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ologist

shortening 48' fluorescent to 24' and overdriving

ologist
17 years ago

i've been searching the forums to get an idea of how to shorten a 48" fluorescent fixture to 24" and how to overdrive it, but i couldn't find an exact description of what i wanted to do. i was hoping someone could help.

i would like to get a 48" 4 lamp fixture and shorten it to 24". this seems like if i just cut out 24" of the reflector and used the existing ends with 4 24" bulbs it would work without a problem because the ballast would "know" what kind of lamp is in it. please correct if i am wrong here.

next, i would like to overdrive the 4 lamps by getting another 4 lamp ballast so that with the first ballast i could overdrive 2 lamps, and with the second ballast i could overdrive the remaining 2. the venerable zink had posted that this was possible by wiring 2 of the lamps end to end in series. however, being that i'm not exactly sure on how to do this i was hoping someone could help with some detailed instruction.

what i thought might be correct was to wire the ballast ends of the 2 lamps together and then connect the ballast end of one lamp to the ballast. then to wire the other ends to each other, and wire one of those to the "yellow wire" or the non ballast connection.

but....

that sounded like parallel to me.

is the correct configuration this:? wire the ballast end of lamp1 to the ballast, then the non-ballast end of lamp1 to the ballast end of lamp2, then the non-ballast end of lamp2 to the the non-ballast end of the ballast?

sorry if this is confusing, but i'm confused myself. any help is much appreciated. and a diagram would be awesome :)

Comments (12)

  • shrubs_n_bulbs
    17 years ago

    Your ballast designed for a 48" tube may or may not drive a 24" tube, but it is simple enough to connect two 24" tubes together to mimic a 48" tube. Just connect the two pins from the end of one tube to the two pins at the end of the other, and then wire the pins at the remaining free ends as if it was a single tube (bent in half). You might wish to move the ballast towards the end that now has all the free pins, since they work best with short wire runs.

    Then your ballast will only "see" two 48" tubes and you can overdrive those with your existing 4-lamp ballast. You will have all the end caps and tube holders you need, and you can cut down the fitting or discard it completely and make your own reflector.

  • globalcooley
    17 years ago

    As an electrician, I would highly advise against it. Ballasts are paired with lamps for a reason.

    IMHO, If you want more light, I suggest checking out T5HO fluorescent lights. Lots of lumens, low power consumption, low heat. I just got a 2ft T5HO fixture off a garden supply on ebay. It works like a champ for an herb shelf. Puts out around 2000 lumens per 24w tube. They also sell 4ft fixtures that put out about 5000 lumens per 54w. It's the best balance of light/efficiency that I have seen to date. It was just under $150 shipped to the house. $150 is much cheaper than redecorating, or rebuilding, the house....oh, and make sure it's a T5H0 and not just a T5, there's a difference...

  • ologist
    Original Author
    17 years ago

    shrubs and bulbs,
    excellent, thank you. that explains it perfectly.

    globalcooley,
    i have been looking around for the safety of overdriving and it seems to me as though nobody has had a problem with fires, explosions, meltdowns, etc. i would love to go the t5ho route, but right now i can't justify the $150 expense. overdriving t8s would be more economical, and i'm not sure how many lumens i'd get out of 4 overdriven 17W for a 24" by 12-18" space, but i imagine it would be enough for an herb garden.

    i may not overdrive at all, it depends on what i find my plants need. i would like to grow kitchen herbs, basil, parsley, thyme, rosemary, marjoram, chives, etc. i don't know how much light these guys need, but if they seem to want more light i'll just throw on the extra wires to try out overdriving. in anybody's experience, would overdriving 4 24" lamps be useful for the setup and the kind of plants i've described, or is it overkill? thanks.

  • maineman
    17 years ago

    I seem to recall that Zink used a Dremel tool to cut a 48-inch shop light down to use 24-inch bulbs. I think it was using a SunPark SL-15 electronic ballast. You might want to do a Search in this forum for Dremel.

    MM

  • ologist
    Original Author
    17 years ago

    shrubs and bulbs,
    you mentioned reflectors. can you recommend a relatively inexpensive 48" 4 light t8 that already has a good reflector, or would you recommend making my own? if i go the diy route, do you know of a good resource i can check out to see how to do this?

