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Old 09-14-2003, 09:33 PM   #1
Mean_Chlorine
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I read the article on how to overdrive normal output fluorescents ( http://www.plantedtank.net/odno.html ) but I still don't quite get it.

Would it work if I hooked 2x18W T8 fluorescents up to a 2x36W electronic ballast, or do I need a 4x36W ballast (as in the example in the article)?

If it works, would I be overdriving the 18W fluorescents by 2x or 4x?
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Old 09-14-2003, 09:54 PM   #2
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The amount of wattage a bulb runs at is determined by the ballast. So a 2x36 ballast would be trying to drive each bulb at 36 watts instead of 18. So in a sense you would already be overdriving them.

The article, if I remember correctly, describes wiring the outputs together to overdrive a singe bulb. So, for example on your 2x36 the 2 outputs would be wired together to make 72 watts going to a single bulb.

The reason they recommend a 4 output ballast is so that you can drive 2 bulbs even with the ballast leads wired together.

Having said all of this however, keep this in mind. Wiring your two leads together to over drive one light at 72 watts is no substitute for driving 2 lights at 36 watts each. A tube can only output so much light before it just physically can't create any more light. You reach a point of diminishing returns.
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Old 09-14-2003, 10:11 PM   #3
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Hmmm....

So, what ballast would I need to get 2x the effect on my two serially connected 18W tubes?

4x18W, 2x36W, or 4x36W?
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Old 09-14-2003, 10:47 PM   #4
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There really isn't a 2x18w or 4x36w ballast. What you'll generally find at Home Depot is a 4-F32T8 ballast that is a load-sensing electronic ballast to run 4 bulbs. If you hook up a F15T8, F32T8 or even a F40T12, the ballast will sense the load and deliver the "proper" wattage to each ballast ouput.
So if you hook up a 18 watt fluorescent to this ballast with only one ouput, you won't be overdriving it to 32 watts (which is the maximum ouput each lead can deliver). I had this same misconception until I measured current draw in various configurations and determined the ballast was load-sensing.
Anyway, the setup I'd use for your two 18watt tubes in series is to run two outputs to them (2x ODNO coaxes about 1 1/2 times more bulb output, 4x ODNO coaxes about 2 times bulb output - illustrating what DLeDeaux meant by diminishing returns). So your two 18w tubes would deliver 54 watts instead of just 36w.

This is the wiring configuration you'd use (except use 18w tubes instead of F20T12's):

This diagram also shows all four ballast outputs being used (4x ODNO four approx double the bulbs normal rated lumens output). Try using only two of the outputs first. If you're not satisfied with the output, you could hook up the other two outputs, but add a fan since the bulbs will get pretty hot and won't last as long.
Even better would be to run two pairs of 18 watt bulbs in series, each being run 2x ODNO, for the most efficient output. Four 18 watt bulbs x 1.5x output = 108watts! *Tim Allen hua hua grunt*
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