Inverter and Battery

Discussion in 'General Electronics Chat' started by Khurram Moon, Mar 11, 2013.

  1. Khurram Moon

    Thread Starter New Member

    Dec 22, 2012
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    Hello,
    I have a question that when a tester is connected to the negative terminal of a 200AH battery, when inverter is also attached with battery then the tester light should glow? as i have tested it and it does. However, everyone knows that this is not the case in AC but is it different in DC? I also connected multi-meter's negative probe with the negative terminal of inverter+battery and positive probe of meter with the ground and the voltage reading was 85V. Does DC behaves this way? This should be case when checking the positive terminal not negative.
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    What tester? What inverter?
    What input/output voltage/configuration?
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Are you using an incandescent light, or a Digital Multi-Meter (DMM)?

    An Incandescent probe light (alligator clip on one end, very pointy spike tip on other) will light at 12V DC or AC. If you try to use it on high voltage (>20V) AC, that's a safety risk, and the bulb will blow immediately.

    A DMM is safe to use on AC or DC as long as it is at least CAT II (minimum)/CAT III/CAT IV ("best") rated (should say near the jacks).

    The battery indicator light (bulb/clip/spike for going through insulation) SHOULD light up while an inverter is running from it, if it doesn't the bulb is burned out or there isn't a good connection. If the battery voltage was Zero Volts (no light), the inverter couldn't run. The voltage WILL lower with the inverter on when measured with a DMM, but not below 11.5V or so, depending on inverter load.
     
  4. timescope

    Member

    Dec 14, 2011
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    I think the OP used a neon lamp tester screwdriver and found that the battery has an abnormal voltage present.
    I got an unexpected unpleasant electric shock from the case of a 12v modified sine wave inverter several years ago when one of the H bridge output transistor insulators broke down and allowed high voltage to be present on the case / heatsink which was not grounded.

    Timescope
     
  5. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Some systems also use a cabinet which is connected to the midpoint of a battery bank. The bank supplies +200V and -200V to the UPS. If touching the + or - pole and the cabinet you would get a very unpleasant shock too.
     
  6. Khurram Moon

    Thread Starter New Member

    Dec 22, 2012
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    An electrician who also makes and sells UPS told me that ur inverter is giving ground to the battery, i do not believe him however, i checked it my self and need your input on this. I used screw driver tester, which he also used, and when i connected it to negative terminal of the inverter+battery, it glows as bright as it does when connecting it with positive terminal of inverter+battery. (Dial used on DMM was 200V DC)
    Then i connected the negative probe of multi-meter with negative terminal of inverter, when it was charging the battery, and positive terminal of DMM with iron bracket on the wall nearby and it showed 81.6V. Then i connected negative probe of DMM with positive terminal of inverter and connected it with iron bracket on wall and it showed 70.6V. Now the thing is that there should be more volts going into positive terminal instead of negative. As far as the screw driver thing is concerned, it glows bright on both terminal when inverter is either charging the battery, discharging it or even after the termination of charging. however, when inverter is tuned off and input is removed from wall power plug then tester never glows.
    NOTE= (As we all normally check the reading on both terminals of inverter+battery and it was 13.7 V, when it was charging. DMM is 99% accurate). In fact used another DMM as well.
    Need your inputs, Many thanks.
     
    Last edited: Mar 15, 2013
  7. timescope

    Member

    Dec 14, 2011
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    Disconnect the wall power plug and run the inverter. Check the battery terminals with the tester and post the result.

    Timescope
     
  8. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    What is the inverter model number?

    A block diagram or user and/or installation manual also helps.

    There are hundreds of different models on the market, they do not all work the same way.
     
  9. Khurram Moon

    Thread Starter New Member

    Dec 22, 2012
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    Thanks for the reply. After removing the input of inverter from the wall power plug, tester did not glow at all on either of the terminals. Inverter was running with battery while the input of inverter was pulled out from the wall power plug and checked with DMM using the same method as stated in the previous post and no readings at all, meaning 1 to 0 V. Is that electrician right or not?
     
