Strange problem with low energy light bulb

So why doesn't this happen all the time ? Answer, the capacitance is very low, as is the frequency.

Graham

Lots of stuff.

Graham

A leak cap has very high impedance, and via the input rectifier can charge the input cap(slowly). Then when a threshold is passed, the circuit produces a flash. And it only happens, if the input capacity of the rectifier circuit is low compared to the leak cap.

Thanks. If there is no danger, I don't need a cure. The flash is not irritating. The CO detector nearby flashes more brightly. I am just worried that it is telling me that something nasty is wrong with my wiring.

-- Se=E1n =D3 Leathl=F3bhair

Hi!

Do you have one of those switches that glows when you turn it off?

I have one attached to set a of conventional fluorescent fixtures (one four tube and one two tube). When the switch is "off" it still passes a tiny amount of current and this makes for a faint flashing in the two tube fixture. As far as I can tell this is perfectly safe...it has never caused any problems for the lamp or myself.

I do, however, have to turn the power off when changing the lamps in the two tube fixture. Otherwise there is the possibility of getting a small shock.

William

On Mon, 25 Jun 2007 07:03:01 -0700, Seán O'Leathlóbhair put finger to keyboard and composed:

There was a similar thread at aus.electronics earlier this year.

CFL "pulses" when off!

"We have found after much research that certain homes that are wired in a way where they are switching the neutral that this may occur with these lamps."

One contributor theorised that the switch wire may act as a capacitance. This would allow the main filter capacitor to gradually charge up via the bridge rectifier to the point where the circuit may "kick", after which the flash would discharge the capacitor and the cycle would start again.

This person experimented with various series caps and resistors:

Here is an interesting site that shows what is inside these lamps:

- Franc Zabkar

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Hi!

See my other reply. Do you have a light switch that glows when you turn it off? This will place a small amount of current flow across the lamp, which may make it flicker.

It may result in a slight amount of wear on the bulb, but I doubt the change in lifetime would ever be noticed.

In many cases, these bulbs contain a small switchmode power supply. Such a power supply will have a transistor, some type of controller, a small transformer and some support components (of which a capacitor would probably be included). Others use a much simpler transformer design.

William

low,

It flashes every 2 seconds or so.

Clearly a very low leakage current won't do that.

Graham

On Mon, 25 Jun 2007 22:28:59 GMT, Eeyore put finger to keyboard and composed:

low,

This fellow experimented with a ~1mA leakage current at 240VAC:

"Changed to 270 kohms and now have a 13W CFL flashing at exactly 1 Hz".

- Franc Zabkar

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This has come up before in aus.electronics though I don't recall if there was a definite cure for it.

Chris

It`s a two way switch, there`s plenty of potential for leakage paths. You can easily get 100v on the neutral if it`s floating above earth potential.

Ron(UK)

Ron - just a quick aside. It was you that I was talking to a few weeks back about the old ILP audio modules, wasn't it ? Well, thought you might be interested to know that the next issue of Elektor ( that'll be the September one as it is currently the July / August Summer Circuits double issue ) is doing a review and lab tests of a number of available pre-built audio modules.

Arfa

The OP said they weren't 2 way circuits though.

Graham

low,

I make that ~ 11nF !

You won't get that easily.

Graham

And none are lighted switches?

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Hmm.

2 way, 3 way , 4 way and any number of ways you want! why would that matter?, the neutral should not be part of the switching circuit.

--
"I'm never wrong, once i thought i was, but was mistaken"
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This is at least partly true.

Low energy lamps including compact fluorescents and normal fluorescents on electronic ballasts use a switching circuit to produce the high voltage for the fluorescent lamp. The input is a bridge rectifier and filter capacitor. Any source of AC even a small amount of leakage through a defective swtich, a switch with a neon lamp night light feature (lighted when off), an electronic timer, a motion sensor-controlled yard light, or a dimmer that isn't fully off, may cause the voltage to build up on the filter capacitor until the "startup circuit" kicks in. This usually has some sort of threshold de vice like a zener diode or diac that won't pass current until the voltage across it exceeds a spec'd value. When that happens, the lamp starts up and strikes but just for an instant since there isn't enough current available on the input to maintain it.

I'm somewhat skeptical of the explanation with respect to inductive or capacitive coupling (though possible under just the right - or wrong - conditions) but it doesn't take that much leakage from some other fault to do this.

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He said there are 2 or 3 switches controlling this lamp. In that case, there are a variety of ways that there could be capacitive and inductive coupling. Very often, there is a "traveller" with 2 parallel wires in it one of which is connected to the source and the other is connected to the lamp when it is off.

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No, you're correct. See my (and other) replies. It is a capacitor charging up - after a rectifier.

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