This article examines the scope for reusing electronic control gear from
dead Compact Fluorescent Retrofit lamps. When Compact Fluorescent Retrofit
lamps first appeared, they were the cheapest source of Electronic Control
Gear for small fluorescent lamps. Indeed, such control gear purpose designed
for discrete fluorescent lamps could be hard to find at any price which meant
in some cases it was worth buying a new Compact Fluorescent Retrofit lamp
just to get the Electronic Control Gear. This is less true today, but the
possibility of reusing control gear which still works from an otherwise dead
lamp is still an interesting possibility.
A word of warning is prudent here. The electronic control gear in these lamps is perfectly capable of delivering lethal electric shocks. The control gear internally runs from rectified mains, and DC at this voltage level is particularly dangerous. Unless you are familiar with working with mains voltages and DC levels above mains voltages, you should not attempt to copy any of this experimentation.
A selection of Compact Fluorescent Retrofit lamps. From left to right:
Top row: GE BIAX 20W, Philips Ecotone 9W, GE Genura 23W;
Bottom row: IKEA 4W, IKEA 7W, IKEA 11W, Philips 11W, B&Q 15W, Philips 20W, IKEA 20W, Philips 23W.
These each contain high frequency electronic control gear, which in most cases can be reused after the integrated fluorescent tube itself has died. One exception here is the GE Genura, which is an electrodeless induction lamp - the control gear in this lamp is not suitable for reuse, and in any case, the failure mode of this lamp is usually the control gear itself, since other than the phosphor, there is nothing to wear out in the glass part of the lamp.
| This diagram shows the control gear within the base
of a Compact Fluorescent retrofit. In this case, the glass tube has been
carefully removed and disposed of, and the plastic peeled away from around
the control gear.
You can see the high frequency ferrite cored transformer in the foreground, next to one of the switching transistors. A second PCB contains further components, and is joined with 3 interconnecting wires in this particular lamp.
Four short connection wires are visible from the edge of the rear PCB. These are the connections to the fluorescent tube.
The following picture shows the first lamp I drove from the reclaimed
control gear out of a dead compact fluorescent retrofit. The lamp being
driven is a 13W T5 tube, and the control gear was extracted from an 11W
compact fluorescent retrofit. The whole circuit was checked with a true power
meter and found to be drawing 15W. I estimate the power dissipation in the
control gear to have been about 1W, which means the lamp was probably being
slightly overrun at 14W. The control gear was also delivering more power
than it was designed to, probably due to a higher tube voltage than the original
integral tube it drove. This did not seem to matter, indeed because the control
gear is now remote from the lamp, it will be running very much cooler than
it was. This lamp was used as an under-cupboard lamp for some 8 years in
a kitchen, and the tube has never been replaced in that time, and still
works today, although it is no longer installed (neither is any of the rest
of that kitchen;). At the time it was constructed, electronic control gear
for fluorescent lamps was very expensive, and in this size, and very difficult
to find at all.
The following diagram shows a closeup of the control gear fitted into
a new box. Disassembling the two circuit boards in order to lay them flat
side by side (rather than keeping the back to back as in the original lamp)
was more difficult than I thought. The main problem is the fragility of the
copper tracks on the PCB - they are much thinner than normal for PCB tracks,
and they come unstuck extremely easily whilst being soldered. The other thing
that was done was replacement of the original electrolytic capacitor. The
original, although still working, was getting hot in use and probably not
much longer for this world. This is the component in the control gear least
able to survive high temperature in the lamp base for extended periods of
time, so this is no surprise. In another conversion, I did have one of these
capacitors spew its contents out, so replacement is probably no bad thing.
Once the control gear is remoted, a new capacitor should last indefinitely
as it won't be running at such a high temperature.
The next project was to refit some downlighters which were designed to
use regular 60W GLS filament lamps. Retrofit compact fluorescents were
tried but hung too low in the fittings, resulting in excessive glare visible
at a wide angle, and the light source being in the wrong position for optimal
downward directing by the reflector. The other issue with the downlighters
was that the plastic lampholders were falling apart after 20 years due to
heat from the GLS lamps, even though the units had only been used with 40W
lamps. However, the units were in good decorative order with good reflectors
and the ceiling already had the appropriate holes obviously, so it was decided
to try converting them to use compact fluorescents.
The compact fluorescent retrofits tried were Philips PL 9W ones. The electronic ballasts from these were to be reused in the conversion, together with 4-pin 10W compact fluorescents (also pictured below). Suitable lamp holders for these were sourced with the same 40mm external thread as the original bayonet cap lamp holders used.
One lesson I learned from doing the original 13W T5 fluorescent lamp is that the circuit boards in the lamp bases of compact fluorescent retrofits are really too fragile to be able to be removed and reconnected, without having to repair a number of broken tracks. This time, I would go for a scheme which didn't require removal of the control gear, but instead used it in-situ in the lamp base, with just the necessary connections brought off to connect to the remote tube. Another factor in this case was that the units would end up out-of-site in the loft, so I didn't want something which might burst into flames. This required they were totally enclosed in metal boxes. Cooling ventilation should not be an issue since the control gear was designed to run in an even more enclosed space in the lamp base, right next to the tube which is a significant source of heat. However, the loft insulation material was moved back from the boxes anyway. In practice, the boxes barely warm up at all when the lamps are operating.