Strange problem with low energy light bulb

[Sam Goldwasser]

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.

This I wouldn't be so sure of. Startup is hard on fluorescent lamps.

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.

The transformer design will not experience this phenomenon.

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[Ken Weitzel]

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.

Perhaps we've finally discovered perpetual motion

Take care.

Ken

 

[James Sweet]

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.

Is one of the switches illuminated? Those will pass enough current to slowly
charge up the filter capacitor in the fluorescent bulb and cause it to
blink.

 

[James Sweet]

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.

--
Seán Ó Leathlóbhair



It'll probably cause the CFL to fail much sooner than it otherwise would.
I'd check the wiring and switches just because it's easy to do, make sure
there isn't any moist gunk between contacts or anything else like that.
Another option is to wire a small incandescent bulb such as a nightlight in
parallel but this is not always practical.

 

[Seán O'Leathlóbhair]

Hi!



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

No, plain simple switches with no good reason to pass any current when
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.

I noticed the problem when putting the bulb in - it blinked. Of
course, my first reaction was that I had left the switch on but this
was not a likely mistake since the previous incandescent bulb was not
dead.

 

[Eeyore]

I noticed the problem when putting the bulb in - it blinked.

There's something very odd going on if it did that.

Have you got a DVM/DMM ?

Graham

 

[Franc Zabkar]

This I wouldn't be so sure of. Startup is hard on fluorescent lamps.

I recently had two lamps (EDAPT 20W) fail in a relatively short time.
Curiosity got the better of me so I cracked them open to have a look.

Lamp A lasted about 3 months, lamp B about one week. Lamp A had an
open filament, and both had open "startup" resistors. Lamp B would
start when it was cold (or completely discharged?) but would not
restart just after it had been switched off. Lamp A would flash
briefly if I tapped it, despite the resistor being open. I'm wondering
whether the failure in the resistor caused the premature burnout of
the filament? If so, then this would be in line with your comment re
startup "trauma".

BTW, I repaired lamp B and it has been working ever since. I should
also mention that lamp A was full of dry solder joints which may have
contributed to its early demise.

- Franc Zabkar

 

[Franc Zabkar]

I make that ~ 11nF !

You won't get that easily.

Graham

Yes, I would think that even 100pF is way too much. The hypothesis
regarding stray wiring capacitance does seem very far fetched.

Maybe this explanation is a better one, a least for the other thread:
http://groups.google.com/group/aus.electronics/msg/1abcf4e439fbd911?hl=en&

AFAICS, you can *very* roughly calculate the amount of leakage current
required to account for the OP's observations by assuming that all the
current is used in charging the main filter cap, say 4.7uF. Assuming
also that the trigger voltage for the DIAC is around 50V, then ...

i = C . dV/dt
= 4.7 E-06 x 50V / 2s
= 0.12 mA

- Franc Zabkar

 

[Seán O'Leathlóbhair]

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 have not examined this particular circuit in detail yet. When I
came to the house, I was surprised to find three switches for this
landing light. I was used to two and knew how they worked but three
was new to me. I checked how it could be done and found this. The
neutral is connected directly to one of the socket terminals. Each of
the switches has two inputs and two outputs. The two inputs are
always connected to the two outputs but when the switch is moved the
connections are swapped. The live goes to one of the inputs to the
first switch. The two outputs from this switch go to the two inputs
of the next and so on through as many switches as you like (three in
my case). Finally one output from the last switch goes to the other
socket terminal. So, it is always possible for any switch to change
the state of the lamp. This will mean that the two possible live
wires run together for a considerable distance, more than the length
of the landing due to detours to the switches but the inductance
theory still surprises me (I am not saying impossible my knowledge of
electromagnetism is too old and rusty to say that). Animal damage or
some other cable damage sounds quite possible, a leakage between these
two lines would not blow a fuse but just allow a small current to
flow. Checking this cable is going to be quite unpleasant since the
loft is very small. The last time that I was up there, a few years
ago, to install aerial cable, the lighting cables appeared to be OK.

I will start by checking out all the switches since this is a
relatively easy job.

I can also use a multimeter and one of those neon screwdrivers to
perform some more tests. Sticking the probes of the multimeter into
the light socket sounds a little scary. This is a UK lamp socket
which may be unfamiliar to US readers and some others. The bulb does
not screw in it is a bayonet mount. You push the bulb in and turn and
a couple or prongs catch the mount and hold the bulb. The contacts
are two sprung pins which press onto contacts at the bottom of the
bulb. The collar is metal. To UK readers and others who know the
system: is the collar connected to anything? If my multimeter probe
touches a contact and the collar, is something nasty going to happen?
Obviously if both probes touch their contacts and the collar,
something nasty may happen.

 

[Seán O'Leathlóbhair]

And none are lighted switches?

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- Show quoted text -

Further details elsewhere but no they are not lighted.

