Chinese "nightlight" !!

[Ioannis]

My mother bought this at a supermarket. It's a "nightlight" that plugs
directly against a wall outlet.

It has no country markings, just "1W", "AC220", "50/60Hz and "CE".
The "CE" is probably bogus. It is probably of Chinese origin.
http://users.forthnet.gr/ath/jgal/nitelite1.jpg

I opened it and it contains a small low pressure mercury lamp, which
contains 3 electrodes on each end. I suspect the third electrode is an
auxiliary one, to initiate the discharge. You can discern the switch and the
integrated circuit which plugs directly on the wall outlet.
http://users.forthnet.gr/ath/jgal/nitelite2.jpg

It's also problematic: Although it starts nicely and its glow looks like
that of a miniature fluorescent the first 3-4 seconds, after 4-5 seconds,
the auxiliary electrodes kick in again and it produces a purple glow around
the electrodes which flickers on and off, similar to the starting argon glow
on the discharge tube of a high pressure lamp.

This leads me to believe that the circuitry is all faulty. It's probably
supposed to be cutting off the current to the auxiliary electrodes, but
instead the current through them continues, causing auxiliary discharges
which keep going and going, causing argon flicker.

Here's a picture of it being lit:
http://users.forthnet.gr/ath/jgal/nitelite3.jpg

The auxiliary discharges don't show on this pic.

I was wondering how safe this thingy is. My impression is that leaving this
thing unattended through the night, one risks the danger of fire. Opinions?

 

[Victor Roberts]

My mother bought this at a supermarket. It's a "nightlight" that plugs
directly against a wall outlet.

It has no country markings, just "1W", "AC220", "50/60Hz and "CE".
The "CE" is probably bogus. It is probably of Chinese origin.
http://users.forthnet.gr/ath/jgal/nitelite1.jpg

Have you no faith in mankind?

I opened it and it contains a small low pressure mercury lamp, which
contains 3 electrodes on each end. I suspect the third electrode is an
auxiliary one, to initiate the discharge. You can discern the switch and the
integrated circuit which plugs directly on the wall outlet.
http://users.forthnet.gr/ath/jgal/nitelite2.jpg

I don't see enough detail in the picture you posted. It
looks like there are connections the lamp in three places,
instead of three electrodes: each end plus the middle. It
also look like there may be more than one wire going to each
end. Can you post a more detailed photo or explain the
connections bit more completely?

It's also problematic: Although it starts nicely and its glow looks like
that of a miniature fluorescent the first 3-4 seconds, after 4-5 seconds,
the auxiliary electrodes kick in again and it produces a purple glow around
the electrodes which flickers on and off, similar to the starting argon glow
on the discharge tube of a high pressure lamp.

This leads me to believe that the circuitry is all faulty. It's probably
supposed to be cutting off the current to the auxiliary electrodes, but
instead the current through them continues, causing auxiliary discharges
which keep going and going, causing argon flicker.

Here's a picture of it being lit:
http://users.forthnet.gr/ath/jgal/nitelite3.jpg

The auxiliary discharges don't show on this pic.

I was wondering how safe this thingy is. My impression is that leaving this
thing unattended through the night, one risks the danger of fire. Opinions?

Must be safe - it has the CE label.

--
Vic Roberts
http://www.RobertsResearchInc.com
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[JB]

Have you no faith in mankind?

Must be safe - it has the CE label.

One of our chinese suppliers sent over a batch of floodlights for
evaluation. I noticed that they had no CE marking so I called them up and
explained.
Two days later an envelope arrived containing a roll of 1000 CE stickers
with a note: "Very sorry, forgot labels. Please stick onto fittings
supplied. You all fully approved now!"
You just got to love 'em.

JB

 

[Ioannis]

Have you no faith in mankind?

No

I don't see enough detail in the picture you posted.

Here are two more detailed close-up photos:
http://users.forthnet.gr/ath/jgal/nitelite4.jpg
http://users.forthnet.gr/ath/jgal/nitelite5.jpg

It
looks like there are connections the lamp in three places,
instead of three electrodes: each end plus the middle.

