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  • #31
    Re: 24v Cordless vs Corded

    Over in Europe they rate power of motors and engines on Watts (in many cases) rather than in horsepower. You can use a dynamometer or a Prony Brake and tachometer. You need a way to measure rotational speed (RPM or RPS) and rotational force. If you have say 100 foot pounds of torque and 100 RPM for example A and 10 foot pounds of torque and 1000 RPM shaft speed for example B they are both doing the same amount of work. You can also obtain power as force applied to move something, how far it moved and how long it took to move it.

    These web sites will help you understand and it has good math formulas too. While it's more about testing power output of engines and farm tractors, the basics are the same for power tools and/or electric motors.

    http://www.buckleyoldengineshow.org/...horsepower.htm
    http://www.steamtraction.com/article/2003-01-01

    The real problem we get into with power tool motors is that they rate them at the maximum they can produce just long enough to get readings. What would be far more useful is if they gave a continious power rating at up to XX ambient temp. While you may be able to run up a flight of stairs in X seconds, what would happen if you tried to keep your speed up and run up 10 flights of stairs at one time?
    Last edited by Woussko; 05-04-2007, 02:54 AM.

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    • #32
      Re: 24v Cordless vs Corded

      As was mentioned, Watts is a measure of power, like horsepower. In fact, the world standard for measuring motor car engine power is Watts and the Society of Automotive engineers publishes all data in Watts.

      Electric motors are very efficient...anywhere from 60 to 80% (I've seen brushless motors as high as 90%.)

      Motors are described with an efficiency curve. They are inefficient at low speeds/high torques...like when lugging a drill, and the efficiency drops off at the top end too...when they saturate as they hit their max. speed (this is typically not an issue with tool motors...as they aren't driven with those type of voltages.)

      Instantaneously, motors can produce very high torques, when they stall (and draw very high currents) but this isn't power (because you have no speed) and this is very tough on the motor and the battery.

      Therefore, if you want to build a good, efficient drill, with lots of driving power, you want to build it with a good motor and an efficient, gearbox with proper ratios, so that you can drive the screw in the efficient torque range of the motor. This, of course, is true with all power tools, not just drills. It is important to properly gear them so that the motor runs the most efficiently.

      Higher voltage yields a flatter efficiency curve allowing the motor to deliver higher torques (at the same power) A power supply that can deliver higher amperages is necessary to deliver high torques too. Therefore, 110 volt powered tools can run more efficiently than 12 volt...220 volt, even more efficiently. The newer higher voltage cordless have a big advantage in torque. A 24 volt tool might be 30% more efficient at higher torques than a 18 volt.

      This is one reason cordless circular saws have smaller blades. It acts like a transmission to gear down the motor so that it works in a more efficient range. Likewise, wormgear drive circular saws are geared for heavy cutting torque.

      I apologize for being wordy but there is a lot more to drill power than max. torque. DeWalt is correct in delivering a UWO number, as this is much more useful. Having said that, it is only measuring one particular case (designed around driving a fastener) and it doesn't necessarilly mean that drill will be the most efficient for all applications (though it is likely it will be more efficient than a drill that doesn't have a well developed transmission or efficient motor.)

      As an added bonus, if you design a cordless tool such that the motor works in it's higher efficiency ranges you will get much better battery life.
      Last edited by Disaster; 05-04-2007, 06:09 AM.

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      • #33
        Re: 24v Cordless vs Corded

        Originally posted by Woussko View Post
        The real problem we get into with power tool motors is that they rate them at the maximum they can produce just long enough to get readings. What would be far more useful is if they gave a continious power rating at up to XX ambient temp. While you may be able to run up a flight of stairs in X seconds, what would happen if you tried to keep your speed up and run up 10 flights of stairs at one time?
        To be more specific, the problem is they rate them at maximum "torque", not power. Which, like you say, is pretty worthless. Give a drill enough power (ie current) and it can produce tremendous torque...for a half a second...before it burns up.

        More important is how efficient it is because that tells you how much power it can produce from it's fixed power delivery system (whether it be 12 volts at 60 amps or 110 volts at 7 amps) and how likely it is to overheat (all that inefficiency turns to heat.)

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        • #34
          Re: 24v Cordless vs Corded

          Thank you for the clarifacation everyone. That answered my question.

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          • #35
            Re: 24v Cordless vs Corded

            Dewalt claims there 36 volt lithium line outperforms some corded tools. Keep in mind the endless power supply from the cord.

            Below is a sampling of the independent testing results of DEWALT’s 36V platform. These results further underscore that high voltage, lithium-ion power tools have the ability to provide users with the power of corded, without the cord.

            • The 36V ½” drill can drill a 1-3/8” hole saw into 20 gauge steel 22 percent faster than the industry’s leading 5.5 amp and 8 amp hammerdrills*.

