flourescent ballast, 48" to two 24"?

Discussion in 'The Projects Forum' started by Lubby, Sep 4, 2010.

  1. Lubby

    Thread Starter New Member

    Feb 20, 2007
    I have a 'shop light' and ballast meant to run two 4' florescent tubes - either 2 x 40w T-12 (48") or 2 x 32w T-8 (48").

    I'd like to take it apart to run 2 x 24" 20w T-8 bulbs for an aquarium.

    Q - could I simply shorten the 48" to 24" and run the 20w bulbs with this ballast? Or, would it burn out the bulbs? (or burn down the house?)

    Q - if that would not work, could I instead run the lights in series; ie 2x 20w 24" giving me 40w - which would be the same as the 48" T-12, only made up with a 24" + 24" in T-8?

  2. marshallf3

    Well-Known Member

    Jul 26, 2010
    Ballasts tend to adjust to a range of different loads and what they'll drive is usually written on the ballast somewhere. Even if you can only find a part # on it you may be able to look it up.

    My guess is that since it will run all the way up to two t-12 lamps at 40W each it is set up to put out more current than you'd want to run through two 24" T-8 lamps, which if I recall are about 17W each.

    On the other hand plant growers intentionally overdrive fluorescent tubes all the time, they get a bit more light out of them at the cost of reduced tube life. You could try it, it's not going to blow up or anything.

    If the lamps come right on and stay on without acting oddly you'll probably be fine, you'll just be replacing bulbs more often.

    Hook them up exactly as they're hooked up now, if you try to put them in series it won't work and wouldn't help anyway.
  3. Dyslexicbloke

    Active Member

    Sep 4, 2010
    lights (Tubes) in series .....
    Havnt seen that in a decade or three ......
    It will work if the start flash is high enough, years ago when UV tubes for effect lighting were hard to find and all balasts were Copper/Iron we used to run 2" tubes in pares on 4" balasts. (just connected pin to pin in the center)
    Not sure what a modern electronic balast would make of this though, make sure you have adiquatly small fuses !!!! just in case.
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
    I think most all the modern tubes take a far healthier pulse to start, has to do with the large reduction of mercury in the tubes.

    We'd still have it if the so-called "ecologists" would have considered that 97% of the mercury we breathe and that gets into our water & soil on a daily basis is a natural thing that isn't going to quit even if we leave the planet - it comes from the currently active volcanos.

    Don't get me wrong, I'm not against lowering the mercury level in the tubes since they run fine with the new ballasts, it's just all the money that was spent creating the scare campaign and forcing the manufacturers to redesign perfectly functional products.