Fluorescent Shop Light Ballast Caps

It never ceases to amaze me that these capacitors appear in the AC power line circuits inside old-school fluorescent shop lights:

Shop light ballast cap
Shop light ballast cap

It really is a capacitor:

Shop light ballast cap A - test
Shop light ballast cap A – test

Its sibling from the other end of the fixture had more ESR:

Shop light ballast cap B - test
Shop light ballast cap B – test

Both were likely within spec, whatever that means.

I have no idea what’s lurking inside the tidy LED tubes now living in that same fixture, of course.

7 thoughts on “Fluorescent Shop Light Ballast Caps

  1. you call that “old school” but isn’t the black tin can filled with tar the “old school” ballast?

  2. I’m not sure, but I might have two shop light fixtures in the barn that are still using fluorescent tubes. These would be the old-school large diameter tubes. I don’t get to that space very often.

    All the rest either started as LEDs or got converted. The fun part is that some of the LED tubes are powered on both sides, while the others need power on one side. Relevant markings on the fixtures for the win. And all tubes skip the ballast.

    1. I made it a point to get LED tubes with Line on one end and Neutral on the other, because I absolutely did not trust the wiring in those crappy little tombstone connectors.

      And, yeah, conspicuous labels announcing LED Only and the wiring arrangement seemed like a really good idea!

      LEDs are now cheap enough that I’ll never convert any more fixtures after emptying the last box of tubes, but it made sense at the time.

      1. Ed, they are metalised polyester capacitors, self healing. They dont go bad easily.

        1. They just look awful!

          I measured one failure in maybe two dozen similar caps. Even though it’s a small sample, it just doesn’t produce a warm fuzzy feeling.

          They’re great cost-performers, though! [grin]

          1. I had 16 fluorescent shop light fixtures in the (38F minimum) barn, with 6 or so in frequent use. I had three fail with bad ballasts. I can take a hint.

            FWIW, we have an open-top fixture with a ceiling fan in the dining room. The third Home Depot-sold “Ecosmart” 9.5W bulb failed after three years. It looks like the power supply in the bulb was too cheapenified.

            Side note: after 10.333 years, the Dish DVR receiver went toes up. I hate the smell of scorched electronics in the morning. (The fail message said 153F in the hard drive–I suspect a bad fan in the power supply…) Dish doesn’t want the old unit back, so I’ll see if the hard drive is actually readable on a Linux system. The diagnostics mentioned fsck, so maybe.

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