Cree LED lighting for the workshop. - Page 1
Forum section: electronics / projects

author: Kibi
author_rank: Unknown
timestamp: January 20, 2013, 08:29:30 pm
content: I have been struggling with a silly 2x 18W fluoro tube light on the ceiling of my workshop for quite a while now. I have been wanting to upgrade it with more up to date LED's.Now, I have used Cree's CXA2011 chips before and they are fantastic, but a bit of a nuisance to drive because they operate at 42V which is quite high. Late last year Cree added some new chips to their CXA range. I went for the CXA2520, which is easier to drive at 36V and produces more light than the CXA2011 modules.So, it was time to design a driver for the CXA2520. As I am converting my workshop power to off grid, a 12V lamp would be ideal so that I don't have to convert to 240V and then down again to drive the lamp.Micrel provided the answer for me in the form of their MIC3223. It was cheap, operates from IIRC 5V -20V input, provides programmable constant current up to 1A and can boost up to 37V MAX. Another bonus is that the switch is built in to the MIC3223, so no silly external MOSFETs are required. It switches at 1MHz. It even accommodates PWM dimming control, but you need an external MOSFET for that function of course, but no big deal.All you need is an inductor, a snubber, diode, a few resistors for programming constant current, high voltage cutoff point and a few capacitors for decoupling.All of the external components will fit within 1206 packages, so a nice easy, small single sided board layout can be used.I designed my circuit pretty close to that described in Micrel's datasheet.I designed the board in Eagle, but I have made it larger that it needs to be because the larger dimension fits nicely inside the case that I intend to use.I soldered it all on by hand because my PID oven project has ground to s shuddering halt.This is the LED on a temporary heatsink for now.At first the circuit powered up and worked straight away - which was a bit disappointing. However, the fun began when the LED started flashing on and off at 1 or 2 second intervals.After much debugging, I figured that the bottom pad, which is also pin 17 or EXP on the diagram did not flow. I figured this by the higher than expected temperature of the MIC3223.I gave the board a quick whirl in my trusty frying pan and then everything worked as it should. The MIC3223's temperature dropped too.At 12V we are consuming 1.7ish Amps. 20.4W.On the output, we are running at about 35.5V, 545mA. 19.34WThis makes the circuit about 94% efficient.The LED current remains constant with input voltages as low as 5V and I've taken it up to 18V with no problems. MAX Vin is 20V. With such low input voltages, I could even make a bicycle light with two Lithium batteriesOf course the current increases, but there you go.The LED can be driven harder than I am, but I'm not so sure it's necessary. The current tube light measures 100 lux from the ceiling with the light meter on the floor. The single LED measures 160 lux and 100 lux if it's 1 metre off axis from the light meter. I'll be making four such lights.Next thing is to do the mechanical bits. I'll update when it's done.

author: mazurov
author_rank: Frequent Contributor
timestamp: January 20, 2013, 11:23:34 pm
content: Where did you buy these LEDs?

author: SeanB
author_rank: Super Contributor
timestamp: January 21, 2013, 05:07:39 am
content: The Cree ones will actually deliver the lumens.

author: mazurov
author_rank: Frequent Contributor
timestamp: January 21, 2013, 07:05:17 am
content: The _real_ Cree ones will actually deliver the lumens. The biggest issue with Crees is that most of them are fakes. Fortunately, CXA are still genuine.

author: Kibi
author_rank: Unknown
timestamp: January 21, 2013, 08:18:24 am
content: I got the LED's off of Digikey. They were the cheapest. Farnell were charging almost double that of Digikey.

author: SeanB
author_rank: Super Contributor
timestamp: January 21, 2013, 04:21:26 pm
content: Consumer grade lamps none are good, they all either overdrive the dies or have insufficient heatsinking and thus they run really hot and die in short order. Or both, along with cost cutting and running capacitors and semiconductors at or beyond the recommended limits.Philips is the same, though they do try to keep close to the edges, not like some I have seen driving a 5mm LED at 100ma to get their light output up, at the expense of a lifetime measured in weeks.If you can get industrial LED units use them.

