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We have occasion to use cordless drills fairly constantly… constantly enough to swap battery packs faster than the charger will re-charge them. And often out in the field w/no 110v power source for the charger.
Can a 12v cordless drill be wired to run off a 12v automotive system. Say from a cigarette lighter or alligator clips right to the battery? That would be easier than dealing with a generator and 110v drill or using a 12v charger.
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Replies
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I presume you've already checked on those inverters for under the hood? I think if you spend enough, you can get one hot enough to plug yer real drill motor in to.
*Had only briefly thought about inverters. The ones I've used were quite expensive in mobile shops or RVs. But now that you mention it, I think I've seen smaller ones in the consumer electronics catalogs. For running your notebook computer, or your coffee pot if 1 cup won't get you to work. Worth a look. Still interested in any ideas on a 12v wiring harness directy to the drill.
*Those invertors have gotten pretty cheap in the last ten years as the cost of the electronics have come down. They go for about 10 cents per watt now. $40 for a 400-watt one. My 400-watt invertor powers my 3/8 Makita nicely and handles a 1/6 hp sump pump. Don't plan on a coffee maker or other heating device (hair dryer, toaster, etc) on a small invertor. Also note that AC induction motors take a lot more amps to start than their names plate amperage indicates. Invertors and generators need to be about 3x the wattage rating of an induction motor to get it going.Back on thread: Yes, you can charge a 12-volt nicad off a automobile. That's why I got DeWalt's 12-volt tools. And because the 12-volt nicads made my other gear more portable (fish finder, GPS, cell phone, caving headlamps, etc.) I've only hooked the nicad to the car directly a few times and only briefly (to top a battery to finish a cut or hole). And then only with the engine off. My concern is the high charging rate from a 13.6 lead-acid battery into a 10-11 volt nicad (a mostly discharged, "12-volt", 10-cell nicad).So I rigged up a high-wattage 1 ohm resistor ($1 at Radio Shack)in series with the alligator clips. Keeps the charging current down to about 1 to 2 amps. I also plug in a discharged battery into a not-running auto only. It then gets 13.6 volts instead of 14+ volts with the alternator putting out. If after 15 minutes, I want it to top off quicker, I start the car. Use a digital voltage meter to confirm exactly what your factory charger brings the nicads up to and check your auto set-up isn't getting them any higher. Or stop a little early (20-30 minutes). Maybe it's not a full charge yet, but it's probably at least 60%Or, just hook it up duirectly (no resistor, car engine off) and see what happens. Nicad can give and get relatively high amps and are relatively tolerate of overcharging (much more so than other battery types). I know my precautions are conservative. They may not be necessary. -David
*Great input Dave. I had found pricing similar to your quotes in the Damark catalog. The inverter is intriguing, but there's still an appeal to carrying only one drill, the12v guy and going on batteries when out of reach and auto power when close enough.Sounds like your principal concern would be with the NiCads. My original thought was to bypass them completely, wire directly to the contacts up inside the drill which the battery normally couples to and connect the other end to the car battery or cigarette lighter. Any thoughts on that approach?Thanks, Scott.
*Try it tomorrow and let us know how it worked.
*I have had quite a bit of experience running cordless tools from external 12V sources. One thing to be carefull about is using a rapid charger with an inverter. Many of the chargers do not stop the charge at the proper time when run from a quasi-sine wave inverter. I have seen several explosions. Some of the chargers will work OK but many won't. They all work properly on true sine wave inverters but those inverters are expensive. A factory 12V input charger is cheaper and safer. As far as external power directly to the drill, it works quite well. Due to the higher current and lower voltage, you will need larger cable and you won't be able to run it as far as for a 120V tool. I gutted an old dead battery pack to make a cord attachment for my 12V DeWalt tools. I often plug it into a Gel Cell in a fanny pack. I use 220volt plugs on the end of the cord so no one accidently plugs it into a 120v outlet. Cigar lighter plugs don't hold the current well.
*Great input Ron, thanks.Can you tell me more about GelCells? I like this solution. Sounds like a wedding photographer. Pop that strobe light all night long from an over the shoulder battery pack. Same idea?Assuming a 12v DeWalt, Bosch or similar, what wire guage/distance combinations would you figure to a 12v automotive source?Thanks again. Scott.
