Voltage Isolation

Discussion in 'General Electronics Chat' started by Dumken, Oct 16, 2014.

  1. Dumken

    Thread Starter New Member

    Oct 7, 2014
    19
    0
    Hi. Pls How can i continue to measure the voltage of my battery as it is charging with an indicator circuit without reading the voltage coming from the charger circuit.
     
  2. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    You can not. The charger is applying current across the battery, putting energy into the battery.
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    You can momentarily disconnect the charger during the time you are making the reading, however that wont give useful information. Most battery chemistries develop a "surface charge" during charging that takes minutes to hours to dissipate. A reading made within seconds of being disconnected from the charger will be misleading...
     
  4. #12

    Expert

    Nov 30, 2010
    16,257
    6,760
    What you do is learn what the charging voltage means compared to the charge state of the battery. This is different for every size battery and every charge rate, but you can get an idea of when to stop charging by experience. With a 30 amp charger, it is already past time to stop charging a car battery (100 amp hours) at 15.5 volts because all the energy is being converted to hydrogen and oxygen at that level.

    Learn as you go. All the rest of us did.
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,093
    3,033
    I assume you don't really care so much what the voltage is, as much as what the the state of charge is? Knowing the current flow at the charging voltage is useful. You can determine the current by placing a low ohms (e.g.. 0.1Ω) shunt resistor in series with the charging current, and measure the voltage drop across the resistor. A ∆V of 1V across a 0.1Ω resistor indicates 10A of charge current. The resistor needs to be rated to at least 2X the estimated power dissipation (I^2 x R) to avoid overheating. And you need to know how the charge current relates to state of charge at the applied voltage.
     
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