Do battery voltages spike near end of life?

Discussion in 'Location Recording' started by mdb, Feb 22, 2011.

  1. mdb

    mdb Active Member

    During a production, a wireless mic required "0" input gain at the console preamp and still had plenty of signal in the level meter (acting like a line-level input requiring -20dB PAD). Very odd. Then, the batteries died. Once they were changed out of the transmitter, the gain staging went back to normal and (as it should) the mic required input gain on the console to get good levels. We use Pro Cell batteries. Is this a normal characteristic of these batteries when hitting end-of-life? If so, what really causes this? :confused:
     
  2. Boswell

    Boswell Moderator Distinguished Member

    The batteries themselves cannot do this. The discharge voltage curve is monotonic.

    I have seen odd things happen to the voltage at the plug-in power pin of the mic connector on a transmitter pack. What make and model is your radio mic?
     
  3. mdb

    mdb Active Member

    It is a Countryman mic using a Shure transmitter/ receiver (I'd have to get the specific model, but it's not a cheap Shure wireless system). Another tech was actually running the sound and called me over. He had decent gain on the meter and the trim pot completely turned off. Then the batteries in the transmitter died about 2 minutes later. Once the batteries were changed the board went back to normal. I didn't have a answer for it and I don't know if it has ever happened before - at least not on my watch.
     
  4. Boswell

    Boswell Moderator Distinguished Member

    No, I've not seen that exact behaviour. I have had loud distorted sound from a Shure transmitter unit shortly before its batteries gave out, but it was very obvious from the distortion that the batteries were on their way out.
     
  5. mdb

    mdb Active Member

    I had that same thing from a bass guitar. As soon as it was plugged into the amp there was RF noise. Dead battery.
    Don't know what to say about the gain increase that occurred. I'm perplexed.
     

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