Low Energy Lamps
Some time ago when these
low energy lamps were fairly new, one of ours failed after a
relatively short period and I cut it open to see what had gone
wrong. I can't recall exactly how many components there were
on the tiny circuit board, but an electrolytic capacitor had
The lamp manufacturer had quoted
the lifetime of the lamp and the figure quoted was utter nonsense.
What's important is the minimum expected lifetime of one particular
part and that is the electrolytic capacitor used for smoothing
the rectified mains supply. These things have published lifetime
figures which are inversely proportional to their operating temperature.
The location of the parts in a lamp is between the emitting tube
and the base where it is very very warm. A cheap 6.8uF capacitor
rated at 400 volts working will have a life of 1000 to 2000 hours
at 105 deg C.
Below is a picture of a daylight
lamp I cut open in September 2015. We have two of these although
one had to be replaced as it was too dim when first used. We
wouldn't have known it was dim if we hadn't already got an identical
desk lamp. These lamps are very good, providing lots of illumination
but one failed the other day after not too many hours of use.
Above you can see the
chopper power supply with its HT smoothing capacitor on long
leads so it can tuck inside the base of the lamp which the designers
thought to be the coolest area.
Here's a list of parts:
Bridge rectifier (4 diodes),
Two power transistors, chopper transformer, toroidal transformer,
four diodes, seven resistors, five small capacitors, one coil,
and one electrolytic capacitor.
As you can see the electrolytic
has burst open and it measured short circuit. The lamp had gone
off a couple of times, made sizzling sounds and nasty smelling
smoke had emerged from it. It then came back on before we turned
it off. As I'd cut an earlier lamp open many years ago I was
familiar with what was likely to be inside and was able to open
this one with minimal damage.
The electrolytic had clearly
failed, and as all the other parts measured OK, I fitted a new
4.7uF 400volt and glued back the base.
It worked OK so it's now back
in use. The old capacitor is marked "KYK CD11G-H, 6.8uF
400V, -40- +125 deg C".
There isn't a maker's name on
the capacitor, but I think "KY" means it's a long-life
variety. Loooking at one manufacturer's specification for an
identical looking product I see its rated at varying lifetimes
depending on the temperature and ripple voltage, but 5000 hours
seems to be claimed. Because of the wide variation in mains voltages
across Europe lamps in the UK will be operating with the worst
ripple voltage and operating temperature so the 5,000 hours may
be an optimistic figure.
How about the maker's name on
the light bulb? I'm afraid there isn't one just "EU-20W
130MA, 220-240V 50/60Hz"
I don't like the "MA"
bit because most engineers would recognise this as not milli-Amps
but Meg-Amps and while I'm complaining about bad English the
capacitor manufacturer I checked used the term "non-lead
free". Is this the same as "lead free" or perhaps
they don't conform to the ROHS standard and they've used the
term deliberately to mislead?
Anyway, to cut a long story
short the repaired light bulb now works perfectly.
Here's another.. this
one's a Phillips Genie11W Energy Saver marked "CE",
made in "PRC" and marked 230-240V~ 50-60Hz and it's
been in our hallway for many years. Being an early one it started
out dim and got dimmer, but brightening up after 10 minutes or
so which was usually after we'd put the torch away and turned
it off. Last night it went off for a fraction of a second about
a dozen times before staying off. After 10 minutes I removed
it, burning my thumb on the plastic in the process.
It uses a small circuit
board much like the higher power lamp above but doesn't use power
transistors but two TO92 types marked "Si 13001", which
is a TS13001, an NPN transistor rated at 100mA @ 400V. The failure
was due to one of the two small 2.2uFx50v electrolytics which
had dropped slightly in capacitance and whose ESR had risen to
9 ohms and 11 ohms. Surprisingly the 2.7uFx400v capacitor measured
about right. This one is mounted on long leads and tucked into
the cavity of the bayonet plug.
You can see from the sawdust
residue how I dismantled the lamp, and the whole assembly pulls
out of the housing once you've freed the two mains connection
wires. The component count is as follows:- chopper transformer,
filter toroid, 4 x ceramic capacitors (2 x 47nF, 2.7nF, 1.8nF,
6 x diodes (1N4007), 2 transistors (TS13001), 2 x 2.2uF 50v capacitors,
1 x 2.7uF x 400v capacitor, 7 resistors (4 x 10ohm, 1 x 1ohm,
1 x 330kohm, 1 x 680kohm) and a small inductor (4.7mH).
More signs of impending
failure are the heavily tarnished connections from the fluorescent
tube, but as this lamp started life dim I didn't bother repairing