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  • #16
    So, use a diode while you are doing the prototype work and just don't use it for the final version. You can leave the diode in until the last step in the final wiring.

    Frankly, not many design engineers, either pro or amateur, will worry about such protection. And I have never seen reverse polarity protection on an input to a motor controller listed in the spec sheet, so good luck finding one.



    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?
    Paul A.
    SE Texas

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

    Comment


    • #17
      Standard schottkys are rated at what- 45 volts- if your input voltage is not going to exceed about 40 volts tops, you could be ok with that. Using inductive loads is going to create voltage spikes, so even if you use 12 volts you could have problems. Over all though, I think it's better to use polarized connectors and forget the diodes. I've used quite a few of those 'deans' connectors that rc guys use- it's a good way to maintain the correct polarity- provided you get it right the first time.

      If you do much in electronics, you learn to get it right the first time. You never just 'try it' to see which way it goes.
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

      Comment


      • #18
        If the caps you blew are on the input terminals of the controller, then no, a fuse will not protect them. The control circuit may not draw enough current when hooked up in reverse, but those filter caps on the input would still see the full supply Voltage and would still go up in smoke. The only good news there is the fuse would not need to be replaced.



        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?
        Paul A.
        SE Texas

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

        Comment


        • #19
          If it is something that will be disconnected and re-connected repeatedly, especially if only used every so often, then the diode and fuse can pay for itself in time, as well as dollars or whatever the local currency is.

          I am definitely surprised that the controller was damaged, unless you had no fuse. The diodes that should be in the PWM to begin with ought to have held the reverse voltage to 2 diode drops, or a bit over 2 volts per common specs. (Diodes are 0.7V, yes, of course, but most drop a volt or so at rated current due to resistances. The 2 in series and PWB resistance can add up to a bit over 2 volts.)

          Maybe the makers are relying on the voltage rating of the IGBT or mosfet to deal with the spikes. Bad design if so, and will not work as well even in normal conditions.

          Originally posted by Paul Alciatore View Post
          If the caps you blew are on the input terminals of the controller, then no, a fuse will not protect them. The control circuit may not draw enough current when hooked up in reverse, but those filter caps on the input would still see the full supply Voltage and would still go up in smoke. The only good news there is the fuse would not need to be replaced.
          Paul, just put the reverse diode across the terminals, and the fuse will blow without applying enough reverse voltage to damage ANYTHING reasonable. It's not difficult.
          Last edited by J Tiers; 07-02-2020, 11:17 PM.
          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


          • #20
            Originally posted by MaxHeadRoom View Post
            If you want minimum voltage drop, use a Schottky version!

            BTW, the common 1n400x series now come in a schottky version, UF400x etc.
            Max.
            WoW! I had no idea schottky was that small, very small.

            Thanks Max.. JR

            https://www.mouser.com/ProductDetail...xoCPm4QAvD_BwE

            My old yahoo group. Bridgeport Mill Group

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

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            • #21
              Originally posted by JRouche View Post

              WoW! I had no idea schottky was that small, very small.

              Thanks Max.. JR

              https://www.mouser.com/ProductDetail...xoCPm4QAvD_BwE
              Diodes in general are pretty tough. The 1n400x series will tolerate about 1 cycle of 30A, IIRC, even though they are nominally 1A diodes.

              But don't count on that. For the reverse polarity diode, use a considerably larger rated diode so as to be reasonably sure the "fuse" that blows is the part you think it is.........
              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


              • #22
                The UF400x don't appear to be true Schottky devices. The UF4001-4003 do have a bit less forward voltage drop at rated 1A current than the standard 1N400x, but the higher voltage devices have higher Vf than the equivalent 1N4004-7 - as high as 1.7 volts at 1 amp. They are mostly superior due to their 50-75 nSec reverse recovery time, which is only important at frequencies of about 10 kHz and higher. The 1N5819 Schottky, rated at 40V, has only about 600 mV Vf at 1 amp.

                You should use something like this, which can handle 2x20 amps and 100 volts, in a T)-220 package, with a Vf of only 400 mV at 1 amp, and costs less than a dollar.

                https://www.mouser.com/ProductDetail...wOv8fwmA%3D%3D

                .
                http://pauleschoen.com/pix/PM08_P76_P54.png
                Paul , P S Technology, Inc. and MrTibbs
                USA Maryland 21030

                Comment


                • #23
                  Originally posted by JRouche View Post

                  WoW! I had no idea schottky was that small, very small.
                  Thanks Max.. JR
                  Your welcome, although I didn't really intend the use for the OP's issue, more of a heads up of a relatively new device.
                  I use them now for relay reverse EMF diodes in place of the IN4007.
                  Max.

