new old stock capacitors..advice please !!

Discussion in 'Help Wanted' started by pp-admin, Jun 12, 2016.

  1. pp-admin

    pp-admin Member

    iam working my way through a new old stock startomatic type electrical control box which contains wire wound and tapped resistors and canned capacitors.

    my trusty digital multimeter has checked the resisters and they are spot on against the makers rating overall and between the tapped points.

    problem is with the 2 capacitors.....

    the 2 mf reads about 0.5

    and the 200mf reads about 150.

    i have doubled checked the readings and thats what iam getting.

    clearly these readings are well below the stated figures so my question is, are they buggered and need replacing or is this about right for 50 year old new spares and they will function properly once they have some power in them.

    physically they are new looking with no blown ends or swelling. they were also in new packaging and really do look new.


    anybody any ideas ???

    thanks,

    gerry
     
  2. ArthurG

    ArthurG New Member

    Gerry,
    my capacitor knowledge is limited to the types I've been involved in making for the last thirty years, oil-impregnated paper and plastic units with foil electrodes and metallised plastic capacitors.

    If your units are oil-filled, then the news is not what you want to hear. In my experience, the oil in ancient oil-filled types has become acidic and they are of little use. None (admittedly a limited sample of magneto condensers) I've tested of that sort more than 40 years old would pass final test, insulation resistance and power factor being well outside of acceptable limits.

    If you could put up some pics to identify them it would help.
     
  3. picklesquirt

    picklesquirt Member

    Gerry,

    Some pictures would help, the 200mfd is probably an electrolytic capacitor unless it is quite physically large. Electrolytic caps rely on an oxide layer forming the dielectric and will be marked with the polarity on the terminals i.e + or positive and - or negative. This may well recover it's full capacitance when it is re-energised. Electrolytic caps usually have a large tolerance in value typically +50% to -20%. Try it and if you can raise the Volts on it slowly so much the better.

    The 2mfd does not look so good, it is probably metalised paper or metalised plastic film and would not have a polarity marked on it. Are they in tubular aluminium cases?
    It may be electrically leaky and therefore give a duff capacitance reading, does it show any Ohms if you try it with your meter -- should be infinity on the highest range after a few seconds.
    Both types are easily replaceable via Google , make sure you get the same or higher working voltage.

    Cheers

    Ewan
     

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