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Transformer question

Discussion in 'Electrical Engineering' started by Pete Brown, Feb 20, 2005.

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  1. Pete Brown

    Pete Brown Guest

    Having trouble with house telephone - the handset batteries constantly run
    down...suspect the small powerpack transformer attached to the phone base
    that plugs into the mains that's supposed to keep battery levels topped up.
    Its a little transformer to convert 240v AC to 9.5v AC/300mA.
    A local shop tested the power pack for me but couldn't comment on the
    results.
    The shop test showed the output was about 11v not 9.5v
    So the question is, is it likely that my phone wont recharge due to this
    difference..or wouldn't that be significant?
    Thanks.
     
  2. Pete Brown

    Pete Brown Guest

     
  3. Is this a cordless model that recharges when sat on its
    base? I guess so.

    If so, and it isn't that the batteries have come to the end
    of their useful life, then it could be that the transmitter
    in the phone is constantly powered up, rather than just the
    receiver. The transmitter should typically only power up
    when needed. If the battery run time is roughly what is
    specified as the battery talk time, this could be your problem.

    Several things can cause the transmitter to stay powered up
    - including the obvious electrical fault that the, often
    discrete semiconductor, switch has failed.

    It can also be that the logic circuity in the handset has
    gone into an undefined state with the switch energised -
    leaving a battery out for a few hours should reset that.

    It can also be that the base unit logic has gone to an
    undefined state, sending requests to the handset which the
    handset has to reply to. Again, leaving it unpowered for a
    few hours can help.

    Deregistering the phone from the base(s) and then
    re-registering it may help - I have done this in the past in
    the somewhat optomistic view that it can't do harm and may
    do some good..By the time the phone and base have exchanged
    umpteen command codes doing the registration bit, I have
    usually forgotten what the original problem is..


    I have two identical DECT phones (same make/ model - one
    happens to be ivory, the other black). The black one now and
    again goes into a wierd "flat the battery in no time " mode.
    I haven't worked out why and leaving it without
    batteries for a few hours restores it normal operation.
    Annoying. The one time I did try to find out the cause, I
    opened it up but this needed removing the batteries. You
    have guess it, when I put the batteries back in, all was
    well and it ran for days, in bits on the bench. I can't
    complain, I got the black one as a "customer return" for
    1GBP, to use as a source of spares for the other - but I
    plugged it in and it seemed to work fine, so I kept it in
    service.. Together with a third phone and base, it gives me
    three phones each registered to 3 bases. I do like DECT. Not
     
  4. Roy Q.T.

    Roy Q.T. Guest

    FIRST: Check the voltage at the charging station, the two contacts where
    the phone rests to recharge and make sure you have a healthy recharge
    voltage there,

    NOTE: when you replaced the batteries you really had to leave it alone
    for a full charge cycle (maybe 24 hours) to fully recharge.

    I left mine off the base for a day (rung a few times while i was out) &
    it gave me trouble too, so, I boosted the almost dead batteries on a
    variable power suply i have, got it to a decent holding voltage again
    and et it alone until the next day...it's been working fine ever since
    ...


    Roy ~ E.E.Technician
     
  5. Pete Brown

    Pete Brown Guest

    TVM for all the useful replies...I'll act on the advice.
     
  6. Pete Brown

    Pete Brown Guest

     
  7. Guest

    One more - which was mentioned already but deserves emphasis.
    Contacts - some of these phones have spring loaded contacts in
    the base unit. It is possible for the contact to bind or otherwise
    fail to press against the handset as hard as it should, which causes
    improper charging. Dirt, a weak spring, a loose screw in the
    base unit etc are possibilities that can cause that condition.
    Good luck.
    Ed
     
  8. a

    a Guest

    whats the spec of the batteries being used ???

    V

    mA/h
    ?????

    allan
     
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