Fullscreen HTML5Med Res (??MB)HTML4

You thought the last one was dazzling? SERIOUSLY BRIGHT 10W 20W LED FLOODLIGHT Last February, we published a DIY 10W LED Floodlight, which has been enormously popular. We said that one was almost blinding – but to paraphrase Croc Dundee, that’s not bright. THIS one is BRIGHT! S Design by Branko Justic* Words and music by Ross Tester CHIP has just returned from two days at the Sydney Electronex exhibition, where we met a large number of existing readers and also (hopefully!) new readers. On our stand, we displayed several recent – and even a couple of future – projects. Believe it or not, one project which attracted perhaps the most attention was the 10W LED Floodlight, featured in our February 2012 issue. This floodlight compared more than favourably with PAR38 incandescent and quartz-halogen floods we all know so well. In fact, few could believe just how bright this was and quite a number wanted the Oatley Electronics phone number so they could order their own kits. ILICON What’s this? A 20W? As luck would have it, waiting for us back in the office was another kit from Oatley Electronics – this time a 20W version of the LED Floodlight. We quickly assembled this kit and, despite a few wrinkles (which we’ll get to shortly) were very impressed with the light output. To the naked eye (no mean feat be66  Silicon Chip cause it was far too bright to look at!) it looked much brighter than the 10W LED version, indeed, much brighter than a 150W QI portable floodlight. We ran some tests using a Jaycar Lux meter on the original 10W LED floodlight, this 20W LED floodlight, the 150W QI floodlight we originally compared the 10W LED to and finally a 500W QI floodlight. The results appear on the photograph opposite but you’d have to agree that they are pretty impressive for the LEDs. Of course, the 500W QI does look a lot brighter in the photos – and it is. But remember, we are comparing this to the 20W LED alongside. That’s 500 compared to 20 – 25 times the power. It sure ain’t 25 times the brightness – both are far too bright to stare into for more than a brief instant. Just a note of caution, though: we don’t know what wavelength that meter is calibrated to. So there could be a “skew” in the figures if it is more sensitive to the bottom (red) end of the spectrum than the top (blue). The QIs look very yellow indeed compared to the LEDs – and we all know that QIs have a very much “whiter” light than do standard in- The heart of the project is this 20W LED array. It contains 20 individual LEDs. Like all LEDs, it requires a constant current supply, as described in this article. The light has hit this module “just right” to highlight the “–” and “+” symbols moulded into the plastic – these tell you the polarity of the two metal tabs (as it happens, the top tab, under the finger, is the positive). siliconchip.com.au candescents. But as a relative A:B:C:D test, the results are quite telling. And of course, the LED lamps run MUCH cooler than the QIs. The LED array As you can see from the photo below, the LED array (or module, if you like) is rather large. The whole thing measures 46 x 53mm (including connection tabs) while the “good bit” (the section which actually produces light) is a rather large 22 x 22mm. Inside this rectangle are 20 individual SMD LEDs, potted in two rows of ten. Together, they produce a 6000-6500K light at between 1500 and 2500 lumens. Given that your average 20W fluoro tube produces about 1100 lumens, that’s a lot of light from a small area. Driving the LED array In common with all LEDs, it’s not possible to simply connect power and away you go! The LEDs do not limit current so will quickly burn out. And driving a high-power LED is a little different from the garden variety LEDs we have been using for several decades. These basically only require a resistor to keep the LED current within bounds. The value of this current-limiting resistor can be easily worked out from Ohm’s Law – and even then, it’s not very critical as long as you don’t overdrive the LED. While you can drive a high power LED using a resistor, it’s better to arrange a constant-current supply, which is exactly what we’ve done here. One advantage of a constant-current supply is that (within reason) it can handle a wide range of input voltages. The claimed operational range of this 20W LED Flood is from 6V to 30V. Too much power! One slight problem with the constant current supply included with this kit is that it can supply a bit too much power to the LED – 25W instead of the rated 20W. This will cause the LED to run too hot, thus reducing its life, so there is a slight modification required to reduce power, which we will get to shortly. The kit includes a 24V, 1A switchmode power supply – which we will also get to shortly. The Oatley kit Everything you need is supplied in the kit, right down to the heatsink compound required to transfer heat from the LED to the case. Speaking of cases, a glass-fronted floodlamp case is included which has provision on the back for the power supply. It is shown assembled above. When we say “kit”, the controller board is already pre-assembled. This is fortunate, because there are a couple of SMD components on the board – the regulator IC plus a Mosfet used for reverse polarity protection. Incidentally, if you’d like an