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CFL ballast design, and using dead lamps for repair

P

P E Schoen

I have a desk lamp, with a magnifier and a 12W T4 circline fluorescent bulb,
that I use constantly for working on PCBs and electronics projects in
general. I bought it several years ago and recently it started flickering
and then died. I replaced the bulb, but still no joy, and after replacing
the blown fuse and two damaged transistors, I found that the little
transformer had an open winding.

So, I thought, a 60W equivalent CFL is actually about 11-13 watts, and the
little circuit in them should work. I had a couple of broken or dead bulbs
ready for recycling, so I opened the bases, cut the leads, and extracted the
PCBs. After a few unsuccessful tries, I was able to get it to work and now
my lamp is once again operational.

I found some schematics of the CFL driver boards here:
http://www.pavouk.org/hw/lamp/en_index.html

Some of those circuits matched what I had almost exactly. It was a little
difficult to follow the explanation of how they operate, but what was
confusing is the four pins shown on the lamp itself, which is also how the
bulbs are made. I assume they are the heaters that are usually activated
with a starter, but I did not find any continuity on those pins. The desk
lamp only had one wire to each of two pins on the circline bulb, but in the
CFLs all four wires were connected to different points on the PCB. It would
only work when I shorted the connections that would have gone to the
heaters, and it seems to work very well. It starts to light at 50 VAC and
reaches full brightness at 100-120V, at which it draws about 100mA. That's
close enough to 12 watts for me!

Here's a little clip of my repair project:

This is good to know. Those little circuits in each CFL have a lot of good
components, including a DIAC and high voltage transistors, and it's probably
possible to use them to drive small fluorescent lamps for DIY projects or
repair. I doubt they could be used for the 40W tubes, but a driver from a
100W CFL should work on a 20W tube such as are in many desk lamps and small
kitchen fixtures.

Does anyone know if there is any problem with this?

Thanks,

Paul

PS: GO RAVENS!!!!!
 
N

N_Cook

I have a desk lamp, with a magnifier and a 12W T4 circline fluorescent bulb,
that I use constantly for working on PCBs and electronics projects in
general. I bought it several years ago and recently it started flickering
and then died. I replaced the bulb, but still no joy, and after replacing
the blown fuse and two damaged transistors, I found that the little
transformer had an open winding.

So, I thought, a 60W equivalent CFL is actually about 11-13 watts, and the
little circuit in them should work. I had a couple of broken or dead bulbs
ready for recycling, so I opened the bases, cut the leads, and extracted the
PCBs. After a few unsuccessful tries, I was able to get it to work and now
my lamp is once again operational.

I found some schematics of the CFL driver boards here:
http://www.pavouk.org/hw/lamp/en_index.html

Some of those circuits matched what I had almost exactly. It was a little
difficult to follow the explanation of how they operate, but what was
confusing is the four pins shown on the lamp itself, which is also how the
bulbs are made. I assume they are the heaters that are usually activated
with a starter, but I did not find any continuity on those pins. The desk
lamp only had one wire to each of two pins on the circline bulb, but in the
CFLs all four wires were connected to different points on the PCB. It would
only work when I shorted the connections that would have gone to the
heaters, and it seems to work very well. It starts to light at 50 VAC and
reaches full brightness at 100-120V, at which it draws about 100mA. That's
close enough to 12 watts for me!

Here's a little clip of my repair project:

This is good to know. Those little circuits in each CFL have a lot of good
components, including a DIAC and high voltage transistors, and it's probably
possible to use them to drive small fluorescent lamps for DIY projects or
repair. I doubt they could be used for the 40W tubes, but a driver from a
100W CFL should work on a 20W tube such as are in many desk lamps and small
kitchen fixtures.

Does anyone know if there is any problem with this?

Thanks,

Paul

PS: GO RAVENS!!!!!


+++++++++

so the original lamp was conventional ballast and 2 pin bimetal switch
starter ?
 