author: Kibi
author_rank: Unknown
timestamp: January 21, 2013, 07:10:41 pm
content: I am actually running some cheap, no-name GU10's in the house. They claim to have Cree LED's in them but they don't appear to.They do have good heatsinking and a reasonably good driver. I have a few 9W GU10's and several 6W GU10's. They have been running for more than a year now and are still giving goo light output. Of the 20 or so lamps one started strobing within a week, but all the rest are OK. If I get three years out of them then I will be happy.The 2W Osram BS lamp outside has been going for years, it often gets left on accidentally, hence the reason for it being 2W.Currently though, if you want high powered lamps that will last, with good quality light then you have to build them yourself I'm afraid, or go down the industrial lamp route as Sean stated. DIY is cheaper.

author: ee851
author_rank: Regular Contributor
timestamp: January 21, 2013, 07:37:01 pm
content: This is definitely something that interests me for bike lights. I am using a 12VDC battery. I have looked at using both the old LM317 current mirror and the newer Goldwater LED current regulator, as well as the humble power resistor and numerous BJT-based current mirrors. Stepping the voltage up as you did would definitely permit driving more Cree white LEDs in series.I am not familiar with this IC. How exactly did you program it?Or is the output current programmed by selection of component values, as with the solutions I mentioned above ?

author: SeanB
author_rank: Super Contributor
timestamp: January 21, 2013, 07:40:37 pm
content: I am looking at the DIY method myself. Costs a lot more but better overall as you choose the compromises you have to make.Did buy a small lathe this afternoon though, little 140mm one. will definitely find it useful in doing them.

author: Kibi
author_rank: Unknown
timestamp: January 21, 2013, 09:30:19 pm
content: The important parameters are programmed with R3, R4 and R5.R3 and R4 form a divider to set the maximum output voltage cutoff as a safety precaution.R5 is the one you really need to be concerned with, this sets the constant current going through the LED.The datasheet makes for good bedtime reading, study it and work your design requirements around that.

author: ee851
author_rank: Regular Contributor
timestamp: January 23, 2013, 05:23:39 pm
content: Thanks!Just curious--have you noticed any RFI from this circuit?

author: Kibi
author_rank: Unknown
timestamp: January 23, 2013, 11:01:02 pm
content: This is a good question which has actually been raised elsewhere. The answer is that I have not noticed any RFI.The circuit oscillates at 1MHz which is definitely RF, but my plans are to house this board in a metal enclosure which will certainly reduce any effects.

author: Kibi
author_rank: Unknown
timestamp: January 28, 2013, 11:39:58 pm
content: A small update.Today I completed the preparation of the reflectors.I found some stainless steel dog bowls on eBay. They have a nice shiny surface on the inside of them and they were cheap. I needed to make a central 35mm hole in the bottom plus some mounting holes outside of that. Now, my lathe is too small to swing the radius of the dog bowls over it's bed, so boring the hole out on the lathe was a no go. As I don't have a punch and die set either, I came up with a plan to do the job on the milling machine.First, I cut a circle out of 3mm ply wood, the diameter of which is the same as the ID of the open end of the dog bowl. The circle is then bolted down centrally on the milling machine's bed. This will centralise the dog bowl and allows for the hole to bored out centrally and then allows changing of the workpiece easily (I have four dog bowls to work on).Then the dog bowl is clamped down upside down and the boring head is set at the correct radius.You wouldn't normally bore straight down into metal like this, but as the metal is so thin, the boring bar has enough clearance. Low RPM, lots of cutting fluid and good tool pressure and the boring bar cut through without too much protest. Stainless steel in interesting stuff to work.Next, the mounting holes needed to be drilled. Another reason for the wooden circle is that I can wind the bed out to the correct hole circle diameter, then simply spin the dog bowl 120º and drill the next hole and so on. I had marked the outside of the dog bowl every 120º beforehand and lined up the marks on the dog bowl with one on the milling machine table.Again plenty of cutting fluid and good pressure and the first three holes went through OK. Then the TiN coated everyday drill bit downed tools and refused to cut any more holes. It was then that I realised that should have used the carbide one. From then it was plain sailing for the rest of the holes. Stainless steelThe edge of the large holes is mighty sharp, so I have dulled it with file. I have a bit of an aversion to holes of around about this diameter in sheet metal because it brings back memories of when I mostly chopped my thumb off on the edge of one such hole in mild steel a few years ago. My thumb has been sewn back on and it works 96% well.OK, cool, that's it for now. I have cobbled my reflow oven together too, so I'll get the rest of the PCB's done soon.

