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 failed.

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" and 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.

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