Why Did Art’s LED Lamps Begin to Flash?

Something interesting happened when Art Reis helped out on a homeowner’s electrical project
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Art Reis, principal of RadioArt Enterprises, writes that lighting seems to be evolving at a rapid pace — as anyone who has had to buy an old-school incandescent bulb recently can attest.

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Fig. 1: LEDs aren’t just for status panels any more. For years, the compact fluorescent bulb has been the replacement of choice for the old hot-filament type; but they have their own demons, including RFI and a hazmat problem.

LED light bulbs have become prominent, but the concern here, at least at the outset, was cost. Lately, that drawback has been evaporating, with LED bulb prices falling faster than the price of oil. Art has seen 60 watt versions in the local hardware store for under $3.

He recently undertook the electrical upgrade of a home where the wiring was over 70 years old and becoming dangerous. As a part of the project, all the original-equipment “push-button” light switches were replaced with glow-in-the-dark switches that have neon bulbs in the handle.

The homeowner had picked up a whole carton of the new, low-priced LED bulbs, so they were duly installed in their new lamps. When power was applied, the bulbs came on perfectly — no latency as with their CFC counterparts, and no “warm-up” time either.

Then Art turned all the lights off.

Within moments, the LED lamps began to flash, every few seconds, without fail. Everywhere there was an LED lamp with a neon-lit switch, there was a flash, and the flashes were not synchronized. They were “dancing” from room to room!

It took Art a moment to figure out what was going on. Can you? We’ll return to the discussion in a moment.

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SBE members are a great resource for today’s broadcast engineer. At a recent chapter meeting, the question of coatings on guy wires came up. Is it necessary; does it help or hurt the guys? Is grease sufficient?

The overwhelming response was the wires should be periodically greased, the thinking being that grease will inhibit rust. A tower contractor took issue with other types of coating, saying those don’t help much because the outer coating would come off, and the internal pressure of the wires making up the guy wire would be enough to keep out foreign material. Greasing the guys is adequate.

Another person whose experience I respect says check with the provider of your guy wires and tower for their recommendation, especially if you operate in a saltwater environment. “I don’t generally see corrosion on guy wires, though once in a great while I see some that are pretty bad, particularly on smaller towers with smaller/cheaper cables. It’s always been my assumption, and that’s all it is, an assumption, that it depends on the material and/or manufacturing process as to how they weather.”

What has been your experience? I’d like to hear from Workbench readers at johnpbisset@gmail.com.

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Bill Bowin is chief engineer for North American Broadcasting Co. in Columbus, Ohio. He was seeking a battery for the amplifier in an old Delta OIB-1 when his wife Sherrie Bowin, CRO, CBNT, ran across a firm that manufactures replacements for batteries that have been obsolete for years. Visit www.exellbattery.com.

One of their products includes a replacement for the “B” batteries found in the older Nems-Clarke, Potomac and other AM field intensity meters. Exell Model 457 is a 67.5 V alkaline replacement battery. Type “457” into the search field of the website.

In addition to periodic recalibration, battery replacement can restore some of these old timers, and batteries from Exell are made in the USA.

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Back to Art’s flashing lamp problem.

Remember that with a neon-lit switch, the circuit is never completely off. There’s always at least a tiny bit of current going through the neon bulb and its companion 100 k ohm resistor, then through the LED lamp. Inside the LED lamp is a tiny digital power supply circuit that sets the proper voltage for the LED. That circuit includes a charging capacitor.

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Fig: 2: The changing face of your local neighborhood bulb shelf. With the light switch turned off, the current to the bulb is reduced to a trickle, but it is still present, so the capacitor charges up much more slowly until it reaches the circuit’s threshold voltage. Then it discharges all at once and the process starts again. What you are seeing is the circuit operating as it always does but in slow motion because the current flow is greatly reduced.

The bottom line is that, at least in Art’s experience, using LED bulbs with neon-lit switches is not particularly recommended.

Art ran this anecdote by a friend who is a lighting consultant, well versed in the latest stuff. He says that while Art’s experience is real, he would experiment with various brands and models of LED bulbs; he doesn’t believe that this trait is universal with this type of bulb.

However — and this is for you radio engineers out there who have studio facilities with neon-lit switches — when the boss shows up one day with a basketful of LED bulbs that he wants you to install in place of the old filament-burners, try one first, watch it for a minute or so, and if you see the thing flashing, let the boss see it, so he or she can decide which stays and which goes.

Contribute to Workbench. You’ll help your fellow engineers and qualify for SBE recertification credit. Send Workbench tips to johnpbisset@gmail.com. Fax to (603) 472-4944.

Author John Bisset has spent 46 years in the broadcasting industry and is still learning. He handles West Coast sales for the Telos Alliance. He is SBE certified and is a past recipient of the SBE’s Educator of the Year Award.

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