T

Tim Williams

Besides the electrolytic and bulb, the starter cap is very failure-prone.
In circuits where the filaments are used, it's in series with the output,
forming a series resonant tank; the low resistance of the cold filaments
draws lots of current, starting the tube quickly. When the tube starts
up, it appears in parallel with the cap, transforming the circuit into a
good old series inductance ballast.

The kind with only two pins skips the heating step and allows the tank
voltage and current to resonate even higher, until the tube breaks down
cold-cathode style. Once ignited, ion bombardment keeps the filaments
warm, keeping the reignition and operating voltages normal.

High voltage film caps are big and expensive, so understandably, they
don't like to use them very much. Often, a poor green (polyester) type is
found, which isn't even green anymore, but black from the abuse. Others
may be burned through, having experienced too many starts (too much peak
voltage) that self-healing has burned away most of the capacitance. The
circuit then either tries oscillating too high (burning itself from
switching loss) or oscillates lazily or latches (resonance no longer
strong enough to draw enough current to provide sufficient feedback).

Tim

--
Deep Friar: a very philosophical monk.
Website: http://seventransistorlabs.com

I have a desk lamp, with a magnifier and a 12W T4 circline fluorescent
bulb,
that I use constantly for working on PCBs and electronics projects in
general. I bought it several years ago and recently it started flickering
and then died. I replaced the bulb, but still no joy, and after replacing
the blown fuse and two damaged transistors, I found that the little
transformer had an open winding.

So, I thought, a 60W equivalent CFL is actually about 11-13 watts, and the
little circuit in them should work. I had a couple of broken or dead bulbs
ready for recycling, so I opened the bases, cut the leads, and extracted
the
PCBs. After a few unsuccessful tries, I was able to get it to work and now
my lamp is once again operational.

I found some schematics of the CFL driver boards here:
http://www.pavouk.org/hw/lamp/en_index.html

Some of those circuits matched what I had almost exactly. It was a little
difficult to follow the explanation of how they operate, but what was
confusing is the four pins shown on the lamp itself, which is also how the
bulbs are made. I assume they are the heaters that are usually activated
with a starter, but I did not find any continuity on those pins. The desk
lamp only had one wire to each of two pins on the circline bulb, but in
the
CFLs all four wires were connected to different points on the PCB. It
would
only work when I shorted the connections that would have gone to the
heaters, and it seems to work very well. It starts to light at 50 VAC and
reaches full brightness at 100-120V, at which it draws about 100mA. That's
close enough to 12 watts for me!

Here's a little clip of my repair project:

This is good to know. Those little circuits in each CFL have a lot of good
components, including a DIAC and high voltage transistors, and it's
probably
possible to use them to drive small fluorescent lamps for DIY projects or
repair. I doubt they could be used for the 40W tubes, but a driver from a
100W CFL should work on a 20W tube such as are in many desk lamps and
small
kitchen fixtures.

Does anyone know if there is any problem with this?

Thanks,

Paul

PS: GO RAVENS!!!!!
 
P

petrus bitbyter

"P E Schoen" <[email protected]> schreef in bericht
I have a desk lamp, with a magnifier and a 12W T4 circline fluorescent bulb,
that I use constantly for working on PCBs and electronics projects in
general. I bought it several years ago and recently it started flickering
and then died. I replaced the bulb, but still no joy, and after replacing
the blown fuse and two damaged transistors, I found that the little
transformer had an open winding.

So, I thought, a 60W equivalent CFL is actually about 11-13 watts, and the
little circuit in them should work. I had a couple of broken or dead bulbs
ready for recycling, so I opened the bases, cut the leads, and extracted the
PCBs. After a few unsuccessful tries, I was able to get it to work and now
my lamp is once again operational.

I found some schematics of the CFL driver boards here:
http://www.pavouk.org/hw/lamp/en_index.html

Some of those circuits matched what I had almost exactly. It was a little
difficult to follow the explanation of how they operate, but what was
confusing is the four pins shown on the lamp itself, which is also how the
bulbs are made. I assume they are the heaters that are usually activated
with a starter, but I did not find any continuity on those pins. The desk
lamp only had one wire to each of two pins on the circline bulb, but in the
CFLs all four wires were connected to different points on the PCB. It would
only work when I shorted the connections that would have gone to the
heaters, and it seems to work very well. It starts to light at 50 VAC and
reaches full brightness at 100-120V, at which it draws about 100mA. That's
close enough to 12 watts for me!

