LED PIR Floodlights Using 5050 chips

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Overview

Very effective 30W LED floodlights can be constructed using 5050, (5mm surface mount), daylight LED chips which can be obtained on eBay direct from China at a cost of 5p per unit or less, but beware, cheaper may mean dimmer - it is worth paying slightly more for the top spec. devices if you can find an honest retailer that gives genuine specifications.
The floodlights I constructed were based around low energy PIR floodlights purchased at a very good price from LIDL. These are basically 500W floodlights fitted with low energy 22W R7s CFL lamps. The problem with CFL lamps is that they are very dim when they first come on in cold weather and I have had several instances where they have not lit at all when it's been very cold. The lamps also do not last very long so CFL floodlights are simply not reliable enough for security purposes
These LIDL PIR floodlight units are very good quality for the money and are fitted with a 5mm toughened/annealed plate glass front which provides the perfect surface for the LED conversion, the glass also acting as a heat sink for the 5050 LEDs, conducting the waste LED heat directly to the open air.
The construction is a very painstaking process, involving creating a ‘light plate’ by gluing 5050 LEDs face down to the inside of the front faceplate using a crystal clear cyanoacrylate glass bonding adhesive, but well worth it as it gives very good results, producing a 30W LED floodlight having a light output comparable to an incandescent floodlight of up to 10 times the power and certainly much brighter than a 22W CFL version situated next to it. This high efficiency is achieved by using the best quality daylight 5050 chips and running them at well below their maximum ratings where they are most efficient and reliable. In the constructed units they run at c. 17mA total per chip, giving a single LED chip dissipation of just over 50mW. The floodlight uses 'multiple redundancy' for supreme reliability - there are 7 separate drivers and 7 separate groups of LEDs, so a single driver or LED failure only affects 1/7 of the floodlight's output whereas with a conventional floodlight a single failure means that your light is out, so these high reliability lights are ideal for critical applications. I have been running three of these 30W LED PIR floodlights for about 2 years so far without a single failure of any sort. I have also produced some 16W versions based on 150W halogen PIR floodlights that once again have proved 100% reliable to date.
The Light Plate Construction.
Take your 500W floodlight housing and mark the outside of the glass by running a broad tipped permanent marker around the inside edge of the front face. This marks out the available area for the 5050 LED chips - make sure there is sufficient allowance to clear the frame and face gasket. Unclip the glass from the frame and place it marked side down on your work surface, (I used paper towel on a standard worktop). Check what available space you have without going over the marked lines. For a 230V mains system the LEDs must be grouped in series stacks of 70-85, so this defines the length and number of rows. For a 110V system it would be slightly less than half the number of LEDs per stack. I had sufficient space for 21 rows of 27 LEDs per row, giving a total LED count of 567 LEDs in 7 groups of 3 rows of 27 LEDs per row, i.e. each of the 7 stacks=81 LEDs. Hopefully the dimensions of the front plate area will allow you to do much the same, but check first!
Thoroughly clean the glass using isopropyl alcohol and dry. Start the first row slightly inside the marked line by applying a globule of crystal clear cyanoacrylate glass bonding adhesive, ( N.B. - use a good quality glass bonding cyanoacrylate adhesive), to the front face of the first LED and fixing it squarely in say the top left corner so the connection pins will abut one another as you position further LEDs. Continue in this way, (OBSERVING POLARITY!), making sure that each LED is the same way round and hard up against the previous one, until you have finished one row. N.B. - leave 5mm space at the end of the row as the next row must be staggered by half an LED length to prevent adjacent row pins being too close. The next row should have the LEDs the opposite way round, (so as to facilitate the series connection), and staggered by half a LED length and so it goes on with each alternate row staggered and having the LEDs the opposite way round to the preceding row. See pictures for a finished plate layout. Remove any excess glue with a craft knife blade and thoroughly clean the glass with isopropyl alcohol before starting each row. Continue in this way until you have placed the requisite number of rows to meet the above connection criteria in the available space. Once all of the LEDs are glued into position then solder all of the abutted individual LED pins. Connect the number of rows in series necessary to give a series stack of 70-85 LEDs for a 230V system, in my case three series connected rows of 27 LEDs form one stack of 81 LEDs. Solder connection wires to the beginning and end of this stack – it will be connected to one driver. Once the plate is fully assembled, lay it flat face down and brush cyanoacrylate adhesive liberally over the rear of the assembly, working it into all the small gaps. This will filter through to the glass and produce a strongly bonded homogenous structure. Pictures of the finished light plate:

Remove the reflector assembly from the floodlight as it is no longer required. Save the screw - the reflector mounting is used to secure the driver pcb bracket.
The Drivers
Each of the 7 stacks of 81 LEDs has its own identical simple mains driver, the circuit of which is as follows:

For a 110V system using about half the number of stack LEDs, the capacitor C1 would probably be in the region of 2.2uF 400V class X, (determine by experimentation to give a stack current of approximately 17-18 mA). R1 is a 22 Ohm 2W fusible resistor.
Normally I would produce a dedicated pcb, but as these are only prototype small quantities I constructed them using stripboard. Driver layouts:

Drill two holes in the above pcb as indicated in the space deliberately left between the drivers for the purpose and construct a U-shaped bracket out of 9mm 16SWG aluminium strip which is used to fix the driver assembly to the screw mounting where the reflector was fixed. The bottom of the U bracket is drilled to take the removed reflector screw and the tops of the U are bent over and drilled with pilot holes to take two self-tapping screws fixed through the previously drilled driver pcb. Make sure the lug dimensions are such that there is adequate clearance to the nearest pcb lines - chamfer corners.
DISCLAIMER AND WARNING - mains electricity is potentially dangerous. Do not interfere with these lamps unless you are qualified to do so and fully understand the principles involved in their design and construction. Any modifications are done at your own risk - no liability can be accepted for any event that occurs as a result of such work. A suitable fuse or fusible resistor must be fitted in one of the lamp supply leads as detailed above.
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  © bobbybear2 2013
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