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  • dc motor controller

    would anybody know if there are controllers of this type out there that are polarity protected? (this one is definitely not.)

    https://www.ebay.com/itm/DC-6-60V-12...72.m2749.l2649

  • #2
    Polarity protection? On the input you mean? All you have to do is add a diode in series with either power lead. You probably will need one that is rated for 35A or more and a Voltage greater than the supply Voltage.
    Paul A.
    SE Texas

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

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    • #3
      Originally posted by Paul Alciatore View Post
      Polarity protection? On the input you mean? All you have to do is add a diode in series with either power lead. You probably will need one that is rated for 35A or more and a Voltage greater than the supply Voltage.
      Mind you I have limited electrical.

      I hate diodes for this use. To bleed energy off to a load that is not the load you are driving IMO is a "Net Loss". JR
      My old yahoo group. Bridgeport Mill Group

      https://groups.yahoo.com/neo/groups/...port_mill/info

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      • #4
        So... you hate diodes. Diodes are easy... losing roughtly 0.6v x current in power; other "add-on" circuits more complex but can achieve a lower Vf. If you want to get into the internals of the cheap controller, you might be able to protect the pwm generator circuits with a small diode, and let the main Mosfet (or whatever) block the main reverse voltage. Devil is in the details.

        A dirt cheap method is fuse the device, then put a reverse diode ACROSS the input power terminals. If you connect it wrong, the fuse blows. Many other techniques.

        In any case, what circumstances other then user error make for reverse polarity? Many devices aren't "protected" because there is an assumption that the user will connect it correctly.

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        • #5
          If you want minimum voltage drop, use a Schottky version!
          BTW, the common 1n400x series now come in a schottky version, UF400x etc.
          Max.
          Last edited by MaxHeadRoom; 07-02-2020, 12:57 PM.

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          • #6
            Or there's the low cost option and just be careful and double check when making your connections?

            If your situation is that you would be regularly connecting and disconnecting the supply power that's different. But I'd suggest physical rather than electronic polarity protection using a connecting lead or inline connectors that are physically polarized so they only go together one way.

            One example of this which is cheap to buy is the XT60 plug and socket as used by a lot of radio control electric models. As the name suggests they are good for up to 60 amps

            https://www.ebay.com/itm/1-Pair-XT60...oAAOxyY9VRUKvA
            Chilliwack BC, Canada

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            • #7
              Are you sure there is nothing in that to provide polarity "protection"? That would surprise me.

              Internal to it will be an IGBT or Mosfet with a reverse diode, and there will be a reverse diode across the load. With the addition of a fuse, you have it. The reverse diode across the supply should already be present.

              You can of course add one in series or across at your choice.
              1601 2137 5683 1002 1437

              Keep eye on ball.
              Hashim Khan

              If you look closely at a digital signal, you find out it is really analog......

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              • #8
                obviously i dont want to do any work on a $10 item. i blew the caps on one being careless, so i have to get another one.

                so maybe just using a fuse will do it? on the positive side?

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                • #9
                  Originally posted by J Tiers View Post
                  Are you sure there is nothing in that to provide polarity "protection"? That would surprise me.

                  Internal to it will be an IGBT or Mosfet with a reverse diode, and there will be a reverse diode across the load.
                  .
                  That is the ideal/preferred method, but with Chinese origin devices, you cannot take anything for granted, found out the hard way!
                  Max.,

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                  • #10
                    Originally posted by MaxHeadRoom View Post

                    That is the ideal/preferred method, but with Chinese origin devices, you cannot take anything for granted, found out the hard way!
                    Max.,
                    Mosfets, typical for low voltage, have an intrinsic diode, no avoiding that. The diode across the load is pretty essential to operation also. Still, never know, when well trained by bottom feeder importers, the chinese engineers have no problem exceeding part specs, leaving out parts, etc.
                    1601 2137 5683 1002 1437

                    Keep eye on ball.
                    Hashim Khan

                    If you look closely at a digital signal, you find out it is really analog......

                    Comment


                    • #11
                      Originally posted by dian View Post
                      obviously i dont want to do any work on a $10 item. i blew the caps on one being careless, so i have to get another one.

                      so maybe just using a fuse will do it? on the positive side?
                      You want to fuse according to your load, a 30a fuse allows alot of 'damage' current before blowing!
                      Max.

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                      • #12
                        Don't know if anyone mentioned but you can use a relay to protect the circuit. The diode only powers the relay coil and if the polarity is correct, the contacts power the circuit.
                        Helder Ferreira
                        Setubal, Portugal

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                        • #13
                          The protection costs $12.91 each time you use it
                          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
                            Most of the "foolproof", effective, and efficient input polarity protection methods proposed add complexity and may cost more than the device you are trying to protect. Much cheaper and better to use color coded wires and matching color on the input connections, and a double check with a multimeter before applying power. Electrical connections are no place for carelessness.
                            http://pauleschoen.com/pix/PM08_P76_P54.png
                            Paul , P S Technology, Inc. and MrTibbs
                            USA Maryland 21030

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                            • #15
                              Originally posted by MaxHeadRoom View Post

                              You want to fuse according to your load, a 30a fuse allows alot of 'damage' current before blowing!
                              Max.
                              Not necessarily.

                              A diode capable of carrying the current for a short time will hold the reverse voltage low enough that damage of any sort is unlikely. It will blow the 30 fuse in a rather short time.

                              A regular schottky rated for the current AND reverse voltage is expensive, so a standard diode rated for 30A would be fine, and costs nothing any time you screw up.
                              1601 2137 5683 1002 1437

                              Keep eye on ball.
                              Hashim Khan

                              If you look closely at a digital signal, you find out it is really analog......

                              Comment

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