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How to wire shunt with chassis ground?

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  • How to wire shunt with chassis ground?

    The shunt I originally ask how to mount has arrived and I tried to connect it to my system in place of the old non-functioning (I thought) meter with the internal shunt. Turns out, I have wiring issues.

    Now, I want to preface this by saying that I know this is not an ideal wiring setup, and I know it looks like crap. I am just trying to configure things, get them working so I understand enough to wire it properly and professionally, so please don't judge by the look right now!

    Right now in my camper van, I have a Blue Sea DC load center, a Drok Meter and shunt... and not much else. I'll be getting the panel and battery and a CTEK 250s to act as a charge controller/isolator, and will later build to panels and a CTEK SmartPass if I need more than 20A charging. I have the Blue Sea DC fuse panel chassis grounded, that might be my main problem. I do not have a NEG return line to the start battery (using chassis ), since I am not sure where I'll put the house battery yet.

    Long story made short. I have this wired wrong, and I feel stupid for not being about to figure it out yet. I have the diagrams on the back of the meters, but neither works as installed, since no current appears to flow through them with the NEG grounded to the chassis... which I have presumed have all been common.

    Here's a pic showing the current set up and I labeled all the connections. I am hoping someone can clarify which connections get hooked to what. The Voltmeter works, just not the ammeter portion of the meter.

    I am almost certain this is because of the chassis ground and no return wire (I will fix that when I get the aux battery setup and only chassis ground where required). Unless this setup requires it, then I will have to go ahead and finalize the location of the aux battery.

    In the pic, the old is still attached (Showing diagram now) and the new it on the right (with the diagram shown also).


    Shunt.jpg

  • #2
    It took all that typing and me hitting POST to figure it out. Connect the load NEG to the shunt and so I force current across it. Man I feel dumb. In BEE, I learned shunt means parallel.... duh.


    HOW TO DELETE A POST?? hahah

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    • #3
      What current are you interested in monitoring? That determines where the shunt or shunts go. You cannot see all currents with 1 shunt. To see everything you need 3 shunts and a micro-controller to derive the 4th current in a system.

      1. Panel Current
      2. Controler Current
      3. Battery charge/discharge current
      4. Load Current.

      With 3 shunts you can monitor all 4 points.
      MSEE, PE

      Comment


      • #4
        Originally posted by Sunking View Post
        What current are you interested in monitoring? That determines where the shunt or shunts go. You cannot see all currents with 1 shunt. To see everything you need 3 shunts and a micro-controller to derive the 4th current in a system.

        1. Panel Current
        2. Controler Current
        3. Battery charge/discharge current
        4. Load Current.

        With 3 shunts you can monitor all 4 points.
        Right now, I just want to monitor load current so I can size my system properly. When I add the aux battery and CTEK, I will understand how to add those shunts in properly and add them as appropriate. I also plan to get much better monitors and a Whiz Bang Jr if I understand that correctly to be a great little piece of gear. The biggest issue I have with the CTEKs is the missing ability to monitor them like a higher end controller can.

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        • #5
          Are you using a Grounded System or Floating?
          MSEE, PE

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          • #6
            Originally posted by Sunking View Post
            Are you using a Grounded System or Floating?
            Well, I am not sure exactly what that means... I don't intend to use the chassis as a (ground) return wire in the future, if that's that you mean. I will ground things to prevent shorts when I get this set up properly. I disconneect the DC loads when I am not using them. When I drive the van, I hook it up to get power to the cameras, and lighting if needed. It's not permanently setup, as is.

            Comment


            • #7
              Here you go. The 3rd Shunt I spoke of is not shown, but would be between the Panels and Controller on the Negative line like you see below.




              Last edited by Sunking; 08-08-2017, 08:11 PM.
              MSEE, PE

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              • #8
                Originally posted by Sunking View Post
                Here you go. The 3rd Shunt I spoke of is not shown, but would be between the Panels and Controller on the Negative line like you see below.
                Ahh... definitely grounded then... excellent Sir! You are awesome!

