I'm going to go out on a limb and say yes, without ever having seen that ballast. Every instant start electronic ballast should be able to overdrive (although there will always be exceptions). Some rapid start ballasts cannot be used because of the way the wiring is done to ignite the tubes.

If you can sketch up or even describe the wiring diagram for your ballast, that would help with a confirmation. Or just wire one of them to a cheap T8 tube and see what it does.

Thanks.
Here is a picture of the ballast. Will it work?

dcarch

{{gwi:1020077}}

Dcarch,

Based on the wiring diagram, it looks like this ballast can drive four bulbs normally or two bulbs in the overdriven mode. Currently there are two red wires going to two lamps. Remove one of those lamps and place both red wires on the remaining lamp.

Likewise, there are two blue wires going to two more lamps. Remove one of those lamps and put both blue wires on the remaining lamp. One yellow wire goes to one lamp and the other yellow wire goes to the other lamp.

It's basically just a subtraction of lamps with the spare wires going to the remaining lamps, while maintaining the basic orientation of the printed circuit diagram.

MM

Dcarch,

Don't construe my previous message to mean that you should mount a 4-bulb fixture containing only two bulbs over your plants. The whole idea of overdriving bulbs is to get more "effective bulbs" over your plants. There is only so much room over your plants for bulbs, and when you can not get any more bulbs over your plants, the only way to further increase the light is to overdrive the bulbs.

Since overdriven bulbs put out 50% more light than non-overdriven bulbs, four non-overdriven bulbs put out more light than two overdriven bulbs. But by using the appropriate fixtures you can place four over-driven bulbs over your plants instead of four standard-driven bulbs and get 50% more light, which would be the equivalent of six standard-driven bulbs.

I hope that is clear. Sometimes I confuse myself.

MM

MM,
My intention of overdriving the bulbs is to increase light output so that I can increase the distance to the seedlings and grow taller plants before transplanting them.

thanks for your help.

dcarch

Standard 4-lamp instant start wiring, should be able to overdrive as described. But there is always the slight chance that the ballast will refuse to do it, depending on how it is designed. Certainly worth trying it with this ballast.

O.K., I re-wired one from four tube to two tube. It works. Just somewhat brighter. I guess the eyes don't see 50% more light as much brighter.

Only thing, It seems to my eyes that when you first turn it on, it's the same brightness as normal, it seem to get brighter after about 5 minutes of warming up.

dcarch

You're right, the eye can't see brightness differences too well, but the result of 2x overdriving is usually quite obvious. But the result varies with the ballast. In theory, 2x overdriving should produce twice the current, but the voltage will drop so you don't get twice the power. Also, most ballasts won't actually produce twice the current and the increase in light generally doesn't match the increase in power (decreased efficiency), so you get quite a bit less than twice the power. A 70% increase is often quoted but it varies. You might like to try measuring the light output if you have a digital camera.

The startup characteristics of electronic ballasts vary. The theory is that they pump out a very high voltage to break down the non-ionised gas, then scale back the voltage. When overdriving, the ballast is working outside its optimum range and results can vary a bit. The tube itself will also become warmer than standard and warmer tubes can become brighter (or fainter if they get too warm!).

SnB,

"When overdriving, the ballast is working outside its optimum range and results can vary a bit."

My overdriving Sunpark SL-15 ballasts are driving only one bulb instead of two, so the ballast is "loafing" and runs cooler. As you mentioned, the overdriven tube itself runs hotter but not a lot hotter. They feel warm to the touch, but won't burn you. I think the non-overdriven bulbs are about 100°F while the overdriven bulbs are about 120°F.

"A 70% increase is often quoted but it varies."

The original classic "I have found the BEST cheap fluorescent ballast/fixture" thread started by the user Zink is no longer in the iVillage GardenWeb archive, but the thread has been saved elsewhere. Zink's original message, on Wed, Nov 26, 03 at 12:29, contained this paragraph:

"Overdriving (which requires a ballast that drives 2 or more lights) involves disconnecting the wires from both ends of one lamp's socket, and join them to the wires of the other lamp. This results in a 32w lamp being driven to output approximately 1.7 times as much light as normally produced. This will reduce the life of the lamp, somewhat, but in the overall picture it is very economical to replace a 32w bulb -- even twice as often. With fluorescent lights, over 95% of the total cost of using the bulb is the electricity, since the bulbs last so long to begin with. I used both a current meter and a light meter to compare my results. The 1.7 times figure was verified by another experimenter I read and your own eyes can DEFINITELY see the difference."

However, later in the continuation of that message thread (the original thread was closed after it reached the 100-message limit), on Thu, Jan 13, 05 at 2:19, Zink said:

"Just to re-clarify the resulting effects of overdriving by 2x:

a) The current will increase by about 70%. Since the load is now shared by TWO ballasts, each ballast is getting a 15% load reduction. (2x.15)+1.70=2.00

b) The lamps will NOT be 70% brighter. It is more like 50% brighter. This is due to the reduced efficiency of overdriving. Fortunately, this is much less expensive than alternatives... and works so nicely too!"

I think the 50% figure is more generally accepted now. But, as they say, your mileage may vary. You can always use a light meter to make your own measurements. There is no question that overdriving makes the tubes considerably brighter.

MM

As I said, after rewired the ballast to overdrive the tubes, I did not notice a real increase in brightness.
Well, today I got a light meter to measure the outputs.

I put the meter directly touching the tubes to avoid the reflector factor to take the measurements.

The overdriven tubes measured 720 Ft. candles.
The regular tubes measured 600 ft. candles.

I guess the eyes cannot realy tell the difference.

dcarch

Something is badly wrong. A light reading in contact with a T8 tube should be much much higher than 600-720fc. I get about 1,500fc at the plants from my non-overdriven T8 setup, several thousand right at the tube. A quick calculation of the total lumen output (~3,000) divided by the surface area of a 48" T8 tube (~1 square foot) suggests you should get around 3,000fc at the tube.

The meter is a GE footcandle meter, "cosine corrected". It has a milk-white window which catches incident light.
I think it may be the nature of the meter which is not designed to measure light directly.
I measured the light from my desk lamp and it reads 100 footcandles, which is about right.
The point is: there is significant increase in light intensity given by the overdriven lamps which the eyes are not perceving the same way.

dcarch

Yes, I certainly wouldn't expect your eyes to notice much difference between 600fc and 720fc, but I would expect 2x overdriving to produce a bigger increase than that.

I don't know what desk lamp you have, but a light intensity reading right at an incandescent bulb should be a lot higher than 100fc. The bulb may only be putting out a few hundred lumens but it is a lot less than a square foot so the intensity is a lot more than the lumen output of the bulb. Your meter seems to be broke. 100fc would be an appropriate reading perhaps 6"-10" away from the bulb. Hard to judge by eye but a single 32W fluorescent tube should be putting out 5-10 times as much total light as your desk lamp.

Cosine corrected means that it will give a correct reading even for a directional light source, such as the sun or a lamp, even when the light enters the window at an angle. Such a meter is designed to measure incident, not reflected, light intensity which means it should work just by pointing it at a fluorescent tube. Is it digital or does it have a dial?

"I don't know what desk lamp you have, but a light intensity reading right at an incandescent bulb should be a lot higher than 100fc. "

I meant measurement was taken on desk top, not on the bulb, which is a 15W compact fluor. bulb.

The meter is an old photocell galvanometer, nothing to go wrong.

BTW, I always enjoyed reading your posts.

dcarch