No. The middle thingy is the evacuation bubble. It doesn't show well on the
previous photos. There's no wire connection there.

It
also look like there may be more than one wire going to each
end. Can you post a more detailed photo or explain the
connections bit more completely?

Both ends have 3 contacts. Can you see the 3 wires on each end? I looked
really close at them through the uncoated windows and two of them end up on
the tungsten loop, while the third one terminates after entry to the tube.
That's probably the auxiliary electrode.

[snip]

 

[JohnR66]

It was not the same as yours, but I had one similar. I opened it and traced
the circuit. Some people doubled my accuracy, but I checked and diagram
seems right. I don't understand the function of the scr.
http://home.att.net/~jriegle/flor.jpg
John

 

[Ioannis]

It was not the same as yours, but I had one similar. I opened it and traced
the circuit. Some people doubled my accuracy, but I checked and diagram
seems right. I don't understand the function of the scr.
http://home.att.net/~jriegle/flor.jpg

yes, that looks like the circuit, although I haven't checked it. The
auxiliary ends make me believe that it's probably identical.

 

[Victor Roberts]

It was not the same as yours, but I had one similar. I opened it and traced
the circuit. Some people doubled my accuracy, but I checked and diagram
seems right. I don't understand the function of the scr.
http://home.att.net/~jriegle/flor.jpg
John

Nice diagram. Due to the short across the electrodes, there
is no way to heat the electrodes so the lamp must be stared
in instant start mode. Since there is no source of high
voltage, the "probe" electrode, attached to the "third" lead
at each end is used to form a small discharge between the
probe and the coiled electrode. Until the lamp starts, the
full peak line voltage appears between the small probe
electrode and the adjacent electrode and this is enough to
initiate a discharge even with cold electrodes. The 10K
resistors serve as the ballast for these small discharges.
There is no switch to specifically shut down the auxiliary
discharges, but the current should be less than 10 ma RMS.

The SCR seems to cycle the lamp off on a regular basis by
shorting it out. Are you sure that is an SCR and not a
Triac, that will conduct in both directions?

Based on some simple calculations, and an assumption that
the lamp operating voltage is 30 volts and the Triac trigger
voltage is 3 volts, the Triac will trigger about 3 msec
after the start of each half cycle. Seems rather strange and
perhaps I am wrong.

--
Vic Roberts
http://www.RobertsResearchInc.com
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[Ioannis]

Nice diagram. Due to the short across the electrodes, there
is no way to heat the electrodes so the lamp must be stared
in instant start mode. Since there is no source of high
voltage, the "probe" electrode, attached to the "third" lead
at each end is used to form a small discharge between the
probe and the coiled electrode. Until the lamp starts, the
full peak line voltage appears between the small probe
electrode and the adjacent electrode and this is enough to
initiate a discharge even with cold electrodes. The 10K
resistors serve as the ballast for these small discharges.
There is no switch to specifically shut down the auxiliary
discharges, but the current should be less than 10 ma RMS.

I left the light on for about 3-4 hours and the auxiliary Argon discharges
on both ends dissappear in about 15-20 minutes after ignition and the lamp
stabilizes to the color of a miniature fluorescent lamp.

So there does not seem to be anything wrong with the circuitry. It does
flicker very strongly, though. The flicker is noticeable using direct
vision. Otherwise its spectrum is around that of regular daylight
fluorescents and the residual phosphorescent light between light cycles has
the same yellow-brown color as that of daylight fluorescents.

The SCR seems to cycle the lamp off on a regular basis by
shorting it out. Are you sure that is an SCR and not a
Triac, that will conduct in both directions?

What's an "SCR"?

Based on some simple calculations, and an assumption that
the lamp operating voltage is 30 volts and the Triac trigger
voltage is 3 volts, the Triac will trigger about 3 msec
after the start of each half cycle. Seems rather strange and
perhaps I am wrong.

