few years and never get into any troubles of discharged too soon. I need to be power independent and that solution work great.

    That's the reason why i don't want any other power sources. That's the reason why i don't want original battery. I won't buy new one. I just hate this little devices ;)

    Yesterday i got a nice set of black & decker jig saw / drill (for bits) / grinder all in one, you replace head. It's called black & decker quattro vp2000.

    I would't buy it because it's not a professional tool (its for home use) and that because it's run on that 7.2V, but i got it... so... i need to make something usable.

    I think we don't need to settle 7.2V , i think 9 volts will be still ok. It should run faster, maybe be hotter but, you still don't use it for an hour...

    But 12v, with is 14v on fully charged might burn engine...
  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
    It sure does, or the battery would weigh 50 pounds. Would help to know the average current draw, I suspect it's less than 2A or maybe 3A.