Fluorescent lamp capacitors can fail

I have written about fluorescent lights technology and fire dangers related to fluorescent lights. I had earlier covered the problems related to starter, bad tube and ballast overheating.

Now there is another risk to consider: most fluorescent lamps powered from 230V AC have a filtering capacitor on power input between live and neutral. This is typically there for interference suppressing and/or power factor correction.

That capacitor is normally X rated “self healing” type, but they can sometimes fail. When they fail their case starts turning black, and they can start putting out smoke – and potentially start a fire.

Here is one example:

Maybe it’s a good idea to start to replace very old fluorescent lamps before they fail. The replacement means replacing the whole lamp – using safety starter or LED bulb does not help in this problem.


  1. Tomi Engdahl says:

    Similar failing capacitors also on other devices:

    EEVblog #1183 – RIFA Madness (Schaffner Repair)

    Repairing the Schaffner NSD200E Mains Interference Simulator.
    And the dangers of bad mains filters capacitors, and RIFA brand in particular.


    The Schaffner IEC connector is almost certain to fail in the same spectacular fashion. I haven’t opened one up but I suspect they have same RIFA caps inside and exhibit the same failure mode.
    In my experience the RIFA caps drop to quite a low insulation resistance before failure so an insulation resistance test from line to earth can be useful for finding dodgy Y caps in an IEC module. I treat anything with an insulation resistance of less than 10 megohms as an imminent failure and replace the filter module.
    However, finding dodgy X caps with an insulation resistance test from line to neutral is less successful since the filter modules commonly have a in-built discharge of a few megohms which masks the leakage of a failing X cap. It is safest to just immediately replace any Schaffner IEC connectors of that vintage.

    I had 2 of these RIFA caps fail in an old sewing machine.

    RIFA caps and VARTA memory backup cells…. Match made in hell.

    Yep, always blame the Rifa, I had one go bang inside a Hoover Junior vacuum, the stink was immense and the stink stuck on the vac for months even after cleaning the mess out. Where there’s a Rifa, there’ll be trouble…

    twocvbloke moisture in compounds remains a modern problem, even with hermetic and conformal coating. Shell up what you may, when things short and go bang the case becomes a potential projectile no matter the construction.

    These Rifa are known for that……after some years of work……I used to work with process recorders in a power plant and they all used these caps. As these recorders were pluged in 24/7, all the caps had to be replaced because of that issue. Good video.

    In German vintage audio forums, these RIFA caps are known as “Knallfrosch”, which translates to firecracker.

    “safety capacitor” and “notorious for failing” don’t go together too well.

    isnt that what makes them safe, they fail open
    if they explode it should fail open, ive had a few go off and its better then a cap shorting and burning up the rest of the circuit that might also catch on fire.

    In europe they might be underrated by now also since we have raised the grid voltage. In my sewing machine there were 220v caps and our grid is now 250. I dont know how much that would matter but the new ones are properly rated anyway.

    the main ac filter is to keep line noise from getting in or out , so basicly for passing ~60hz and bolcking anything else that is unwanted noise. most crap today its to keep that unwanted noise from getting out because the high speed switching power supply’s polluting the airwaves … and power lines

    I’d argue it’s not “because” those are Rifa, but those metallized paper mains-caps are indeed notorious for failing.

    Believe it or not, these RIFA caps are still available!

    I once replaced a bunch of those RIFA capacitors in analog dimmer packs of an old theatre, those things really stink when blown!


  2. Tomi Engdahl says:

    Fluorescent Tube Lighting

    A look at switch start linear fluorescent lighting, how the tube, starter and ballast are wired and theory of operation.
    Also features an old more unusual type of tube connection.

  3. Tomi Engdahl says:

    EEVblog 1486 – What you DIDN’T KNOW About Film Capacitor FAILURES!

    You might think you know how film capacitors fail and degrade in capacitance over time – self-healing due to surges, right? WRONG!
    Capacitor expert and AVX Fellow Ron Demcko confirms what’s really going on after a teardown of some failed and one good polypropylene X class capacitor.

    00:00 – Teardown of a some failed film capacitors
    00:52 – Self Healing and drop in capacitance
    01:44 – Capacitance Measurements
    02:15 – Teardown of a new Suntan brand polypropylene X2 film capacitor
    03:03 – Different failure modes based on size and winding pressure
    05:52 – Unwrapping the film
    07:51 – The film inside a NEW film capacitor
    09:19 – Teardown of the FAILED uTx brand heater capacitor with half capacitance
    10:06 – How Schoopage and the end pin terminations work
    12:23 – Teardown continues…
    12:45 – WOW! What on earth is this?
    14:54 – Elecami Wolf also did a teardown
    16:05 – Teardown continues…
    17:01 – Separating the film showing both slef-healing and extensive metal film corrosion
    18:29 – Another uTx brand failed film capacitor from a Corsair PSU, with 90% loss in capacitance!
    Elecami Wolf Youtube Channel: https://www.youtube.com/c/ElecamiWolf
    19:55 – Let’s call an expert! Ron Demcko from AVX tells us the REAL REASON for the failure!
    It’s moisture ingress and corona demetallization!

    Full discussion with Ron Demcko:

  4. Tomi Engdahl says:

    Metallized Film Capacitor Lifetime Evaluation and Failure Mode Analysis

    One of the main concerns for power electronic engineers regarding capacitors
    is to predict their remaining lifetime in order to anticipate costly failures or
    system unavailability. This may be achieved using a Weibull statistical law
    combined with acceleration factors for the temperature, the voltage, and the
    humidity. This paper discusses the different capacitor failure modes and their
    effects and consequences


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