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Archive for February 26th, 2016

LED Shoplight Conversion: Fluorescent Fixture Teardown

The weakest fluorescent shop light fixtures always fail during cold weather (apart from the usual early tube failures) and this winter’s cold spells triggered the usual carnage, so I picked up half a dozen (cheap) 22 W LED T8 tubes and set about rewiring three defunct (cheap) fluorescent fixtures from the recycle heap. The new LED tubes run directly from the AC line; you must remove the fluorescent fixture’s ballasts / capacitors / starters and rewire the “tombstone” lampholders accordingly.

The first challenge, as always, involved taking the fixtures apart. Turns out prying the endcap away from the fixture enough to clear the pair of bumps punched into the metal does the trick:

Fluorescent Shoplights - endcap latches

Fluorescent Shoplights – endcap latches

Each endcap contains the ballast inductor / choke and power-factor correction capacitor for one tube. The inductors from one shoplight had a fancy plastic tab that might have held the capacitor in place, but that’s about the only difference:

Fluorescent Shoplights - ballasts

Fluorescent Shoplights – ballasts

The 150 kΩ resistor has its leads twisted around the capacitor leads without benefit of that fancy solder stuff one might think necessary for a good connection.

The capacitor contacts use the minimum possible amount of material:

Fluorescent Shoplights - capacitor termination

Fluorescent Shoplights – capacitor termination

I think the caps use metallized Mylar film, but who knows?

The inductors measure 280 mH and the caps a whopping 5 µF. I might trust the inductors in a low-voltage circuit, but the caps have no redeeming features and went directly to the trash.

The starter PCB lived in the center of the fixture:

Fluorescent Shoplights - starter circuit

Fluorescent Shoplights – starter circuit

I deliberately picked LED tubes with the AC line contact on one end and the neutral contact on the other, so as to not put line and neutral contacts in the same tombstone. After rewiring, the neutral endcap looks like this:

Fluorescent Shoplights - neutral endcap

Fluorescent Shoplights – neutral endcap

The other endcap holds the power cord and has a green earth ground wire snaking out to a little tab passed into a slot punched in the metal case. I replaced the tab with an actual screw / solderless connector / toothed washer, but have no pix to show for it.

The LED tubes run at 6500 K and contrast harshly with the warm-white tubes in the fluorescent shoplights. I went with the highest light output, because even the best (cheap) LED tubes produce barely half the output of the fluorescents: 2000-ish lumens vs 3900-ish.

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