Here's a little clip of my repair project:

This is good to know. Those little circuits in each CFL have a lot of good
components, including a DIAC and high voltage transistors, and it's probably
possible to use them to drive small fluorescent lamps for DIY projects or
repair. I doubt they could be used for the 40W tubes, but a driver from a
100W CFL should work on a 20W tube such as are in many desk lamps and small
kitchen fixtures.

Does anyone know if there is any problem with this?

Thanks,

Paul

PS: GO RAVENS!!!!!

The traditional way of igniting TLs is first heating the heaters and then
start it with a relative high voltage puls. But heating first is not
necessary. The lamp will ignite if only the voltage of the ignition pulse is
high enough. Nevertheless, the heaters cannot be omitted as they provide the
electrons required for the current through the tube. Especially low power
TLs are sometimes ignited this way. When used with low frequencies i.e. 50Hz
or 60Hz, it is said to shorten the lifetime of the tube. The circuit I ever
found in a handheld 8W TL lamp did work but gave a flickering light.

I also use a magnifier lamp but a bigger one containing a 22W circline. It
came with an old-fashioned iron ballast and no starter. I had to start it
by hand using the special switch. That is I had to push the button and keep
it pushed for a 6s. During this time the heaters were on. Relieving the
button ignited the lamp... Most of the times. But over time igniting failed
more and more and the circlines seemed to worn out faster and faster.
Investigating revealed the special switch to be worn out beyond repair. So I
got a 20W CFL, got out the electronics, put them in a box and connected it
to the circline. Works fine for several years now already.

petrus bitbyter
 
P

Phil Allison

"P E Schoen"

It starts to light at 50 VAC and
reaches full brightness at 100-120V, at which it draws about 100mA. That's
close enough to 12 watts for me!


** You are mixing up "watts" and "VA".

CFL inverters, like most simple SMPS, have a PF of about 0.6 due to the
peaky current wave shape drawn from the AC supply - so VA and watts
numbers differ by about a 2:1 ratio.

You did use a wide band "true rms " meter to measure the AC current -
didn't you ?



.... Phil
 
D

[email protected]

Besides the electrolytic and bulb, the starter cap is very failure-prone.
Click to expand...

FWIW, of the modest pile of CFLs I autopsied from my own house, 100%
of the failures were from failed heaters.

This may be atypical. I get good service from CFLs running them
without enclosures; the enclosed, base-up fail modes may be different.
 
T

Tim Williams

FWIW, of the modest pile of CFLs I autopsied from my own house, 100%
Click to expand...
of the failures were from failed heaters.
This may be atypical. I get good service from CFLs running them
Click to expand...
without enclosures; the enclosed, base-up fail modes may be different.

I don't know if any do fail specifically due to the start cap -- as you
note, the filament tends to fail first. I haven't measured any of the
caps to see the capacitance loss, but the color change is reason enough.

EPCOS makes capacitors specifically for this service; their graphs of peak
voltage vs. capacitance are reminiscient of the Write-Only Memory's
"insertions vs. pins remaining" graph. ;-o

Base-up tends to cook the capacitor; better ones don't mind so much. My
parents have a GE "long life" model on their front porch, an enclosed
(vented enough that bugs find their way in, but not so much that they find
their way out before dying and making a pile...), base-up fixture.

I installed them something like four years ago; the other outdoor lights
(upright, even) have since failed, but the front porch, surprisingly,
still works.

I think. Come to think of it, I didn't look closely last time I was by;
the front porch may've been replaced, most likely under pressure, the
other "low priority targets" simply being "left in the dark"... :)

Tim
 
P

P E Schoen

wrote in message
FWIW, of the modest pile of CFLs I autopsied from my own house,
100% of the failures were from failed heaters.
Click to expand...
This may be atypical. I get good service from CFLs running them
without enclosures; the enclosed, base-up fail modes may be different.
Click to expand...

