Exploring an LED bulb that went pop
Added 2025-04-14 04:29:38 +0000 UTCIn hindsight I would have tested the capacitor differently. (Rectifier and a tungsten bulb in series to limit the current.)
But the fusible resistor did an admirable job of limiting the fault current and breaking the circuit.
Comments
It was bought secondhand too. When someone upgraded to a combined tester.
Big Clive
2025-04-16 03:07:37 +0000 UTCYeah, I realized that the tester discharged the cap afterwards. Hindsight is a wonderful thing.
Big Clive
2025-04-16 03:06:54 +0000 UTCAt 1.6mA, it only takes ~2s to charge 6.8uF to 500V. What you are seeing is the insulation algorithm trying to make sense of declining current as the dielectric absorption (soakage) settles. For reference, a Polarization Index test runs for 10 minutes. The important thing is you're getting a steadily moving reading rather than an unstable one. Also important for safety, the tester discharges the load at the end of test. If you want a pop you need to detach the leads with the test still running.
Mike Page
2025-04-14 22:13:03 +0000 UTCThat DIT400 - yes, all the rubber overmould from that era is breaking down. I suppose they must be ~18 years old now. I don't know if newer products will have the same issues. As you say disappointing but it's not like you paid Fluke money for it ...
Mike Page
2025-04-14 22:05:26 +0000 UTC
