EEVblog #362 - LED Tube Lighting Install & Theory

[EEVblog]

Dave.

[tom66]

I got hold of a Philips LED fluro replacement. It came with its own replacement starter. I looked inside and all I could see was a poly capacitor. I guess it's a cheap way of limiting the current but seems a little dodgy to me. The tubes themselves didn't seem to have any other components but I didn't look in detail as they weren't mine to do a teardown on   .

[mikeselectricstuff]

The description of the old style starter was wrong (Unless they use different type in Oz)- these are a glass envelope with 2 bimetal contacts. They start off open - on powerup the gas ionizes, heats the contacts til they close, which powers the tube heaters. The short extinguishes the gas, it cools and the contacts open, striking the tube (This can take several attempts).
Once the tube has struck,  the voltage across it is no longer enough to ionize the gas in the starter so it stays open.

I recall using these as random xmas light flashers when I was a kit  - annoyed the hell out of my parents as a random flash is very distracting!

[Baliszoft]

I recall using these as random xmas light flashers when I was a kit  - annoyed the hell out of my parents as a random flash is very distracting!

Same here.

[T4P]

What all the starter does is delay the mains long enough to charge up the inductor and therefore arc across the tube to "start" the gas with a few thousand kV and then returns to normal operation

[tom66]

I would imagine a similar procedure is used in DLP and projector lamp assemblies - using a ballast to generate a multi-kV pulse...

[HKJ]

What all the starter does is delay the mains long enough to charge up the inductor and therefore arc across the tube to "start" the gas with a few thousand kV and then returns to normal operation

No, the old fashion starter heats up the filament at the end of the tube.
You can also start a tube with a a high voltage, but you do not really needs kV, less will do (At least at 25 degree and not to long a tube).

[SeanB]

The ones inthe video are preheat start. The initial condition when mains is applied is that the starter glows, and this heats up the one electrode inside which is made from a bimetal strip. This then shorts out the glow bottle, and this high current heats up the tube filaments. After a second ortwo the bimetal cools and breaks contact, this then interrupts the current through the ballast, generating a high voltage pulse and applying about 600V across the tube, enough to start it conducting. The tube then draws a constant current and generally drops from 50V to 100V, depending on size, age, temp and fill gas. This is less than the 90-150V required to start the glow bottle in the starter and it stays off. As th tube gets old and the voltage drop increases it will eventually try to start continuously, giving the flashing of an EOL tube. If left long enough the filaments go open circuit from the repeat starts ( only on T12 tubes, T8 do not do this often) or the starter goes short circuit ( the tube is out with orange ends) and the fitting draws typically 3 times the normal power until it burns out, if poorly designed or made.

The other method is to have a magnetic ballast that provides 4VAC to each heater, and provides a 600VAC current limited supply to the tubes. This is Rapid start, and typically starts the tubes without flashing in under a second.

The last method is Instant start, where the heaters are shorted together ( either in the end cap which has one pin or in the socket) and the tube has 1-2kV applied to cold start it.

Most electronic ballasts ape preheat, either using a capacitor and varying the high frequency voltage applied depending on load, or use a PTC thermistor to do the heating during startup.

The LED replacements can only be used with preheat systems, all others need rewiring and ballast removal, as well as a sticker inserted to warn about the LED tubes only being replaceable with the same, not a regular tube.

[SteveyG]

The description of the old style starter was wrong (Unless they use different type in Oz)

Agreed. There were a few bits of misinformation in this video.

They were good for 'fire' lighting effects on stage before lighting desks had enough patterns to simulate fire.

[plexus]

I felt this was a good reason to resurrect an old topic. In this video, an assembly error results in a blown LED driver PSU. The component that blew was the sense resistor. The action starts at 34:35. The mains was connected to the output of the PSU because the case was assembled wrong. The sense resistor took the hit. Dave wondered what the failure mode was on the resistor....



Just today another youtube guy I followed posted this. He has done some interesting things along the lines of destruction with electricity. I am surprised he's still alive, could be testament to his respect for electricity. But this video is not only a cool video of resistor destruction, but its also quite beautiful and amazing! So Dave, this is apparently what happens and why there is all that wispy char but also what looks like an explosion. Wow!