battery charger hum

Discussion in 'General Electronics Chat' started by robbie53, Oct 20, 2007.

  1. robbie53

    robbie53 Thread Starter New Member

    Joined:
    Oct 20, 2007
    Messages:
    3
    Hello everyone! I'm new to this so please bear with me. I have a battery charger connected in my RV to maintain the batteries. Problem is: If I try to use the 12v radio, I get a hum if the charger is on. Sounds like 60 cycle, but I'm not sure. There is a .22v AC component with the charger on the low (3A) setting, ~.5v AC at the 10 amp setting. Is there a way to filter this, or should I just buy one of the new "smart chargers"? I've looked at the Rectifier/Filter circuit in the Volume VI experiments. Will this work? Any help would be appreciated!
  2. GS3

    GS3 Active Member

    Joined:
    Sep 21, 2007
    Messages:
    268
    I would definitely try filtering the power supply as a first measure. A good sized choke and a couple capacitors should be a good starting point.

    In the end though it could be that some or most of the hum is coming in the antenna and that would require other measure. To test this you can power the radio momentarily from a separate battery which is not being charged and see if the noise disappears.
  3. wireaddict

    wireaddict Active Member

    Joined:
    Nov 1, 2006
    Messages:
    133
    Location:
    E. Central MI [Temp.]
    Besides an L-C AC ripple filter, make sure you have a good battery or batteries & the connections are clean & tight; the battery provides some filtering itself. One way to check the battery operation & connections is to unplug the charger with some lights on; if they immediately dim then the battery isn't doing its job, either because of poor connection or it's nearly dead & won't charge.
  4. GS3

    GS3 Active Member

    Joined:
    Sep 21, 2007
    Messages:
    268
    I think you are missing the point here which is that the battery is not being charged by DC but by a pulsating rectified AC and this causes the ripple as the battery goes from charging to discharging at twice the mains frequency.
  5. thingmaker3

    thingmaker3 Moderator Staff Member

    Joined:
    May 16, 2005
    Messages:
    5,072
    Location:
    Rural, Oregon GMT -8
    Try a filter on the radio itself. Filtering 100% of the current used by the RV is not needed (and not easy). Only the current drawn by the radio need be filtered.

    Get a pair of electrolytic capacitors and a small "step-down" transformer from a surplus electronics dealer. Cover the transformer secondary leads with wire-nuts or heat-shrink, so that they will never make electrical connection with anything. Hook each transformer primary lead to the "+" terminal of each of the capacitors. Hook the "-" leads of the capacitors to each other, and to the "-" of your 12V power cord. Hook "+" of power cord coming in to one of the "+" terminals of the capacitor. Hook "+" of power cord out to radio to the other capacitor's "+" terminal.

    This should greatly reduce the hum.

    To learn how this circuit works, run a Google search on the exact phrase: "pi filter."
  6. robbie53

    robbie53 Thread Starter New Member

    Joined:
    Oct 20, 2007
    Messages:
    3
    I checked out the antenna - same problem. Thanks for the info!
  7. robbie53

    robbie53 Thread Starter New Member

    Joined:
    Oct 20, 2007
    Messages:
    3
    Makes perfect sense to me! A friend just told me that Radio Shack sells a "Noise Filter" which is exactly what you described. Supposedly available in a 15 - 20 amp version. That should take care of my radio and amplifiers. Thanks for your help!
Similar Threads: battery charger
Forum Title Date
General Electronics Chat Emitter Follower Battery Charger Circuit Aug 13, 2014
General Electronics Chat BATTERY charger for samsung Jul 16, 2014
General Electronics Chat YES! another battery charger question, you love it! Jul 9, 2014
General Electronics Chat Solar Battery Charger Questions Jun 28, 2014
General Electronics Chat Is my new battery charger faulty? Jun 12, 2014

Share This Page