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A bit OT.Reducing DC Voltage.

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  • A bit OT.Reducing DC Voltage.

    I have a LED pack that runs on 4.5volts worth of AAA batteries. I want to replace the batts with a walwart. I have a 5.3vdc .800amp wallwart. approximately how much resistance should this require?
    " To me, the soundstage presentation is more about phase and distortion and less about size. However, when you talk about bass extension, there's no replacement for displacement". Tyger23. 4.2015

    Quote Originally Posted by hongrn. Oct 2014
    Do you realize that being an American is like winning the biggest jackpot ever??

    http://www.midwestaudioclub.com/spot...owell-simpson/
    http://s413.photobucket.com/albums/pp216/arlis/

  • #2
    Re: A bit OT.Reducing DC Voltage.

    How much current does the LED pack draw at 4.5 volts? Once you know that you can calculate the required series resistance by dividing the required voltage drop of 0.8 volts by the current in amps. Then calculate how much power will be dissipated by the resistor (voltage drop times current) and use one rated 5-10 times that power to ensure no detrimental effects from self-heating.

    Another possibility is to use one series silicon diode instead of a resistor; its 0.6-volt typical drop in the forward direction may be close enough, ending up with ~4.7 volts delivered to the LED pack. The diode would have to be able to safely pass the required current.
    Paul

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    • #3
      Re: A bit OT.Reducing DC Voltage.

      thanks
      " To me, the soundstage presentation is more about phase and distortion and less about size. However, when you talk about bass extension, there's no replacement for displacement". Tyger23. 4.2015

      Quote Originally Posted by hongrn. Oct 2014
      Do you realize that being an American is like winning the biggest jackpot ever??

      http://www.midwestaudioclub.com/spot...owell-simpson/
      http://s413.photobucket.com/albums/pp216/arlis/

      Comment


      • #4
        Re: A bit OT.Reducing DC Voltage.

        Be careful, many LEDs drop well beyond the std silicon diode drop of 0.7v. Some high eff LEDs drop 2, 2.5, even 2.8v.

        Comment


        • #5
          Re: A bit OT.Reducing DC Voltage.

          I'm NOT an expert so don't take my statements as anything but points-to-ponder and investigate: Power supplies often lose voltage as current is drawn so your walwart might be fine. Also, your LEDs may be okay with 5.3v anyway because circuits usually have some leeway built in.
          "We are just statistics, born to consume resources."
          ~Horace~, 65-8 BC

          Comment


          • #6
            Re: A bit OT.Reducing DC Voltage.

            I dug through my collection and found a 5vdc. letting it run now. seems dandy.
            " To me, the soundstage presentation is more about phase and distortion and less about size. However, when you talk about bass extension, there's no replacement for displacement". Tyger23. 4.2015

            Quote Originally Posted by hongrn. Oct 2014
            Do you realize that being an American is like winning the biggest jackpot ever??

            http://www.midwestaudioclub.com/spot...owell-simpson/
            http://s413.photobucket.com/albums/pp216/arlis/

            Comment


            • #7
              Re: A bit OT.Reducing DC Voltage.

              Paul K's second suggestion would have been my first choice. Typical forward voltage drop of a rectifier diode is 0.7 V. A 1N4007 cost less than a quarter, can be purchased at Ratshack, and would have worked fine. But your 5 volt wall wort should work fine. Output light level will be a little brighter, LED life expectancy will be slightly shorter.
              Craig

              Comment


              • #8
                Re: A bit OT.Reducing DC Voltage.

                1N4007. will the RS guy/gal know what I want?
                " To me, the soundstage presentation is more about phase and distortion and less about size. However, when you talk about bass extension, there's no replacement for displacement". Tyger23. 4.2015

                Quote Originally Posted by hongrn. Oct 2014
                Do you realize that being an American is like winning the biggest jackpot ever??

                http://www.midwestaudioclub.com/spot...owell-simpson/
                http://s413.photobucket.com/albums/pp216/arlis/

                Comment


                • #9
                  Re: A bit OT.Reducing DC Voltage.

