Cree CXA Floodlight Mod

jtr1962

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I had two 300 watt halogen floodlights in the yard which haven't worked for a while. I decided to mod them with LEDs rather than just replace the lamps. In truth, I wanted to do this a few years ago but LEDs hadn't reached the point where it was cost effective to do so. Also, there weren't any available in 5000K and 90+ CRI. The Cree CXA series changed all that. I decided to mod one to see the results before attempting the other one. I bought 4 CXA 1507s from Mouser at $5.60 each. These were 635 lumens at 85°C, 200 mA, and 37 volts. CCT was 5000K and CRI was 90 minimum, 95 typical.

First order of business was to prep the fixture for the LEDs. The inside wasn't flat so I had to make a few pieces of aluminum which were flat where the LEDs were mounted, but which also matched up to the shape of fixture reasonably well. I wasn't aiming for perfection. I figured even if the mismatch averaged 0.1mm, the thermal impedance with thermal epoxy would be on the order of 0.5°C/W. This would only result in a few degrees C higher operating temperature. Here's what I came up with (note that I reused the reflector but cut it to fit around the LEDs):

FixturepreppedforLEDs_zpsf9e8bcbe.jpg


Here are the LEDs mounted:

LEDsMounted_zpsefbf801a.jpg


Here is the driver circuitry:

DriveCircuit_zps99ea682d.jpg


This is the finished result:

FixtureComplete_zps1b2257a5.jpg


Here it is mounted by the garage:

FixtureInstalled_zps52138377.jpg


And here are some night views:

YardLitUp1_zpsb980272e.jpg

YardLitUp2_zps0b2c31d0.jpg


I kept the driver circuit super simple:

CreeCXA1507FloodlightSchematic_zpsae34cf85.gif


Yes, there isn't any isolation between the 120 VAC and the LEDs but I don't plan to have the light running when nobody is around. The nice thing about the CXA1507s (and most of the CXA series) is that four in series come pretty close to the voltage of rectified, filtered 120 VAC. This simple linear drive circuit only burns up about 2.5 watts of power. It would burn up slightly less with a 68 uF cap instead of 100 uF but the 100 uF was all I had handy. The nice thing about this circuit is Vbe of Q2 decreases with temperature, effectively creating a safety mechanism which reduces drive currents if things get too warm. At normal room temperature the drive current starts at 230 mA when the fixture is cool but this drops to about 210 mA after the fixture warms up. The power factor is about 0.63, which is surprising given that I made no attempt at power factor correction. Case temperature of the LEDs is around 55° C. According to the data sheet then, each LED is putting out roughly 685 lumens, and the total fixture output is about 2740 lumens. Power consumption starts at 36 watts but drops to 33 watts, giving an overall efficiency of 83 lm/W-not bad for a high CRI light source. If Mouser had the 730 lumen bin available, efficiency would have topped 95 lm/W. Of course, I could have exceeded 140 lm/W by going with the CRI 70 parts, using 8 pieces, and underdriving them, but efficiency wasn't the main goal here given that these won't be on more than a few hours a day during the warmer months only. I wanted a high CRI light source with decent efficiency. I'm not sure how the light output compares to the original halogen lamps but it seems pretty close to my eyes. The 300 watt halogen lamps at best put out 6000 lumens, but probably only 4000 lumens or less actually makes it out of the fixture.

Anyway, I'm quite pleased with the result. I'll be modding the other fixture next time I order from Mouser. This turned out to be a very effective and low cost (<$25 with all parts) mod thanks to the Cree CXA series.
 
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JohnR66

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Nice work JTR. I like the simple negative coefficient regulator circuit. I'm planing on modding my biax CFL style security lights with the CXA LEDs. I'm thinking of a low voltage system with light sensor controller that turns all the lights on at night. I might buy one of those inexpensive halogen light for modding.
 

MichaelW

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Yeah, the halogens aren't 5000K CCT.
5000K outdoors is a bug magnet.
 

