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Why does the battery show a minus voltage when checked with the voltmeter?

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    Why does the battery show a minus voltage when checked with the voltmeter?

    Hi from Sweden :D

    My charger stopped working so i bought a new one and that one did not work either..

    Then I started to measure it with my multimeter and found out that minus are now plus?

    Any tips what i can be or what i can do? Please see pictures.

    EVERYTHING else works and it´s "driveable" but wont charge only...

    TO BE SUPERCLEAR THE CABEL ON THE PICTURE COMES DIRECTLY FROM THE BATTERY AND ARE USED AS A "CHARGING CABEL".

    The cabels from the battery that are used to drive the motor shows correct value..

    Can it be some kind of fault only for the charging bit on the battery?

    Kind regards !
    Attached Files
    Last edited by ingolf915; 07-15-2021, 11:41 PM.

    #2
    In your two pics, is one showing "+" and one showing "-"? What changed between the two pics? Your cables and selector look correct for DC voltage. I'm assuming you have a 52-volt class battery and system, correct? What kind of detail can you provide on your current "new" charger? I'm neither a battery or electrical system guru on these ebike systems at this point...LOL!...but are you hooking up your multimeter to the battery charge and discharge ports directly for the test, or are you hooking up through something else? Your pic appears that you are going through some kind of junction. Can you clarify?

    Comment


    • ingolf915
      ingolf915 commented
      Editing a comment
      +red on battery to +red cabel on the multimeter and the same with the black one as it should be when you measure it correctly. And when i do that i get -58 volt... And when i measure it the "wrong way" black to red it´s shows normal +58v ... It´s like plus has become minus on my battery.

      If i disconnect all other things show on the picture it shows the same fault when measured...

      Thanks for the answer! :)

    #3
    Yes, your pics are pretty clear, but it's not clear what the junction consists of or what else it might be connected to. By "junction" of course I'm talking about the block you have your leads touching for the voltage test. Have you checked just the charge port of the charger? What I'm not clear on, have you tested the battery as a stand alone component on the charge and discharge ports, and have you tested just the charger as a stand alone component in its charge port? Your pics "appear" to have a lot of wiring of components all connected, so I would be suspicious of the diagnosis. I may be missing what you've actually been able to diagnose, but unless I was able to test the battery and charger solely on their own, I would wonder.

    Comment


      #4
      In the two pics, clearly the measuring probes have been reversed and so it's no surprise that in one case it shows a + voltage and the other a - voltage. I'm not sure I understand the question but if the OP is saying the new charger has polarity reversed from the original one, he needs to either (i) open up the charger and swap where the red and black wires go OR (ii) cut the wire that goes from the charger to the battery, reverse the wires and resolder/insulate OR (iii) build an adapter that connects to the end of the charger output wire and reverses the polarity there.

      If it were me, I would do (i).

      Comment


      • ingolf915
        ingolf915 commented
        Editing a comment
        +red on battery to +red cabel on the multimeter and the same with the black one as it should be when you measure it correctly. And when i do that i get -58 volt... And when i measure it the "wrong way" black to red it´s shows normal +58v ... It´s like plus has become minus on my battery.

      #5
      The reading change from + to - when he swapped the probes as you'd expect

      But who the heck knows what's going on in that rat's nest... pictures don't help me much...

      Will say that when the meter reads - the red probe is on a contact with a black wire and vice versa

      Comment


      • ingolf915
        ingolf915 commented
        Editing a comment
        +red on battery to +red cabel on the multimeter and the same with the black one as it should be when you measure it correctly. And when i do that i get -58 volt... And when i measure it the "wrong way" black to red it´s shows normal +58v ... It´s like plus has become minus on my battery.

        If i disconnect all other things show on the picture it shows the same fault when measured... Not the best pictures but i wanted to show that i measure correctly and not that hard to see.

        Thanks for the answer! :)

      • AZguy
        AZguy commented
        Editing a comment
        Best guess is that somewhere in that rats nest in the original pictures posted the wires got swapped...

        Nowhere near enough information to help really...

      #6
      AZguy I disconnected everything and still the same... What more info do you need? :)

      Info from other forums are that it´s probably the BMS that are failing..
      Attached Files
      Last edited by ingolf915; 07-16-2021, 11:42 PM.

      Comment


      • AZguy
        AZguy commented
        Editing a comment
        How about a wiring diagram? All I saw in the picture was a mess of wires? And the initial pictures (why were they deleted?) definitely showed the red wire on the terminal strip as + and the black -. What's the history? Battery polarity doesn't just spontaneously swap

        Regardless, the more information you give the better the help you get...

      #7
      A lead acid battery can be charged backwards but I'm not sure about others or what type of battery this is. With a BMS involved I would think that would prevent that even if the battery type could allow it. I too saw that original photo and it looked like a big mess of wires so seems like a good chance something was screwed up there. Perhaps some confusing in the series parallel department?

      Comment


        #8
        ingolf, no one here is trying to give you grief on the attempted diagnosis you're seeking. Especially in the diagnosis of electrical components, as much detail as is possible is necessary. I see you've changed your pics in the first post. Why? You have to admit that your question coupled with your original pics were confusing. You had a block with connectors going between who knows what. I'm sure you know what they went to because you're looking at it in person. Also you did have the positive and negative probes of your multimeter swapped in those pics which would appear to answer some of your question.

        Now...all that aside, you indicate you disconnected all of the wiring and that block and tested directly to the charge and discharge ports of the battery and still get erroneous readings. If that's the case, then you may indeed have a BMS issue...hard to tell at this point. Maybe some of this confusion is due to translation. I see Sweden as your location. Granted, you may speak English better than most of us...and you may not be Swedish...LOL! But no one here is trying to give you a hard time. This is the internet, and it brings its own set of communication snafus that can occur.

        Comment


          #9
          Maybe I'm missing something, but to be sure I understand what's going on:
          1. On the discharge side (to the controller) everything seems fine?
          2. On the charge side where the charger attaches, the red wire from the BMS shows -ve and the black wire +ve? So when a charger is attached, its +ve would go the -ve (red) on the battery and its -ve would go the +ve (black) on the battery/BMS.
          3. So why not just swap those two wiresthat come out of the BMS and into the charger connector? (Maybe the guy who built the battery was colorblind!)

          Comment


            #10
            Check the bms monitoring wires to the cell groups. Make sure none are broken or shorted.

            Comment


              #11
              Not to kind to open the battery! I have som knowledge of other eletrics repair but zero for batterys.

              Any videos on youtube or any that could me if open it?

              Comment

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