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Cordless Phone Charger

Discussion in 'Electronic Repair' started by Larry B, Feb 10, 2004.

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  1. Larry B

    Larry B Guest

    I have a Panasonic cordless phone and the 3.6vdc Ni-Cad batteries fail
    pretty quickly. I measured the voltage to the charging contacts and it is 11
    VDC. Seems like a quick-charging, short battery life scenario. Please
    confirm.

    I put a potentiometer on the + side of the charging leads and found that it
    took 10M ohms to get it to drop to 6vdc. With the battery rated at 850mAh,
    is it reasonable to put in a dropping resistor?? If so, what kind of
    resistor can I use to drop the voltage without turning the phone into either
    an expensive space heater or even a plastic-melting fire danger?? Is there
    another way to do this??

    Thanks!! LarryB
     
  2. gothika

    gothika Guest

    This is a bit crude and probably not the most scientific way to
    correct overcharging cell phone batts.
    I use a wall wart rated at 3.6 volts with a charge rate of from 50-100
    milliamps.
    I rigged the handset with a dc coaxial jack and jusr plug the wall
    wart into the handset whenever the battery runs down.
    I've noticed my batteries last much longer than when I used the base.
    I have one cordless that uses nicads and they require alot more care
    when charging, hence the wall wart.
    I also have a cordless that uses lead acid rechargables.
    It tends to be much more durable and memory free as well.
     
  3. Jerry G.

    Jerry G. Guest

    The opened end voltage from the phone charger will be in the 10 to 12 volt
    range. It is current limited to be proper for your battery. The problem is
    that your battery is no longer able to hold the charge. Get a new battery,
    and it will charge properly. The life span of these batteries is about 2
    years under ideal conditions in these cordless phones.

    --

    Greetings,

    Jerry Greenberg GLG Technologies GLG
    =========================================
    WebPage http://www.zoom-one.com
    Electronics http://www.zoom-one.com/electron.htm
    =========================================


    I have a Panasonic cordless phone and the 3.6vdc Ni-Cad batteries fail
    pretty quickly. I measured the voltage to the charging contacts and it is 11
    VDC. Seems like a quick-charging, short battery life scenario. Please
    confirm.

    I put a potentiometer on the + side of the charging leads and found that it
    took 10M ohms to get it to drop to 6vdc. With the battery rated at 850mAh,
    is it reasonable to put in a dropping resistor?? If so, what kind of
    resistor can I use to drop the voltage without turning the phone into either
    an expensive space heater or even a plastic-melting fire danger?? Is there
    another way to do this??

    Thanks!! LarryB
     
  4. JM

    JM Guest

    quoting:

    I've got a Uniden phone that ate batteries in 6 months. I replaced the Nicad
    with a NiMh version, still going strong 3 years later.

    This works because cordless phone chargers are often slow dumb type. NiCad
    "shake and bake" overcharge on these chargers, kills them fast. NiMh does
    not overcharge when charged constantly at a slow rate.
     
  5. Larry B

    Larry B Guest

    Thanks everyone. My next one will be NiMH but I already have a new NiCad.
    The first one lasted about 6 months. I just put in a resistor that dropped
    the charging voltage (under load) to 7.7vdc. We'll see what happens.

    Larry
     
  6. Larry B

    Larry B Guest

    Well, the resistor messed with the charging circuit so we'll just have to
    burn out another battery and go for the NiMH next time.

    Larry
     
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