Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old December 28th 04, 01:07 AM
 
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Default Run a 9.6 volt Makita drill off 12 volt car battery - voltatage dropping resistor ?

I want to run an old Makita 9.6 volt drill off my car battery 12 volt (
actually 13.6 volt ) . What is the approriate resistor to use ?
-thanks


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Old December 28th 04, 01:24 AM
Sam Goldwasser
 
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writes:

I want to run an old Makita 9.6 volt drill off my car battery 12 volt (
actually 13.6 volt ) . What is the approriate resistor to use ?


Simplest is a few high current diodes in series to drop the voltage.

You can't use a resistor because the current is not known and not
constant.

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Old December 28th 04, 01:33 AM
NSM
 
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wrote in message
ups.com...
| I want to run an old Makita 9.6 volt drill off my car battery 12 volt (
| actually 13.6 volt ) . What is the approriate resistor to use ?
| -thanks

Do you want to charge the 9.6 V batteries from the car?

N


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Old December 28th 04, 02:25 AM
G
 
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Well......unless you're automotive battery is hooked to a typical charging
system, your auto battery at rest will be more like 12.3 to 12.6
volts........current will only be in the range of a few amperes but will be
quite variable as pointed out. I'd try a string of 4 silicon diodes inline
with your made up cord for a typical voltage drop of 2 volts which will be
somewhat constant despite the current drawn. These could be nearly
anything with a rating of say 10 amps @ 50prv min and wouldn't have to be
even the same........use what ya have. This solution will have the added
benefit of giving you reverse polarity protection should your cable to the
auto battery get reversed. If you bring your cord into the bottom of the
old battery compartment there'd be enough room to include the string right
in there as it's quite long....strain relief below that. Realize that
your auto battery voltage will sink as you use it (uncharged....portable so
you can lug it close to where you want) and this won't hurt things at all.

Let me know how ya make out (have a couple of these drills myself). I can
picture powering it off of one of those booster battery packs as a good
solution for portability..........use a cigarette lighter plug so you can
power right off this or your vehicle or via a battery clip adapter for open
other types of batterys.


Gord


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Old December 28th 04, 05:06 AM
mike
 
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G wrote:
Well......unless you're automotive battery is hooked to a typical charging
system, your auto battery at rest will be more like 12.3 to 12.6
volts........current will only be in the range of a few amperes but will be
quite variable as pointed out. I'd try a string of 4 silicon diodes inline
with your made up cord for a typical voltage drop of 2 volts which will be
somewhat constant despite the current drawn. These could be nearly
anything with a rating of say 10 amps @ 50prv min and wouldn't have to be
even the same........use what ya have. This solution will have the added
benefit of giving you reverse polarity protection should your cable to the
auto battery get reversed. If you bring your cord into the bottom of the
old battery compartment there'd be enough room to include the string right
in there as it's quite long....strain relief below that. Realize that
your auto battery voltage will sink as you use it (uncharged....portable so
you can lug it close to where you want) and this won't hurt things at all.

Let me know how ya make out (have a couple of these drills myself). I can
picture powering it off of one of those booster battery packs as a good
solution for portability..........use a cigarette lighter plug so you can
power right off this or your vehicle or via a battery clip adapter for open
other types of batterys.

I'd recommend against using the cigarette lighter plug. They use some
mighty flimsy wiring in auto dashboards these days. And newer cars
switch the lighter socket with a relay of unknown current capability.

Worry about the drop in the wire. It's gonna be long if you expect to
use the drill outside the vehicle. And for flexibility, you'll want the
smallest wire you can get away with. Sounds like some actual
measurements on the system in question are in order.
mike


Gord




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Old December 28th 04, 05:26 AM
rpbc
 
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I use a couple of those drills, including a 7.2 volt Makita, all the time
directly off the vehicle battery. They are very tough, you just get more
torque and rpm. I was actually just curious at first, figuring I'd just
throw the drill away if it burned up. I use them all the time though and
they continue to work fine. If you want to drop the voltage the diodes in
line are the cheapest and best way to go. Resistors are no good for when
current increases due to motor load demand, voltage distrubition to the
motor will be decreased and there will be an overall loss of power
available at the motor. My advise is to just hook it up to the 12 volts
and don't worry about it.

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Old December 28th 04, 06:51 AM
[email protected]
 
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rpbc,
That's good to know. I've had a 7.2 V Makita hand vac that I use with
the 9.6 V batteries all the time since I've got 2 9.6 V drills, 2
flashlights and a recip saw. That little vac screams at 9.6 V and works
very well. It has thrown a turbine disc in the 7 years I've been
running it that way but that was easily repaired with a part from Tool
Barn. The salesman that sold it too me showed me that trick.
Richard

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Old December 28th 04, 02:13 PM
[email protected]
 
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Thanks Gord - This sounds like it might be the a good solution . I
now need to look around for some of the diodes you mentioned ,

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Old December 28th 04, 08:07 PM
James Sweet
 
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wrote in message
oups.com...
Thanks Gord - This sounds like it might be the a good solution . I
now need to look around for some of the diodes you mentioned ,


You can get them anywhere, even Radio Shack. Personally I would just run the
drill straight off 12v though, these little motors have very wide voltage
rating ranges, the 12v drills probably use the same motor, just a bigger
more expensive battery pack.




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