120V/240V Switchable HID Light Ballast

Discussion in 'General Electronics Chat' started by mossman, Sep 3, 2010.

  1. mossman

    Thread Starter Member

    Aug 26, 2010
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    Can someone explain how a switchable 120V/240V light ballast works? I know increasing the voltage to 240V decreases the required current by half, but how is it doing this? i.e., does switching the ballast from 120V to 240V change the resistance of the lamp so the wattage remains the same?
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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  3. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    A simple switchable ballast just puts inductor windings in series or parallel to allow changing the input voltager.

    An electronic high frequency switching ballast is just looking for the expected current and adjusts to the situation.
     
  4. mossman

    Thread Starter Member

    Aug 26, 2010
    131
    3
    So adding additional windings increases the reactance of the circuit thereby decreasing the current flow and maintaining the same power delivered to the load?
     
  5. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    Sounds like you've got it.
     
  6. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Actually, if they're built like the universal ones sold to be used with fluorescent fixtures, they simply vary the pulse width going into the driving portion of the ballast section such that the lamp current is limited to the proper amount.

    Most would argue, but when you really boil it down an HID lamp operates much in the same way an instant start fluorescent does, it just takes them longer to reach operating temperature thus the ideal current consumption.

    The word "ballast" is not going to be on my favorite list of words for a while, we're starting to convert about 24,000 square feet of the building over to a different usage and it appears I've got about 20 or so ballasts to replace in some of the fluorescent strips. At least most of these are only 10' in the air and some time back I bought a really nice scissor lift with a big platform on it.
     
  7. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    Working over my head is not my favorite thing to do. I would be doing one a day and have them done in 4 weeks assuming, that wasn't the only thing that I had on my schedule and a month was soon enough to have it finished.
     
  8. marshallf3

    Well-Known Member

    Jul 26, 2010
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    When we first moved into our new (to us) facilities it was in a terrible state of disrepair. The building had been vacant for about 6 - 7 years and copper thieves made a mess out of some of the main wiring I had to correct. THe previous tenants must not have given a darn about the condition either because I think I had to replace about 65 ballasts in one warehouse area alone. Only got bit a few times but that 277V (one leg of 480V 3 phase) can really pack a wallop no matter how insulated you are from ground, it's as if it can conduct merely through the humidity in the air.

    The existing older ones keep failing from time to time and I've got replacing them down to a fine science. Of course keeping these around helps:
    http://www.smarthome.com/7877P/4-Conductor-Wall-Nuts-100-Pack-Wire-Connectors/p.aspx
     
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