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could voltage return from inverter input?

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  • could voltage return from inverter input?

    hi all ,,,,,
    system of ( 4x panels 12v, each 200w connected to PWM charge controller feeding 3x batteries 12v ,each 200amh connected in parallel then going to an modified inverter 2kw )
    that is the system of power.
    on out put of inverter connected a load of 300w . after 3 days by sudden I got an electric shock when I touch one terminal of a battery ,
    when I touch the other end also the same,,, I felt like there is 220v ( but how can happen coming back from inverter to batteries ).
    I brought a tester screw driver that work on 220v normally , and when I put it in any of batteries terminal it shows that there is a high voltage . cuz the light in tester wont ( light up ) with voltage much less than 220v .
    i brought a voltmeter when i connect 1 end of the voltmeter in ( + ) of battery and the other end on ground ( i mean the floor where i am standing ) the meter read 35v ,
    when i connect 1 end of the voltmeter in ( - ) of battery and the other end on ground ( i mean the floor where i am standing ) the meter read 49v.
    anyway i split the system that connected to output of inverter and checked it 1 by 1 ,,,
    i found i have this problem only in the cable ( i mean the cable only connected to inverter alone no load at end and no touch between L and N cable ),
    and when i use a new cable connected to load every thing is ok ( i mean there is no problem from load ).
    until here every 1 will say the problem is in cable and that is obvious ,
    BUT .... why it happened ? and the cables are brand new and of good quality and they can handle the load .
    Last edited by zolar; 12-03-2018, 02:23 PM.

  • #2
    Is your system grounded? If so where? Does the inverter manual discuss "legal" grounding schemes? With cheapo inverters you can see problems if you common the return line and ground (which is how homes are wired.)

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    • #3
      It sounds like you have an ungrounded system which has the potential to generate a high voltage between the inverter output terminals and your body which is grounded at the time you touch them.

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      • #4
        hi ,,,,

        thanks a lot jflorey2 and thanks a lot suneagle.

        1- the system not grounded yet , but why first 2~ 3 days nothing was there? if the problem due to ( not grounded ) it should have been happened from first working system, right ? or it could happen later?

        2-
        Originally posted by SunEagle View Post
        It sounds like you have an ungrounded system which has the potential to generate a high voltage between the inverter output terminals and your body which is grounded at the time you touch them.
        suneagle ,,,you mean the time I touch the inverter output terminals ? or batteries terminals ? cuz I mean the I got shocked when I touch the batteries terminals.

        3- btw for all ,,,, remember I got and get shocked only when I plug that load , which is only 300w , when change to an ( air heater ) which its load 1350w every thing ok , when I use a ( drill ) with load of 1500w also every thing ok , also most important thing I used another 2 inverters and the problem exist only with that load in all 3 inverters I switched , that's why I splited that system and I followed the cables , and when I connect the load with a new cable it goes fine , and when I connect the new cable with old cable ( as an extension ) even with load removed I find the problem . that's why I got the result that the cables got damaged , although they are new, but my question ..... WHY CABLES GOT DAMAGED?
        could it happened with the time if the system not grounded I mean after few hours or some days working.
        ( BTW I MEAN CABLE DAMAGED CUZ THATS WHAT I RESULT , OTHERWISE WHEN YOU LOOK AT THE CABLES THEY CAN BE SEEN FINE ( NO BURN OR COLOR CHANGE ) , MAY BE I HAVE TO SAY PHYSICALLY DAMAGED IF THE WORD CORRECT )

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        • #5
          Originally posted by zolar View Post
          1- the system not grounded yet , but why first 2~ 3 days nothing was there? if the problem due to ( not grounded ) it should have been happened from first working system, right ? or it could happen later?
          It can happen later. Changing capacitance from neutral to ground or hot to ground (depending on loads and/or cabling) can cause unexpected potentials at various places in the system (if the system isn't grounded.)

          Again, what does your inverter installation manual say about grounding?
          most important thing I used another 2 inverters and the problem exist only with that load in all 3 inverters I switched , that's why I splited that system and I followed the cables , and when I connect the load with a new cable it goes fine , and when I connect the new cable with old cable ( as an extension ) even with load removed I find the problem . that's why I got the result that the cables got damaged , although they are new, but my question ..... WHY CABLES GOT DAMAGED?
          Why do you think the cables got damaged?

