What happens when a flourescent ballast "goes out"?

It seems to me that a flourescent ballast is probably just a transformer and a high-voltage electrolytic cap. And when it "goes out" it's probably because the cap failed. If these are true, could I just replace the cap and make it work again? Assuming (hate that word) of course that I could get the ballast open. What thinks the group? Please offer whatever laughing criticism or encouragement you feel is appropriate. I do not need a fire hazard in the kitchen...

Many thanks,

Dave

Reply to
Dave
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If you were that bothered. Like to see you get the right type though.

Why not replace it with an electronic ballast ?

Graham

Reply to
Eeyore

Yeah... My Scottish soul hates to throw away anything that might be fixable though. Still. Are there different types of caps for ballasts? Probably not worth bothering with...

Thanks,

Dave

Reply to
Dave

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Now if IIRC, the passive ballast for flourescent lights is a big inductor which serves two purposes, the first is to store the energy needed to ignite it (400 Volt-ish IIRC), the second is to lower the voltage over the light to the operating voltage of the tube (which varies= ).

And taking a quick look on my flourescent tube over the kitchen sink, the components are (in no particular order): Ballast/Inductor, tube, igniter (small cylindrical thingy, say 15mm dia by 30 (or so) mm length) and a cap. And having assembled compact flourescents, I know that some of them come with the igniter built into the tube.

As to failures, I know that all components have a tendency to wear out, and that at least in the bigger, tube, models, the igniter and tube can be replaced (and should be replaced at the same time), and the other could too (although it could be difficult to find the correct values for the latter (have you tried the manufacturer?)).

As to electronic ballasts, they eliminate that irritating flicker on switch-on and, IIRC, have less losses. I know that there are electronic ballasts from many manufacturers (try Osram and Sylvania) for all sorts of flourescents, though you might want to check with the local laws and regulations whether it's something you can do yourself or leave to a pro.=

I've seen DYI electronic ballasts schematics, in the swedish version of Elektor, but that was ages ago (early/mid 90's).

Another point that comes to mind is the issue of RF interference, some ballasts, DYI or not, self-installed or not, have a tendency to cause unwanted signals in the HF band.

As to fire hazards, I have more than once seen the fire dept called out somewhere when the ballast has overheated (usually due to leaving a failed tube on for too long), emitting all sorts of interesting odors.

Well, that's what I can squeeze out of my brain for $.02 for the moment.

/T.

--=20 Teodor V=E4=E4n=E4nen | Don't meddle in the affairs of wiz= ards, | for you are good and crunchy with

formatting link
| ketchup. Remove stupidity to reply. |

Reply to
Teodor Väänänen

Now if IIRC, the passive ballast for flourescent lights is a big inductor which serves two purposes, the first is to store the energy needed to ignite it (400 Volt-ish IIRC), the second is to lower the voltage over the light to the operating voltage of the tube (which varies).

And taking a quick look on my flourescent tube over the kitchen sink, the components are (in no particular order): Ballast/Inductor, tube, igniter (small cylindrical thingy, say 15mm dia by 30 (or so) mm length) and a cap. And having assembled compact flourescents, I know that some of them come with the igniter built into the tube.

As to failures, I know that all components have a tendency to wear out, and that at least in the bigger, tube, models, the igniter and tube can be replaced (and should be replaced at the same time), and the other could too (although it could be difficult to find the correct values for the latter (have you tried the manufacturer?)).

As to electronic ballasts, they eliminate that irritating flicker on switch-on and, IIRC, have less losses. I know that there are electronic ballasts from many manufacturers (try Osram and Sylvania) for all sorts of flourescents, though you might want to check with the local laws and regulations whether it's something you can do yourself or leave to a pro.

I've seen DYI electronic ballasts schematics, in the swedish version of Elektor, but that was ages ago (early/mid 90's).

Another point that comes to mind is the issue of RF interference, some ballasts, DYI or not, self-installed or not, have a tendency to cause unwanted signals in the HF band.

As to fire hazards, I have more than once seen the fire dept called out somewhere when the ballast has overheated (usually due to leaving a failed tube on for too long), emitting all sorts of interesting odors.

Well, that's what I can squeeze out of my brain for $.02 for the moment.

/T.

--
Teodor Väänänen                | Don't meddle in the affairs of wizards,
   | for you are good and crunchy with
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Reply to
Dave

In all of the flourescent fixtures I've seen that use a cap, it was just a small ceramic disk capacitor wired across a little NE-4 or similar bulb, both contained in the easily replaced "starter" can. (But those were *OLD* fixtures - At least 20 years old) No caps to be seen anywhere else in them.

The failure mode I've always seen with dead ballasts has been breakdown of the coil insulation, usually resulting in a short/arc between the secondary and either the core or the case (or both, since most of them seem to have the core and the case electrically connected, either intentionally via a lug on the core with a strap to the case, or incidentally because the core was laying directly on the case) of the ballast.

The ones I've taken apart have all been buried in potting compound, and I have yet to see one with a cap inside the unit that could be replaced.

