Having had a less than excellent experience with the high power LEDs in my bench floodlights, I though it might be interesting to remove the reflector and mount four 10W LEDs in parallel to create an effective 40 watt array, but just being run at a much more sensible 20W. That would also spread the thermal dissipation across a larger area on the heatsink.
To do this would require the version of the LED with the nine chips in series to give a combined forward voltage of around 27V. There are two types of these LEDs. The most common seems to use the three by three series parallel array with a forward voltage of around 9V at 900mA. This is the type favoured by naughty Chinese factories using a standard 3W driver to make a “10W” floodlight light up.
I’ve also been hearing good reports on the quality of stuff from Sure and have used them myself in the past with no problems. So by getting a pack of ten of these LEDs it would give me a chance to do a test on them all for rogue LEDs with parasitic parallel resistance issues. (When random series LEDs are at different intensities at a given current.)
First notable thing was the packaging. The LEDs were wrapped in low static generating pink bubble-wrap and then shipped in proper metallised static shielding bags. This is kinda rare for a typical Chinese supplier and an indication that some care is being taken to protect what could be good components.
I tested them by lining them all up in a row and then setting my bench power supply to the threshold where the series string of 9 chips started passing current of about 1mA.
Placing the leads across each LED in turn showed all the series chips in each lighting at the same intensity at that current. Some whole LEDs were slightly dimmer, but that was most likely due to the use of a fixed voltage showing slight combined forward voltage variation.
I suppose another approach to the use of these LEDs in a 20W fixture is to put three or maybe even four of the 3×3 series parallel version of this LED in series.
Here’s a link to the listing I bought these LEDs from.
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