                  Comment


                  • #24
                    Originally posted by PStechPaul View Post
                    The UF400x don't appear to be true Schottky devices. The UF4001-4003 do have a bit less forward voltage drop at rated 1A current than the standard 1N400x, but the higher voltage devices have higher Vf than the equivalent 1N4004-7 - as high as 1.7 volts at 1 amp. They are mostly superior due to their 50-75 nSec reverse recovery time, which is only important at frequencies of about 10 kHz and higher. The 1N5819 Schottky, rated at 40V, has only about 600 mV Vf at 1 amp.

                    You should use something like this, which can handle 2x20 amps and 100 volts, in a T)-220 package, with a Vf of only 400 mV at 1 amp, and costs less than a dollar.

                    https://www.mouser.com/ProductDetail...wOv8fwmA%3D%3D

                    .
                    Quite true. The UF series is an "Ultra-Fast" type.... hence the "UF". It is not a Schottky. The true Schottky is somewhat intrinsically a low voltage device, although there are now higher voltage devices that have the same characteristics. I am not sure they are actually "Schottky barrier diodes".
                    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


                    • #25
                      Regardless of the technology, I use them now in place of the 1N4 version for suppression due to their higher operating speed.
                      Max.

                      Comment


                      • #26
                        Originally posted by Noitoen View Post
                        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.
                        what do you think about this?

                        https://www.youtube.com/watch?v=rbkXg60bhJI
                        Last edited by dian; 09-23-2020, 06:32 AM.

                        Comment


                        • #27
                          I have seen a lot of DC circuits and a simple diode is perhaps the most common way to protect against reverse polarity, when that is a concern.

                          Another good way is to just pay attention when you are hooking it up. You can always use the diode to test the wiring and then remove it from the circuit.

                          And, as Maxheadroom said, there are Schottky diodes which have lower forward Voltage drops.

                          Another way is with an FET. This would be before any of the motor controller circuit, capacitors included. And with this, you don't have to replace any blown fuses.

                          https://components101.com/articles/d...ity-protection

                          I searched with "FET based reverse polarity protection". That is just one hit. It did not take a lot of Google fu.



                          Originally posted by JRouche View Post

                          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
                          Last edited by Paul Alciatore; 09-24-2020, 01:04 AM.
                          Paul A.
                          SE Texas

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

                          Comment


                          • #28
                            an interesting idea is to use a brigde rectifier:

                            https://www.youtube.com/watch?v=Atl3cv3XRqo

                            Comment


                            • #29
                              Originally posted by dian View Post
                              an interesting idea is to use a brigde rectifier:

                              https://www.youtube.com/watch?v=Atl3cv3XRqo
                              The problem with regular diodes is voltage drop. If running of a power supply than this can be compensated but, running from batteries, it's just a waste of energy.
                              Helder Ferreira
                              Setubal, Portugal

                              Comment


                              • #30
                                Originally posted by Paul Alciatore View Post
                                I have seen a lot of DC circuits and a simple diode is perhaps the most common way to protect against reverse polarity, when that is a concern.

                                Another good way is to just pay attention when you are hooking it up. You can always use the diode to test the wiring and then remove it from the circuit.

                                And, as Maxheadroom said, there are Schottky diodes which have lower forward Voltage drops.

                                Another way is with an FET. This would be before any of the motor controller circuit, capacitors included. And with this, you don't have to replace any blown fuses.

                                https://components101.com/articles/d...ity-protection

                                I searched with "FET based reverse polarity protection". That is just one hit. It did not take a lot of Google fu.


                                The problem with an FET, typically a MOSFET, is that there is an intrinsic diode in the device, poled to conduct in the reverse polarity. So a single MOSFET is not suitable for a protector unless you know the polarity to begin with. Obviously for a reverse polarity protector, the whole point is to block current in the reverse polarity.

                                A double MOSFET, one each of N and P channel, will work. P channel devices are less common than N-channel, and the channel resistance tends to be higher for a P channel for various reasons (newer devices may have changed that somewhat).

                                The protectors typically depend on enhancing conduction in what is actually the MOSFET reverse current path, the path that would turn on the intrinsic diode. There is some ability to enhance conduction in that direction, which may depend on the exact characteristics of the device. The enhanced conduction serves to bypass the diode and reduce the losses below what the diode would produce.

                                The blocking direction is then the "normal conduction" polarity.

                                Not all MOSFETs are best for this use.
                                Last edited by J Tiers; 09-26-2020, 01:01 PM.
                                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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