CFL filament burnt - jump it?

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  • ben7
    Capaholic
    • Jan 2011
    • 4059
    • USA

    #1

    CFL filament burnt - jump it?

    So I recently had a CFL go dead on me. Well, I took it apart, and the electronics look good. Was in an upright position, so the PCB hasn't turned black xD

    I wrote the date on it when I put it in ... it's almost 5 years old.

    But, one of the filaments has burnt out. I bypassed the open filament and the bulb works again.
    Now, for any lamp experts here, Is it ok to have it run like this? I know it won't heat the gas/mercury up as fast, so could this damage the ballast in the long term?

    I measured the current draw and it was about 160mA ... the bulb is rated for 200mA ... go figure. Interestingly, as the bulb warmed up, the current increased! Just by a few tens of mA.

    -Ben
    Muh-soggy-knee
  • kaboom
    "Oh, Grouchy!"
    • Jan 2011
    • 2507
    • USA

    #2
    Re: CFL filament burnt - jump it?

    If you were measuring AC line current, that increase is normal.

    As the tube heats up, more voltage appears across it. Since lamp current is more or less regulated, a voltage increase corresponds to an overall power increase.

    This is reflected by the input current going up- the "ballast" is a form of buck converter.

    What you really did was connect both ends of the (open) filament together, obviously connecting an area with more cathode material "closer" to the circuit.

    You could often do something similar with linear fluro tubes, to get a few weeks/months out of them when they got cranky, by rotating 180 degrees (not end-for-end) in the sockets.
    "pokemon go... to hell!"

    EOL it...
    Originally posted by shango066
    All style and no substance.
    Originally posted by smashstuff30
    guilty,guilty,guilty,guilty!
    guilty of being cheap-made!

    Comment

    • ben7
      Capaholic
      • Jan 2011
      • 4059
      • USA

      #3
      Re: CFL filament burnt - jump it?

      Originally posted by kaboom
      As the tube heats up, more voltage appears across it. Since lamp current is more or less regulated, a voltage increase corresponds to an overall power increase.
      Yep, that is what I thought.

      Originally posted by kaboom
      What you really did was connect both ends of the (open) filament together, obviously connecting an area with more cathode material "closer" to the circuit.
      lol, not sure what you meant by making the material "closer" to the circuit.

      -Ben
      Muh-soggy-knee

      Comment

      • SteveNielsen
        Retired Tech
        • Jun 2012
        • 2327
        • USA

        #4
        Re: CFL filament burnt - jump it?

        When the cathode material fails the cathode separates into two parts opening the circuit. One part will contain more filament material than the other. Shorting the cathode leads completes the circuit again and puts a high potential on the remaining filament material.

        Comment

        • kc8adu
          Super Moderator
          • Nov 2003
          • 8832
          • U.S.A!

          #5
          Re: CFL filament burnt - jump it?

          my educated guess is that there is no emitter left and it will finish burning up what little is left.then the ballast will blow up.wont be as spectacular as the f96t12's we have in the shop though.

          Comment

          • SteveNielsen
            Retired Tech
            • Jun 2012
            • 2327
            • USA

            #6
            Re: CFL filament burnt - jump it?

            I think the other cathode is probably going to fail before the ballast fails, but it depends on how tolerant the ballast circuit is. If it can tolerate the increased power dissipation then when the other cathode fails the circuit becomes open again. Remember, the "good" cathode has a higher voltage across it now. That is going to shorten its life further.
            Last edited by SteveNielsen; 05-03-2015, 09:22 AM.

            Comment

            • stj
              Great Sage 齊天大聖
              • Dec 2009
              • 30989
              • Albion

              #7
              Re: CFL filament burnt - jump it?

              you just doubled the current to the remaining heater, it's not gonna last.

              more interesting, how is it controlled?
              i have seen 3 types.
              a mylar cap between the heaters << this is really shitty.
              a PTC - this is the correct way to do it.
              and some cheap lamps that use continuous drive (the location for a ptc is linked) < very bad!!

              Comment

              • SteveNielsen
                Retired Tech
                • Jun 2012
                • 2327
                • USA

                #8
                Re: CFL filament burnt - jump it?

                The cathode current remains the same (Kirchoff's Law) but the voltage has increased which increases the power dissipation (Ohm's Law). The end result is the same, the cathode runs hotter and the emitting material will become depleted faster and fail.

