NOS CFL's

[Beta 5]

@Alex, Interesting, I guess that goes with the territory of the cheap Chinese lamps, probably poor quality components to begin with.
I've got a 12V DC cold cathode CFL, I'll have to keep an eye on it in case it suffers the same thing.

@Oliver, I wonder, would that one that smoked and carried on working actually be a case of the dreaded Rifa PME271 class Y capacitor? I think some of the old CFL's had these wired across L-N for interference suppression, but like the ones in the old HF ballasts when they get old they crack and then eventually smoke out like that.

@Kev, Yeah the Panasonic ones look decent, I've got an NOS 1998 20W one in service at the moment actually.

[Flurofan96]

I suspect that could have happened with one of the GE Biax Hungarian made stick CFLS but also possibility of the tube seal being compromised for some odd reason - it didn't go past the preheating phase and then smoke started coming out of the base!!! That was sometime back in 2024

However I've not encountered a CFL stop working due to capacitor disintegration ever since

[Beta 5]

Do you still have that CFL flurofan? It would be interesting to open it up and see what has gone, if it was the main electrolytic capacitor or something else? Also to try the tube on some other gear and see fi that still works of has lost vacuum?

[Ash]

"tssss" is the electrolytic. There are a couple small film capacitors there but i think they are way too small to make any such sound if they fail

With the electrolytic gone, the CFL may keep going but flicker at 100Hz (and may appear dimmer because of this). Besides, it is possible that a localised area of the capacitor was boiling away while the rest of it still had liquid electrolyte in it and could hold charge, in which case the CFL would just light normally

I did have a larger film capacitor fail in a PC power supply in a way that it was stinking up the room (without visible smoke, as it was blown by the fan fast enough to be dispersed in the air such that it is invisible), yet the PC was working. I figured it is it when i caught a whiff of the smell

Those power supplies (cheap ATX stuff of the early 00's) are nearly all based on half bridge circuit, same as CFL ballasts. The rectified mains is applied to 2 electrolytic capacitors in series, each charged to 160VDC. The mid point between them goes to one end of the transformer primary winding, the other end is switched to the +cap or -cap in alternating order by 2 transistors to generate symmetrical HF AC

In theory the PSU would work like this just fine. In reality, the electrolytics may have some difference in the voltage across them due to uneven leakages. This would result in assymetrical AC wave applied to the transformer, and this will lead to its saturation (you dont want this). To force the waveform to be symmetrical no matter what, a film capacitor of 2.2uF or so is added in series with the transformer. The film cap has very low leakage, so it will block any assymetry (the DC shift will be charged in the capacitor and this way subtracted from the voltage that the transformer sees)

In this power supply this film capacitor went into meltdown like plastic PFC capacitors in fluorescent fittings do. It was cracked and melting plastic was pouring out of it. The PC still worked because apparently the electrolytics were balanced enough that it worked without assymetry

The circuitry in a CFL is similar with some differences due to the low power (compared to ATX power supply) and desire to cut down costs. The mid voltage is not taken from a divider, but from one of the poles of the DC (often +). The film capacitor then is charged to 160VDC or so (ie. making up for half the mains voltage) instead of normally voltages close to 0V in an ATX power supply with proper mid point. Finally, instead of a transformer there is the choke, tube and starting capacitor

[AngryHorse]

Interesting discussion , however, of all the hundreds of CFL I have, none to date have had this fault yet?