Perhaps I should test it by connecting it to the probes of my 125 Amp
welding machine as well, to see if the "CE" sticker is valid

 

[Victor Roberts]

I left the light on for about 3-4 hours and the auxiliary Argon discharges
on both ends dissappear in about 15-20 minutes after ignition and the lamp
stabilizes to the color of a miniature fluorescent lamp.

So there does not seem to be anything wrong with the circuitry. It does
flicker very strongly, though. The flicker is noticeable using direct
vision. Otherwise its spectrum is around that of regular daylight
fluorescents and the residual phosphorescent light between light cycles has
the same yellow-brown color as that of daylight fluorescents.

The flicker may be caused by the Triac shorting out the lamp
- perhaps to reduce the energy consumption.

What's an "SCR"?

Silicon Controlled Rectifier. The forerunner of the Triac.
It's like a Triac but carries current in only one direction.

Perhaps I should test it by connecting it to the probes of my 125 Amp
welding machine as well, to see if the "CE" sticker is valid

Before you do that can you take a look at the lamp current
waveform or the light output waveform to see if it is being
shut down each cycle about midway through?

--
Vic Roberts
http://www.RobertsResearchInc.com
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[Ioannis]

Ï "Victor Roberts" <[email protected]> Ýãñáøå óôï ìÞíõìá
[snip]

Before you do that can you take a look at the lamp current
waveform or the light output waveform to see if it is being
shut down each cycle about midway through?

Sorry, I don't have the equipment to do this. The best I can do is compare
its strobo frequency to that of a normal fluorescent by direct eye
inspection. I'll try that later tonight if I have time.

 

[Ioannis]

It was not the same as yours, but I had one similar. I opened it and traced
the circuit. Some people doubled my accuracy, but I checked and diagram
seems right. I don't understand the function of the scr.
http://home.att.net/~jriegle/flor.jpg

Nobody answered by question yet: How safe is this thingy left unattended at
night?

Two years ago, I by mistake left a "CE" marked Chinese tabletop 9W
fluorescent on, only to return after a week to find the entire fixture
melted. Everything. Lamp, transformer housing and wiring. Any chance of this
happening here?

Also, does anybody know anything about life expectancy for this thing?

 

[Victor Roberts]

Nobody answered by question yet: How safe is this thingy left unattended at
night?

I don't think anyone of us has enough information to answer
this question.

Two years ago, I by mistake left a "CE" marked Chinese tabletop 9W
fluorescent on, only to return after a week to find the entire fixture
melted. Everything. Lamp, transformer housing and wiring. Any chance of this
happening here?

Did you ever figure out why this other lamp melted?

Also, does anybody know anything about life expectancy for this thing?

This would require life tests to be conducted on more than
one sample. Unless someone has access to such life test data
or has more than 10 of these in their own homes, I don't see
how personal experience or a guess will give an accurate
answer.

If you are not comfortable with it, then you should not use
it.

--
Vic Roberts
http://www.RobertsResearchInc.com
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[Ioannis]

On Sat, 27 Aug 2005 18:52:28 +0300, "Ioannis"


Did you ever figure out why this other lamp melted?

In the beginning the tabletop was operating fine and I could detect a
certain temp on the ballast housing. When I came back after this one week,
the ballast housing was a lot hotter and melted. The primamry cause seems to
have been either a ballast meltdown or some other reason which caused the
overheating of the ballast. The wiring and lamp simply followed suit.

What exactly can cause a fluorescent ballast to meltdown?

Thanks.

[snip]

 

[Victor Roberts]

In the beginning the tabletop was operating fine and I could detect a
certain temp on the ballast housing. When I came back after this one week,
the ballast housing was a lot hotter and melted. The primamry cause seems to
have been either a ballast meltdown or some other reason which caused the
overheating of the ballast. The wiring and lamp simply followed suit.

What exactly can cause a fluorescent ballast to meltdown?

Thanks.

