You never quite go to Bunnings without leaving with quite a few items. While walking around the aisles, the Nelson Cougar 60 caught my eye.
This is an electronic transformer designed for use with halogen downlights up to 60 watts. The big surprise, at least for me, is that a single transformer is being sold for AU$7.86 at retail, with ten packs at AU$61.98. You can even get a version with a plug and lead for use with GPOs for AU$10.33. There are also Osram Redback 40VA units available for a little more, and higher-end Nelson “tradesman” models. I remember when electronic transformers were much more expensive than this, which was why I never really ever played with these units. As a result, I decided to throw some money at it, despite not really needing it, just to see what ~$8 gets you.
The unit itself is very small, about palm size. I’ve never met a transformer lighter or smaller. That’s what technological progress brings you!
It has a two tone curved plastic motif, which is pretty trendy for something that’s virtually never seen and should never be heard. The model and specifications are printed on the top, although slightly blurred. It has a high power factor rating of >0.99. It claims a level III efficiency rating (>=84% under load with <=0.75W idle), which isn’t as efficient as it could be. The output is unusual, as it claims to be 12.5v (a little higher than 12v) which is the opposite of most transformers, which put out a little less than 12v to ensure longer filament life. The unit is dimming compatible, with trailing edge dimmers.
The secondary contacts are left open at the end to the outside, whereas the primary contacts are enclosed by a plastic screw-down cover, which also has side “click” latching. The cover needs to be pried off to install the cable initially.
The opposite side is marked 15W04 230, which may be a specific model number.
A flat base is provided for mounting against flat surfaces. No ribbing or elevation is provided, which implies that the transformer doesn’t put out much heat. Two screws are used to hold it down – one fixed end, and the other as a slot to accommodate slight drilling errors. The design is a simple plastic casing with no screws used in the construction.
The unit comes apart once you remove the mains cable cover, and then pry around the white to blue plastic seam, where four “clips” are used to hold the cover down. Internally, the PCB is wrapped by a plastic insulating sheet.
The PCB is a single layer paper type PCB, with green solder resist and limited silk-screening on the underside. The solder joints on the underside look very consistently made. A clear demarcation between primary and secondary is visible. The PCB is marked ET60W-5.
From the top, we can see there are no heatsinks and no ICs throughout the design. There are two main transistors, and a pair of transformers (one primary/secondary, and a feedback) which are responsible for the operation of the device. To support this, there are a handful of diodes, resistors, capacitors and a single transistor.
The input appears to be protected by a fuse wrapped in heatshrink, and an inductor provides some RF filtering.
Components near the edge of the PCB are covered with a woven tube for fire protection.
The output has a very unusual winding. For double-insulation isolation reasons, the inner winding is separated from the outer secondary by a plastic shell, and exceeding requirements, is the use of insulated wire for the outer winding. This loose coupling may be part of the reason for a slightly lower efficiency than expected.
When the transformer is powered with no load, it makes an audible buzz. Checking the output shows a spiky output which follows the mains envelope, much like the Osram Redback transformer, but with a limited peak voltage of about 14v and an AC RMS value of 3.48v.
Unloaded, the individual spikes seem to cycle at a rate of 5.5khz, and shows a characteristic “ringing” style waveform that you might find from a ringing choke converter, which gives you an idea of the simple regulation method used.
Loaded with a 50W (nominal) halogen downlight globe, the transformer performed superbly, producing an average of 12V RMS AC over the globe – perfect.
Of course, this means a peak voltage of about 18v, but this is of little significance as the filaments of the globe are more sensitive to the RMS value which is accurate – although less than the claimed 12.5v. With the correct load, the converter “rings” quicker at 51.72khz. The waveform resembles more of a square wave.
Reducing the load with a 10W Philips LED replacement, the transformer still ran without audible noise, and the LED globe seems to work happily. The output from the transformer seems to contain taller spikes with ~25v peaks. This is why marrying electronic transformers with LED replacements can sometimes result in unexpected failures.
The waveform oscillates even quicker at 66.86khz, with two components to it. It is nice to see that it works though.
This electronic transformer seems to behave similarly to the Osram Redback 60VA transformer I tore down before. For the price and weight, electronic transformers are a marvel. There isn’t even a single IC in the design, which reminds me of the ballast designs of CFLs. Their output, however, is more unpredictable from a waveform and frequency standpoint, so it isn’t that useful for repurposing. That being said, for ~$8, it definitely works, and only buzzes when unloaded.