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  • Chinese powerfeed question.

    My chore for tommorrow is to replace the potentiometer in my Ah-So powerfeed. Prior to it shooting craps, its working range was always down in the 0-2 area. Anything above that was too fast. I know from a long ago experience that subbing a different pot. can spread that working range out through more of it's range, but its' been long enough that I don't recall the details. I know some of you have been through this with your units. Can you help?

    Thanks,
    Scotty M.

  • #2
    If it is wired as a potentiometer (3 wires used), you would need to add a fixed resistor to change the range. For example, if you have a 1K pot, replace it with approximately 200 ohm and and 800 ohm resistor to spread the lower 20% of the range over the full rotation.. If it is used as a two terminal variable resistor, just substitute 200 ohms if the speed is proportional to the resistance but you need 200ohm pot plus 800 ohm resistor if it is wired so lower resistance makes higher speed.

    If wired as a pot, the total resistance across it may not matter too much, depending on the circuit. You might install, for example, a 500 ohm pot in series with a 1500 ohm resistor with a switch to short out the 1500 ohm resistor, giving you a total resistance of either 500 or 2000 ohms and two speed ranges 0-25% and 0-100%. I.E. use a pot half the original value and a fixed resistor 1.5 times the original value. If your existing pot worked fine, it wouldn't hurt to try a fixed resistor of about 3X the original value with it.

    Insert the series resistor in series with the terminal nearest the fastest setting, i.e the terminal the wiper is near when turned to full speed.

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    • #3
      Chinese powerfeed question.

      Whitis, it's time for me to reveal that I'm electronically challenged.

      My pot. is indeed wired with three wires. Also there is an electronic component wired between two of the terminals. I don't know yet what this is. Could it be the resistor you mentioned? It is just some little brown dipped part. I didn't look before I left the shop to determine the resistance of my current pot.

      About my only current recourse is to rely on someone at Radioshack tommorrow or if they dont have one, I have to wait until Monday to go to an electronics store that is only open during the week.

      Thanks,
      Scotty

      Comment


      • #4
        Radio Shack? Good luck ... "You got questions, they've got dumb looks"

        Besides, you'll be luck if the even sell resistors any longer.

        Just clip or desolder one leg of the unknown component and use a/your DVM to read the resistance. If the value does not quickly stabilize close to a standard value and climbs then it is most likely a capacitor, but I'm betting it is a resistor. Should not be hard to find what you need.
        Last edited by RKW; 02-13-2010, 12:38 AM.
        "Work hard. Tell everyone everything you know. Close a deal with a handshake. Have fun!"

        -- Harold "Doc" Edgerton

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        • #5
          a good trick is to just buy some trimpots of a similar value and put those in series with your new pot

          then adjust the trimpots as needed to fine tune the range to your exact liking
          Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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          • #6
            that brown diped thing is called a ceramic capasitor.

            resistors are color coded red green blue black and so on silver and gold bands indecate tolerance, size in diameter is wattage, the smaller it is the lesser the larger the bigger..

            caps are ceramic, electrolitic,and so on,, also ratings such as pecoferrit and micoferit, pU for peco and UF for microferrit and so on

            next we get into k and ohms and the list goes on,,

            a capasitor stores current where as a resistor resist's current. dpending on the color bands on it determeans how much it will resist,

            you might try going from a 1 k pot to a 5k or 10 k pot but in anycase you will need to know what cap you will need to use now as your resistance values are now going to change ..

            Comment


            • #7
              My spelling sucks, so I should be the last one to complain but this just hurts me.

              a microferrit is a very small furry animal.

              Id guess a pecoferrit is some kinda exotic ferret.

              Microfarad (uF)
              Picofarad (pF, Not pU, thats a short pun)
              Note while millifarad's exist, No capacitor is ever marked in them, Capacitors marked in mFD are really in Microfarads, And no capacitor is marked in mF to prevent confusion with mFD.
              Capacitor

              The rest of you'r mispellings I can tollerate as my spelling sucks too, but please try and learn to spell the metric system
              Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

              Comment


              • #8
                Most people go through life spelling words only one way...it is up to some of us with creative minds to offer alternatives...if they don't see the genius in that, there is little else we can do for them....

                Joe

                Comment


                • #9
                  Pinkoferret

                  DZER

                  Comment


                  • #10
                    Well, this thread certainly took an unexpected turn.

                    RKW, your absolutely right about Radio Shack, ... yesterday I was a bartender, today I'm your neighborhood electronics expert. However, where I live if you need an electronics part on a Saturday they are the only choice.

                    Black Moons, I'm afraid trimbots are something I've never even heard of. More evidence of my lack of exposure.

