Fluorescent light fixture--theory and problem

Thread Starter

tab a

Joined Jan 14, 2015
42
I've got a couple of 4' fluoro tube fixtures in which only one bulb lights. I thought I might be able to combine them into one fully working fixture, and pulled them apart. Neither has the old electronic ballasts, but they are different. Can't find much on the net to explain to me the theory of how these newer styles work.

The first is extremely simple and I've drawn the schematic below. The transformer and cap on one end have considerably different values than those on the other, so I wonder if that is likely the problem? I also have no idea what's in the white 'box' (current limiter?) noted on the schematic and in the pic.

The other fixture is very similar to the first with regards to transformers and caps, but in addition has PCBs--which I presume limit current. Maybe they are taking the place of the white 'boxes' in the first fixtures? This fixture has a transformer that measures open, so I'd guess that's the problem here.

Thoughts? I think/hope I've drawn the schematics correctly!
Thanks.

IMG_1752.jpgIMG_1734.jpgIMG_1736.jpgIMG_1753.jpgIMG_1735.jpg
 

AlbertHall

Joined Jun 4, 2014
10,792
Are those measurements with the tubes still connected to the fitting?
If so repeat the measurements with the tubes disconnected.
What are the values of the resistors in parallel with the capacitors, labelled R3 in the second fitting?
 

Dodgydave

Joined Jun 22, 2012
9,876
The fluorescent tube has an inductor in series with it and a starter to ignite the gas by pulsing the inductor, that's the principle,,

Yours has an electronic starter looks like a Triac dimmer type, measure the tube pins resistance disconnected , they should read low ohms, also the Inductors, .
 

Thread Starter

tab a

Joined Jan 14, 2015
42
Are those measurements with the tubes still connected to the fitting?
If so repeat the measurements with the tubes disconnected.
What are the values of the resistors in parallel with the capacitors, labelled R3 in the second fitting?
No, tubes were disconnected. R3, on both fixtures, are 750K.
Thanks.
 

Thread Starter

tab a

Joined Jan 14, 2015
42
Just go to Home depot and pick up a new style electronic ballast, cheap.
Max.
I actually have a new electronic ballast on the shelf, and will use it in one of the fixtures. If I was going to buy anything, I'd get LEDs. The way I'm trying to do it, was hoping I'd learn something, along the way. :) Thanks.
 

Thread Starter

tab a

Joined Jan 14, 2015
42
The fluorescent tube has an inductor in series with it and a starter to ignite the gas by pulsing the inductor, that's the principle,,

Yours has an electronic starter looks like a Triac dimmer type, measure the tube pins resistance disconnected , they should read low ohms, also the Inductors, .
I had presumed the Triac was a way to shut down the current, as needed--but that was a real WAG on my part.
Do I have inductors?
 

ThePanMan

Joined Mar 13, 2020
56
Just bought two LED panels for my kitchen. Each panel is 2' by 4' rectangular and less than one inch thick. Plenty of light and uses less power than the fluorescent fixtures I had before. Though I had to build a box to house the lights and put up crown molding. All in all, I'm very happy with the quality of light as well as the quantity of luminosity.
 

Thread Starter

tab a

Joined Jan 14, 2015
42
Are those measurements with the tubes still connected to the fitting?
If so repeat the measurements with the tubes disconnected.
What are the values of the resistors in parallel with the capacitors, labelled R3 in the second fitting?
Any other thoughts?
 

Thread Starter

tab a

Joined Jan 14, 2015
42
Did you measure the tube pins resistance?
If you mean measure the resistance on the tubes themselves, no. I've switched tubes in the fixtures and it's not the tubes.

You also mentioned measuring the inductors. I don't know if what I pictured are transformers, or inductors (which is why I asked), but the values I measured are on the schematics.

Thanks!
 

MisterBill2

Joined Jan 23, 2018
7,779
The way florescent tubes with starters work is that initially current flows through heaters, (filaments) at each end, and then when the starter suddenly switches off, a voltage spike from the current drop through the inductor causes the gas in the tube to ionize and start conducting. At that point the reactance of the inductor is supposed to limit the current, and the voltage between the ends drops to about 60 volts.
IN the new electronic ballasts there is a much higher voltage at a much higher frequency and so the gas starts to conduct much sooner. At that point the control circuit limits the voltage to hold a constant current.
LED lights moostly have long strings of LEDs in series and many include a current control circuit within the tube. So far I have come across tubes with the internal supply and the strings running at about 73 volts or 35+ volts.
 
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