explanation as to the how, when, where and why of using a Mosfet for reverse Measurements using Digitech (Jaycar) QM1587 Light Meter 50 lux <at>1m 7.5 lux <at> 10m 25 lux <at>1m 4.5 lux <at> 10m 51 lux <at>1m 9.5 lux<at> 10m 250 lux <at>1m 40 lux <at> 10m Comparison shot between (left to right) a 150W QI, 10W LED, 20W LED and 500W QI. This pic really doesn’t do justice to the LED floods – they are rather brighter than would appear here. In fact, they’re dazzlingly bright! siliconchip.com.au November 2012  67 Some readers may remember the night-time shots of my fishpond comparing the 10W LED to a 150W QI flood. Here’s a similar comparison, this time between the 10W LED floodlamp (left) and the 20W LED floodlamp (right). Both were taken from the same place, with the floodlights in the same place, using identical exposures (1/4s <at> f/4). polarity protection, see the “Circuit Notebook” entry in the April 2012 issue (p70). It’s much better than using a diode for the same thing. Construction The first thing we need to do is make the modification alluded to earlier. This involves removing the 0.33Ω SMD resistor on the right side of the PCB and replacing it with three 1.2Ω resistors in parallel (ie, 0.4Ω). Removing the SMD resistor is a bit tricky – we used a thin blade to lift one end while we heated the solder join. Having got one end off the board, complete removal is easy. Obviously, three 1.2Ω resistors (even 1/4W types) in parallel are going to take a bit more space than one SMD resistor. But there is room to place them – twist their leads together first and bend the leads back under to make a “C” shape and tack them to the pads (on the top of the board) vacated by the SMD resistor. What’s the zener for? There is a second modification required to the PCB if you plan to run the flood from a 24V supply – either the included supply or any other. The problem here is that the Mosfet used for reverse polarity protection (STM4410A) has a gate-source absolute maximum of 20V so is in dire danger of being popped at 24V. The way around this dilemma is to fit an 18V zener diode between the aforementioned gate and source. Fitting this zener is also a bit fiddly – fortunately, three of the pins (1,2 and 3) are connected together as the source on the STM4410A and these make a handy point to solder the anode of the Zener to. The cathode (stripe end) can be soldered to the inner pad of the 10kΩ SMD resistor (again, it is tacked to the top of the PCB). Note again this mod is ONLY required if you intend to operate the LED Floodlight from a supply greater than 18V (it is quite happy to run at 12V, by the way, with full brilliance). DC power supplies Here’s where we struck a snag – and we thought we’d better mention it before final assembly as it might make a difference to what you do. We mentioned earlier that Oatley Electronics include a Chinesemade 24V, 1A switchmode power supply with the kit, which should be more than adequate to drive the power supply and LED array. (20W/24V=830mA; add a bit for losses and it should still be well under 1A). But the power supply couldn’t cope – it was as if it was continually starting and shutting down under overload. The effect was that it “strobed” the LED array – fine if you’re looking for a party light but not very practical for a floodlight! Oatley Electronics told us they had received occasional reports of this happening but equally, large numbers where it didn’t. So we tried our prototype with three other (identical) power supplies and the same thing happened. Switching over to a 12V, 3A supply solved the problem completely – obviously the floodlight drew more current (20W/12V=1.7A) but that was no drama for a 3A supply. So if your floodlight strobes like ours did, you’re going to need a different power supply. The circuit diagram says a DC input from 6 to 30V; bear in mind that the lower the supply voltage, the higher the power supply current. At 6V, you’re going to need a supply capable of nearly 4A; at 30V, the supply can be less than 1A. Assembly Now that we have the fiddly bits At left is the PCB as supplied by Oatley, while the one at right has our two modifications (circled). The zener is only needed for operation on supplies >18V. 68  Silicon Chip siliconchip.com.au At left you can clearly see the four tapped mounting holes for the LED array. The two outer holes are for power wire entry. At right, the LED array has been mounted (with heatsink compound underneath) and the two power wires (red and white) soldered to their respective tabs. Note the red and black marks we put on to show which was which! + V+ L1 out of the way, it’s time to put it all together. First, you need to identify the “+” and “-” terminals of the LED. It’s not easy! Unless your eyesight is in the macroscopic class, you’ll probably need a magnifying glass. You’re looking for a + and – symbol moulded into the white plastic “case” which surrounds the LED array itself. Once you’ve found them you can then identify which of the two metal tabs is positive and which is negative. (Our photo shows which is which). We kept losing the symbols (especially under normal office light) so in the end put a spot of red marker pen against the + symbol. It helped! On the inside of the main (large) case, you’ll find six holes. The four smaller holes form a square and these