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  • Electrical question - 12v

    Many, many years ago an air compressor motor gave up its life so I could learn about long orange extension cords and a thing called "voltage drop" , so I'm trying to avoid another lesson from destruction.

    I've also learned the difference between "I KNOW this will work" and "I THINK this will work"

    Subjects:

    1 - Oregon electric chain sharpener, runs on 12v, instructions say it uses 20-29 watts while grinding.

    2 - Battery charger, settings for 12v - 6 amps and 12v - 2 amps.

    I realize the battery charger puts out maybe 13.5 v. but I THINK I can connect the two and sharpen chains in my nice, air-conditioned shop, instead of outside in the heat next to my pickup, without destroying either one.

    So, for the electrically gifted here, any reason why this won't work? Better to set on 6 amps or 2?

    Thanks folks.

    Steve

  • #2
    To run the sharpener on your charger will push the charger to the limit.

    To run the sharpener off a spare battery will be a cruise. It doesn't have to be a battery good enough to start a car. A battery that's recently been discarded in favour of a new one will do - even a duff battery will keep a charge for a day or so.

    The main thing is to wire a good fuse - 5 amps would be appropriate - in series. A battery can dump a lot of amps through a dodgy motor.
    Richard

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    • #3
      I guess I should clarify that the Oregon sharpener comes with alligator clips to be used on an automotive battery.

      Steve

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      • #4
        P=IxE

        P= Power (watts)
        I= Current (amps)
        E= Electromotive Force (volts)

        Just remember PIE. It's the easiest.

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        • #5
          Another thing to consider is that battery charger is a pulsating 12 volts and not a steady output.

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          • #6
            My suggestion, connect the battery charger to a battery, as rohart said even a duff or aged battery will be good enough and connect chain sharpener to the battery too. The battery could be any 12v lead acid battery such as from a motorcycle or a bigger one from your truck etc.

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            • #7
              Note id your DMM says the voltage on the battery exceeds 13.8v after full charge, its NOT good to leave that charger on the battery. Generaly not a good idea to run loads off a charger either. You can often run em off by connecting to a battery (even a crappy one that barley holds a charge) and then connecting the load after an hour or so charging.
              Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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              • #8
                Most newer battery chargers will not turn on unless there is about 10 volts connected. Which means a battery that needs charging. The 6 amp at 12 volt setting is fine and if you can get the charger to run it should work without problems.

                Bob

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                • #9
                  I do not see any reason why the 30 watt grinder could not be run off the battery while the charger is connected. The battery will limit the voltage the grinder sees and will provide a smoother supply than the grinder would see on the charger alone.

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                  • #10
                    Originally posted by radkins
                    Another thing to consider is that battery charger is a pulsating 12 volts and not a steady output.
                    There's a thought. Given only a Greenlee $80 multimeter is there any way to see if the charger is outputting unfiltered, pulsating DC? Or should that just be assumed on a home use type of charger?

                    Um, guys. If I had a spare battery laying around or wanted to sit in the heat next to my truck, guess what I would have done already? Looking for a little out of the box education.

                    Steve
                    Last edited by SteveF; 07-09-2011, 06:35 PM.

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                    • #11
                      Your grinder is just a series motor it would run fine on about 18 volts AC. Just like a 110 volt AC drill will run on 90 -120 volts DC.

                      Bob

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                      • #12
                        Steve,

                        Just put any lead acid 12v battery into the circuit and it should be fine. The sharpener wants to run off of a battery, and the charger wants to charge a battery. Make 'em both happy.

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                        • #13
                          The chain saw sharpener will turn a little faster on 14v than it will on 12v- probably a good thing and the motor will like it. In other words it's nothing to worry about if the voltage is high by that small amount.

                          Other than that, a battery charger in general does not make a good power supply. I agree with others to run the sharpener from a battery, and keep the battery up. A trickle charger will be all that's needed, since the average current draw is probably going to be much smaller than the trickle charge current anyway. The trickle charger doesn't need to be any larger than a wall wart- it just needs to be suitable for a 'connect it and forget it' useage.

                          Got one of those power failure lighting units? There will be a gel cell in there and a proper maintenance charger rated for being continuously powered. The gel cell can supply 30 watts for probably 2-3 hours- all you would need to do is run a pair of wires out directly from the battery lugs, and wire in a fuse. I wouldn't go less than about 7 amps for the fuse since it has to handle the full starting current for the motor. A lesser fuse will fail prematurely.

                          I bought a lead acid battery from Princess Auto that would run the sharpener- cost me $10. You can get a garden tractor battery for about $30- either way you have to cater to proper charging to avoid killing the battery prematurely.

                          Another option- do you use a 12 or 14v cordless drill? Make a couple fittings that will connect to the terminals on one of those batteries, then mold some epoxy putty or something around them to make a connector. You may or may not get an hour of run time from the battery, but you already have a suitable charger-
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                          • #14
                            Or just park the truck in the shade.

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                            • #15
                              Originally posted by Robin R
                              Or just park the truck in the shade.
                              Inside the shady, air conditioned shop maybe?
                              Steve
                              NRA Life Member

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