            • The 36V ½” drill has the ability to drill an average 67 holes using a 2-9/16” self- feed bit through a 2”x10”, which is 2.6 times the amount of the number drilled by the industry’s leading 18V drill. **

            • The 36V reciprocating saw was able to make cross cuts in 2”x10” material in 7.34 seconds, 28 percent faster than the industry’s leading corded reciprocating saw*.

            • The 36V reciprocating saw made an average of 64 cross cuts of a 2”x10”, two times the amount of the industry’s leading 18V saw**.
            Industry data clearly shows that high voltage lithium-ion tools do in fact have the ability to perform equal to, or better than many of the industry’s leading corded tools. With these performance levels, it is clear that a transition to cordless tools provides the cost-effective benefit of increased productivity on the jobsite. Finally, users can untangle themselves from the burden of power cords.
            *3rd Party testing performed November 2005. Average results based on 150 applications using 6 units. ** 3rd Party testing performed November 2005. Average results based on 30 discharges using 6 units.

            You can read the whole article here http://www.dewalt.com/us/articles/ar...rdless&ID=1486

            More on power, torque and speed
            http://www.dewalt.com/us/cordless/powerrating/?p=2
            http://www.dewalt.com/us/cordless/powerrating/?p=4
            http://www.dewalt.com/us/cordless/powerrating/?p=1
            http://www.dewalt.com/us/cordless/powerrating/?p=5

            I think within 10 years when the next generation of cordless tools are released we will see a battery or some sort of capacitor for energy stores. At that point we will probably have mass stores of portable energy, enough to perform for days of constant use without the need to charge. Maybe some sort of pendulum so when we use a drill, for example, it will be charging as well. Think of a Rolex watch, it charges by motion.
            I am hoping to cut the cord sooner but manufacturers still have huge amounts of money to make on the lithium line which was actually discovered back in the 1970's.
            Maybe we have longer to wait after all.........
            http://www.cgiconnection.com/download

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            • #36
              Re: 24v Cordless vs Corded

              Originally posted by onlycordless View Post
              I think within 10 years when the next generation of cordless tools are released we will see a battery or some sort of capacitor for energy stores. At that point we will probably have mass stores of portable energy, enough to perform for days of constant use without the need to charge. Maybe some sort of pendulum so when we use a drill, for example, it will be charging as well. Think of a Rolex watch, it charges by motion.
              Capacitors, as a longer term energy storage, are a little ways off. There are a couple issues. One is that capacitors bleed energy even faster than NiCds...minutes and hours vs. weeks. A second is that they store power at very high voltages. A device that has ultra high energy storage will most likely have ultra high voltages...on the order of tens of thousands of volts. I've read of one company that claims a breakthrough...energy density several times what current batteries hold, and long term storage on par with conventional batteries. It will be interesting to see if this pans out.

              In the meantime, brushless motors have been around for years and are 20% more efficient than brushed. They also don't require brushes so they are practically maintenance free. They are HUGE in RC now. The Panasonic 14.4 volt impact driver uses a brushless motor. What is holding them back now is the added cost of the controller. Brushless requires a "smart" controller to switch the magnet poles (do the job of the brushes.) Brushless should be the next revolution.

              I wouldn't count on recapturing energy from tool motion any time soon. Current regeneration systems are heavy, and inefficient...not something you'd want hanging off your tool.
              Last edited by Disaster; 05-07-2007, 06:52 AM.

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              • #37
                Re: 24v Cordless vs Corded

                Originally posted by Disaster View Post
                Capacitors, as a longer term energy storage, are a little ways off. There are a couple issues. One is that capacitors bleed energy even faster than NiCds...minutes and hours vs. weeks. A second is that they store power at very high voltages. A device that has ultra high energy storage will most likely have ultra high voltages...on the order of tens of thousands of volts. I've read of one company that claims a breakthrough...energy density several times what current batteries hold, and long term storage on par with conventional batteries. It will be interesting to see if this pans out.

                In the meantime, brushless motors have been around for years and are 20% more efficient than brushed. They also don't require brushes so they are practically maintenance free. They are HUGE in RC now. The Panasonic 14.4 volt impact driver uses a brushless motor. What is holding them back now is the added cost of the controller. Brushless requires a "smart" controller to switch the magnet poles (do the job of the brushes.) Brushless should be the next revolution.

                I wouldn't count on recapturing energy from tool motion any time soon. Current regeneration systems are heavy, and inefficient...not something you'd want hanging off your tool.

                Are you refering to EESTOR. The company promising to revolutionize the battery with an ultracapacitor?
                They are promising a lot and if they can do it, we will have the next generation of storage in 2008. However, some claims seem to defy the laws of physics.

                I wouldn't expect manufacturers to hang something from the tool, instead a penudlum inside the handle.
                I think if we give up some torque and use some sort of generator in the gearing, we might gain 5 to 7% or so in runtime.
                http://www.cgiconnection.com/download

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                • #38
                  Re: 24v Cordless vs Corded

                  Originally posted by onlycordless View Post
                  Are you refering to EESTOR. The company promising to revolutionize the battery with an ultracapacitor?
                  They are promising a lot and if they can do it, we will have the next generation of storage in 2008. However, some claims seem to defy the laws of physics.

