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EOL F15T12 Lamp

EOL F15T12 Lamp

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I knew there was something wrong with this lamp the other day. Given the increased flicker and large piece of the cathode that had broken off, I didn't expect it to last too much longer. I left it on unattended and I returned only to find that the ballast had overheated and shut down. Fortunately the thermal protection did reset. You can see how hot this end becomes, it glows incandescent for several seconds after I flip the switch off. It seems there's not much chance this lamp will gently rectify. If left alone it's either going to operate in cold cathode fashion until vacuum loss if it doesn't take the ballast out first.

youtube_4kAzf99JLq8.jpg philips-f15t8-spec35.jpg eol-f15t12.jpg fluorescent-flicker.jpg

Light Information

Light Information

Manufacturer:General Electric
Model Reference:F15T12-SW
Lamp
Lamp Type:Fluorescent
Fixture
Ballast Type:Magnetic Trigger Start
Electrical
Wattage:15

File information

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Filename:eol-f15t12.jpg
Album name:Patrick / Fluorescent
Keywords:Lamps
File Size:181 KB
Date added:Feb 22, 2015
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themaritimegirl
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Feb 22, 2015 at 03:05 PM Author: themaritimegirl
Wow! Yeah, it's interesting how rapid start ballasts generally can't tolerate rectifying lamps, while preheat ballasts are usually just fine.

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streetlight98
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Mike McCann


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Feb 22, 2015 at 03:13 PM Author: streetlight98
Wow! What would cause this to happen?! With preheat, if the lamp is rectifying, won't the starter eventually try and re-fire the lamp? My preheaters sometimes do that. I've never seen a lamp rectify on RS or TS though.

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Feb 22, 2015 at 03:21 PM Author: themaritimegirl
The rectifying lamp causes both lamp and line current to go way up. Why, I don't know, and I don't know why the same thing doesn't happen on a choke circuit. Usually on a choke circuit the opposite happens because the apparent arc voltage goes up, but somehow a rectifying lamp on a rapid start ballast lowers in arc voltage.

I once ran an EOL F14T12 on one of my RLQ-120-TP ballasts, and whenever it rectified, both lamp and line current about tripled. I unknowingly left it like this for about half an hour, and when I came back, it was still running, and the ballast was so hot that you could hear the tar boiling inside it. The whole setup was drawing over 100 watts of power.

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streetlight98
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Feb 22, 2015 at 03:24 PM Author: streetlight98
Wow! How common is this behavior? It must not be too common, or ballasts probably wouldn't last very long?

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Feb 22, 2015 at 05:52 PM Author: don93s
Yeah I learned early on those NPF trigger start ballasts don't do so well with rectifying lamp, especially 14w or 15w. They might tolerate a 20w depending on ballast. Something in the way the ballast is designed....the rectification nulls the necessary reactance to control the current, maybe due to low coil impedance, whereas a choke has a high enough impedance to not cause the current to rise. Some of the early single lamp circline rapid-start were like this too...they were designed more like a trigger-start and tended to overdrive even a good lamp. It seems that even the modern magnetic rapid-start 22w can still over heat with EOL lamp.

In the case of slimline series ballasts, a different situation seems to occur: lamp current doesn't go up but the "power factor" goes down causing the primary current to go up, thus, overheating the ballast when the lamp on the blue wire side rectifies.
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Feb 22, 2015 at 06:53 PM Author: themaritimegirl
Yeah, I wondered if the rectification somehow abolished the reactance of the secondary winding, thus making the primary winding the only impedance. I've fried two lamps on my Advance, and the behavior was exhibited both times, but I also once put an EOL lamp on my Universal, and it just calmly rectified.

Mike: Well, consider a 40 year old ballast. Such a ballast is only going to see a few lamps in that timeframe, and if it was part of a replacement schedule, it may never see an EOL lamp at all. Combine that with thermal protection, and I would think that the chance of a ballast succumbing to an EOL lamp would be quite small.

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Feb 22, 2015 at 07:00 PM Author: streetlight98
True, but I've never seen this happen before. Is it only smaller fluorescents or NPF ballasts? Would an F40 ballast/lamp do this on a HPF ballast?

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Feb 22, 2015 at 07:06 PM Author: Alights
no F40's on HPF wont rectify at EOL since the cap blocks DC current, the OCV isn't high enough either to fry it like here ^ however wired for 1 lamp is a different story the ballast wont be harmed in this case either
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Feb 22, 2015 at 07:35 PM Author: ace100w120v
Oh yeah they will! I have a .77a Advance Kool-Koil that will let a spent or improperly installed lamp rectify just like LPF! Never left it like that though to see if it will migrate, though I should test that sometime!
It also trips it's thermal cutout sometimes, I think maybe the cap is bad. And it contains PCBs too...oh great!
In the same 3-lamp fixture as said Advance ballast I have a half-dead Universal Therm-O-Matic wired for one lamp and THAT thing will put on a bit of a show with a spent lamp...orange flashing at the bad and violent flicker and "zapping" sounds but it's never caused vacuum loss to date (At one point I was "using up" spent lamps in there that still had a few hours in them yet but wouldn't light on 2-lamp ballasts, especially LPF).
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Feb 22, 2015 at 07:50 PM Author: streetlight98
Ah so on HPF the lamps will not rectify? That's good news. I guess I just need to keep and eye out on my NPF fixtures if/when I put them into regular service. @ Andy: maybe the bad cap is allowing the lamps to rectify?