author: croberts
author_rank: Regular Contributor
timestamp: January 29, 2013, 10:23:06 pm
content: Hello KibiI had the posts a while back on the solar powered LED lighting system. I've been following your progress on the LED lights and just wanted to say it looks like you're doing a great job! I've been using a carbide tipped hole saw to cut that center hole in the reflector. So far so good. It looks like you worked out a way to mount the Cree to the heat sink (I remember that was one of the differences with the Bridgelux I use...no mounting holes). Keep up the good work!

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: January 29, 2013, 10:36:38 pm
content: I hate drilling SS especially formed, I have been doing a bit of LED lighting too, with Cree Leds. I use XTE. Because they're cheaper than XPG.I do really like the look of stainless but it is so hard to work with.I was told that some white painted surfaces give almost 100% reflection. So they might be an option too.It seems to me the hardest thing about making the light fittings is making them look good. On on off.I am struggling getting good led diffusion too. As I am more interesting in spread room lighting than downlighting.Diffusion is probably not an issue for you.

author: Kibi
author_rank: Unknown
timestamp: January 30, 2013, 10:59:26 am
content: Hello Croberts, yes I do remember your thread. You gave me some ideas which you may notice that I have used in my design.As far as mounting the LED goes, I was going to glue it to the heatsink with arctic silver. The dog bowl would mount to the heatsink with the three small holes that I drilled. Now I might have changed my mind, but I am not too sure yet. I might go back to my original idea and make a nylon LED holder which would hold the LED on to the heatsink and also secure the dog bowl. I'll have to give it some more thought.

author: mrflibble
author_rank: Super Contributor
timestamp: January 30, 2013, 12:12:19 pm
content: Love the DIY led lighting posts. Great source of inspiration.Keep it up!

author: cwalex
author_rank: Frequent Contributor
timestamp: January 30, 2013, 12:41:43 pm
content: Another post here just so you know i have nothing productive to add for you just wanted to say I follow your posts with great interest too

author: Kibi
author_rank: Unknown
timestamp: January 30, 2013, 02:16:43 pm
content: Thanks to everyone for the kind comments.I didn't answer the question about diffusion. I hope that the dog bowl will provide a degree of diffusion by bouncing the light around a bit inside before it exits. In addition to this I plan to use some of that plastic prismatic diffusion sheet, the type that is often used in office lighting.

author: Kibi
author_rank: Unknown
timestamp: January 30, 2013, 06:18:36 pm
content: Another thing. I had just noticed that in my first post I stated that I was using the CXA2530. This is complete and utter lies. I am using the CXA2520.I apologise for misleading anyone. I have modified my first post to reflect the truth.

author: Kibi
author_rank: Unknown
timestamp: January 31, 2013, 11:22:45 pm
content: So, I cobbled a reflow oven together. I found a brand new, although crappy, toaster oven in Argos for £12.99, it was the last one too! It's really small too, but perfect for most jobs. Then I got a PID controller for £11.99 and a Crydom SSR off of eBay for £3 (it was £9 for three of them). I already had a thermocouple Sorted, a reflow oven for less than £28!! Bonus.So I have got the PCB's assembled.I finally decided that I'd go down the Arctic Silver thermal glue route. The cases are drilled, tapped and the LED's glued down.With any luck, I'll get on to the final assembly and installation later this week.

author: mazurov
author_rank: Frequent Contributor
timestamp: January 31, 2013, 11:28:57 pm
content: You're going to regret gluing the LED down before soldering the wires to it.

author: Kibi
author_rank: Unknown
timestamp: January 31, 2013, 11:39:21 pm
content: Quote from: mazurov on January 31, 2013, 11:28:57 pmI did think about that and I understand what you are saying, however, I think my iron can cope with it. I have soldered 8mm brass nuts and bolts with that iron and it was totally OK with it.