*Ron: ditto on the true-sine versus quasi-sine inverters for powering a battery charger. The cheap inverters work fine for an AC motor but increasingly, battery chargers instructions warn against them.Scott: Gell cells are sealed lead-acid batteries in which all the electrolyte is in gell form in matts between the plates. So they can be used in any position without dripping acid. Better in every way except price. Radio Shack has small ones for portable phones, etc. For bigger ones, look to marine supply stores (e.g. WestMarine) but I've occassionally seen them at Costco.Running the tools designed for a 10-cell Nicad pack (nominal 12 volts, actually 13.5 with no amp draw) on a 12-volt automotive/marine lead-acid battery (13.6 volts without the alternator running) will work great. The larger amp rating on those batteries will make your drill act like it has a very fresh nicad for a long time.Wire size: Assuming the tool runs at 10 amps of 12 volts gives an impedence/resistance of the tools of about 1 ohm. If you are willing to give up 1 volt to the wire, then wire resistance should be 0.1 ohms or less (0.05 ohms for the positive wire and 0.05 ohms for the negative wire). In 16 gauge wire, that's 12 feet. In 14 gauge, 19 feet. In 12 gauge, 31 feet and in 10 gauge, 49 feet. Twice those distances if you're will to accept 2 volts of voltage drop. If using 3-wire cord, you might as well wire two conductors together for positive and use the remaining one for negative. That will allow 33% more length than quoted above. Hope that helps, David
*David, that's very helpful, thanks. 2 more questions. 1) The gel-cells are rechargable? (Special charger?). 2) Would the 2 volt drop simply give you a little less oomph or would it also shorten tool life?
*Gel-gells are just as rechargeable as other lead-acid (automotive) batteries. The same chenistry is going on just the electrolyte can't leak out. So use standard automotive chargers. And don't drain them completely.Lower voltage would not harm the tool. It's just like operating in the middle of a nicad's charge. I'm tempted to go hook up a volt meter to see what voltage drop is noticeable.
*Finally got around to doing the experiment. My 12-colt DeWalt drill must not pull 10 amps but more like 4 amps because 25 feet (each direction) of 16 gauge only gave me 0.7 volt drop from line loss. Plus another 0.8 volt drop in the battery. And the drill seemed fine at the resulting 11.3 volts. With an automotive battery, you'll get almost no voltage drop in the battery, so you could go at least 50 feet with 16 gauge. -David
*Tell me again why you want to turn a battery powered, take anywhere tool into a corded tied to the power source tool?Maybe the answer is to buy more chargers and batteries?
*Fred, the reason for the original question is as follows: The task involves repetitive drilling in the field, typically out of reach of AC power and often out of reach of even a vehicle stationed AC generator. The task involves a few holes in each location with lots of moves to new locations. So lugging the generator at each move is a waste of time. However, many of the locations are quite close to the vehicle and could run off 12v DC from the vehicle. That would preserve the batteries for the others. Batteries are not cheap and even taking 4 or 5 into the field may not last till it's time to go recharge. Or maybe you buy two 12v chargers but they didn't charge up yet and you're standing there waiting.The drill is coupled to a testing instrument that requires each drilled hole to be 12" deep, so even the few holes at each location require a lot of torque and tax the batteries pretty quickly. Some of the holes are off the ground (working from a ladder or aerial lift) so stopping to swap batteries is cumbersome.The thought was the most reliable, lowest cost, least lugging of stuff, least swapping of tools to the coupled instrument alternative might be to mix 12v ni-cads with a tethered 12v automotive system.David's experience seems to indicate it would work and by converting an old battery case into a cord adapter (rather than hard wiring the tool) the flexibility is preserved.
*David, thanks for running the experiment. Sounds like like a really manageable cord system.
*The under $100 car boosters are a good choice of battery and case. Many of them have a 17 AH Gel-Cell.
*DScott: Thanks for the info. I think if you are that close to a vehicle rather than go to all the mickey-mouse of modifying your battery powered drills put an inverter on the vehicle and use cheap corded drill/drivers. Inverters of adequate size for a couple drills wouldn't be very expensive.Then the battery units are used in the field and the corded units are used within, say a 100', of the vehicle. No cobbled together systems, reliable, uses standard cords and fittings, flexible and probably little or no more cost than modifying the battery units.
*D. Scott, You've got us all going, please tell us what the hell it really is you are doing. Otherwise, I'm with Fred B.
*Dave,What load did you have on your drill when you measured 4 amps?Ron
*The German made instrument is called a Resistograph. It is coupled to a Bosch cordless drill. The coupling collar requires the diameter of the Bosch drill chuck; DeWalt etc. will not fit. Even if the Bosch 110v AC drill fits, swapping drills requires disassmbly and is not efficient.There is a chuck and gearing mechanism that works something like a screw machine. The chuck is held flush to the work surface and the bit is fed through the turning chuck. The instrument senses variable resistance (torque) over the drill bit's travel and transmits readings to a piece of graph paper through a stylus. At the end of the test the chuck remains flush to the work piece and the drill is reversed to withdraw the bit.The purpose is to detect the presence and extent of internal decay in structural timbers or pilings, wood utility poles, trees, etc.
*I knew there had to be some good reason. When you are out doing this, what do you call yourself?
*Consultant.Actually I spec the tests and one of a number of other consultants who own the instrument and use it frequently enough to a) amortize the cost and b) reliably interpret the results actually does the testing. Tool junkie though I am I've not been tempted to buy one myself.I've observed the battery problem with two of them and was just curious for the input of this knowledgable crowd! The input will be useful to the others and might save my clients some money by creating field efficiency.
*Ron: Just my gloved hand around the chuck to provide some drag. About as much as a 3/8 bit into wood. If a larger bit or hole saw is used, it might well pull more amps. -David