Voltage down

Discussion in 'The Projects Forum' started by Lightfire, Apr 15, 2011.

  1. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010

    My materials specifications.

    12V/12AH Lead-Acid Battery
    12V/5W Compact Fluorescent Lamp, YES it is. :)

    I have calculate how many hours can the lead acid battery run the cfl. it's about 28. due to some safety reasons, let's move it to 10 hours. :D

    My question is. OK, I runned the lamp 10 hours. can the battery voltage still the same from the first to the last (after 10 hours) or there will be a voltage down/drop?

    Thanks. :)
  2. JDT

    Well-Known Member

    Feb 12, 2009
    The 12V 5W Fluorescent lamp will also lose some power in its inverter. So let's say it takes 6W from the 12V battery. That's 0.5A. Theoretically, that will run for 24 hours from a 12A/H battery.

    The battery voltage will drop during this time. Fully charged will be over 13V. For most of the discharge the voltage will be around 12.6V. When the battery gets nearly fully discharged the voltage will start to drop fast. The A/H rate is specified to a "fully discharged" voltage. You will probably have to look at the battery spec to find out what this is. But might be as low as 10V.

    Also the A/H capacity of the battery will reduce with age (number of discharge/charge cycles) and how well it's looked after. Example: if the battery is left in a discharged state for any length of time.
  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    First, battery chemistry is the primary determinant of the output voltage of a battery. That potential changes as a battery is discharged. Call that the discharge curve. Different battery chemistries and configurations show different discharge curves.

    This is a review of batteries:

    Here is another good review with discharge curves:

    Finally this reviews the effects of concentration (e.g., discharge) on battery voltage. Look about half way down the page to the Nernst equation. I know it is complex, but knowing it exists may help you understand why the electrochemical potential of a battery changes with discharge.