I measured the heaters on one of the new circline lamps and they appear to
be about 3 ohms each. So in series, using a starter, they would draw a high
current surge and then probably much lower as they become nearly
incandescent. Of course the ballast would limit the current to some much
lower value. I figure that an ordinary magnetic ballast for 12W would drop
about 30 volts at 100 mA during normal operation, so probably about 400 mA
into the heaters.

But since this lamp had only two wire zipcord going from the electronic
ballast to the lamp, it obviously did not use the heaters with the original
circuit. So I just shorted the connections for the heaters at the board, and
it works perfectly well. I can't see where the 6 ohms of filament resistance
would make much difference to a circuit designed for 100 mA, and I don't
know why the CFLs use the heaters at all, or why they should burn out. It
does appear that the heaters of the one dead CFL are open, although I
thought I had continuity through one when I first measured it. One of the
CFLs actually got broken when I hit it with a flyswatter as I waged war on
the stinkbugs that love to circle the lamp. It seemed to continue to glow
for a while, which may have been the heaters.

The defunct circline lamp shows discoloration on one end and that heater is
open, while the other is OK. I don't know how it can burn out if there is
only one wire connected to it. Perhaps it just vaporizes because of the
current flowing from it into the fluorescent plasma? I don't really know the
details of operation.

When I was still in High School I made a little multivibrator circuit that
fed a 12V transformer and I connected the 120V winding through a capacitor
to a small fluorescent lamp in a camping lantern. It originally used a big
high voltage battery (maybe 90 volts and maybe two of them), and maybe some
sort of vibrator as in old tube type car radios to get the AC voltage for
the lamp. Will it work on just DC? My conversion worked on a 12V motorcycle
battery, and it was instant start, whereas the original had a starter
button. I think I still have that lantern somewhere. I should find it and
look inside.

I also have an old lantern that originally used two big doorbell batteries
(remember them?), and I replaced them with a NiCad battery that was made of
plexiglass so you could see the plates and electrolyte inside and possibly
even service it. My father worked for a company that made exotic batteries
for the military and I think this came from there, probably 50 years ago.

Paul
 
M

Mike Tomlinson

petrus said:
Nevertheless, the heaters cannot be omitted as they provide the
electrons required for the current through the tube.
Click to expand...

In other words, used like this, they are not heaters but cathodes.
Presumably this is what a 'cold cathode' tube is.
 
P

petrus bitbyter

Mike Tomlinson said:
In other words, used like this, they are not heaters but cathodes.
Presumably this is what a 'cold cathode' tube is.
Click to expand...


Sure. During the classic startup you can consider the heaters to be direct
heated cathodes. Once the light is on they are pretty hot cold cathodes :)

petrus bitbyter
 
W

William Sommerwerck

Most CFLs have PTC thermistors that increase current flow
Fortunately, I have not had this problem. The CFLs in my bathroom and bedroom
have lasted two to three years, and are turned on and off several times a day.
 
K

[email protected]

Fortunately, I have not had this problem. The CFLs in my bathroom and bedroom
have lasted two to three years, and are turned on and off several times a day.
Click to expand...

Two or three years? I have incandescents that last a lot longer than
that.
 
L

legg

I have a desk lamp, with a magnifier and a 12W T4 circline fluorescent bulb,
that I use constantly for working on PCBs and electronics projects in
general. I bought it several years ago and recently it started flickering
and then died. I replaced the bulb, but still no joy, and after replacing
the blown fuse and two damaged transistors, I found that the little
transformer had an open winding.

So, I thought, a 60W equivalent CFL is actually about 11-13 watts, and the
little circuit in them should work. I had a couple of broken or dead bulbs
ready for recycling, so I opened the bases, cut the leads, and extracted the
PCBs. After a few unsuccessful tries, I was able to get it to work and now
my lamp is once again operational.