  • shrubs_n_bulbs
    17 years ago

    overdriving t8s would be more economical

    Don't rely on it! I've said this before, and I suspect I'll have to say it many times again, but the largest cost in plant lighting is the electricity, so it makes sense to look for the most efficient solution without paying huge money. Plan on $5/month for 4 overdriven 17W tubes, so several hundred dollars by the time you are replacing the tubes. I estimate you'll be getting around 70 lumens/watt from overdriven F17T8s, barely more than a spiral compact fluorescent and considerably worse than a 2' compact fluorescent like the 55W models. Personally I think that 2' tubes are generally a poor choice in efficiency terms and you'd be better off looking at whatever compact fluorescent will fit your small space.

    Of course $150 for a 2' fluorescent fitting is a lot of money and you are unlikely to save that much on electricity no matter what lights you use, especially as replacement tubes are about $10. Maybe they'll be cheaper by the time they need replacing ;)

    It is worth noting that 4' T8 tubes produce more light per watt than 2' T5HO tubes, as always overdriving (which is all the high output means) and short tubes reduce the efficiency. Longer tubes are better and the 54W 4' T5HOs are as efficient as the standard 4' T8s, an 8' T8 is more efficient than either, and the 28W standard T5s are more efficient still.

  • shrubs_n_bulbs
    17 years ago

    Electrical wiring always runs the risk of a fault causing a fire. Competent qualified electrical contractors and off-the-shelf electrical equipment reduces this risk to a minimum, although things like mice eating through wires can always cause problems. Modifying electrical equipment or wiring increases the risk, not by much if you do it properly, by a lot if you do it poorly. If you are struggling to work out the difference between parallel and series then you maybe should just buy a couple of power compacts :)

  • ologist
    Original Author
    17 years ago

    thanks again s'n'b,
    i'm not concerned so much about my wiring skills since i tend to be pretty meticulous, it was more a question of whether the lamps were safe being driven with more power. the series/parallel thing is pretty clear, i just don't know how current passes through the lamps, so i didn't know you could think of it as a long resistor.

    anyway, i saw on a recent thread that you recommended 2x55W twin-tube compact fluorescents for a 2' by 1' grow space like you are here. would this be the best option for an herb garden of this size as well? i want to be able to have cooking herbs as year round as possible (basil, parsley, thyme, marjoram, chives... etc). would 2 55w 2' compacts serve me well? would one be enough? what color temp lamps should i steer towards?

  • globalcooley
    17 years ago

    1 competent qualified electrical contractor (20+ yrs experience) advises against this practice. "Rigging" electrical devices to work outside of their engineered purpose is never smart.

    I started my kitchen herb garden with a 2" T12 with 1 3000K tube and 1 6500K tube. Not the best for the power bill, but it worked fine.

    Any way you look at it, it's a balacing act. It's either going to be a high initial cost, but cheaper long term (operating cost) or cheaper initial cost, but more expensive operating cost.

  • deweymn
    17 years ago

    Ground
    Grounding
    Grounded

    3 things to consider and none of them are dirt involved.

  • dcarch7 d c f l a s h 7 @ y a h o o . c o m
    17 years ago

    "Ground
    Grounding
    Grounded
    3 things to consider and none of them are dirt involved."

    Same techniques for raising children? :-)

    I am not sure I am completely in agreement with you, globalcooley.
    I respect you as a qualified electrical contractor; however I don't think that all the stuff involved with overdriving lights are that dangerous which can lead to blowing up your house. Bottom line: anyone who has work with electrical wiring will have no problem doing this safely and anyone who has not done this before shouldn't.

    dcarch

  • globalcooley
    17 years ago

    I have seen the light.(ha!)

    It took me a while to wrap my brain around the reason anyone would want to do this. Initially, it seemed only logical that if you need more light... buy a bigger light. But after bantering back-and-forth about this one, I finally sat down and did the math. Though it is not something I would ever recommend, and it is certainly nothing I would ever do for anyone, the theory (on paper) points towards a realization of 125-180% output from a standard tube with an actual decreased load on a standard type ballast. You'll spend more money replacing tubes, but all things considered it's not bad, per se..

    Sorry for the unecessary doom and gloom. I hate being a reactionary, but when I hear people talk about "rigging" things, I immediately cringe because I've seen lots of accidents happen because people weren't using the right tool for the job, or they "rigged" something to work outside it's designed purpose....

    Be Safe first, creative second...

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