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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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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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#3
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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. --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/ Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/ +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html Note: These links are hopefully temporary until we can sort out the excessive traffic on Repairfaq.org. Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
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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 |
#5
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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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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 -- Return address is VALID. Wanted, Slot 1 Motherboard 500MHz Tek DSOscilloscope TDS540 Make Offer http://nm7u.tripod.com/homepage/te.html Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121 Bunch of stuff For Sale and Wanted at the link below. http://www.geocities.com/SiliconValley/Monitor/4710/ |
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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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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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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 , |
#10
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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. |
#11
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No , the batteries are shot . I just want to run the drill off my car
battery ( cable and clamps to battery ) |
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