 

[Seán O'Leathlóbhair]

On a cold wet miserable winter day in the early 70's. I was
troubleshooting a newish car, that wouldn't start, that had just been
serviced by a car dealership. a few days before. To cut a long story
short, they lubricated the Point Breaker mechanism with a clear Grease
that they probably used for years with no problems ! With 2 to 6 Amps
flowing, the contact mechanism probably cooked off any wet or
conductive grease. With the newer Hybrid Transistor switched points the
DAMP grease appeared as a Dead Short to the few milliamps required to
actuate the Transistor.

I would suspect the switches (All three) are lubricated with a grease
that is conductive enough read (dirty enough)to cause the problems
indicated !

The quick and dirty, to clear the excess grease is to replace the lamp
in question with a 60 - 100 watt bulb and switch On and Off a few
times. in the Off position any conductive grease will be burned away.

I may try that since it is easy. The previous bulb was a 40W
incandescent but we would not normally switch it on and off rapidly.
Would cleaning the contacts with something like WD40 be a good or bad
idea? I have never used this on mains voltage devices.

 

[Arfa Daily]

Is one of the switches illuminated? Those will pass enough current to
slowly charge up the filter capacitor in the fluorescent bulb and cause it
to blink.

If it's leakage from anywhere, a bog-standard electricians neon test
screwdriver should show that up. Or try wiring a mains rated neon indicator
straight across the lampholder without the lamp in place. If it glows, you
have leakage either across one of the switches, or between lives. Bear in
mind that with a two way circuit, there are two wires, one or other of which
is always live, running (normally) in a common cable sheath, between the two
switches. Also bear in mind that the poster said in his third reply that not
only is there a two way switch at either end of the landing, there is
actually a third switch at the half way point where a corridor joins the
main hallway. I'm not quite sure how you factor a third switch into a
'standard' two-way circuit, but it occurs to me that it might well be
'stealing' its live either from a second lighting circuit, or from some
considerable distance around the lighting circuit, from where the main live
for the circuit is taken. Either way, that third switch must join into the
actual landing light circuit, via some kind of junction box, which may be
part of the light fixture ceiling rose, if that's nearby, or a separate
entity in the loft. It could be potentially another place for some kind of
leakage taking place.

Did anyone see in the Sunday paper, an article regarding these CFLs causing
pre-fit symptoms to epilepsy sufferers ? Seems it's becoming common, and the
same people don't suffer with ordinary flourescents. Some research suggests
that it might be to do with the (apparently) very uneven spectral response
of the tri-phosphors used to try to get an 'incandescent' colour. Hmmm ...

Arfa

 

[Seán O'Leathlóbhair]

Perhaps we've finally discovered perpetual motion

Take care.

Well this light may be free in the sense it is being powered by energy
that was previously leaking unnoticed but I doubt that is free in the
sense that no energy is being consumed. The waste may even have been
reduced, the incandescent bulb may have drawn more from the leakage.

 

[Seán O'Leathlóbhair]

If it's leakage from anywhere, a bog-standard electricians neon test
screwdriver should show that up. Or try wiring a mains rated neon indicator
straight across the lampholder without the lamp in place. If it glows, you
have leakage either across one of the switches, or between lives. Bear in
mind that with a two way circuit, there are two wires, one or other of which
is always live, running (normally) in a common cable sheath, between the two
switches. Also bear in mind that the poster said in his third reply that not
only is there a two way switch at either end of the landing, there is
actually a third switch at the half way point where a corridor joins the
main hallway. I'm not quite sure how you factor a third switch into a
'standard' two-way circuit, but it occurs to me that it might well be
'stealing' its live either from a second lighting circuit, or from some
considerable distance around the lighting circuit, from where the main live
for the circuit is taken. Either way, that third switch must join into the
actual landing light circuit, via some kind of junction box, which may be
part of the light fixture ceiling rose, if that's nearby, or a separate
entity in the loft. It could be potentially another place for some kind of
leakage taking place.

I do have a mains rated neon screwdriver so that will be one of my
first tests.

The third switch puzzled me when I moved to the house. I researched
how it could be done and I have posted a description elsewhere in the
thread. The system is rare in the UK but I read that it is common in
Spain and some other places. I have not yet checked whether my house
is wired as described but flicking any switch at any time will change
the state of the light so the switches are not simply in series or
parallel. If the wiring is as expected, there will be two alternative
live wires (always one live and one dead) running together for a
considerable distance, rather more than the length of the landing . A
leak between these two would explain the problem but not cause a fuse
to blow or an RCCB to trip.

 

[Seán O'Leathlóbhair]

Yes, I would think that even 100pF is way too much. The hypothesis
regarding stray wiring capacitance does seem very far fetched.

Maybe this explanation is a better one, a least for the other thread:http://groups.google.com/group/aus.electronics/msg/1abcf4e439fbd911?h...