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          • #6
            hi again jflorey and thanks for your help,

            Originally posted by jflorey2 View Post
            It can happen later. Changing capacitance from neutral to ground or hot to ground (depending on loads and/or cabling) can cause unexpected potentials at various places in the system (if the system isn't grounded.)

            Again, what does your inverter installation manual say about grounding?

            Why do you think the cables got damaged?
            1- sorry friend but due to ( English is not my first language ) , what you mean by ( Changing capacitance from neutral to ground or hot to ground )?
            2- I will again read the manual later on and let you know about it .
            3- i think the cables damaged cuz as i said ( when i connect a new cable from inverter output directly to the load terminals , everything go fine no problem ) and when i connect the new cable with the old cable ,( you can say as an extension) EVEN with load removed i find the problem again. 1 end in inverter and other end free ( not connected to anything ).
            also when i connect any other load directly to inverter or using the new cable ( i mean not using the the damaged cable) , i have no problem , every thing ok.

            Comment


            • #7
              Originally posted by zolar View Post
              1- sorry friend but due to ( English is not my first language ) , what you mean by ( Changing capacitance from neutral to ground or hot to ground )?
              If your system is ungrounded, then putting a capacitor between the hot line and ground can cause high voltages on the neutral line, which can be reflected on the DC side.

              "But I am not putting capacitors between hot and ground!" you say. Unfortunately, many things (loads with EMI filters, even wiring with ground and hot close to each other) create capacitance between hot, neutral and ground.
              i think the cables damaged cuz as i said ( when i connect a new cable from inverter output directly to the load terminals , everything go fine no problem ) and when i connect the new cable with the old cable ,( you can say as an extension) EVEN with load removed i find the problem again.
              The cable is likely not damaged. You can check it with an ohmmeter to make sure that there is no connection between the three conductors.

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              • #8
                hi ...
                thanks again jflorey for your time and help, also thanks for explaination.
                and when i mean cable damaged i didn't mean the core melted and there is touch between metal part of 2 wires , cuz in this case there will be a short circuit ,
                but( i mean the cable strength not became as efficient as before after the problem happened ) or something like that .
                sorry i don't know how to say that.
                but just few minutes ago i tried earthing the system , so i joined a copper cable between ( - ) terminal of batteries and the house earth point which is located in DB ( distribution box ).
                and when i test the terminals , there is no any mark of back voltage , and every thing going ok , i will let the load working till tomorrow to check.
                but 1 more question please >>> the erthing cable could be joind to ( + ) terminal or ( - ) terminal of batteries , either one ? OR should be only to ( - )?

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                • #9
                  Originally posted by zolar View Post
                  but 1 more question please >>> the erthing cable could be joind to ( + ) terminal or ( - ) terminal of batteries , either one ? OR should be only to ( - )?
                  What does your inverter manual say on the topic?

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                  • #10
                    hi ,,,
                    and thanks again jflorey
                    sorry brother, till yesterday I was searching , but didn't find it , I think its in the car that brother toke, he will come within next 2 days I will let you know.

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                    • #11
                      hi again ,
                      sorry jflorey2 couldn't find the manual of the inverter.
                      but I have another question ,,,, now since I connect the batteries terminal to ground to avoid the back voltage from inverter , doesn't that mean some of electricity coming from panel go to ground also?

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                      • #12
                        Originally posted by zolar View Post
                        hi again ,
                        sorry jflorey2 couldn't find the manual of the inverter.
                        but I have another question ,,,, now since I connect the batteries terminal to ground to avoid the back voltage from inverter , doesn't that mean some of electricity coming from panel go to ground also?
                        If your inverter was designed to accept negative battery ground - then only a very small amount of current will flow, negligible compared to the production of your panels.

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                        • #13
                          oh ,,,,
                          you mean not always negative terminal of the battery should be grounded?
                          I think I must find that manual.
                          Last edited by zolar; 12-11-2018, 03:46 AM.

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