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18 Volt to 12 Volt down converter.

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  • 18 Volt to 12 Volt down converter.

    The 18V to USB adapters that RIDGID and others have for sale got me thinking about a 18V to 12V down converter that could power some high amperage 12V DC equipment. I'm thinking of powering equipment like a 35 watt GMRS radio.

    I was thinking of using an old dual battery charger and gutting it. One or two 18V batteries could be plugged in to provide power as needed. The intention is to be able to use the power tool batteries without damaging them so they can still be used with the power tools. The converter would be used to power devices drawing up to 15 amps. The charger housing would house the converter electronics and the AC charging circuit would be no more. I'd like to be able to use the batteries in parallel to get the higher current out, but the setup would allow one battery to be used.

    I know some people here have hacked various brands to mash them together using RIDGID batteries on Ryobi tools and the reverse or for other purposes so I thought I would throw this out and see if anyone had considered something like I propose. When you don't have AC power and you need to stay in contact by radio you could that pile of 18V batteries to power the radio or some other 12V equipment.

    There are of course 12V batteries available that would make this much easier but you have to maintain those batteries. Being able to use your existing 18V batteries to supply power and not have another battery to worry about for those few times when you might need it is the goal.
    "It's a table saw, do you know where your fingers are?" Bob D. 2006

    https://www.youtube.com/user/PowerToolInstitute

    https://www.youtube.com/channel/UC1p...qcZKHyrqKhikFA

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  • #2
    I have the older 18v USB adapter that came with the heated jackets. The output to the Jacket is 12v, but I do not know the amp rating of it, and Ridgid is tight lipped about it, and wont give me details. Although, I have easily run LED lights off the port without issue.

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    • #3
      Thanks AC, I was thinking I would hear from you because I know you have been inside
      these batteries from a couple brands. I'm looking to get about 10 Amps @ ~12.5V DC.
      I doubt the adapter you are talking about produces that much current. You could put an
      amp meter in line and find out how much the jacket draws. That would require making a
      cable or modifying the existing cable which you probably don't want to do.

      Do all the recent (past couple years) Li-Ion batteries have protection built-in ? Do they
      shut down if the battery overheats from high discharge rates and when the battery voltage
      drops to a certain point? Is that protection circuitry built in to the battery or the tool?
      I'm thinking its in the battery which for my purposes would be good.

      But the down converter circuit would still need to maintain the output voltage within a
      specified range as the voltage of the supply batteries dropped off. Ideally output voltage
      would be between 13.8 and 12.8 volts.
      Last edited by Bob D.; 11-21-2016, 05:07 AM.
      "It's a table saw, do you know where your fingers are?" Bob D. 2006

      https://www.youtube.com/user/PowerToolInstitute

      https://www.youtube.com/channel/UC1p...qcZKHyrqKhikFA

      ----

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      • #4
        I think the battery protection is in the tool and not the battery, (the example: is the Dewalt 18 to 20 volt adapter) the nicad batteries did not have the protection as far as I can tell, and in Dewalt case the adapter is not workable on a few tools, and my guess is there to high draw, (possibly use a zener diode), http://www.electronics-tutorials.ws/diode/diode_7.html

        DC voltage limiting circuits https://www.google.com/search?q=dc+v...w=1067&bih=721

        one may have to oscillate it and use a triac as in a dimmer circuit and then rectify it back to DC

        (Disclaimer: I know enough about electronics, just to be dangerous)
        Push sticks/blocks Save Fingers
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        "The true measure of a man is how he treats someone who can do him absolutely no good."
        attributed to Samuel Johnson
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        PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

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        • #5
          Cheapest way is to get a buck converter off Ebay. http://www.ebay.com/itm/321576507977...%3AMEBIDX%3AIT
          just make sure not to hook up the + and - backwards as they don't like it. I use a diode to protect mine. so far I've never had any problems pulling 7 amps or so continuously thru mine for 1/2 hour at a time.
          the little brass screws on top of the blue things ( potentiometers ) are used to control voltage and current outputs so you need to use a multimeter to check voltage and then turn the other one to set max current output.

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          • #6
            But isn't output voltage tied to the input voltage in this type of power supply (or step down converter as this is).

            I want/need constant output voltage/current even if the input voltage varies or drops.

            If the battery produces a constant output voltage (+/- a volt or two) and shuts itself down when the minimum
            voltage is reached to protect the battery, that should keep the input voltage fairly constant. At least that is what
            I have observed of the Li-Ion batteries I have, they produce the specified voltage/current until they are near their
            cutout point then shut down.

            I want minimum ripple on the output. These packages don't have very large capacitors but my housing (the gutted
            charger case) should provide ample space for larger output capacitors.

            Is it possible to run two of these buck converters in parallel for greater combined output current? I guess it would be
            better to find a suitable multiphase buck converter to accomplish this though as the timing issue would be a problem
            between two independent buck converters.

            Something like this looks interesting as it has provision for powering a fan at either the input or output voltage and
            constant current/voltage out. Or this for even higher output current. I'd like to be bale to run at 10A out without running
            the supply at full capacity. I would feel better with a supply capable of 15A and drawing 10A max. Components should run
            cooler and have longer life.
            Last edited by Bob D.; 11-24-2016, 07:17 AM.
            "It's a table saw, do you know where your fingers are?" Bob D. 2006

            https://www.youtube.com/user/PowerToolInstitute

            https://www.youtube.com/channel/UC1p...qcZKHyrqKhikFA

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