Would you try this?

[JDgreen227]

Yesterday we had someone come out to hook up Direct TV to our house, and the installer needed to drive some lag screws into the treated post I had set for the dish. He had a Black and Decker 12 volt cordless drill with a run down battery and no second battery or charger. I offered to go fetch one of my cordless drills and upon returning with it he had popped the hood of his S-10 and was trying to hook up his drill with 14 gage wire clipped to his battery via jumper cables. I was able to convince him the safer option was to use my drill.

His reasoning was, 12 volts is 12 volts. But I value my tools too much to try that method. Any comments?

 

[40Kchicks]

That sounds pretty funny. I have never heard of that one before. However he is correct. A 12 volt supply is only going to pull so many amps through a certain resistance no matter if the supply is a battery or coming directly out of the hoover dam generators.

Amperage = Volts / resistance.

The trouble is if the resistance goes lower like if he shorts the leads then all of a sudden you have a lot of amps that can do a lot of damage.

Eric

 

[theonlybull]

yeah,

i've got an old 9.6V black and decker cordless that the battery died on a few years back, and my new 14.4V works just fine, so i'm going to put a cigar lighter adapter and some wire on the 9.6V so i can run it off my truck, and our booster pack.

 

[PineRidge]

Eric is correct it is not the voltage that normally does all the damage it's the amperage. I used to work on old F-50 Honeywell air cleaners and got hit from time to time with 3500 volts. /forums/images/graemlins/blush.gif It made you let go real quick but the power was measured in milliamps.

 

[have_blue]

Yep!

I have a 12v Makita, and one battery died. Well, I wired up a dummy battery pack to act as a connector to a 12v battery. Works like a charm. I still use my good packs with it for out-of-the-way places.

 

[JDgreen227]

Thanks to all for the input, I have done a lot of new construction electrical work and rewiring on old houses but I am weak on electrical math, I thought the amperage of a vehicle battery would fry the drill. Should I ever see the cable guy again I will tell him TBN says he was RIGHT and I was wrong.

I have two older B&D 9.6 volts with no batteries that I can now use again. Your advice is appreciated !!

 

[theonlybull]

the 12v on the 9.6v drill, may fry something, but i race alot of r/c trucks, and they are built for 7.2v, but can run on 14.4v. i figure if the drill's no good, what harm is it going to do by trying it on 12v. /forums/images/graemlins/cool.gif

 

[MossRoad]

Just remember... if you short the battery terminals together on the drill battery, not much will happen. If you short the battery terminals together on the car battery, you're now doing some welding /forums/images/graemlins/smile.gif

I was always told to compare the volts to the water flowing in a hose and to compare the amps to the pressure of the water in the hose. So compare that to hydraulics... volts is GPM(gallons per minute) and amps is PSI(pounds per square inch). In a hydraulic circuit, you can get soaked(high GPM) with low pressure(low PSI) hydraulic oil with no injury to you what so ever. But a very high pressure(high PSI) stream of very little hydraulic fluid(low GPM) can cut you in half /forums/images/graemlins/shocked.gif Same goes for electricity.

 

[jinman]

</font><font color="blue" class="small">( volts is GPM(gallons per minute) and amps is PSI(pounds per square inch) )</font>

David, I think I know what you meant, but your analogy is just the reverse of what it is. Volts (electromotive force) can be equated to pressure and amperes (current flow) can be equated to GPM. The problem with short circuits is that the current gets so high, it's "undefined." Using Ohm's law, voltage divided by resistance is equal to amps. Therefore if you have 12 volts divided by zero, it's undefined, and the same would apply to any voltage. That's the danger of a pure short circuit of zero ohms. The 12 volt nicad rechargeable battery has much higher source resistance than the lead acid automobile battery. If you short it's terminals together the internal resistance of the nicad battery will limit the amount of current flow. The lead acid battery will not limit its flow and you will arc weld with it.

Whew! I didn't mean to make this so technical, but I see I got there pretty quickly. /forums/images/graemlins/blush.gif /forums/images/graemlins/tongue.gif For me, I'd say it's just not a good idea to short the terminals of any battery, even if it's a little AAA cell. /forums/images/graemlins/smile.gif

 

[keeney]

In regards to: "Just remember... if you short the battery terminals together on the drill battery, not much will happen. If you short the battery terminals together on the car battery, you're now doing some welding"

Actually, those battery packs in the cordless drills can generate quite a bit of heat if you short them out as well.

NiCd batteris have a very low internal resistance. So if you short them out with a low external resistance, the current will be very high. Could be maybe 10's of amps. 12v x 20 amps = 240 watts - plenty of heat to ignite, burn, melt, or maybe even weld something. A 2.5 Amp-hour battery can sustain that 240 watts for over 5 minutes.

This was made clear to me by a simple demonstration using a similar battery pack (12v x 4 Amp-hours, NiCd used for starting lawn mowers). The battery was shorted with a paperclip. The paperclip welded itself to the terminals, then it turned white hot like a light bulb filament. Finally, it sagged over and burned itself through, but not before it had melted into the plastic casing on the battery.

Heck, a garden-variety 9-volt transister radio battery can start a fire if shorted with the right resistance wire to maximize its output.

- Rick