T5 fluoro tubes blackening at one end - bad elec ballasts? - Page 1
Forum section: electronics / general

author: Whales
author_rank: Super Contributor
timestamp: August 13, 2020, 04:42:30 am
content: At one of the buildings used by my business we're seeing the lighting fail at silly high rates. We don't own the property, so we're always nagging the (charity) owners to send over their electricians to fix it.I don't normally work at this site, but I had a quick look at the lighting when I was there yesterday:All 2x 28W T5 fluro fixtures in the ceilingModel "PC-R 2/28 T5" electronic ballasts by "TRIDONIC ATCO". Ie no traditional ballast + starter.All of the faulty tubes are heavily darkened on one end (and only mildly on the other end)Both tubes in each fixture always darken at the same end of the fixtureBad ends:Good ends:My immediate thoughts are that the electonic ballast is over-running the electrodes at one end of each tube and evaporating them. Or it's somehow putting some DC into the tubes.Is it normal for tubes to heavily (and reliably) darken at one end and not the other, or does that suggest bad electronic ballasts?EDIT1: Corrected company name, added photos

author: james_s
author_rank: Super Contributor
timestamp: August 13, 2020, 05:50:07 am
content: It's actually the opposite situation usually that causes end blackening, under-heated cathodes sputter rapidly and blacken the end of the tube. It is common with the old rapid start T12 fixtures if you get a bad socket or install the tube improperly with only one of the two pins making contact. Many T8 tubes are instant-start and don't heat the cathodes at all, I'm less familiar with T5, do these ballasts have two wires for each end of the tube? You can also have a situation where a tube with a bad cathode behaves as a rectifier and that tends to exacerbate the problem and is not nice to the ballast either but I usually saw that with the single pin T12 tubes on the old magnetic ballasts.

author: coppercone2
author_rank: Super Contributor
timestamp: August 13, 2020, 05:51:21 am
content: https://www.milwaukeetool.com/Products/Instruments/Lighting-Testers/2210-20might be worth while for a business if its large enoughI don't own it because I don't have enough of those fixtures, but taking them apart is unpleasant because of how thin the metal is. BTW you should fix it because a business looks like garbage if the lights don't work. Nice thing is that that tester is non invasive and it should be enough to convince a non technical building owner and facilities people there is a problem if milwakee says so. I think if you try to explain tube physics to building people they will give you a endless run around/bullshit. Might even try to blame you for touching their stuff to get out of paying.

author: Whales
author_rank: Super Contributor
timestamp: August 13, 2020, 07:30:51 am
content: Photos added to first post + corrected the maker name.Quote from: james_s on August 13, 2020, 05:50:07 amAh, that makes sense. I note that both ends of the tube in this particular feature are glowing yellow during (attempted, failing) startup, so it's at least running them for start.QuoteYes. Looks like they actually try and run the heaters.Quote from: coppercone2 on August 13, 2020, 05:51:21 amThat looks like a tool for testing traditional inductive ballasts + starters. Electronic ballasts are too varied & complicated to (in my understanding) be tested generically or in a standard manner.

author: coppercone2
author_rank: Super Contributor
timestamp: August 13, 2020, 08:10:45 am
content: it says its for electronic ballasts and not for induction ballastsThe BALLAST Test works for all T8 Electronic Ballasts. A BALLAST Test cannot be done if the fi xture is turned off. 1. Turn power on to the lighting fi xture.2. Extend the antenna to desired length. Always retract the antenna when not in use.3. Turn the dial to BALLASTFor Lit T8 Lamps:4. Holding the tool by its insulated gripping sur-faces, place the antenna end within 1" of any part of a lit lamp. Do not contact the fi xture's live electrical parts. 5. Hold down the TEST button.6. Two possible outcomes:a. The tool indicator does not beep or fl ash red, indicating that the ballast is not working properly. • Replace the ballast. Continue checking all lamps in the fi xture as multiple ballasts may be present.b. The tool indicator beeps and fl ashes red, indicating the fixture has a functioning electronic ballast.• Continue with next step.

author: Whales
author_rank: Super Contributor
timestamp: August 13, 2020, 09:49:30 am
content: Quote from: coppercone2 on August 13, 2020, 08:10:45 amMy apologies.I'm looking through the PDF manual. Not sure if it provides much more than a pass/fail for each part, I'm more interested in the nitty gritty detail of what has gone wrong and how to avoid it. The manual says "contact a qualified electrician to service the fixture." if (edit) all the tests failQuoteYep, I can imagine that happeningI'm really curious as to what the problem is for myself, we might also be upgrading our other (self-owned) sites to electronic ballasts at some point. The best I can do in the current situation is give a suggestion of what the problem is.

author: james_s
author_rank: Super Contributor
timestamp: August 13, 2020, 04:27:59 pm
content: You don't need any fancy tools to sort this out. Keep track of how long the tubes are actually lasting, generally they should be group relamped all at once as they approach end of life rather than spot relamping specific fixtures as they fail. Then pay attention and note whether a few specific fixtures are blackening the lamps rapidly or if it's happening similarly across all of them. Double check that you are running the correct lamps, T5 is the diameter but there are multiple types of T5 lamps, at least here in the USA there are are standard and high output lamps, if you put a standard lamp on a high output ballast or vice versa it will not last long.

author: LaserSteve
author_rank: Super Contributor
timestamp: August 15, 2020, 02:42:38 am
content: Group Relamping / contract repair by a skilled lamp contractor works wonders. Key word here is skilled and experienced, by using quality parts and measuring the illumination needed in advance.Usually re=lamping is best done by a specialist, not the local yahoos... Mainly because the specialists buy enough fixtures or lamps per year to get cost effective deals.LED conversion is a bit pricy if done by a skilled lamp contractor. However it has proven at my place of work to pay for itself in two years or so. Again, it is picking the right lamp assemblies, not buying the cheapest crud on the market.One other thing, motion switches kill tubes from startup cycles. Plasma based lamps like to stay lit. All in the name of saving energy, but they can mean buying more lamps, plus more mercury in the environment. Temperature also matters, too cold is not good for lamp ends. Low temperature lamps have ~1% N2 added to the inert gasses, to heat the lamp discharge, causing mercury pressure to rise.Don't get me started on the short lifetime "Eco" tubes, with almost no Hg, or the new ones with no pressure maintaining amalgam in the lamp.Steve

author: james_s
author_rank: Super Contributor
timestamp: August 15, 2020, 05:20:02 pm
content: Cycles are indeed hard on fluorescent lamps but how hard varies greatly. Instant start ballasts use brute force to strike the lamps without preheating the cathodes and this results in a significant life penalty, especially if they are in an application where they are started more than once a day. The best ballasts are "programmed start" and have some kind of active control in them to preheat the cathodes and then strike the arc gently once the cathodes are hot.

author: Kjelt
author_rank: Super Contributor
timestamp: August 16, 2020, 10:09:55 pm
content: Also check if the lamps are dimmed (sometimes by a daylight sensor) through Dali or 0-10V interface.Dimming TL5 tubes significantly lowers their lifespan.The reason is to keep the plasma hot and the lamp burning there now needs to flow current on both sides Through the tube filaments.Running a tl5 on 100% for hours a day could normally last 15000 to 20000 hours.Running the same tl5 on 10% for hours will reduce this to aprox 5000 hours