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ace100w120v
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Feb 22, 2015 at 07:56 PM Author: ace100w120v
Quite possibly. I'm testing one of my Universal 14/15/20w single lampers now to see how hot it gets as opposed to yours.
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Feb 22, 2015 at 08:56 PM Author: don93s
@ace, occasionally those older HPF ballasts will have the oil filled cap short out...I've had a couple do that. It basically just becomes a NPF ballast. I think they will then usually light two lamps dimmer and will rectify if EOL, but a one-lamp shunt will cause it to overheat, as it causes the lamp current to jump whereas a cap usually limits that.

Oh, if the "starting" side of cap shorts, then it will light only one lamp that is NPF, will rectify, and overheat the ballast.
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Feb 22, 2015 at 09:13 PM Author: streetlight98
It would be cool if ballasts came with an integral plug where an appropriate capacitor could be plugged in to make the ballast HPF and if no cap is desired, a jumper can be inserted into the plug. That would be a cool feature but magnetic ballasts are a thing of the past now I guess...

I had a cap with my 400W HPS Westinghouse ballast go open circuit. I lit it once, it was fine. Then i lit it again and one of the terminals on the cap started arcing and then nothing would happen. Fortunately the ballast and igniter were fine and a new cap solved the issue. The capacitor was the original GE dry capacitor from the 80s (yep GE cap with a Westinghouse ballast lol. Thomas & Betts lights in the 90s typically had GE caps too). The replacement is also a GE and of a similar age. It's an identical replacement.

The other time I had a capacitor fail was with my 1950s long john shoplight (at least the consensus here was that the cap was to blame) which went out violently. There was a LOT of PCBs from that one! And a good amount of tar came out too. At some point the ballast circuitry went open circuit somewhere (perhaps it was the cap itself that went open circuit after several minutes) which saved my house from burning down, although it was too late for the fixture. The PCB oil had lifted the paint inside off the metal (I guess that crap is good paint remover lol) and the ballast got hot enough to brown the fresh white paint on the outside of the reflector where the lamps are. I had restored the fixture with new paint and all new screws and it was all for nothing I guess. At least it was a suspended fixture so the house didn't burn down. I honestly would have loved to watch the destruction though. It would have probably been cool to watch. The lamps survived but are pretty blackened now, suggesting that they were being very overdriven at the time of the ballast EOL. The freakiest thing that ever happened to be with lighting! Coincidentally it happened when my brother left the lights on overnight by accident. That was the longest period of time it had ever ran, so perhaps it was an accident waiting to happen all along and the capacitor was never charged long enough or the ballast never got hot enough to fail?

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Feb 22, 2015 at 09:27 PM Author: themaritimegirl
HPF fluorescent lamp ballasts are CWA, not HX, so you actually do need the cap for them to run properly. If they were HX, then indeed, such a feature would have been neat. You can replicate the same thing on any LPF ballast though, even a choke. Just determine the proper value of the cap, put it across the line input, and you'll cut current draw by about half.

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Feb 22, 2015 at 09:29 PM Author: streetlight98
Oh so they ARE CWA? I thought they were just NPF ballast with a power factor-correcting capacitor? How do you determine the proper cap value to convert a NPF ballast to HPF?

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Feb 22, 2015 at 09:33 PM Author: themaritimegirl
Yeah. That's how they are able to regulate the lamp current over a wide range of arc voltage. An HX ballast will behave just like an LPF ballast in that regard.

It's quite a mathematical process to find the proper cap value, but I was able to condense the required calculations into one equation. I posted it somewhere here because TheUniversalDave1 wanted to know too. If I find it I'll post it here.

The only thing is, you need to know things like the current draw and power factor of the ballast, so you would need a Kill A Watt to determine that.

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Feb 22, 2015 at 09:38 PM Author: don93s
I also believe that you can't just add a cap to a designated NPF ballast...something about the way they are designed. I've tried it and it just doesn't work right. Lamp current might register as "normal" but it clearly would be dim....like maybe a horrible crest factor or something.
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Feb 22, 2015 at 09:41 PM Author: streetlight98
Ah I see. So not as cut and dry and it sounds.

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Feb 22, 2015 at 09:42 PM Author: themaritimegirl
I've done it with no problem. They are connected in parallel, so it shouldn't affect it in any way. It would be the exact same result as if you plugged the light into one outlet and plugged the capacitor into a completely separate outlet.

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Feb 22, 2015 at 09:42 PM Author: ace100w120v
So is there any danger in using a ballast with a shorted oil-filled cap as long as it doesn't overheat? (Which mine sometimes does)
That Universal I have shunted for one lamp has a pretty toasty label, suggesting it got pretty hot one or more times in the past. Would a failing cap be to blame there as well? It's never tripped the thermal cutout though running shunted in regular use since May 2013.
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Feb 22, 2015 at 09:44 PM Author: themaritimegirl
Depending on how the ballast was designed, the loss of capacitance may cause lamp current to be higher than normal, which would explain the overheating.

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Feb 22, 2015 at 10:27 PM Author: don93s
@Trent, I was referring to cap in series with lamp, as typical with most autotransformer style HPF ballasts.
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Feb 22, 2015 at 10:30 PM Author: themaritimegirl
Oh. Well yeah, if you do that, you're either going to overdrive the lamp (because the capacitor reactance subtracts from the choke's reactance), or underdrive it (because the capacitor's reactance is more than twice the choke's reactance, thus causing the impedance vector to go in the opposite direction, with a length longer than just the choke's reactance). The appropriate way to improve the power factor of any inductive load is to just put the cap in parallel with the load at the power input. I would indeed be cool to try a CWA setup, though.

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Mar 02, 2015 at 06:29 PM Author: suzukir122
I've seen some rather impressive EOL shows from high power factor rapid start and even trigger start ballasts. I guess
it depends on the ballast though. I've never seen one actually rectify a lamp however!

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