                  Originally posted by [email protected] View Post
                  1N4007. will the RS guy/gal know what I want?
                  maybe, maybe not. it'll be in the component parts bins, probably around $1.49 each. i didn't see it when i searched, only the 25-pack of various diodes for $3.59, #276-1653. If they have a 1n4001, i don't see why that wouldn't work in this application.

                  or if you're ordering here soon...
                  http://www.parts-express.com/pe/show...tnumber=1N4007
                  TM (RS125/TB25-302), TM RS150S / Vifa BC25SC06, RS150-4 / Vifa ML-TL, 3CR-AL Ultra Budget: Electric Blue TM, TMM, MTM, Dragonflies , Mounties: Mini HT Satellite,sub for minions

                  Comment


                  • #10
                    Re: A bit OT.Reducing DC Voltage.

                    we have two in town. One has some, the other has all the little shtuff. thanks.
                    " To me, the soundstage presentation is more about phase and distortion and less about size. However, when you talk about bass extension, there's no replacement for displacement". Tyger23. 4.2015

                    Quote Originally Posted by hongrn. Oct 2014
                    Do you realize that being an American is like winning the biggest jackpot ever??

                    http://www.midwestaudioclub.com/spot...owell-simpson/
                    http://s413.photobucket.com/albums/pp216/arlis/

                    Comment


                    • #11
                      Re: A bit OT.Reducing DC Voltage.

                      by the way, this will go in series on the positive side, right?
                      " To me, the soundstage presentation is more about phase and distortion and less about size. However, when you talk about bass extension, there's no replacement for displacement". Tyger23. 4.2015

                      Quote Originally Posted by hongrn. Oct 2014
                      Do you realize that being an American is like winning the biggest jackpot ever??

                      http://www.midwestaudioclub.com/spot...owell-simpson/
                      http://s413.photobucket.com/albums/pp216/arlis/

                      Comment


                      • #12
                        Re: A bit OT.Reducing DC Voltage.

                        The 1N4001-1N4007 should work. The link shows a forward voltage compared to current load. The 1N4004 is rated at a 0.8v MAXIMUM AVERAGE forward voltage drop and is available at Radio Shack. If your curious, I would through it in the circuit and measure with DMM to see what you get. I have some on hand so for me "trying" it wouldn't be too hard...

                        http://www.diodes.com/datasheets/ds28002.pdf

                        Put two in series and see the forward voltage drop double.
                        Jason


                        "In my opinion, there are more tactful ways to state your opinion."

                        Comment


                        • #13
                          Re: A bit OT.Reducing DC Voltage.

                          Silicon diodes are now the most reliable DC "voltage wasters" this side of the DC voltage converters (from IC's to 90 amp boxes that can take 5 volts and bump it to 48 volts or more or the other way.) They aren't load dependant, you can string 100 together and they stay linear with only tiny picofarad bypass caps (value doesn't really matter much) about every half-dozen to dozen. You can "back feed" full-wave quad rectifiers and get rock-solid 2.8V DC from them to power LEDs. I have a 1/2" thick softback (out of print sadly) print book intended for model railroaders, of 1001 (+) "projects" using diodes, just the surplus ones that you can get for 3 cents (or less) a piece by the mix-or-match 100 for 3-10 amp ones under 300WDCV, or by a "grab bag". I got 1000 IRC "sweepings" for $4 free S&H from Allied in Tejas. All lead types, 1-12 amp, all types. A three day special.
                          You need to sign-up for the e-mail notices on these things from the big electronic houses and surplus houses. "Sweepings" and close-outs, clearances on what ever you want can save you thousands of dollars, even counting the storage units for them from Herber Fraught to keep them in! The ERSE "grab-bag" of audio caps I bought, which are useful values, I don't think I paid 3 cents on the dollar for.

                          Comment


                          • #14
                            Re: A bit OT.Reducing DC Voltage.

                            Originally posted by [email protected] View Post
                            I have a LED pack that runs on 4.5volts worth of AAA batteries. I want to replace the batts with a walwart. I have a 5.3vdc .800amp wallwart. approximately how much resistance should this require?
                            For this job you'd use a zener diode or a voltage regulator, not resistors.
                            www.billfitzmaurice.com
                            www.billfitzmaurice.info/forum

                            Comment


                            • #15
                              Re: A bit OT.Reducing DC Voltage.

                              I see that now. I hooked up a 3kohm sandcast I have and it only dropped .o2. I'll pick up a diode.
                              thanks for the help.
                              I'll post a pic of the project when its ready for prime time.
                              " To me, the soundstage presentation is more about phase and distortion and less about size. However, when you talk about bass extension, there's no replacement for displacement". Tyger23. 4.2015

                              Quote Originally Posted by hongrn. Oct 2014
                              Do you realize that being an American is like winning the biggest jackpot ever??

                              http://www.midwestaudioclub.com/spot...owell-simpson/
                              http://s413.photobucket.com/albums/pp216/arlis/

                              Comment

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