AFAICS, you can *very* roughly calculate the amount of leakage current
required to account for the OP's observations by assuming that all the
current is used in charging the main filter cap, say 4.7uF. Assuming
also that the trigger voltage for the DIAC is around 50V, then ...

i = C . dV/dt
= 4.7 E-06 x 50V / 2s
= 0.12 mA

That's reassuring, 0.12mA does not sound too frightening. So, if your
assumptions and calculations are correct, the capacitor holds 235uC
just before the flash and just under 12mJ will be released. This
sounds plausible for the faint flash. It is easily seen in the dark
but could not be described as bright. It is almost impossible to see
in daylight.

 

[Ron(UK)]

Would cleaning the contacts with something like WD40 be a good or bad
idea? I have never used this on mains voltage devices.

WD40 = Bad idea. Save it for the rusty gate hinges.

Ron(UK)

 

[Ron(UK)]

Ron(UK) wrote:

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.

It will if any of the switches are wired up wrong.

Ron(UK)

 

[JANA]

If the switch that is series with the light bulb has a night light in it,
the current pass of the night light will cause the CFL to flicker.

If the CFL is connected to a switch that is electronic, the small leakage of
the electronics will cause the CFL to flicker or in some cases to not turn
off.

Regular CFL's cannot be used on standard light dimmers and many of the
electronic timers. This is a big inconvenience for many people.

When regular lamps become unavailable, I can see a lot of problems with
these new types of lamps. The biggest one will be the pollution from their
disposal. They use mercury, phosphors, and many types of materials that are
very harmful for the environment. There is also the electronics circuit
board, which contain components that have the same recycling problem as used
in most electronics. Even though they last longer, when they are eventually
put out in to the garbage, they will eventually end up in the land fills.
They are going to be a very big problem compared to the simple light bulb
that was made of simple glass and metals.

Regular light bulb materials are about 85% recyclable. There are almost no
materials in these that are bad for the environment. Most CFL's materials
are not recyclable, and their materials are very polluting.

It looks very strong that the government is pushing the CFL's to save some
electricity to sell to large industry. This is the only answer that is
logical. There are NO green house gasses from using regular light bulbs.
When more electricity is sold to industry, the pollution problems from its
generation will actually increase, unless the generation is from water
power, or nuclear power.

--

JANA
_____


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)

 

[Blash]

JANA wrote on 6/26/07 7:50 AM:

If the switch that is series with the light bulb has a night light in it,
the current pass of the night light will cause the CFL to flicker.

<<SNIP>>

Couldn't you think of any more newsgroups to cross-post to???
24hoursupport.helpdesk,
aus.electronics,
misc.invest.stocks,
rec.audio.tech,
sci.electronics.basics,
sci.electronics.components,
sci.electronics.repair,
sci.engr.television.advanced

 

[Arfa Daily]

If the switch that is series with the light bulb has a night light in it,
the current pass of the night light will cause the CFL to flicker.

If the CFL is connected to a switch that is electronic, the small leakage
of
the electronics will cause the CFL to flicker or in some cases to not turn
off.

Regular CFL's cannot be used on standard light dimmers and many of the
electronic timers. This is a big inconvenience for many people.

When regular lamps become unavailable, I can see a lot of problems with
these new types of lamps. The biggest one will be the pollution from
their
disposal. They use mercury, phosphors, and many types of materials that
are
very harmful for the environment. There is also the electronics circuit
board, which contain components that have the same recycling problem as
used
in most electronics. Even though they last longer, when they are
eventually
put out in to the garbage, they will eventually end up in the land fills.
They are going to be a very big problem compared to the simple light bulb
that was made of simple glass and metals.

Regular light bulb materials are about 85% recyclable. There are almost no
materials in these that are bad for the environment. Most CFL's materials
are not recyclable, and their materials are very polluting.

It looks very strong that the government is pushing the CFL's to save some
electricity to sell to large industry. This is the only answer that is
logical. There are NO green house gasses from using regular light bulbs.
When more electricity is sold to industry, the pollution problems from its
generation will actually increase, unless the generation is from water
power, or nuclear power.

These are my (well known) views also, but I fear we are squeaking like
little lost mice in the dark ...

The general public are not told - and would not understand anyway - the
wider implications of these knee-jerk government interventions in our lives.
All too often, they are poorly thought through, and are dreamed up as a
response to the latest bit of pseudo science to hit the news stands. At the
moment, anything with the words 'green' or 'eco' or 'environment' or 'global
warming' are fair game for this sort of nonsense, and to add to its
'validity' in the public's eyes, they've already started inventing new bits
of techno-babble like 'carbon footprint' and 'carbon offsetting' to justify
what amounts to little more than opinions by a vociferous band of scientists
getting paid large amounts of money and credibility ratings, to promote the
government line. As you say, these CFLs are just trading one form of alleged
pollution, for another definite one ...

Arfa

Arfa