are used to mount the LED module. First, though, apply a good coat of heatsink compound (supplied in the kit) to the rear of the LED array and smooth it out. Mount the LED array with four of the small countersunk-head metal screws – the holes are already tapped. Any heatsink compound that oozes out the edges should be removed with a cloth. The other two holes will be used to 10k 10k + K G D V– (5-8) SC 2012 Q1 STM4410A (4) A ZD1 18V # – 220F 20W LED ARRAY  3 SW 4 VIN 2 630V DC # 5536 (60V, 3A) – 5 IC1 FB EN XL6005E1 GND 1 + 220F 0.4 –  3x 1.2 IN PARALLEL S (1-3) IC1 Q1 # SEE TEXT 20W LED Floodlight driver 8 4 1 5 1 Here’s the circuit of the 20W LED driver, published more for interest’s sake than anything else because it comes pre-assembled on a small PCB. All you need do is change a resistor value and, if needed, add a zener diode. pass the power cables through shortly. Wiring You need to connect the wiring to the PCB before mounting it in its case. The case containing the power supply PCB is actually separate from the main case and is attached to it via four screws. In fact, it is the lid which is attached to the case and the case body screws down onto the lid. There are four wires required to connect it – two “DC in” and two “LED out”. The two LED out wires are simple – just solder some relatively heavy duty pickup wire to the two terminals marked LED OUT + and –. These wires pass through the two holes into the main case and are soldered direct to the metal tabs on the end of the LED array – after once again checking you have identified the + and – tabs. The DC in wires are simple enough, a positive and a negative, but depend on whether you are going to use the power supply in the kit or some other supply. Either way, a cable gland is supplied in the kit which suits the round cable from the DC supply. Pass the cable through the gland and the hole in the case, leaving the gland loose for the moment. Around 100mm of wire inside the case is needed to make connection simple. The power supply PCB has a heatsink attached to the back which needs to be in intimate contact with the case. Rather than drill and tap holes, we used a pair of TO-3P mounting pads which are self-adhesive both sides and therefore keep the board in place, while transferring any heat to the case. siliconchip.com.au November 2012  69 There’s a pre-drilled hole in the case to accept the cable gland (supplied). It ensures that the box is watertight and won’t provide a warm, happy home to ants and insects. At right is the PCB mounted in the case lid attached to the main lamp body. There’s no screws on the PCB: it’s held in place by a couple of self-adhesive thermal transfer pads. It’s probably easiest to cut any plug off the DC supply and wire direct to the PCB but you may need to identify the + and – wires from the supply; in our case there were four wires, red, black, green and white. The positive lead was red, as expected, but the negative lead was the white, not the black. If you solder direct, make sure you insulate the ends of the other two wires, as well as the red and white, to prevent shorts. The alternative is to leave the plug on the power supply and drill a hole in the side of the case and fix a panelmounting socket to the case, wired to the PCB. This will make the floodlight a lot more portable, if that’s your want! Mounting the power supply The power supply PCB has two mounting holes but we cheated a bit and glued it in place with self-adhesive thermal pads intended for TO-3P transistors. These are more than capable of sticking to the heatsink fins and also to the case itself. (These are not supplied in the Oatley kit). 70  Silicon Chip For convenience, we mounted the PCB on the case lid, with the wires going directly from there through to the LED. Solder the power leads to the tabs on the LED array, again making absolutely sure which way around they go. With the + and – symbols towards the bottom, the + tab is at the top and the – tab is on the bottom. Pull any excess wire back into the power supply case. Putting it together From here, it’s simply a matter of screwing together the various bits – screws are supplied. The reflector mounts inside the lamp assembly so that it sits on the outside of the LED array; the glass front slots into its frame and, via a gasket (supplied) screws to the outer rim of the floodlamp. On the back, the PCB case back screws onto its lid which should have come already connected to the floodlamp. The U-bracket, used for mounting, should also be already connected to the floodlamp but you may need to tighten its screws once in position. In fact, you’ll probably have to remove it to facilitate mounting. Choose a mounting position (say) under an eave or overhang. There’s not much heat given out so that’s not normally a worry. SC Where From, How Much? The 20W LED Floodlight kit was designed by Oatley Electronics, who retain the copyright. It is available as a kit (K329), for $40.00 inc. GST from Oatley Electronics, PO Box 89, Oatley NSW 2223. This kit includes all components (PCB is pre-assmbled) and the case as shown in this article. A 24V 1A switch-mode supply is also included. If operating from a supply higher than 18V, you will also need an 18V zener diode, as described in the text. *Branko Justic is the owner of Oatley Electronics. siliconchip.com.au