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  1. #1
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    Battery Internat Resistance Without OCV

    Hello,

    I am working on a project that will meausre internal resistance of a lead acid battery. I know DC Load Test but my problem starts with Open Circuit Voltage(OCV). My batteries always connected to power source and i cannot switch my batteries and power source.

    MY CONNECTION :

    (-)-----POWER SOURCE--------(+)
    (-)-----LOAD (REAL)-----------(+)
    (-)-----BATTERY FOR BACKUP--(+)


    I can measure instant current and instant voltage and i can switch power source but as i sad before i cannot meausure OCV.

    Thanks for help

  2. #2
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    Re: Battery Internat Resistance Without OCV

    Then just measure the battery voltage directly at the terminals for two different currents.
    The battery internal resistance is then just the voltage difference divided by the current difference.
    Zapper
    Curmudgeon Elektroniker


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  3. #3
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    Re: Battery Internat Resistance Without OCV

    Quote Originally Posted by crutschow View Post
    Then just measure the battery voltage directly at the terminals for two different currents.
    The battery internal resistance is then just the voltage difference divided by the current difference.
    Thanks for your interest.
    I think i could not explain my problem clear. I have any test load and i can not change current. CUrrent change up to real load performance.

    http://47.88.160.31/product.php?id=56

    Here is a product that can do what i want.



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    Re: Battery Internat Resistance Without OCV

    I think what it is doing is measuring voltage directly across the battery and using a Hall sensor to monitor the current to one or more batteries in a chain (the current will be the same in them all as they are in series). That allows power to charge the battery to be measured and power drawn from the battery to be measured but I can't see how it can measure internal resistance unless there is a change in current. The web page shows the batteries disconnected by a switch so that would prevent any current reading anyway.

    As I see it, the batteries must be discharging before internal resistance can be measured that way and the calculation would have to be made by adding time to the equation, in other words monitoring voltage drop per second based on the current being drawn. I would think that measures battery capacity more than internal resistance though.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



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    Re: Battery Internat Resistance Without OCV

    Hi,

    I donīt understand.
    If you have a test load, then why is it not possible to change current? Simply connecting/disconnecting the load to the battery will change the battery current.

    Klaus



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    Re: Battery Internat Resistance Without OCV

    Quote Originally Posted by betwixt View Post
    I think what it is doing is measuring voltage directly across the battery and using a Hall sensor to monitor the current to one or more batteries in a chain (the current will be the same in them all as they are in series). That allows power to charge the battery to be measured and power drawn from the battery to be measured but I can't see how it can measure internal resistance unless there is a change in current. The web page shows the batteries disconnected by a switch so that would prevent any current reading anyway.

    As I see it, the batteries must be discharging before internal resistance can be measured that way and the calculation would have to be made by adding time to the equation, in other words monitoring voltage drop per second based on the current being drawn. I would think that measures battery capacity more than internal resistance though.

    Brian.
    Thanks. That makes clear something for me. If I know relation between battery internal resistance and capacity, I can calculate internal resistance.

    I can integrate battery model in my system and increase my system accurate.



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    Re: Battery Internat Resistance Without OCV

    [QUOTE=yagizhanugur;1559902............. If I know relation between battery internal resistance and capacity, I can calculate internal resistance. .....[/QUOTE]There is no direct relation between battery internal resistance and capacity.
    Zapper
    Curmudgeon Elektroniker



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    Re: Battery Internat Resistance Without OCV

    Quote Originally Posted by KlausST View Post
    Hi,

    I donīt understand.
    If you have a test load, then why is it not possible to change current? Simply connecting/disconnecting the load to the battery will change the battery current.

    Klaus
    I sad i do not have test load, so i cannot change the current.
    Quote Originally Posted by crutschow View Post
    There is no direct relation between battery internal resistance and capacity.
    Have any idea what can i do ?

    - - - Updated - - -

    I have solved problem with Kelvin (4-wire) Resistance Measurement Circuit.
    Kelvin (4-wire) Resistance Measurement
    http://www.allaboutcircuits.com/text...e-measurement/
    Thank you.



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    Re: Battery Internat Resistance Without OCV

    Hi,

    test load:

    then there must be a typo in your post#3:
    I have any test load
    ***
    So where exactely is the problem:
    * You really donīt have a test load? --> every resistor, or a small transistor circuit is suitable
    * Or you donīt want or can not connect a load? --> Could you explain why?

    ***
    Alternatively it is possible to "monitor" the load current and wait for the load current to change. Measure different currents with the appropriate voltages. Calculate resistance.

    Klaus



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    Re: Battery Internat Resistance Without OCV

    Quote Originally Posted by KlausST View Post
    Hi,

    test load:

    then there must be a typo in your post#3:

    ***
    So where exactely is the problem:
    * You really donīt have a test load? --> every resistor, or a small transistor circuit is suitable
    * Or you donīt want or can not connect a load? --> Could you explain why?

    ***
    Alternatively it is possible to "monitor" the load current and wait for the load current to change. Measure different currents with the appropriate voltages. Calculate resistance.

    Klaus
    My system working about 120-140A. If i connect 1-2 A test load, it's affetct will be too small. If i connect smaller loads for high amps their size are too big and prices are expensive.

    Secondly,

    You are right about monitoring voltage and current but if i use that method i will probably make mistake because of the battery chemical issues. Sometimes battery voltage drop or increase due to the crystallization of battery.



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    Re: Battery Internat Resistance Without OCV

    There is ohmic resistance, which is present in the battery whether charged or discharged. It is probably outweighed by ohmic resistance in wiring and connectors.
    And there is a figure associated with the formula V/A and which has to do with the maximum current available from the battery's chemistry, at any given moment.

    Do you wish to examine Peukert effect? The greater Amperes you draw, the greater power is wasted by parasitic resistance.

    It would be interesting to know both types of resistance values, however I'm not sure there is an easy way to measure them. In my mind it requires putting a severe load on the battery. That is something to avoid.

    My system working about 120-140A.
    Suppose you draw 100A, and voltage is 12V. Then total effective resistance is .12 ohm.
    Or suppose voltage is 9V. Total resistance .09 ohm. Not much difference in ohm values, is there? The more interesting figures are V & A. They are also easier to measure.



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