Disregard my previous comment about a $4 4 bulb T8 ballast. It seems like that was incorrect info. Looks like they start at around $17 bucks. Still, that is cheaper than buying two more 2 bulb fixtures and I would not have the extra carcases lying around.

i overdrive using 4 lamp ballast to run 2 x t8. make sure the ballast will fit the case - i am using a nice Sasi ballast from ebay, but my lamp case is big enough to hold it, because the fixture was originally for the t12 40 watt x 2, and the 40 watt magnetic ballast is quite big, so lots of room for the 4 lamp t8 ballast.

You don't have to cannibalize ballasts from fixtures to overdrive. You can simply buy extra ballasts to do the overdriving. And when the ballast in a fixture goes bad, you can simply replace the ballast, and not the fixture.

I hope this doesn't sound ignorant, but I am and ignorance is curable...You are talking about overdriving T8 light fixtures (mine are 4', 2 bulb units; bulbs are 32 watts each). So, if I add a ballast (not sure how to do this) how much does this increase lumen output, and what is the impact on the electric bill? Does it double? Instead of adding a ballast, why not just buy a larger ballast and replace the one in the unit? One more questions; if you overdrive a PC (computer), you can overheat it and fry it. What is the fire risk for overdriving you T8 fixtures?

I made a video that shows exactly how to do this. It's cheaper to buy 2 fixtures at Walmart for $10 each than buy a $10 fixture plus a $22 ballast. There is no fire hazard. In the video I hook it up to a Killawatt to show electrical use.

Overdrive T8 Instructions

Here is a link that might be useful: Overdrive T8 Instructions

I want to tack on to this thread and ask a question about overdriven lamps.

The standard fluorescents have done just fine for me for growing seeds (veg & Flowers) to transplant size - so why bother overdriving them? Will the stronger light make healthier plants? Or are these used more for growing full size and tropical plants? I know there will be more light, but I won't be able to fit any additional plants in the space, so I am not sure that I am understanding the point.

bushier more husky plants with bigger leaves, very squat and stout, short internodes. just like a plant on steroids

MD,

"Will the stronger light make healthier plants? Or are these used more for growing full size and tropical plants?"

Like OverDrive said, the greater light intensity will produce better seedlings. I grow a lot of zinnias, and zinnias have a big appetite for light, and will stretch and become somewhat leggy or spindly under regular fluorescent lighting. This is an example of zinnia seedlings that were staying compact and healthy under overdriven T8s.

{{gwi:4096}}

The strategy for providing fluorescent lights to your seedlings is first, hang as many regular fluorescent fixtures over them as will physically fit. Then continue to increase the light on those plants by overdriving those fixtures.

If you have two two-bulb T8 fixtures and you cannibalize one to get a second ballast for the other, you will only get about 70% more light from the single overdriven fixture as compared with 100% more light if you simply hang the second fixture over your seedlings. So it doesn't make sense to overdrive your fixtures until you have hung as many of them as you can over your seedlings.

In "the good old days" when you could get a bargain two-bulb T8 shoplight fixture from Home Depot for $4, it did make sense to buy fixtures and cannibalize them, because then most sources of T8 ballasts cost more than $4 per ballast. I continued to buy and cannibalize 2-bulb T8 shoplights from Home Depot up until a few years ago when the price of a fixture went over $8.

At that time I quit cannibalizing T8 ballasts and started buying separate ballasts for two reasons. First, the ballasts in the cheap shoplights were themselves cheap and they didn't last very long. Typically, my T8 bulbs would outlast my cheap cannibalized T8 ballasts. And second, I found a source of reasonably priced higher quality 2-bulb T8 ballasts that I could use to overdrive my existing fixtures and replace the rapidly failing ballasts in my original overdriven fixtures.

So I now have a supply of better T8 ballasts that I use to replace my cheaper T8 ballasts as they fail. I am still a big fan of overdriving. The next step up from overdriving T8s (and possibly T5s) is HID lighting, and that costs considerably more money.

ZM

Thanks Zenman,
I never quite could concieve the concept of taking two 2 bulb fixtures and creating One 2 bulb fixture to come up with something that puts out 30% less lumens than the two 2 bulb fixtures mounted closely side by side.
My local wallymart sells these fixtures for about 11 bucks, but the ballasts that come with them look like junk, and are probably the cheapest made component in the entire 11 dollar assembly.
~Ken~

Wow, didn't know you could this. I got 4 (T8) two bulb fixtures and 2 (T12) that I would like to overdrive. The T12 can use T8 bulbs. ZM where do you get your ballasts from?

Mori,

I got my ballasts from the Nextech Lighting online site.

ZM