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Strange problem with low energy light bulb

  • Thread starter Seán O'Leathlóbhair
  • Start date
S

Seán O'Leathlóbhair

Jan 1, 1970
0
Seán O'Leathlóbhair said:
I am not sure if this is an appropriate group for this question. If
not, please suggest a better one.

I have a light in the house which I have wanted to switch to a low
energy bulb for a long time. The hold up was that I needed a very
small bulb. At last, I have found a small enough bulb but something
odd occurred as soon as I put it in.

When it is switched on, it works as expected.

When it is switched off, it blinks every few seconds. So, I guess
that there must be a problem with the switch If it is passing nothing
then it would seem impossible for the bulb to do anything. I did not
notice any problem with the previous incandescent bulb but I guess
that if the switch is leaking a tiny amount, the filament would glow
too little to be seen.

I have a few questions:

What is going on? Is a tiny current leaking, building up a charge in
a capacitor somewhere until a sufficient voltage builds up to spark in
the bulb and discharge the capacitor, and then the cycle repeats.

Is it safe?

Will it wear out the bulb very fast?

Is it likely to be enough to replace the switch? (Actually three
switches can turn this bulb on and off).

Might I have to replace the wiring? (Much harder than just replacing
the switches)

So many replies that it is hard to know which one to reply to so I
will reply here.

A curious feature that I forgot to mention is the regularlity of the
flashes: every 2 seconds with no variation that I can detect with a
stop watch. This is why I thought of a capacitor charging up until it
reaches a critical voltage. But I was thinking of DC. AC is not going
to charge up a capacitor over 2 seconds. What is inside these bulbs? A
rectifier? A capacitor?

I will do some checking at the weekend. Climb into the loft space for
a look. Get the multimeter out. Trying other low energy bulbs. Try the
higher rated bulb. Etc.
 
E

Eeyore

Jan 1, 1970
0
Sjouke said:
Capacitive leakage from the HOT wire to the switch
wire?

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

Graham
 
S

Sjouke Burry

Jan 1, 1970
0
Eeyore said:
So why doesn't this happen all the time ? Answer, the capacitance is very low,
as is the frequency.

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.
 
S

Seán O'Leathlóbhair

Jan 1, 1970
0
Chris said:
This has come up before in aus.electronics though I don't recall if there
was a definite cure for it.

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.
 
W

William R. Walsh

Jan 1, 1970
0
Hi!
When it is switched on, it works as expected.
When it is switched off, it blinks every few seconds.

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
 
F

Franc Zabkar

Jan 1, 1970
0
I am not sure if this is an appropriate group for this question. If
not, please suggest a better one.

I have a light in the house which I have wanted to switch to a low
energy bulb for a long time. The hold up was that I needed a very
small bulb. At last, I have found a small enough bulb but something
odd occurred as soon as I put it in.

When it is switched on, it works as expected.

When it is switched off, it blinks every few seconds. So, I guess
that there must be a problem with the switch If it is passing nothing
then it would seem impossible for the bulb to do anything. I did not
notice any problem with the previous incandescent bulb but I guess
that if the switch is leaking a tiny amount, the filament would glow
too little to be seen.

I have a few questions:

What is going on? Is a tiny current leaking, building up a charge in
a capacitor somewhere until a sufficient voltage builds up to spark in
the bulb and discharge the capacitor, and then the cycle repeats.

Is it safe?

Will it wear out the bulb very fast?

Is it likely to be enough to replace the switch? (Actually three
switches can turn this bulb on and off).

Might I have to replace the wiring? (Much harder than just replacing
the switches)

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

CFL "pulses" when off!
http://groups.google.com/group/aus.electronics/msg/9cf60300f04b7d5a?hl=en&

I don't know if anything was resolved, but the distributor of a
certain CFL brand wrote:

"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:
http://groups.google.com/group/aus.electronics/msg/544641abb5398c8c?hl=en&

Here is an interesting site that shows what is inside these lamps:
http://www.pavouk.org/hw/lamp/en_index.html

- Franc Zabkar
 
W

William R. Walsh

Jan 1, 1970
0
Hi!
I have a few questions:

What is going on?