I've lost track of the design features of this other lamp.
If it has an inductive ballast, it is always possible for a
turn-to-turn short to develop, but those are unusual. If the
output of an inductive ballast becomes shorted, it will draw
more current than when it is operating a lamp and that could
cause overheating.

The circuit we were discussing earlier in this thread uses a
capacitor ballast if I remember correctly. It is possible
for a capacitor to develop an internal short, but that is
unlikely with a new capacitor. If the output of the
capacitor ballast is shorted the capacitor should not
overheat.

There were also a few resistors in the power circuit posted.
Any of them could have overheated.

The problem with low cost electronics is often not the
components but the construction. Poor solder joints that can
overheat, thin circuit board traces that can overheat, or
traces placed too close to each other on the circuit board
that can cause flash-over shorts which can cause other parts
to overheat.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

 

[Ioannis]

Ï "Victor Roberts" <[email protected]> Ýãñáøå óôï ìÞíõìá
[snip]

I've lost track of the design features of this other lamp.
If it has an inductive ballast, it is always possible for a
turn-to-turn short to develop, but those are unusual. If the
output of an inductive ballast becomes shorted, it will draw
more current than when it is operating a lamp and that could
cause overheating.

The circuit we were discussing earlier in this thread uses a
capacitor ballast if I remember correctly. It is possible
for a capacitor to develop an internal short, but that is
unlikely with a new capacitor. If the output of the
capacitor ballast is shorted the capacitor should not
overheat.

There were also a few resistors in the power circuit posted.
Any of them could have overheated.

The problem with low cost electronics is often not the
components but the construction. Poor solder joints that can
overheat, thin circuit board traces that can overheat, or
traces placed too close to each other on the circuit board
that can cause flash-over shorts which can cause other parts
to overheat.

Ok, thanks. But on the circuit we are discussing, this is still a low
pressure mercury vapor lamp, which still has a negative resistance
characteristic. So, if, just if, for some obscure reason, the circuit gets
mangled (due to a short or some other reason) and the lamp faces the full
voltage of the wall outlet (because of a short in the circuit), then it will
probably blow up.

This particular tube has no safety molybdenum end seals which could prevent
the more dire consequences of a direct short, so giving it a 220V
unrestricted, will most likely cause it to "flash" causing its end points to
at least melt in the best possible case, or explode in the worst possible
case.

Am I not right?

 

[Victor Roberts]

Ï "Victor Roberts" <[email protected]> Ýãñáøå óôï ìÞíõìá
[snip]

I've lost track of the design features of this other lamp.
If it has an inductive ballast, it is always possible for a
turn-to-turn short to develop, but those are unusual. If the
output of an inductive ballast becomes shorted, it will draw
more current than when it is operating a lamp and that could
cause overheating.

The circuit we were discussing earlier in this thread uses a
capacitor ballast if I remember correctly. It is possible
for a capacitor to develop an internal short, but that is
unlikely with a new capacitor. If the output of the
capacitor ballast is shorted the capacitor should not
overheat.

There were also a few resistors in the power circuit posted.
Any of them could have overheated.

The problem with low cost electronics is often not the
components but the construction. Poor solder joints that can
overheat, thin circuit board traces that can overheat, or
traces placed too close to each other on the circuit board
that can cause flash-over shorts which can cause other parts
to overheat.

Ok, thanks. But on the circuit we are discussing, this is still a low
pressure mercury vapor lamp, which still has a negative resistance
characteristic. So, if, just if, for some obscure reason, the circuit gets
mangled (due to a short or some other reason) and the lamp faces the full
voltage of the wall outlet (because of a short in the circuit), then it will
probably blow up.

This particular tube has no safety molybdenum end seals which could prevent
the more dire consequences of a direct short, so giving it a 220V
unrestricted, will most likely cause it to "flash" causing its end points to
at least melt in the best possible case, or explode in the worst possible
case.

Am I not right?

I have never heard of a fluorescent lamp exploding. The gas
pressure is just too low.