    Last edited: Mar 13, 2013
  10. Khurram Moon

    Thread Starter New Member

    Dec 22, 2012
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    Thanks for the reply.
    Cyberpower Inverter
    CPS 1200EILCD

    The issue is that i have lead acid battery and i got it checked and battery guys says battery is fine. I used the inverter and battery for almost 8 months and every thing was fine but now inverter tends to keep on charging the battery for long time. some times terminates the charging after reasonable time but some times i goes on charging for 4 to 6 hours.
     
  11. timescope

    Member

    Dec 14, 2011
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    This would indicate that the battery charger is defective and is causing mains voltage to be present on the low voltage circuits. This can be caused by a failed component or breakdown of the transistor insulators if it is a switched mode supply.

    Dangerous voltages are present in the inverter and battery charger so you should get it repaired by a qualified technician if you are not familiar with these circuits.

    Timescope
     
  12. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    The battery terminals are supposed to be safe to touch in my opinion, at least I don`t see any warning in the manual. That means if you measure live voltage from battery to earth there is indeed something wrong.
    If you don`t have the experience to service this UPS then I recommend the same as Timescope. There is not much we can advise you to do.

    I would probably put a 220V/40W light bulb or some other light load from to battery terminal to earth, check if the voltage is sustained and measure the current, then open the device and try to find out where it comes from.
     
  13. Khurram Moon

    Thread Starter New Member

    Dec 22, 2012
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    Thankyou so much for your replies.
    Oh yes i will get it repaired from service center but first the main task will be to convince those deceptive guys that there is indeed a real problem in the inverter, so that they do not deceive me that its fine, as they usually do when people visit there for claiming warranties of electronic products.

    I wanted to ask another question that inverter+battery's negative probe was when grounded to iron wall bracket through DMM, then it showed approx 11 V more than the positive terminal of inverter. Lets suppose, if inverter was fine then positive terminal when grounded with earth through DMM should have shown slightly more volts or equal to negative terminal rather than negative side showing up more volts. Am i right?

    secondly, when i tested both terminals of DMM with both terminals of inverter+battery then why it shows 13.7V why not more? like it does when i ground one terminal through DMM, there it shows 70+V.

    I do not know how much damage this huge voltage might have caused to my 200 AH battery?
     
    Last edited: Mar 13, 2013
  14. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Your battery only cares about voltage applied to it's terminals (and the resulting current). It does not care about voltage from one of its terminals to ground or any other point in your circuit.

    If you have a sustained voltage (I mean it can supply current) from a point you can touch outside you inverter to earth ground then you have a problem. It could damage your inverter but most importantly someone could get hurt.
     
  15. Khurram Moon

    Thread Starter New Member

    Dec 22, 2012
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    I just wanted to ask another thing that i do not have ground wiring at home(we do not have three wires, only neutral and phase) is that the reason voltages are showing on battery terminals when i use DMM with earth?
     
  16. timescope

    Member

    Dec 14, 2011
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    Have you performed the test with the 40W bulb and what is the result ?
    This test will determine the magnitude of the leakage current.
    A simple method to measure leakage current is to connect a 1.5k 10watt resistor in parallel with a 0.15 uF capacitor between the case of the equipment and ground and measure the ac voltage across the resistor. The voltage should be less than 0.74v rms which corresponds to 0.5 mA leakage current.

    This would suggest that your house has not been wired properly and may not have adequate wire sizes, over current protection etc.

    An earthing system prevents electric shock by conducting any leakage current from the chassis of the equipment to earth. If the leakage current is large, a fuse or circuit breaker should open to protect the wiring from over heating or causing a fire.

    I suggested that you get the equipment checked to determine whether the leakage current is normal or caused by a fault but you have not posted the result.

    Most switched mode power supplies have some leakage current but it is usually low enough to be safe.

    Timescope
     
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  17. praondevou

    AAC Fanatic!

    Jul 9, 2011
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