Need help with flourescent shop lights

[Cheap5.0]

My dad is replacing bulbs in his 1-2 year old no name shop lights. These are the smaller ones (they may have been aquarium lights from the looks), about 30" in length he has hung over a small desk.

The problem we are running into is we cant get any of the bulbs to fire, but if we remove the starter from the fixture they fire right up (but obviously wont turn back on once turned off). We have tried 4 different bulb manufcaturers, all using the same spec/length and it did not make a difference.

What would cause this? The starter is my prime suspect, but why would it not turn on with the starter in...but when you remove the starter it turns right on?

Its got me stumped.

The fixtures are using a Sylvania FS-2 rated up to 20 watts. The bulbs are 18 watts.

 

[NUTTSGT]

Maybe there's a bad connection at the starter? When you take it out, it's making contact but in it normal position, it's failing to make a connection.

 

[Cheap5.0]

Maybe there's a bad connection at the starter? When you take it out, it's making contact but in it normal position, it's failing to make a connection.

Good idea. It could be the part that holds it in place, maybe the manufacturer got a bad lot of starter holders. Ill see if i can find another source of them and try them out.

 

[Cheap5.0]

Maybe there's a bad connection at the starter? When you take it out, it's making contact but in it normal position, it's failing to make a connection.

After testing this idea out, its not the problem. We pulled a starter holder from a known working fixture and put it in a bad fixture and still had the same problem.

I failed to mention something...when we pull the starter out it fires up, but the part i forgot to mention is that when you put a starter back in it turns off.

Weird?


A quick video of whats going on

 

[Greatbear]

Do you have proper bulbs installed? Bulbs meant for instant start ballasts won't work properly with starter ballasts. If the working fixtures have the same bulbs, try switching the bulbs around.

 

[Cheap5.0]

Do you have proper bulbs installed? Bulbs meant for instant start ballasts won't work properly with starter ballasts. If the working fixtures have the same bulbs, try switching the bulbs around.

We are using Einko (sp) F17T8's, and we have tried sylvania and a no name bulb also F17T8.

Its weird, only some fixtures have this problem and some dont. We have swapped every part there is but the problem doesn't follow the parts.

Its stuff like this that makes me think its something simple i am missing.

 

[Cheap5.0]

Well we never figured out what it was. A friend brought over 2 fixtures that were identical, and we swapped parts around on those without finding any cures.

Then we put one back together with all the original parts, but using his bulb (Hitachi F20T8) and it worked. We put the other 3 new bulbs in it that we bought, and it would do the same thing (only fire up when we removed the starter, then turn off when the starter went back in).

 

[Greatbear]

This is starting to make sense. I am thinking the ballasts are the "problem." They are probably rated for a 20 or more watt bulb. In setups that use starters, the starter is wired across the ends of the bulbs, on one side of the filaments. The other side of each of the ends go to the power line, with the ballast in series with the hot wire. The starter is energized by the voltage across the bulb when first turned on. Inside is a neon bulb with a bimetallic spring contact. The current flowing through the neon gas heats the spring. which then momentarily shorts itself out. This causes the filaments in the bulb to heat. The starter will then reopen. This also releases an inductive surge from the ballast, creating a voltage much higher than the line voltage which is needed to start the fluorescent bulb. This causes an arc of sorts in the bulb, ionizing the gas inside it and making light. The ballast performs three functions during the start process. It first acts as a resistor to limit the current through the filaments when the starter is closed. It then acts as a source of high voltage once the starter opens and "unleashes" the voltage that is made by the built-up magnetic field. Finally it once again acts as a resistor once the bulb is lit in order to prevent too much current flow.

The problem happens when a bulb of insufficient wattage is used in the fixture. The bulb does not draw enough current through the circuit, and this causes the voltage across the ends to be too high. Normally, once the bulb is lit, the voltage across it is too low to fire the neon bulb inside the starter, allowing normal operation. If the bulb is improper (or wearing out), the voltage goes too high, the starter thinks the bulb is not lit, so it goes through its motions trying to relight the bulb. Since it is basically shorting the bulb out when doing so, the light goes out. Removing the starter opens the circuit, allowing the bulb to light.

These days, some starters use a solid-state device rather than the old neon bulb and bimetal spring setup. These are supposed to be interchangeable with the older style, and supposedly start the bulb with less flickering. But these are not 100 percent compatible with all fixtures and ballasts.

My suggestion is to replace the bulbs with the same kind as you substituted with success.

 

[Cheap5.0]

So any F20T8 should suffice? We were using F17T8's.

And thank you, i cant believe i actually understand what you wrote...but i did. Well done!

 

[nehog]

You did replace the starters, right?

 

[Norcal]

So any F20T8 should suffice? We were using F17T8's.

And thank you, i cant believe i actually understand what you wrote...but i did. Well done!

F17T8 lamps are commonly used w/ electronic ballasts.

 

[Cheap5.0]

You did replace the starters, right?

Yes, many times with many new starters lol.

F17T8 lamps are commonly used w/ electronic ballasts.

Hmm good to know. So the F20's must be the common replacement with mag ballasts? Which is what we have in these fixtures.


Thats what i was confused on though. I thought fluorescent lights wattage was a mathematical result of the length & diameter X something. So every T8 bulb that is 18" long (normal output) should have the same wattage, but they dont. I see 17 watt, 18 watt, and 20 watt. How can that be?

 

[cderalow]

Power = voltage^2/resistance

You have two variables, since voltage is the same.

power & resistance.

the lower the wattage, the higher the resistance provided by the bulb.

in the case of a flourescent bulb, resistance is a function of the amount and composition of the internal gases.

 

[Cheap5.0]

Power = voltage^2/resistance

You have two variables, since voltage is the same.

power & resistance.

the lower the wattage, the higher the resistance provided by the bulb.

in the case of a flourescent bulb, resistance is a function of the amount and composition of the internal gases.

Well dang, that makes sense. I understand how the same tube length/diameter can result in different wattages now. Thanks man!