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I have an older light timer that controls my porch light. It draws a small amount of current to keep running by feeding a small amount of current through the bulb all the time. In the days of incandescent bulbs, the current the switch used would flow through the filament, not being enough to heat the filament to make light.

The problem is that this doesn't work with LED bulbs. The small amount of current is enough to power the bulb up, but not enough for it to power up fully. This in-between state causes the bulbs to die fairly quickly.

This is the second dimmer/timer I've dealt with that does this.

I measured that the switch draws about 0.1A. I'm wondering if there is something like this socket extender that has a ~1000Ω resistor between the hot and neutral which would allow current to power the switch without killing my LED bulbs?

This is not something I am going to DIY directly, but I am curious if there is any solution for my situation.

older timer switch light with the switch off light with switch on

(Note the bulb which is off is partly unscrewed and not connected)

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    At 12 watts continuous consumption I'd be looking for a modern timer (or a photo cell). – isherwood Jul 13 '18 at 4:25
  • Is there a reason you can't put in a timer that uses neutral instead? – ThreePhaseEel Jul 13 '18 at 4:39
  • @isherwood Good point. 12W is a lot of power to be using all the time for no good reason. – John Jul 13 '18 at 5:20
  • @ThreePhaseEel Mostly I was looking to not replace something that is mostly working, but now that I see how much power the switch uses, it is probably greener to replace with the right switch. – John Jul 13 '18 at 5:27
  • @isherwood 12W is a lot of constant draw. Over 100KWh/year. $1/month at my rates. Can you check my method? I unscrewed the bulb and put the current meter between the collar and center pin of the socket when the switch was off. Any reason to think it would read higher due to my measurement? – John Jul 13 '18 at 5:30
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You'd think a dimmer would just lower the voltage. Nope. That'd be a variac, and would make the dimmer weigh about 20 pounds. Actually, old dimmers use one of a couple of "hacks" to dim cheaply, at the cost of doing really weird things to the AC power waveform. These methods are extremely optimized for incandescent bulbs only. (This happens at the cost of power factor and adding a lot of line noise to your house's electrical system. if you were to hook a 120V-rated speaker to your power line, you wouldn't hear the perfect sinewave hum, you'd hear a crunchy bunch of noise, and not the pretty MBV kind. Your other equipment doesn't really like this.)

However, the LED screw-in-bulb manufacturers are perfectly aware of these obsolete dimming techniques. It is possible, though not exactly "free", to build an LED that can

  • dim
  • "read the tea leaves" of the weird waveform to determine what brightness the dimmer is trying to make
  • include a circuit to actively allow the current leakage that old "neutral-less" dimmers require

This ability is not free. The cheapie manufacturers hedge for price, hard, and big-box sellers like Home Depot and Walmart really pin their providers to the wall to shave every fraction of a penny. So you bet those features are not included in run-of-the-mill bargain price bulbs as many consumers prefer.

Use quality bulbs engineered for this use

On the other hand, upscale vendors know there's a need and have labored to fill it. Again not a thing you'll find at the Dollar General. But if you deal with a Tier 1 supplier like GE (who has built a lightbulb or two in their history), Sylvania, Philips, Cree... so basically the Phoebus Cartel plus Cree... you will find plenty of LEDs that will do the job.

You may find them from Tier 2 vendors also, one of my faves being Ikea, whose quality is unearthly good for the price point. I don't count LoA, Utilitech and Feit, they fall in the last category IME and I have the dead bulbs to prove it.

Remember the bulbs you need should not be as cheap as the bottom shelf grab-candy. If they are, they're cutting too many corners. Playing nice with old dimmers is a hard problem and the builders need their price to make a quality product.

As far as those Tier Fell off a truck in Shenzhen vendors like you find in the old Dollar General, stop buying from them. Those products are specifically designed to sell to suckers.

  • We have a Lutron dimmer rated for LEDs on the main kitchen lighting which is four Cree (100 W ?) equivalent screw base LEDs in ceramic bases surface mounted on a "tin" ceiling. My new Fluke 115 TRUE RMS MULTIMETER reads 117 V and 59.97 hz. The dimmer works fine although we don't use it as much as we thought we would. Would this dimmer be putting noise on our wiring? – Jim Stewart Jul 13 '18 at 17:20
  • @JimStewart RMS doesn't measure PF. You'd need something more sophisticated. You could measure the lamp side with a $20 Kill-a-Watt's power factor indicator, measuring the line side is tougher. – Harper Jul 13 '18 at 17:32
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Put a low wattage incandescent bulb (20 W, 10 W ?) in one of the two sockets and an LED in the other. You can probably get the waste power down to a lower level. I don't know if this would damage the LED, but I doubt it.

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