Connect with us

Battery Voltage Drop

Discussion in 'Power Electronics' started by Sadlercomfort, Aug 4, 2014.

Scroll to continue with content
  1. Sadlercomfort

    Sadlercomfort Ash

    424
    55
    Feb 9, 2013
    Hi Guys,

    I have a battery which is supposed to show 6v on the output when charged, but is only showing 4v. I noticed that the charging voltage should be 7.2v-7.5v however the adapter which is being used has 6v output.

    So just to verify, If i use a 7v adapter to charge my battery will my battery show the correct output of 6v?

    Here's a link which shows the battery I have. It's an Aroma 6v 4AH Rechargeable VRLA 3-FM-4 (Lead Acid Battery).

    http://www.kidsatplayextra.co.uk/kidsplay-6v-4ah-replacement-battery-a-151-p.asp
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,489
    2,830
    Jan 21, 2010
    It sounds like your battery has dropped a cell. It has (had) 3 cells, each nominally 2V. A 6V lead acid battery reading 4V is either very very badly discharged, or only has 2 working cells.

    You might find that there is some swelling around maybe 1/3 of the battery.
     
  3. cjdelphi

    cjdelphi

    1,096
    104
    Oct 26, 2011
    That or the charger has failed...
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,489
    2,830
    Jan 21, 2010
    Yes, that would be "very badly discharged". And at that level, likely undergoing a largely non-recoverable sulphation process.
     
  5. Sadlercomfort

    Sadlercomfort Ash

    424
    55
    Feb 9, 2013
    I see three cells none with any signs of bulging, how do I rule out the possibility of sulphation. Will a full charge cycle then a test again of the output voltage work?

    It would good to learn how to test these batteries properly with guidance.
     
  6. Arouse1973

    Arouse1973 Adam

    5,165
    1,087
    Dec 18, 2013
    Hi Sadlercomfort

    Sulphation always happens in lead acid batteries but is normally reversed by fully charging. So if you have not charged the battery for a while or it never gets a full charge between uses then it's sulphated for sure. Whether it can come back depends on how long it's been stored in that state. If it's reading 4 volts with just a DMM connected, then this could be bad news. Fully charge the battery and then connect a smallish load say 100R across the battery and see if the voltage holds at all. If the reading drops quickly I would say if was naff.

    A 6 Volt battery should read higher than 6 Volts when fully charged a good indication of near fully charged battery is 2.1 Volt per cell off load.

    Adam
     
  7. Sadlercomfort

    Sadlercomfort Ash

    424
    55
    Feb 9, 2013
    Hey Guys,

    I gave the battery a full charge cycle, including the appropriate extra time for efficiency losses. I now have a steady 6.2v.

    Thanks guys!
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-