imj
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Kinda says it all.....I took a cheap Philips T5 tube of 21w on a 18/20w T8 ballast. It lights fine but tend to be quite flickery at the electrodes. http://www.youtube.com/watch?v=zsXlFjHJE-YIMJ |
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« Last Edit: September 13, 2010, 07:53:18 PM by imj »
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Medved
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| The lamp is ~50% overloaded (if the ballast deliver correct 0.37A into 55V F18T8, it would deliver about 0.32A into 105V F21T5, instead of 0.22A), so electrode filaments are severely overheating by the current (pure resistive dissipation on cathodes is too much).
To reduce this load, you might put one diode (e.g. 1N4007) parallel to each filament, with cathodes to the starter side, so for each current direction one is in forward effectively shorting the lamp cathode side filament, so allow the current to flow from the hot spot trough both sides of the filament. This will reduce the resistive power dissipation on electrodes by ~20..30%
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SuperSix
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| I've heard of proper T5 magnetic ballasts but never seen them, I'd use T5s if it weren't for the electronic ballasts.
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Atlas Lamps - Seeing Is Believing!
http://www.youtube.com/user/P42STUFF
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imj
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Yes the electrodes are overheated....I was trying my luck since this same ballast could run a 26w Dulux D. Thanks for the idea of the diodes..  . Most of the T5 electronic ballasts are instant start and they also blacken the lamp after first overnight use...I've seen them in actual installations. IMJ |
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DieselNut
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John
  
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I've heard of proper T5 magnetic ballasts but never seen them, I'd use T5s if it weren't for the electronic ballasts.
Me too! I despise the cheap electronic throw away crap where the lamps usually outlast the ballast! |
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Preheat Fluorescents forever!
I love diesel engines, rural/farm life and vintage lighting!
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Kev
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| I have had T5 14W 840 running on T5 13W magnetic ballasts just fine long term in a shop.
@ Dieselnut You are genuinely not wrong despite the fact i do not like T5 this is only because of the pathetic electronic ballasts. If they made a magnetic solution i would use them as they are bright when they work!
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Voted to leave the EU and proud! 👉🏻🇪🇺🇬🇧
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imj
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| From this experiment of running T5 on magnetic gear I think it would only work well up to 14w. This 21w tube was unstable at the electrodes although the tube itself lighted well. The electrodes flickered quite a bit and would be annoying for proper installations. Electronic ballasts are stable since it generates HF not 50/60Hz so regardless of tube length there's no visible flicker.
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Medved
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| @imj: The difference is mainly the fact, then electronic does no have to reignite the lamp each 10/8ms (because the frequency is so high, the ionization does not change during one periode). At second electronic ballasts have higher output impedance (so the current change with lamp voltage way less) then the series choke, what lead to much more stable discharge.
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imj
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Yeah I din't know how to explain it...  . Is it normal for T5s to turn blackish when left on for long periods because our flat premises have converted the T8 fitting to T5 but is very unsightly as the tube have some blackening I din't see it switch on so I don't know if it's rapid start or preheat start. They became abit black after first overnight use and more black the next night makes me think T5s are 'lousier' than T8s in terms of asthetics. |
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DieselNut
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John
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| If there is a magnetic ballast for a F54T5, I would love to have one (or some)!
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Preheat Fluorescents forever!
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xmaslightguy
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Somewhere There Is Light(ning)
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| Last night I fired up a F54T5 lamp (along with a F40T12) on a 2-lamp F40T12 Rapid Start ballast ... it actually did light (after a minute delay) but flickered horribly, like a lamp going EOL.
A F40T12 Preheat ballast wouldn't light it.
Maybe I'll try a F32T8 Rapid Start ballast
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« Last Edit: October 12, 2010, 02:52:16 PM by xmaslightguy »
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xmaslightguy
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Somewhere There Is Light(ning)
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Update: The T8 ballast worked in my test image posted here |
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Medved
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| Now i see, as "magnetic" you are talking about US RS.
These frequently use capacitor as the main ballasting impedance, what is not good for electrode life, mainly for thin T5, where the reignition voltage peak is high (the voltage overshoot, when the lamp has to reignite after current zero cross), what lead to very high current crest factor. So these ballasts would be T5 lamp-killers...
I think using "35W MH" HX transformer (deliver 0.5A to 70V arc, so the current wold be the correct 0.46A into 120V arc of F54T5HO) in preheat configuration would yield to more stable arc and less electrode stress...
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xmaslightguy
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Somewhere There Is Light(ning)
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Yep in this case the 'magnetic' ballast was a RS .. I tried a F40T12 magnetic preheat ballast as well, that didn't work (i'm assuming not enough voltage). I've got an actual F54T5 ballast too for normal use...but its electronic  \ |
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« Last Edit: October 12, 2010, 06:20:17 PM by xmaslightguy »
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Medved
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| If the F40T12 preheat was of "lead" type, it is again the capacitor stuff.
Lead circuit was well tolerated by T12, only moderately by T8, but really not the stuff for T5...
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