                Comment

                • stj
                  Great Sage 齊天大聖
                  • Dec 2009
                  • 30989
                  • Albion

                  #9
                  Re: CFL filament burnt - jump it?

                  Originally posted by SteveNielsen
                  The cathode current remains the same (Kirchoff's Law) but the voltage has increased which increases the power dissipation (Ohm's Law). The end result is the same, the cathode runs hotter and the emitting material will become depleted faster and fail.
                  your missing the point,
                  if the heaters fail then you cant vaporise the mercury and the lamp wont start.

                  you can start a lamp with a big spike, but cfl's dont use that method because it's dangerous and the polyester cap is too big.

                  Comment

                  • TechGeek
                    Computer Geek
                    • Jan 2015
                    • 2254
                    • USA

                    #10
                    Re: CFL filament burnt - jump it?

                    Originally posted by ben7
                    So I recently had a CFL go dead on me. Well, I took it apart, and the electronics look good. Was in an upright position, so the PCB hasn't turned black xD

                    I wrote the date on it when I put it in ... it's almost 5 years old.

                    But, one of the filaments has burnt out. I bypassed the open filament and the bulb works again.
                    Now, for any lamp experts here, Is it ok to have it run like this? I know it won't heat the gas/mercury up as fast, so could this damage the ballast in the long term?

                    I measured the current draw and it was about 160mA ... the bulb is rated for 200mA ... go figure. Interestingly, as the bulb warmed up, the current increased! Just by a few tens of mA.

                    -Ben
                    Dude, solder a 10K ohm resistor across the leads. That outta reduce the voltage.
                    Don't buy those $10 PSU "specials". They fail, and they have taken whole computers with them.

                    My computer doubles as a space heater.

                    Permanently Retired Systems:
                    RIP Advantech UNO-3072LA (2008-2021) - Decommissioned and taken out of service permanently due to lack of software support for it. Not very likely to ever be recommissioned again.
                    Asus Q550LF (Old main laptop, 2014-2022) - Decommissioned and stripped due to a myriad of problems, the main battery bloating being the final nail in the coffin.


                    Kooky and Kool Systems
                    - 1996 Power Macintosh 7200/120 + PC Compatibility Card - Under Restoration
                    - 1993 Gateway 2000 80486DX/50 - Fully Operational/WIP
                    - 2004 Athlon 64 Retro Gaming System - Indefinitely Parked
                    - Main Workstation - Fully operational!

                    sigpic

                    Comment

                    • SteveNielsen
                      Retired Tech
                      • Jun 2012
                      • 2327
                      • USA

                      #11
                      Re: CFL filament burnt - jump it?

                      Originally posted by stj
                      your missing the point,
                      if the heaters fail then you cant vaporise the mercury and the lamp wont start.

                      you can start a lamp with a big spike, but cfl's dont use that method because it's dangerous and the polyester cap is too big.
                      What point? The one you just brought up that was not being specifically discussed? That's absurd!

                      Comment

                      • kc8adu
                        Super Moderator
                        • Nov 2003
                        • 8832
                        • U.S.A!

                        #12
                        Re: CFL filament burnt - jump it?

                        post pics of the outcome.
                        my guess is the excessive cathode fall will overheat and melt the glass.

                        Comment

                        • ben7
                          Capaholic
                          • Jan 2011
                          • 4059
                          • USA

                          #13
                          Re: CFL filament burnt - jump it?

                          Originally posted by stj
                          more interesting, how is it controlled?
                          i have seen 3 types.
                          a mylar cap between the heaters << this is really shitty.
                          a PTC - this is the correct way to do it.
                          and some cheap lamps that use continuous drive (the location for a ptc is linked) < very bad!!
                          It's got the cap between the heaters. It's a GE lamp. I've taken apart a number of different CFLs and never seen a PTC. I guess it must be rare.
                          They always have the cap-between-the-filaments. Actually, one bulb (a n:vision) had blown this cap. It had a split in the side of it. I replaced it and the bulb worked again. I think it is still in use as well

                          Originally posted by TechGeek
                          Dude, solder a 10K ohm resistor across the leads. That outta reduce the voltage.
                          I think the 10K resistor might burn out, with the kind of voltages that are used here. Also, the "normal" filament resistance is around 2 to 3 ohms (from what I have measured in the past).