                  I wouldn't expect manufacturers to hang something from the tool, instead a penudlum inside the handle.
                  I think if we give up some torque and use some sort of generator in the gearing, we might gain 5 to 7% or so in runtime.
                  Yes, EESTOR, looks to be the one I heard about. I'm not prepared to buy stock yet. I still remember, 30 years ago, when IBM talked about how "bubble" memory would revolutionize the computer industry. Still waiting on that one. ;-)

                  I don't think you would recapture enough energy to be worth the weight, cost and complexity of a regeneration system inside a tool. You'd be better off putting the system on the worker with a some sort of storage device mounted on his back...or belt...but I doubt anyone would want to lug something like that around.

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                  • #39
                    Re: 24v Cordless vs Corded

                    True enough, no matter what you're still on a battery. Let's face it. Even if 36 gives you twice the runtime and you're getting 10 minutes of total cutting per charge instead of 5, you'll still be juggling batteries under really heavy situations.

                    That being said the lithium ion batteries are hands down superior because they don't fade out nearly as bad as NiCad. You get a much more useable portion of the battery cycle before it dies.

                    Based on my experience 36 is up to the job that you would expect out of similar-sized corded versions. There isn't any job within that context that I would hesitate at throwing at them. Save for something really intense that you'd be using a corded worm drive saw for exclusively. Or a super duper hole hawg running 4 5/8" self feed bit. That's a bit out of range. The comparison has to be taken within context.

                    Originally posted by onlycordless View Post
                    Dewalt claims there 36 volt lithium line outperforms some corded tools. Keep in mind the endless power supply from the cord.

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                    • #40
                      Re: 24v Cordless vs Corded

                      Originally posted by Disaster View Post
                      Yes, EESTOR, looks to be the one I heard about. I'm not prepared to buy stock yet. I still remember, 30 years ago, when IBM talked about how "bubble" memory would revolutionize the computer industry. Still waiting on that one. ;-)

                      I don't think you would recapture enough energy to be worth the weight, cost and complexity of a regeneration system inside a tool. You'd be better off putting the system on the worker with a some sort of storage device mounted on his back...or belt...but I doubt anyone would want to lug something like that around.
                      I agree with you about the energy storage and not enough generated to give much energy with todays technology, however, I read an article on "Popular Mechanics" in which "Hybrid Technologies" overhauled a mini cooper by replacing the gas engine with an all electric plug-in. The company was able to get a 200 mile range with the vehicle. We are moving fast with battery technology. http://www.popularmechanics.com/blog...s/4215495.html

                      Vehicle costs $50,000
                      Last edited by onlycordless; 05-07-2007, 06:03 PM.
                      http://www.cgiconnection.com/download

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                      • #41
                        Re: 24v Cordless vs Corded

                        Originally posted by onlycordless View Post
                        Vehicle costs $50,000
                        I'll take two of them. ;-)

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                        • #42
                          Re: 24v Cordless vs Corded

                          Okay, this cordless vs. corded discussion has got me curious lately, so I setup a test.

                          So what would you call a taxing task for a 7 1/4" sidewinder circular saw? How about ripping down the length of a PT 4x4 post with the blade at full cutting depth? (about 2 1/2")

                          My 36V saw plows through it. And I wasn't easy on it either. I was givin' it a good push. This was with a fresh battery. In fact after, I realized I had gone through a knot too! Blade is a Bosch 24T combo carbide.

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                          • #43
                            Re: 24v Cordless vs Corded

                            Speaking about the Rolex watch, there are flashlights where by either shaking them or turning a little crank you charge the rechargable battery within. Maybe for fun we can do an exercise bike with a generator setup to charge our power tools. While we are working the YUPIE type can exercise and charge our batteries for us.
                            Last edited by Woussko; 05-08-2007, 10:49 PM.

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                            • #44
                              Re: 24v Cordless vs Corded

                              what do you figure the UWO of that exercise bike will be? LOL do you think it could charge a battery in an hour?

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                              • #45
                                Re: 24v Cordless vs Corded

                                Originally posted by Sceeter W Wheels View Post
                                what do you figure the UWO of that exercise bike will be? LOL do you think it could charge a battery in an hour?
                                I actually happen to know this (I'm not kidding). A professional cyclist (someone like Lance Armstrong) can burst up to almost 1000 watts at the pedals and can sustain about 500 watts for extended efforts of a few minutes. For a period of hours at a time a very fit person can continuosly sustain about 200-250 watts. So do the math The Dewalt 18v 1 hour charger draws about 220 watts so in theory assuming little or no energy is lost attaching a generator to my bike I should be able to just about exacly charge my 18v batteries in an hour.

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