author: croberts
author_rank: Regular Contributor
timestamp: February 01, 2013, 03:38:07 pm
content: Hello KibiI preheat my LEDs to 150 deg C before soldering wires. I attach the LEDs to a power resistor and use a PIC control circuit to hold the temp at 150. LEDs on the control circuit tell me when the temp has stabilized. The power resistor is centered in a jig that holds the wires just as I want them so both hands are free when I solder. It works great and allows me to solder the wires with a small iron.

author: Kibi
author_rank: Unknown
timestamp: February 02, 2013, 11:57:45 pm
content: I had no trouble soldering the wires on to the LED's with my soldering iron. No pre-heating was required either.It was about as easy as the gentleman demonstrates in this video. To be fair he is using the same iron as I am.I did get the hole circle diameter wrong for the three dog bowl mounting holes. The diameter was 2mm over size, I don't know how I managed that, but I drilled another three 60º "out of phase" and slotted them. No big deal really, but a silly mistake to make.Things were starting to look good.Until.......Now, this happened when pressure was applied to the screws whilst screwing the dog bowl to the case. The case obviously flexed and the ceramic substrate of the LED did not. The glue stuck fast even after running them for an hour prior to screwing the dog bowl in position.I scraped the glue off the LED and tried again, this time rubbing the area with 800 grit paper, still same problem. I also did not like the thermal performance of the glue, it wasn't bad, but not good enough. It'd probably be fine with a bigger heatsink and the glue would definitely stay stuck down when applied to a rigid base.I did come up with a ghetto solution which is working, so I may well leave it like it is.Now what remains is to see how well the aluminium case works thermally. I'll have to leave the lamp on for a few hours to verify that.

author: Kibi
author_rank: Unknown
timestamp: February 03, 2013, 09:32:57 pm
content: The thermal performance tests failed today. The case temperature went up to 85ºC after just 30 minutes. The die temperature was 105ºC. No good.A re-design was needed. I was trying to avoid using bigger heatsinks as they increase the protrusion of the lamp. Also they are expensive. I do however have some good heatsinks from a previous project. Integrating these into the design meant almost an entire rework of all the mechanical parts. I had to turn the cases over because the surface that I originally had the LED mounted to now has more holes in it than a second hand dart board. Some of the existing holes would interfere with the new design.So these are the heatsinks I am now using with the LED, once again, glued on with Arctic Silver epoxy.I then enlarged the hole in the centre of the dog bowl to allow for better flow of convection currents. Besides, the mounting holes are now on a much larger diameter.Now the thermal performance is much improved. I left the lamp on for two hours and the heatsink temperature rose to 50ºC and the die reached about 85ºC. That die temperature is actually what these LED's are binned at so that was a nice coincidence. The glue is performing well now that it is bonded to a better performing heatsink.Here are two of the lamps in position. Now I am getting 2500 lux on my worktops for less energy as opposed to the 250 lux I was getting from the fluorescent lamp. Granted, the fluorescent lamp was not in the same position, but directly below the fluorescent lamp at the same height I get 450 lux.Shadows are a minor problem, about the same as you'd get from a CFL. I plan to reduce the shadows with some diffuser material.

author: mazurov
author_rank: Frequent Contributor
timestamp: February 03, 2013, 09:40:18 pm
content: This is what I use - Rosewill RCX-Z80-AL CPU Cooler, $7 plus shipping. Designed to dissipate 70W. CXA-2011@1A, AS-5. Both heatsink and module case at ambient with fan at full speed, +5C above ambient when fan is at 5V.

author: Kibi
author_rank: Unknown
timestamp: February 03, 2013, 09:45:20 pm
content: I actually bought an Intel 3220T CPU a few weeks ago. It came with the heatsink and fan which is useless to me. I have been thinking about using this heatsink in my next LED project which will be to convert the horrible 300W uplighter in the living room to LED.

author: mazurov
author_rank: Frequent Contributor
timestamp: February 03, 2013, 09:57:13 pm
content: CPU heatsinks are very efficient - I use them all the time. Usually, I get them free from my overclocker friends. The ones made for Intel are rated for 100W.The issue with CPU heatsinks is that you need to drive the fan somehow and keep it in good working order.