I found some schematics of the CFL driver boards here:
http://www.pavouk.org/hw/lamp/en_index.html

Some of those circuits matched what I had almost exactly. It was a little
difficult to follow the explanation of how they operate, but what was
confusing is the four pins shown on the lamp itself, which is also how the
bulbs are made. I assume they are the heaters that are usually activated
with a starter, but I did not find any continuity on those pins. The desk
lamp only had one wire to each of two pins on the circline bulb, but in the
CFLs all four wires were connected to different points on the PCB. It would
only work when I shorted the connections that would have gone to the
heaters, and it seems to work very well. It starts to light at 50 VAC and
reaches full brightness at 100-120V, at which it draws about 100mA. That's
close enough to 12 watts for me!
Click to expand...

One other thing you can learn from this exercise - low cost part
types.

Typical gapped core sizes commonly used in this application can be
designed in elsewhere for $0.02. Similar price ranges for bobbins,
semiconductors, film caps, fuses and electrolytics.

Lots of other things you can do with this stuff, knowing you won't be
beat on material cost.

RL
 
S

Spehro Pefhany

Even stupid people should know better than put CFLs in a fitting like that!
Click to expand...

I must be stupid then. I've got a CFL in a totally sealed (shower)
fixture and it's been working fine for years. (I even conformally
coated the lamp before sealing it in the fixture).

I only buy name brand (eg. Philips) products though, and probably
they're made a bit better than the ones that come 8 to a card. Never
seen any perforation of the housings on failure.
 
S

Spehro Pefhany

Nope. I lost three Philips to one power surge and on pulling them apart I
can confirm they use the same caps or worse - mine were marked as 350V DC.
Considering the mains was 240v AC thats not a lot of a safety margin. I
now use whatever is cheapest seeing as it makes no difference to the
quality.
Click to expand...

Parts that are marked the same are not necessarily the same. The $1.00
bulbs may contain gold-colored caps marked as 630VDC/125°C.

http://www.discovercircuits.com/dc-mag/Issue_4/Photos/FakeCapacitor1.jpg

Not sure if the 240V input makes much difference.. they are likely
using a doubler circuit in our (120V) lamps.

I have heard enough stories of people who bought the cheap ones and
had initial failures, exciting failures, and such like to avoid the
low end stuff.

It would be nice if LED lamps got anywhere close to the brightness of
CFL, halogen or incandescent bulbs at a reasonable price, but they are
not very close yet. Maybe in a few years. I bought a couple MR11
"brightest on the market" bulbs to unload the halogen xfmr and allow
me to put a bigger halogen in the centre bulb of a 3-light string, and
they're not even comparable. I'll have to take some quantitative
measurements at some point.
 
G

George Herold

"Ian Field" <







** See the second half of this page for pics of the actual CFL and fitting.

http://sound.westhost.com/articles/il-cfl-6.htm

The are no ventilation a holes at the back of the fitting and all the spiral
CFLs were a neat fit.
Click to expand...

Nice artcile Phil, But don't worry about the legislature's doing
anything. What's needed is some lawayer to get a hold of it and sue
the manufacturers.

(That's the US way :^)

George H.
 
S

Spehro Pefhany

Nice artcile Phil, But don't worry about the legislature's doing
anything. What's needed is some lawayer to get a hold of it and sue
the manufacturers.

(That's the US way :^)

George H.
Click to expand...

The offshore manufacturers are probably not easy to get substantial
judgements against- but the stores, especially those who do their own
importing, have deep pockets and can't easily escape.

They do have a good defense though- if it has safety agency approval,
it's presumed to be safe. Maybe report it to the safety agencies- but
I don't see anthing there that would really raise the alarm-
incadescents break and short internally and implode from time to time,
and none of the burn- through incidents shows support of combustion.
Any fixture designed for a normal incandescent ought not to burn the
office or house down. The one that 'exploded' is the closest one- the
mfr may have substituted a cheaper non-fiberglass sleeving on that
diode.
 
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