                          Originally posted by stj
                          if the heaters fail then you cant vaporise the mercury and the lamp wont start.
                          Yes, I know, but, what if only one heater has failed? That is what I am asking about.

                          Originally posted by kc8adu
                          post pics of the outcome.
                          my guess is the excessive cathode fall will overheat and melt the glass.
                          I haven't put it back into use yet.
                          By the way, what exactly is cathode fall? I looked it up, but, why would only one filament being used cause "excessive cathode fall"?

                          Originally posted by SteveNielsen
                          I think the other cathode is probably going to fail before the ballast fails, but it depends on how tolerant the ballast circuit is. If it can tolerate the increased power dissipation then when the other cathode fails the circuit becomes open again. Remember, the "good" cathode has a higher voltage across it now. That is going to shorten its life further.
                          Yeah I thought it would shorten the life. The HV cap in there between the heaters is 4.7nF. I wonder if I halve that, maybe the current will be reduced to a more normal level on the remaining filament? Either that, or I can put a capacitor in parallel with the filament.

                          Originally posted by kc8adu
                          my educated guess is that there is no emitter left and it will finish burning up what little is left.then the ballast will blow up.wont be as spectacular as the f96t12's we have in the shop though.
                          Well, the bulb was run while not working for a while. It didn't blow up, interestingly.
                          The circuit closely resembles this:
                          http://cdn.makezine.com/make/blogs/b...kea7wschem.png
                          Except there is no R5 (PTC). I think there is also no C4.
                          Muh-soggy-knee

                          Comment

                          • stj
                            Great Sage 齊天大聖
                            • Dec 2009
                            • 30989
                            • Albion

                            #14
                            Re: CFL filament burnt - jump it?

                            btw, a tube will last forever other than heaters and phosphor.

                            i have a 30year old atleast UV tube in an eprom eraser with broken heater.
                            i just warm the tube with the hot-air station before i plug it in and it strikes and runs every time!!!
                            (yes, i know i'm cheap!)

                            Comment

                            • ben7
                              Capaholic
                              • Jan 2011
                              • 4059
                              • USA

                              #15
                              Re: CFL filament burnt - jump it?

                              Originally posted by stj
                              i have a 30year old atleast UV tube in an eprom eraser with broken heater.
                              i just warm the tube with the hot-air station before i plug it in and it strikes and runs every time!!!
                              (yes, i know i'm cheap!)
                              L - O - L !!!

                              You sir, get the cheapskate of the year award!!!
                              Muh-soggy-knee

                              Comment

                              • TechGeek
                                Computer Geek
                                • Jan 2015
                                • 2254
                                • USA

                                #16
                                Re: CFL filament burnt - jump it?

                                Originally posted by stj
                                btw, a tube will last forever other than heaters and phosphor.

                                i have a 30year old atleast UV tube in an eprom eraser with broken heater.
                                i just warm the tube with the hot-air station before i plug it in and it strikes and runs every time!!!
                                (yes, i know i'm cheap!)
                                Nice. Another great way to save electronics. You might wanna consider attempting to rejuvenate the heaters or replace them.
                                Don't buy those $10 PSU "specials". They fail, and they have taken whole computers with them.

                                My computer doubles as a space heater.

                                Permanently Retired Systems:
                                RIP Advantech UNO-3072LA (2008-2021) - Decommissioned and taken out of service permanently due to lack of software support for it. Not very likely to ever be recommissioned again.
                                Asus Q550LF (Old main laptop, 2014-2022) - Decommissioned and stripped due to a myriad of problems, the main battery bloating being the final nail in the coffin.


                                Kooky and Kool Systems
                                - 1996 Power Macintosh 7200/120 + PC Compatibility Card - Under Restoration
                                - 1993 Gateway 2000 80486DX/50 - Fully Operational/WIP
                                - 2004 Athlon 64 Retro Gaming System - Indefinitely Parked
                                - Main Workstation - Fully operational!

                                sigpic

                                Comment

                                • stj
                                  Great Sage 齊天大聖
                                  • Dec 2009
                                  • 30989
                                  • Albion

                                  #17
                                  Re: CFL filament burnt - jump it?

                                  i dont have a vac chamber or glass blowing skills.
                                  besides, a new tube is only 5-10€
                                  (but that € is better spent on beer. )

                                  Comment

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