Unusually low resistance of incandescent bulb?

Discussion in 'General Electronics Chat' started by Tekk, Mar 1, 2014.

  1. Tekk

    Thread Starter Member

    Apr 18, 2009
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    Hello circuitonians,

    I bought a really cool 120v/300w light bulb from the 1910s and want to make a lamp out of it. Before plugging it in, I measured the resistance to make sure it hadn't turned into a dead short over the past 100 years (not likely, but whatever).

    The cold filament resistance turned out to be 1 ohm. This seems really low. My bulb will be drawing 120 amps, at least for a few milliseconds until it heats up and the resistance increases! Should I be worried? I live in a big building without circuit breaker access, and I don't want to knock out the power for my neighbors/floor.

    Basically, my question is: does standard 120V/20A wiring have provisions for surges in current?
     
  2. tcmtech

    Well-Known Member

    Nov 4, 2013
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    That's not an uncommon resistance value to find on a higher wattage bulb.

    Yes your 20 amp circuits will handle the 1 or 2 cycles that it takes for the bulb to heat up without a problem.
     
  3. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    It will be a quite bright lamp, or maybe you plan to put a dimmer on it?
     
  4. Tekk

    Thread Starter Member

    Apr 18, 2009
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    I was going to put a dimmer on it after I verify that the light bulb works and doesn't burn out immediately from air leaking in. :)
     
    Last edited: Mar 1, 2014
  5. crutschow

    Expert

    Mar 14, 2008
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    How will you know if there's air in the bulb before it burns out? :confused:
     
  6. Tekk

    Thread Starter Member

    Apr 18, 2009
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    I won't - that's why I'm testing it!

    Edit: Just tested. It burned out immediately. Probably should have used a variac. My eyes hurt. Thanks everyone. :p
     
  7. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    Why would you even mess with it? Did you really expect that light bulb to maintain a vacuum after 100 years? It was a collectors item and now I am sure you have reduced it's value because of the lose of the filament.
     
  8. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Sorry for your loss.
     
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Who collects light bulbs? :rolleyes:
     
  10. crutschow

    Expert

    Mar 14, 2008
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    The same type of person who collects old electronics. ;)
     
  11. inwo

    Well-Known Member

    Nov 7, 2013
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    Rats,

    I was just testing one to warn you.:(

    This 500 watt bulb is over 3 ohms.

    It must have been really large watt or most likely a low voltage bulb.

    Did it say on the bulb 120v and 300 watt? Doesn't make sense.
     
  12. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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  13. Tekk

    Thread Starter Member

    Apr 18, 2009
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    Yeah, it came in a box with a sticker that said 120v and 300w. No big deal. It wasn't worth anything anyway.

    I didn't really expect it to hold up after 100 years of sitting in storage....
     
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