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                • #9
                  Originally posted by joerossjr View Post

                  Ahh... definitely grounded then... excellent Sir! You are awesome!
                  You are welcome.
                  MSEE, PE

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                  • #10
                    Hmmm... If those 3 green grounds are actually connected in any way, the shunt is going to
                    be "shunted" and read low. Might need to relocate in the other lead. Bruce Roe

                    Comment


                    • #11
                      Originally posted by bcroe View Post
                      Hmmm... If those 3 green grounds are actually connected in any way, the shunt is going to
                      be "shunted" and read low. Might need to relocate in the other lead. Bruce Roe
                      That is possible if the Inverter and Controller Chassis are bonded to Batt NEG. You would be right as we created a parallel path with the Battery Negative supply conductor. OTOH if they are not internally bonded and open circuit, there are no issues with parallel paths. To facilitate proper operation of OCPD the battery Neg Term must be solidly Grounded, so that eliminates one great solution to move the Shunts.

                      The issue I struggled with is Metering OEM's making their equipment use the Negative Polarity rather than Positive. They know dang good and well most manufacturers bond Chassis to Bat NEG, thus compromises the system. This is why NEC will not allow that to happen on AC systems.

                      I know why they do it like that, I just don't care for it. They put it in Neg because that is a Grounded Circuit Conductor referenced to Ground aka Neutral with no voltage on it. That way when you run those little Shunt Wires outside the battery area, thet are not Hot Battery looking for a place to get loose if pinched or cut.

                      Move the Shunts to Positive polarity problem solved, or FLOAT your system.
                      Last edited by Sunking; 08-08-2017, 10:41 PM.
                      MSEE, PE

                      Comment


                      • #12
                        Originally posted by Sunking View Post

                        Move the Shunts to Positive polarity problem solved, or FLOAT your system.
                        So FLOAT as in not chassis grounded... or like FLOAT... on a boat (Same thing??) How do boats ground if they are fiberglass or wood?

                        Comment


                        • #13
                          Originally posted by joerossjr View Post

                          So FLOAT as in not chassis grounded... or like FLOAT... on a boat (Same thing??) How do boats ground if they are fiberglass or wood?
                          There are two types of electrical systems:

                          1. Grounded System.
                          2. Non Grounded of Floated.

                          Look at the two diagrams and note what is different. Floating system the battery is NOT BONDED to Ground and uses fuses on both positive and negative polarities. Now look at the Grounded system.

                          Your problem is you are associating Ground with Dirt or Earth. Stop doing that. Ground is a reference point and can be anything. Like the chassis of a boat, car, plane, or space ship.
                          MSEE, PE

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                          • #14
                            Originally posted by Sunking View Post
                            Your problem is you are associating Ground with Dirt or Earth. Stop doing that. Ground is a reference point and can be anything. Like the chassis of a boat, car, plane, or space ship.
                            I do get the difference, and I don't actually associate it with Earth... although I may have given that impression. I get that it's the reference potential. I thought that maybe the name came from boats or some other weird etymology, but I guess it's just a..... *puts on shades* common sense name (please forgive the pun ).

                            Former Sailor here, so things like that intrigue me... learning new stuff about boats is always interesting to me. I have been dying to ask @JSENSI if he was in the USN.

                            Just so I understand... Are you saying my shunts really should go on the positive side of the circuits to avoid ground loops or anything similar? (That part I don't entirely grasp yet.) I can engineer that properly now that the light bulb came on, if that's the case.

                            Comment


                            • #15
                              Originally posted by joerossjr View Post
                              Former Sailor here, so things like that intrigue me..
                              Same here Silent Serrvice

                              Just so I understand... Are you saying my shunts really should go on the positive side of the circuits to avoid ground loops or anything similar? .[/QUOTE]

                              They should but most OEM add-on units use return of the Grounded Circuit Conductor because it is Neutral. That way you are not taking Hot Raw Battery outside. There would not be a problem if equipment manufacturers did not bond Chassis to the NEG BATT Terminal. That forces all Negative Battery current to flow on Ground Conductors. Extremely dangerous practice.

                              MSEE, PE

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