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  1. #1
    6146-B Billy T's Avatar
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    Question So.....Is a watt always a watt?

    I was idly looking at the electronic ballast from a modern fluorescent fitting (when I should have been working) and noticed that the RoT figures for watts in vs watts out were very close together. That caught my attention, and a couple of quick calculations later I came up with 110.4 watts of electricity in, for 108 watts of light out (3 x 36 watts tubes) and that yielded an apparent conversion efficiency of 97.8%.

    I thought that looked too good to be true, and power factor came to mind as an unknown, then I saw in the fine print that the claimed power factor was better than 0.95.

    If this is correct, then the whole fitting should dissipate just 2.2 watts in heat from conversion losses. That didn't compute, so I decided that the heat losses from the tubes would probably be lumped into the tube rating, which left the 2.2 watts to the electronic ballast.

    Point is, the ballast gets a darn sight hotter than a mere 2.2 watts could ever manage, reaching over 70C on the top of the casing.

    So, what am I missing here, or is the manufacturer indulging in porkies?

    Cheers

    Billy 8-{)

    RoT = Rule of thumb
    Some days it's not even worth chewing through my restraints!

  2. #2
    Senior Member godfather's Avatar
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    Default Re: So.....Is a watt always a watt?

    But - how did you measure the "36 Watts light output" of each tube?

    It might be true only for those days when high tide and a solar eclipse coincide, during an odd numbered day of an even numbered month.

    For all other times they might be 32 Watts...

  3. #3
    cablewinderuperer personthingy's Avatar
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    Talking Re: So.....Is a watt always a watt?

    Perhaps its a "watt" just like them little miniature 20watt flouros that plug into a bayonet socket to replace a filament light bulb and claim to give 75watts of light?

  4. #4
    6146-B Billy T's Avatar
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    Default Re: So.....Is a watt always a watt?

    Quote Originally Posted by godfather
    But - how did you measure the "36 Watts light output" of each tube?...
    I stood with my left foot in a bucket of de-ionised water, placed my right foot behind my left shoulder, then while holding a paper bag of assorted watts in my teeth, I measured them individually with a calibrated stick of Standard Euro-Inches.

    I then compared the results of my measurements with the label on the box the lamps came in, and was not at all surprised to find that in each case the answer was exactly 36 watts.

    I did have a packet of lumens handy in case I needed them but the watts came through to the finish so strongly that they didn't even feature in the also-rans.

    So, I am left with the same unanswered question, and assuming that when a lamp manufacturer applies a rating of 36 watts to an electrical product, I cannot easily escape the simplistic view that they actually meant the product of volts x amps.

    Cheers

    Billy 8-{)
    Some days it's not even worth chewing through my restraints!

  5. #5

    Default Re: So.....Is a watt always a watt?

    Jeepers, what a dilema.

    BT < CB
    According to the forum's "superior and wiser" members, it is a common courtesy to do your post signage in the actual post rather than in the signature box.

    So being the polite person that I am, I have decided to do the same.

  6. #6
    Senior Member godfather's Avatar
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    Default Re: So.....Is a watt always a watt?

    The accepted standard wattage (ballast included) for a single 36 watt fluorescent tube is 47 Watts, or 51 VA. That is with a PF of 0.92.

    Unfortunately the register I have does not consider dual fluorescent 36 Watt lamps.

    Its a scientifically and technically measured value and is used as the basis for "unmetered supplies" and their assumed usage, for the Balancing and Settling Code in the UK.

    But that just makes your "dilemma" worse.

    Perhaps you have indeed stumbled across an "over-unity" device where the sum of the electrical input power is less than the sum of the output power.

    If so, expect to either be an instant millionaire or to mysteriously go missing.

  7. #7
    6146-B Billy T's Avatar
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    Default Re: So.....Is a watt always a watt?

    Quote Originally Posted by godfather
    The accepted standard wattage (ballast included) for a single 36 watt fluorescent tube is 47 Watts, or 51 VA. That is with a PF of 0.92.
    That would be the lossy, steam-driven and reliable inductive ballast though, not the modern sophisticated and highly strung smoke-releasing electronic variety I suppose.

    Perhaps you have indeed stumbled across an "over-unity" device where the sum of the electrical input power is less than the sum of the output power. If so, expect to either be an instant millionaire or to mysteriously go missing.
    Hmm.... Rudolf Diesel comes to mind, and look how long it took to get his name back on the front page. It needed Audi and their all-singing all-dancing 12 cylinder diesel behemoths to restore credibility to his good name, long associated with more foul smelling smoke than than a darts club meeting on a free cigars and baked-bean specials night at their local pub.

    I fancy the millionaire bit, but with my luck the man in front of me in the queue at the patent office would have a working model of a quantum mechanics energy generator that makes all energy sources run backwards leaving trails of free energy behind them wherever they go.

    Cheers

    Billy 8-{)
    Some days it's not even worth chewing through my restraints!

  8. #8
    Senior Member roddy_boy's Avatar
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    Default Re: So.....Is a watt always a watt?

    Is a watt a what now?

  9. #9
    6146-B Billy T's Avatar
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    Default Re: So.....Is a watt always a watt?

    Quote Originally Posted by roddy_boy
    Is a watt a what now?
    Sorry RB, amidst all this confusion, I simply don't know what's watt.

    Cheers

    Billy 8-{)

    (This was originally a serious question, and I am still looking for an answer, but don't watch this space.)
    Some days it's not even worth chewing through my restraints!

  10. #10
    Frank and Earnest. Cicero's Avatar
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    Default Re: So.....Is a watt always a watt?

    Quote Originally Posted by Billy T
    Sorry RB, amidst all this confusion, I simply don't know what's watt.

    Cheers

    Billy 8-{)

    (This was originally a serious question, and I am still looking for an answer, but don't watch this space.)
    Sad to see you confused B.

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