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.
Will it wear out the bulb very fast?

It may result in a slight amount of wear on the bulb, but I doubt the change
in lifetime would ever be noticed.
What is inside these bulbs? A rectifier? A capacitor?

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
 
E

Eeyore

Jan 1, 1970
0
Sjouke said:
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.

It flashes every 2 seconds or so.

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

Graham
 
C

Chris Jones

Jan 1, 1970
0
Seán O'Leathlóbhair said:
I am not sure if this is an appropriate group for this question. If
not, please suggest a better one.

I have a light in the house which I have wanted to switch to a low
energy bulb for a long time. The hold up was that I needed a very
small bulb. At last, I have found a small enough bulb but something
odd occurred as soon as I put it in.

When it is switched on, it works as expected.

When it is switched off, it blinks every few seconds. So, I guess
that there must be a problem with the switch If it is passing nothing
then it would seem impossible for the bulb to do anything. I did not
notice any problem with the previous incandescent bulb but I guess
that if the switch is leaking a tiny amount, the filament would glow
too little to be seen.

I have a few questions:

What is going on? Is a tiny current leaking, building up a charge in
a capacitor somewhere until a sufficient voltage builds up to spark in
the bulb and discharge the capacitor, and then the cycle repeats.

Is it safe?

Will it wear out the bulb very fast?

Is it likely to be enough to replace the switch? (Actually three
switches can turn this bulb on and off).

Might I have to replace the wiring? (Much harder than just replacing
the switches)

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

Chris
 
R

Ron(UK)

Jan 1, 1970
0
Eeyore said:
Ron, when the switch is off, there is no circuit. The neutral potential
literally doesn't matter.

Graham

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)
 
A

Arfa Daily

Jan 1, 1970
0
Ron(UK) said:
If the neutral wire isn't properly grounded enough voltage can be induced
by or leak from other 'live' circuits, maybe enough to cause the
fluorescent fittings to randomly flicker. It could be a faulty switch
leaking across the contacts.

You don't live beneath an electricity pylon do you? It might also be the
rays from guvmint mind control experiments entering your house. ;)

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
 
E

Eeyore

Jan 1, 1970
0
Ron(UK) said:
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.

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

Graham
 
S

Sam Goldwasser

Jan 1, 1970
0
=?iso-8859-1?B?U2XhbiBPJ0xlYXRobPNiaGFpcg==?= said:
Se=E1n O'Leathl=F3bhair said:
A good question but no.

It is a landing light. There are three switches, one at each end and
a third in the middle where a small corridor from the bathroom joins
the landing. All simple on off switches (well they must be changeover
switches but, from the user's point of view, they are just on off).

And none are lighted switches?

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J

Jamie

Jan 1, 1970
0
Ron(UK) said:
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)
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.
 
S

Sam Goldwasser

Jan 1, 1970
0
Eeyore said:
That would appear to be the case.

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.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.
 
S

Sam Goldwasser

Jan 1, 1970
0
Eeyore said:
Makes no difference. When the switch is off, the circuit is broken.

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.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.
 
S

Sam Goldwasser

Jan 1, 1970
0
=?iso-8859-1?B?U2XhbiBPJ0xlYXRobPNiaGFpcg==?= said:
So many replies that it is hard to know which one to reply to so I
will reply here.

A curious feature that I forgot to mention is the regularlity of the
flashes: every 2 seconds with no variation that I can detect with a
stop watch. This is why I thought of a capacitor charging up until it
reaches a critical voltage. But I was thinking of DC. AC is not going
to charge up a capacitor over 2 seconds. What is inside these bulbs? A
rectifier? A capacitor?

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

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.
 
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