How do ballasts in flourescent tubes work?

[beer]

I'm trying to get an understanding of ballasts but I'm not clear on a few things. I have a bit of e/m (2 semesters) but no quantum mechanics or anything like that (yet).

Correct me if I'm wrong:

1. To turn on a bulb, you need a much higher electric field to cause the electrons to excite, but once they're excited a stronger current is needed to keep them flowing.

2. A magnetic ballast is just like a coil transformer that ramps up the voltage really quickly to turn the bulbs on and then drops back down to household voltage to operate the lamp.

3. Some good ballasts (electronic) ramp up to 400+ Hz to increase the inductive coupling efficiency of the transformer, but its still inductive coils that ramp up the voltage.

If my bulbs aren't turning on immediately, but in a time uniformly distributed between 0-5 minutes (it seems), it's probably a bad ballast, right?

And also:

If I have a 4-bulb bank, residential installation, they should all be wired in parallel right? Just like everything else? When I was playing with my bulbs, if I yanked any of the two inner ones out, the other immediately shut off. Same with the outer two bulbs. This leads me to think they're operating in some sort of voltage-divider configuration - which doesn't seem appropriate, but I don't know anything about the NEC.

 

[thermalpaste]

IF you have a 40Watt ballast, you can run 2 bulbs of 20 watts connected serially, but with 2 starters......
So therfore your fixture has a single ballast running 2 tubes and not 2 individual ballasts.

If my bulbs aren't turning on immediately, but in a time uniformly distributed between 0-5 minutes (it seems), it's probably a bad ballast, right?

Change both the starters (those small round things that have a metallic strip in them that help to crank up those bulbs) and then your bulbs will light up immediately. The ballast isn't at fault.

Some good ballasts (electronic) ramp up to 400+ Hz to increase the inductive coupling efficiency of the transformer, but its still inductive coils that ramp up the voltage.

An electronic ballast uses a resistor that gets down the voltage to a certain level. Then there is a rectifier bridge that converts it into D.C voltage. The transistors convert this D.C voltage to an extremely high frequency A.C voltage (something like 400Hz and can go upto 25Khz) . This A.C voltage is amplified by a small ferrite core transformer and then this resultant output is fed out to the flourescent tubes/bulbs. Because of this high frequency a starter isn't needed to trigger of the bulb. And besides, even blackened bulbs/tubes work on very high frequencies.

 

[thermalpaste]

If one bulb is blackened out, then in your case you will need to change that bulb in order for the bulbs to start fast, because they are connected serially. Changing Both the starters does this trick otherwise. Starters come with capacitors inside and they tend to melt off after some time.

 

[TechnoKid]

I assume you have the typical 4 tube T12 setup with a regular magnetic ballast? If so, i'd reccomend upgrading to a T8 electronic ballast setup. No flicker, instant on. I changed over the setup in my kitchen, and there is no flicker upon startup, even in the winter time (which is where the old T12 were at their worst). The T8 bulbs also put out more lumens than T12 bulbs. Its also energy star copmliant. American Flourescent markets something called Resi-Tronic, an electronic ballast setup where it can use both T8 and T12 bulbs. I have these Resi-Tronic shop lights in my garage, and they are loads better than traditional lights. They can be found at Lowes (I have not seen any resi-tronic fixtures at home depot, though HomeDepot does sell T8 ballasts, 2 tube and 4 tube setups).

 

[beer]

Originally posted by: TechnoKid
I assume you have the typical 4 tube T12 setup with a regular magnetic ballast? If so, i'd reccomend upgrading to a T8 electronic ballast setup. No flicker, instant on. I changed over the setup in my kitchen, and there is no flicker upon startup, even in the winter time (which is where the old T12 were at their worst). The T8 bulbs also put out more lumens than T12 bulbs. Its also energy star copmliant. American Flourescent markets something called Resi-Tronic, an electronic ballast setup where it can use both T8 and T12 bulbs. I have these Resi-Tronic shop lights in my garage, and they are loads better than traditional lights. They can be found at Lowes (I have not seen any resi-tronic fixtures at home depot, though HomeDepot does sell T8 ballasts, 2 tube and 4 tube setups).

What kind of cost over typical T12 bulbs are we talking about?