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Question about current in a filter choke?

Discussion in 'Tube Audio' started by Kennyg2209, Sep 13, 2018.

  1. Kennyg2209

    Kennyg2209 Active Member

    Messages:
    147
    Location:
    Pittsburgh, Pa
    Is the current rating giving the maximum current rating for the choke? The reason I ask is. It never says maximum current rating. Plus it always says at higher current there will be less inductance and at lower current there will be more inductance. I always assumed it was the max rating, but it makes you think. If it's a 5H, 150ma choke, is it 5H drawing 150ma? Is it 8H when only drawing 50ma and 3H when drawing 200ma? Or is it more like 5H at 75ma, and less at 150ma? Who knows there chokes!

    Kennyg
     
    Last edited: Sep 13, 2018

     

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  2. primosounds

    primosounds SE KT120 w/ 6J5G drivers. Subscriber

    Messages:
    2,714
    Location:
    Terra, 21st century CE
    Some chokes will list more info than others. But, they should all give the specs in terms of DCR , current and inductance. For example 5 henries, 100 ohms dcr, 200ma. Swinging chokes would give more info 2H @ 200ma , 12H @ 50ma, 150 ohms DCR. Some chokes will list a different voltage measurement, like 5H 100 ohm, 200ma @ 12V. Some chokes will list the AC frequency like 40 to 120 CPS , or @ 400cps, If the choke only has a part number then you will have to do some research.
    Potted chokes are usually preferred for choke input power supply because potting helps to reduce the vibration that occurs for a LC PS. Chokes also have a built in safety margin but it is wise to not exceed the recommendations.
    So, the listed current rating would be the "maximum" or recommended limit.
     
    Kennyg2209 likes this.
  3. Bob

    Bob AK Subscriber Subscriber

    Messages:
    2,261
    Location:
    West coast
    don't go over the max current, run two. look at common mode chokes if hum is your holy
    grail.
     
  4. BinaryMike

    BinaryMike Pelagic EE Subscriber

    There's no need for an absolute maximum current rating because iron-core chokes generally become useless at an operating current well below the value that would cause overheating.
     
  5. trobbins

    trobbins Active Member

    Messages:
    471
    Location:
    Melb, Australia
    The inductance and DC current rating should be at the same operating condition. Hopefully the spec also states the AC voltage across the choke for that same operating condition, as that rating is just as important for appreciating the applications your choke can be used in.

    You can measure those values with a bit of diy effort:
    https://dalmura.com.au/static/Choke measurement.pdf

    Going above the rated current certainly does typically cause a droop of inductance, and an increase in internal temp from increased power dissipation. But choke failure is most likely from a short circuit downstream, rather than just going a bit above the current rating.
     
    Kennyg2209 likes this.

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