Last year, we had the ballast in an 8 foot fixture die, and it came scary-close to burning down the barn - I walked in for evening feed after one of the boarders had left the aisle lights turned on for most of the day, only to encounter the stench of "on the edge of starting to burn"-hot tar, a buzz like a swarm of angry bees, a cloud of smoke hovering near the ceiling, tar "icicles" dripping out the end of the fixture, and a puddle of tar on the floor below it. After killing the circuit and inspecting, found that the ballast had overheated to the point of blowing the potting compound all over the inside of the fixture, and the ballast case had most of its paint burned/scorched off it, with the metal obviously heat-discolored. It was so hot that touching it would have been good for at least a blister. That led me to checking the hayloft for hotspots, where I found that the 3/4 inch plywood decking that makes up the ceiling/hayloft floor was so hot above the failed unit that the plywood had started to de-laminate. Once the fixture was removed for replacement (I sure wasn't going to diddle around with trying to repair the thing with all that potting compound splattered everywhere) found obvious scorching on the downstairs side of the plywood. *WAY* too close for my liking...

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Don Bruder - dakidd@sonic.net - If your "From:" address isn't on my whitelist,
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Reply to
Don Bruder

Yes, not your ordinary type.

Graham

Reply to
Eeyore

Ahh. Thank you. Definetly replacement time...

Will not fiddle with it.

D
Reply to
Dave

There are several different kinds of fluorescent ballasts.

  1. Simple choke - has 2 leads, usually used with a starter (occaisionally a "push-to-start" switch). There is normally no capacitor.

When they fail, there is generally no repair other than rewinding (extremely unlikely to be worth the time and effort), and sometimes the core is welded together.

  1. High leakage reactance autotransformer - has 3 leads, and is effexctively a choke combined with a step-up transformer. Same story as
  2. A variant is the 1-lamp trigger start ballast, which has filament widnings added. It is still essentially non-user-serviceable.

  3. The USA-usual "traditional" dual-4-footer - high leakage autotransformer with a capacitor in series with the secondary. Also has filament windings and a small capacitor (in the ballast case along with all other parts) to leak a small amount of current around one lamp to help start the other when both are not conducting but voltage is applied. The
2 lamps are in series with each other.

If the lamp-series capacitor (which is not electrolytic) shorts, lamp current will be somewhat high and ballast input current will be very high.

There are similar "trigger start" ballasts for 2 2-footers.

The case is usually packed with tar. This one is also essentially non-user-serviceable.

  1. Electronic ballasts - more repairable than the others, but only by those who know how to troubleshoot and repair them *safely*. Capacitors may store charge, and improper repairs may add a fire risk. It may be difficult to verify that replacement parts are of suitable grades (temperature rating, life expectancy at given temperature, voltage and frequency, also failing less catastrophically, any flame retardance/resistance) and with suitable characteristics (such as losses sufficiently low to prevent overheating - and capacitors have 2 main losses). Also, one is unlikely to repair a ballast for less (including value of time) than to replace it.

Bottom line: Fluorescent lamp ballasts are generally unrepairable.

- Don Klipstein ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein

Thank you, Don. This backs up the conclusion I had basically come to, making me feel better about replacing the offending ballast. Much appreciated.

Dave

Reply to
Dave

hypothetically speaking yes.

But a flourescent balast is not the capacitor and the capacitor where present is typically not electrolytic.

the balast is the inductor. (transformer looking thing) the capacitor where present gives a measure of power factor correction.

if it's an iron balast it's only got iron and copper inside

if it's an electronic balast it could be a failed capacitor inside but could be a failed semiconductor etc....

probably best to go out and get a new balast.

Bye. Jasen

Reply to
Jasen Betts

the power factor correction caps are optional in some settings (eg domestic use) and required in others (eg commercial use), wether or not the cap is needed is a matter for the makers of the electricity regulations.

When you get 100 or more florescent fixtures all running at once (like you could in a school or supermarket) the large load with a power factor would be pretty horrible, the caps clean it up a bit.

I remeber the electricians discarding pitch-filled capacitors what had partially de-potted themselves while they were doing maintenance on the flourescent fixtures at high school.

8-foot? is that two 4 foot tubes? or do they make 8 foot tubes? the longest I've seen are 5 foot tubes.

hmm, I should dig out inverter I made and make me a light sabre :)

that bulb in the starter is not a simple neon either, there's a bi-metallic strip in there that un-shorts it when it warms up, while the starter is shorted the power flows through the filaments in the tube and warms up the electrodes.

Bye. Jasen

Reply to
Jasen Betts

And also all the smoke leaks out!!

Reply to
Ronbo

If you see the two ends of the flourescent tube are blackened, then the life of the lamp is over. You will need to replace the tube, not the capacitor.

Reply to
kkitsum

Often in normal end-of-life, only one end blackens.

If lamp life is unusually short, and there is end blackening to indicate that the lamp did indeed die, then chances are fairly high the ballast needs replacing.

- Don Klipstein ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein

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