The cheapest 7W LED bulb I could find - Teardown and Modification.

Hi,

just because I had nothing better to do, I ordered the cheapest 7W LED bulb I could find on eBay. The're from "Hakkatronics". Rule of thumb says, they replace 60W incandescent. They come in packs of 6, and although I paid €9 for them, the eBay history shows winning bids for as low as €5. Shipping is €5, so I paid around €2 per piece - not bad so far.

http://www.ebay.de/itm/6-X-7W-LED-B...D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

Album here:

http://imgur.com/a/p4oiO#0

My expectations weren't high, and I was not disappointed, so to speak.

Nothing unusual on the outside:



http://imgur.com/a/p4oiO#0


http://imgur.com/a/p4oiO#1


Mechanically, the lamp feels solid, all components were firmly connected, and with a tight grip, the dome and the E27 base could be screwed off.


http://imgur.com/a/p4oiO#2

There are 35 LEDs in total, Groups of 5 in parallel, 7 of those in serial. Each LED sees 3V, I measured 21V total. At 7W, this means 330mA current in total, and 67mA per LED.


http://imgur.com/a/p4oiO#5

The driver was surprisingly small and glued in, I did not bother to pry it out and analyze it. At least it sits in the coldest part ob the assembly. In the heatsink itself, there is a free cylindrical space of 27x60mm, so I could repair the lamp with this, for example:
http://www.ebay.de/itm/10W-100W-Pow...61372357&tpos=unknow&ttype=price&talgo=origal

So far, so good. Now the problems begin. The manufacturer did not really pay close attention on how to fix the LED board to the heatsink properly. A kind of countersunk spaced thread screws was used. They deformed the holes in the heatsink, leading to burrs which cause a gap between both parts. Also the holes of the heatsink and LED boards did not align very well, so the screws were skewed.


http://imgur.com/a/p4oiO#3


http://imgur.com/a/p4oiO#4


http://imgur.com/a/p4oiO#6

As one can see, the gap was large enough to not even spread the thermal paste properly. So, my education as a mechanic need to be put to practice again. I wiped all the paste off, deburred the heatsink, also at the center hole which had a burr as well. I enlarged the LED board's holes to 4mm. After deburring, I scraped all holes with the blunt front side of a box opener knive blade, which works like a precision scraper to remove even the tiniest flatness imperfection.
Afterwards, I applied some of may favorite thermal grease, Wacker P12, and assembled everything using self-tapping M3 screws.


http://imgur.com/a/p4oiO#7


http://imgur.com/a/p4oiO#8


http://imgur.com/a/p4oiO#9


http://imgur.com/a/p4oiO#10

Much better! Now I can sleep well at night. I operated the bulbs for 15min or so at 18°C ambient, and the LED board reached 53°C. At the very end just before the base, the heatsink had 50°C. This would roughly be the temperature the driver is exposed to. So, thermally speaking, everything is within reason now.
Light color is just like your typical 3000K lamp. Good for a cosy living room, but for work I'd chose 6500K. They are totally silent, no buzzing.
The seller claims a lifetime of 50 000h. Most likely, average capacitors with a 7000h rating @ 85°C are used. Given a temperature inside the bulb of around 55°C, and applying the 10k rule, I calculate 56 000h before capacitor failure. This would be 6 years of continous operation. If that holds true, it would be more than impressive. I doubt it though, as there are more failure-inducing mechanisms apart from temperature alone.

I'll inform the seller of my findings, maybe they will bother to forward them to the manufacturer.

All in all this bulb has potential, but if you have more money than time, buy a name brand. But sometimes it is sad to see, that with just a little more attention to detail from the side of the manufacturer, a product can experience quite a bit of improvement.

Regards,

Julian

Good chance there are things missing in the driver for surge protection, EMI, etc. not to mention the capacitor as you stated. I would be careful without measuring that the output is isolated (and not just via the diode bridge).

7W is to the driver, likely only 5.5 to the LEDs so the current is lower.

Semiman

I bought some of those cheap generic Chinese LED bulbs back when the good stuff was still expensive. I wasn't too impressed, I had a few failures, I found the color rendering to be poor. The wattage and light output almost universally well below claims. Most had safety issues that made them marginal at best here in 120V land but on 240V it would be scary. On top of that, most pumped out massive amounts of RFI. I don't use those anymore, with Philips and Cree LED bulbs so reasonably priced these days, I don't buy anything else.

Driver entirely wrapped in heat-shrink tubing -> makes it even harder to shed its heat in already warm surroundings. Reducing component life for capacitor etc.

Of course for electrical safety, parts on the driver shouldn't be able to go near metal casing. But better would be: circuit board fixed in place somewhere, with enough space between components & casing. Then without additional heat-shrink tubing, air cooling would be much improved and driver temps not so much above bulb temperature.