                    Airsmith, thanks for the refresher. About forty years ago I had an electronics course in H.S. and had the vaguest memories of resitors being the one with the color coded bands, but didn't trust my memory or wether things might have changed.

                    By the way, pinkoferret doesn't look real happy in that getup. But then again I'd have to be awfull drunk...

                    Thanks guys. Ill let you know how this turns out.

                    Comment


                    • #11
                      Don't want to get into a big debate but resistors are not always marked as they should be. Sometimes there is only a value and tolerance without color bands. A meter will let you know if it isn't marked at all.

                      Originally posted by airsmith282
                      that brown diped thing is called a ceramic capasitor.

                      resistors are color coded red green blue black and so on silver and gold bands indecate tolerance, size in diameter is wattage, the smaller it is the lesser the larger the bigger..
                      "Work hard. Tell everyone everything you know. Close a deal with a handshake. Have fun!"

                      -- Harold "Doc" Edgerton

                      Comment


                      • #12
                        RKW, I just now got this pot out of the powerfeed. My little "unknown" is just a brown little rectangle soldered between the No.1 and no.2 legs of the pot.

                        I just stuck a meter on the pot and if I'm checking between 1 & 2, I only get continuity with the pot turned all the way down. When I checked between 2 & 3, I only got continuity when it was turned all the way up.

                        Comment


                        • #13
                          A picture would help... But the 'little brown box' sound like it might a small ceramic capacitor.

                          The meter is this measuring resistance or is it simply checking for continuity? What if you check between 1&3? If you are lucky the pots value might be stamped in somewhere.

                          Comment


                          • #14
                            CountZero, I don't ahve a camera with me today. I just came back from Radio Duh. Just a waste of time.

                            I know from past dealing that I've seen these with the value on them, but this one I can't decipher. I'll list the three lines on this one.

                            RV24YN 20S
                            B103
                            062C

                            Thanks again to everybody for your efforts.
                            Scotty

                            Comment


                            • #15
                              I have two concerns to voice about this.

                              First, if the control is connected with three wires, it is most likely wired as a potentiometer, not as a variable resistor which would be a two wire connection (possibly with one wire connected to two terminals of the control). A potentiometer is basically a Voltage divider which has an output Voltage on the wiper (2 in my drawing) that is a fraction of the input voltage (across the other two terminals – 1 & 3). This fraction is determined by the rotational setting of the control.



                              When you are replacing a control like this, it can be important to keep two different considerations in mind. First, the current available on the output pin (2) must be sufficient to drive whatever component it is connected to. If larger values of resistance are used in a replacement, the current available here will be diminished and the circuit may not work as expected. So the total resistance in the final replacement should not be much higher than the value of the original control.

                              Second, there is a certain amount of current that is going to flow through the control just because it is connected (terminals 1 and 3 in my drawing) across a Voltage source. This current is just wasted as it serves no real purpose in the circuit, but it is unavoidable. The Voltage source that produces this current will have limits as to the amount of current that it can provide. If a new control with lower resistance is substituted, then the current will be higher and this can cause problems in both the source of the Voltage and in the control itself as higher current means more power dissipated and more power dissipated means more heat which can slowly or even quickly destroy the control. So the total resistance of the final replacement should not be much lower than the value of the original control.

                              Therefore, the total resistance value of the replacement should be neither higher nor lower than the original. How do we do this?

                              Well, the best solution is to use a variable resistor (pot) with a lower value than the original to provide the finer control, but add a fixed resistor in series with it (on pin 1 in my drawing) to bring the final resistance back to the original value. Hence, the values of resistances A and B in my drawing should add up to the original resistance R. The ratio of A/B will give you the magnification factor for the sensitivity of the control. If A/B = 4 then the new control will be four times as sensitive but the highest speed will be only 1/4 the original.

                              It is usually impossible to get exact values, and in electronics there is usually a broad range of values that will work. Since we have no details of the exact circuit, it is hard to say how large this range is. I would suspect that a total resistance value (A + B) that is between perhaps 75% and 200% of the original value (R) would be just fine.

                              Your mystery component is probably a capacitor. I have shown it, marked with a question mark, in the most likely position in the circuit. When replacing the pot, just remove this mystery part from the old one and put it on the same terminals on the new one. If it has any markings to indicate polarity of the leads, reconnect it in the same polarity. These markings are usually things like a black band or bar by one lead or perhaps a + or – sign. If there are no such markings, it is probably OK to replace it in either orientation.
                              Last edited by Paul Alciatore; 02-13-2010, 12:43 PM.
                              Paul A.

                              Make it fit.
                              You can't win and there is a penalty for trying!

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