author: IanB
author_rank: Super Contributor
timestamp: February 03, 2013, 09:59:39 pm
content: Quote from: Kibi on February 02, 2013, 11:57:45 pmBut his soldering looks neater than yoursFascinating project to see though. My main concern for ambient lighting would be to get good colour rendering. I always find fluorescent and LED lighting to be lacking in viewing comfort--it somehow feels cold and artificial.

author: SeanB
author_rank: Super Contributor
timestamp: February 03, 2013, 10:07:26 pm
content: I converted mine to 70W double ended MH a long time ago. Bought a dozen spare lamps this weekend at a flea market for R30. Actually 33 lamps, but 20 are 150W MH lamps. Those will be going out to somebody else. I think 12 Philips China lamps will do a few years with me.

author: Kibi
author_rank: Unknown
timestamp: February 03, 2013, 10:30:18 pm
content: Quote from: IanB on February 03, 2013, 09:59:39 pmLol, a bit neater, I think the problem was that I was wearing neither rubber gloves nor a coat.These particular lamps are 3500K. I'd probably use 2700K or 3000K in the house as these are much more comfortable. 4000K is verging on the clinical side of things for me, not too harsh though.Quote from: SeanB on February 03, 2013, 10:07:26 pmThat is not a bad price at all for even one MH lamp.

author: SeanB
author_rank: Super Contributor
timestamp: February 03, 2013, 10:38:44 pm
content: Last price was R130 each.......... I got them for less than R3 each.

author: M. András
author_rank: Super Contributor
timestamp: February 03, 2013, 10:51:20 pm
content: maybe a custom heatsink a polsiehd copper block + heatipes soldered in them to some flat alu heatsink or copper sheets?btw care to share where you got those nice reels?

author: Kibi
author_rank: Unknown
timestamp: February 03, 2013, 11:10:17 pm
content: If some sort of heatpipe heatsink system came up cheap one day, it might be worth considering. Although the protrusion of my units is more than I would have liked, it's not really that bad. It's 180mm from the ceiling to the lip of the dog bowl. The standard CFL in my kitchen protrudes 170mm.I bought the reels of cable from Rapid. They do all the standard colours (11 colours) on 100m reels in a job lot. 7/0.2 is just standard go to instrument wire, so I thought why not.http://www.rapidonline.com/Cables-Connectors/Equipment-Wire-7-0-2-11-Reels-of-100m-01-0480

author: gxti
author_rank: Frequent Contributor
timestamp: February 04, 2013, 12:18:41 am
content: Water cooling would make more sense than heatpipes. Water blocks are shorter than air coolers, too, and you only have one or two moving parts total rather than one per lamp as they would all be on the same liquid circuit. Much more exciting failure mode, though.

author: eat_those_lemons
author_rank: Newbie
timestamp: June 22, 2013, 11:04:34 pm
content: how did you get the pcb?and where?

author: ftransform
author_rank: Frequent Contributor
timestamp: June 23, 2013, 01:22:53 am
content: I think that water cooled house lighting is ridiculous.

author: eKretz
author_rank: Frequent Contributor
timestamp: June 23, 2013, 04:16:16 am
content: Are you kidding?! That's nerdgoldright there!

author: Kibi
author_rank: Unknown
timestamp: June 23, 2013, 08:54:21 pm
content: Quote from: eat_those_lemons on June 22, 2013, 11:04:34 pmI laid out the PCB in Eagle myself and then sent off for the PCB's to be made at iTead Studio.

author: gxti
author_rank: Frequent Contributor
timestamp: June 24, 2013, 04:03:12 am
content: Lighting the room evenly with that much light would be wasteful. The lamps in the picture are directly over a work area, and lighting that is more important than lighting the middle of the room. It's a workbench, not a cube farm.

author: steve30
author_rank: Frequent Contributor
timestamp: June 25, 2013, 03:17:32 am
content: I agree with mojo-chan, I like my lights nicely diffused, and got rather fed up of a downward pointing light in the middle of the room.I guess it just depends on the individual circumstances.

author: cthree
author_rank: Frequent Contributor
timestamp: June 25, 2013, 03:59:14 am
content: Quote from: mazurov on January 21, 2013, 07:05:17 amDon't buy brand name components on ebay. Buy them from a distributor and they will be 100% authentic.