If you operate a fluorescent lamp without a proper ballast
the first thing that will happen is that the electrodes will
be destroyed. This ruins the lamp but causes no damage
outside the lamp.

If you have enough voltage to keep the discharge operating
with only the electrode support leads, and this happens
quite often in the US on instant start circuits and could
happen with your short lamp, especially on 220 volts, then
the ends of the lamp will overheat, which will often cause
the glass to crack, allowing air inside the lamp, which
extinguishes the discharge. If the lamp is a pin-base CFL
with the lamp ends surrounded by a plastic base, that base
can melt and under some circumstances can start a fire. If
the lamp is a linear instant start lamp, when the glass
cracks the lamp can fall out of the fixture and damage
property located below or injure a person who may be seated
or standing below the fixture.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
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site without written permission.

 

[JohnR66]

Nice diagram. Due to the short across the electrodes, there
is no way to heat the electrodes so the lamp must be stared
in instant start mode. Since there is no source of high
voltage, the "probe" electrode, attached to the "third" lead
at each end is used to form a small discharge between the
probe and the coiled electrode. Until the lamp starts, the
full peak line voltage appears between the small probe
electrode and the adjacent electrode and this is enough to
initiate a discharge even with cold electrodes. The 10K
resistors serve as the ballast for these small discharges.
There is no switch to specifically shut down the auxiliary
discharges, but the current should be less than 10 ma RMS.

The SCR seems to cycle the lamp off on a regular basis by
shorting it out. Are you sure that is an SCR and not a
Triac, that will conduct in both directions?

Based on some simple calculations, and an assumption that
the lamp operating voltage is 30 volts and the Triac trigger
voltage is 3 volts, the Triac will trigger about 3 msec
after the start of each half cycle. Seems rather strange and
perhaps I am wrong.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

Vic, I googled BT169D and it found a PDF datasheet. It is a passivated,
sensitive gate SCR. The way it is wired, it seems to be activated by a
voltage across the ballast components, perhaps during starting. Why an SCR?
not sure. Creating asymetrical waveform condition?
John

 

[Victor Roberts]

Vic, I googled BT169D and it found a PDF datasheet. It is a passivated,
sensitive gate SCR. The way it is wired, it seems to be activated by a
voltage across the ballast components, perhaps during starting. Why an SCR?
not sure. Creating asymetrical waveform condition?
John

OK - new theory of operation

First of all, my previous explanation assumed that the gate
was connected to the lamp side of the capacitor ballast,
which is incorrect. The gate is connected across the line,
except for the parallel 390 ohm resistors which can't drop
much voltage when the lamp is operating. And, as you say,
it's an SCR.

Before the lamp starts, the SCR will be triggered during the
cycle when the right hand power lead is positive with
respect to the left lead. This will quickly charge the 1uF
capacitor to just about peak line voltage with its left lead
positive with respect to the right lead, with the charging
current spike being limited only by the series resistance of
SCR and the two parallel 390 ohm resistors - 195 ohms.

The discharge time constant of the 1 uF capacitor and the 1
meg resistor is 1 sec, so the capacitor will remain almost
fully charged when the line polarity reverses a few msec
later. When the right hand input terminal becomes negative,
the voltage on the capacitor adds to the line voltage,
providing twice the peak line voltage across the lamp to
start it.

However, what I can't figure out at this late hour is what
makes the SCR stop triggering each cycle. If it continues
triggering each cycle, then the lamp will be operating for
one full half cycle and only a part of the other half cycle,
leading to significant flicker.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
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[Don Klipstein]

In the beginning the tabletop was operating fine and I could detect a
certain temp on the ballast housing. When I came back after this one week,
the ballast housing was a lot hotter and melted. The primamry cause seems to
have been either a ballast meltdown or some other reason which caused the
overheating of the ballast. The wiring and lamp simply followed suit.

What exactly can cause a fluorescent ballast to meltdown?

I would think shorting of turns of wire in the winding in the ballast.

This could result from two events that I could think of:

1. The design was marginal and sooner or later this was likely to occur.

2. The lamp fails, and a glow switch starter gets stuck shorted after a
enough thousands of blinks. The ballast is supposed to survive this,
but I have seen how this led to a fire in the elevator in an apartment
building that I was living in several years ago.

If you know the beand and model of the ballast (or fixture), and any
numbers on the certification sticker, you should report all such info to
the agency that supposedly certified the ballast (or fixture).
If the certification is in any way invalid, I wonder if whoever is
falsely applying certification stickers is hoping that any resulting fires
burn up names/numbers to use against the offenders.

- Don Klipstein ([email protected])

 

[Don Klipstein]

Ï "Victor Roberts" <[email protected]> Ýãñáøå óôï ìÞíõìá
[snip]

I've lost track of the design features of this other lamp.
If it has an inductive ballast, it is always possible for a
turn-to-turn short to develop, but those are unusual. If the
output of an inductive ballast becomes shorted, it will draw
more current than when it is operating a lamp and that could
cause overheating.

The circuit we were discussing earlier in this thread uses a
capacitor ballast if I remember correctly. It is possible
for a capacitor to develop an internal short, but that is
unlikely with a new capacitor. If the output of the
capacitor ballast is shorted the capacitor should not
overheat.

There were also a few resistors in the power circuit posted.
Any of them could have overheated.

The problem with low cost electronics is often not the
components but the construction. Poor solder joints that can
overheat, thin circuit board traces that can overheat, or
traces placed too close to each other on the circuit board
that can cause flash-over shorts which can cause other parts
to overheat.

Ok, thanks. But on the circuit we are discussing, this is still a low
pressure mercury vapor lamp, which still has a negative resistance
characteristic. So, if, just if, for some obscure reason, the circuit gets
mangled (due to a short or some other reason) and the lamp faces the full
voltage of the wall outlet (because of a short in the circuit), then it will
probably blow up.

I think that the lamp will survive faults well enough to force faulty
ballasts to act as fuses unless the short is severe enough to blow an
actual fuse or trip a breaker.
And if the fault causes the lamp current to be a few times what it
should be, I expect that in many cases the lamp will survive long enough
to cause the malfunctioning ballast to overheat enough to further fail and
maybe do so quite spectacularly (and possibly pouring or spitting drops of
molten copper, of temperature a little under 1100 degrees C).
High pressure sodium may usually be either more forgiving or drag things
out farther, by having an overpowered lamp vaporize excessive sodium, and
once the arc voltage reaches about 76-80% or so of the ballast output open
circuit voltage, the "negative resistance" of the arc typically outweighs
the output impedance of the ballast in some way to make the arc unstable
upon decrease of current - and the next downward fluctuation of arc
current during the next half-cycle puts the arc in a decreasing-current
tailspin, and the lamp goes out. You get something similar to
"end-of-life cycling", only you hope the lamp spends enough time being
"off" or gets worse fast enough to not let the ballast overheat enough to
make things worse.

This particular tube has no safety molybdenum end seals which could prevent
the more dire consequences of a direct short, so giving it a 220V
unrestricted, will most likely cause it to "flash" causing its end points to
at least melt in the best possible case, or explode in the worst possible
case.

Am I not right?

I think that some few ballast failures resulting in lamp current a few
times that of "normal" could result in lamp current that does not make the
lamp "act as a fuse", but merely ages the lamp badly, and the lamp may
"keep on ticking" long enough for the ballast to get worse - and maybe in
especially bad cases put on a fireworks show or put out molten copper.
I do admit that this is an extreme case, but falling a little short of
this is still an obvious fire hazard. If the ballast windings overheat
enough to produce a flammable concentration of vapors of insulating
materials and then a wire shorts or breaks with a spark, at that point you
could have a fire. This is still a very rare event, but this is something
that I think should be planned around (for adequate avoidance and/or
survival) in order to receive a UL or CSA or CE sticker.

- Don Klipstein ([email protected])