Lightdoctor

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jr1962,

Wow, I'm impressed. Haven't yet considered making my own LED fixture yet, but this has given me ideas.

How's the heat sinking on that fixture?
 

jtr1962

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Nice work JTR. I like the simple negative coefficient regulator circuit. I'm planing on modding my biax CFL style security lights with the CXA LEDs. I'm thinking of a low voltage system with light sensor controller that turns all the lights on at night. I might buy one of those inexpensive halogen light for modding.
Low voltage might be better for something with a sensor, or if dimming is required. Incidentally, it's not all that difficult, at least by me, to occasionally find discarded halogen floods in dumpsters. I'd prefer that over buying new given that I would be discarding the lamp and parts needed for it. I might look around for some more to mod as I can find a few places outdoors which could use a bit more light.

Yeah, the halogens aren't 5000K CCT.
5000K outdoors is a bug magnet.
It depends. I still have a halogen flood in the yard which works. I'll put it and the LED one on just to see if 5000K attracts more bugs. I highly doubt it as I've seen more than enough bugs swarming around outdoor incandescents. Anyway, the CXAs are available in high CRI in 2700K, 3000K, 3500K, 4000K, and 5000K. That lets anyone attempting a similar mod choose whatever suits them.

jr1962,

Wow, I'm impressed. Haven't yet considered making my own LED fixture yet, but this has given me ideas.

How's the heat sinking on that fixture?
The heat sinking is pretty good considering this is a fairly thin cast aluminum fixture. I'm putting 33 watts into it. I'd say about 9-10 watts comes out as light. The remaining 23-24 watts only causes the temperature to rise about 30°C above ambient at the point where the LED is mounted. Remember Cree bins the CXAx at 85°C. This gives leeway to drive the CXA1507s at or close to their maximum of 375 mA if you need more light. Just for kicks, according to the data sheet at 85°C and 375 mA the fixture would be putting out about 3900 lumens and using about 60 watts. That's 65 lm/W which isn't horrible for a high-CRI source with the LEDs driven at their maximum.
 

MichaelW

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Funny, a change from 3000K halogens to 3000K LED exterior garage bulbs has led to less bugs, and as a side effect spiders.
 

dspiffy

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I have a couple 500w ones still in use . . . I hate them, but I needed something dimmable, wide spread, with a low profile fixture. I'd love to convert them to LED but they would have to remain dimmable, and not lose any light output.
 

jtr1962

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Funny, a change from 3000K halogens to 3000K LED exterior garage bulbs has led to less bugs, and as a side effect spiders.
Probably because most flying insects are attracted to UV, and LEDs don't emit UV but halogens do. I would imagine you wouldn't get all that many bugs even with 5000K LED.
 

orbital

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jtr,

you have invented the Claymore Light Mine to blast any unwanted animals off your property

:eek:oo: :faint: :xyxgun:
 

brickbat

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I like the simplicity of your driver circuit. However, I'm leery of the CXA's ability to safely hold off the line voltage from the housing. I'm afraid it's the sort of thing I'd dis a cheap Chinese product for...
 

jtr1962

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jtr,

you have invented the Claymore Light Mine to blast any unwanted animals off your property

:eek:oo: :faint: :xyxgun:
Yeah, this will be great for keeping the raccoons away! Now they sometimes come late nights and rummage through our pails.

I like the simplicity of your driver circuit. However, I'm leery of the CXA's ability to safely hold off the line voltage from the housing. I'm afraid it's the sort of thing I'd dis a cheap Chinese product for...
See page 23 here. The dielectric of the CXA was tested in excess of 4 kV. I'm not terribly concerned about line voltage leaking into the housing given that the light is waterproof. I even sealed off where the wires come in with silicone sealant. The case is grounded via the conduit. Any line voltage leaks will likely either trip the breaker, or eventually cause a component to fail and open up the circuit. That said, if I did this for anyone but myself I would have used a commercial driver providing isolation. I didn't deem it necessary because I don't plan to have the light on when I'm not home. In all honestly, when the light was wired for halogen you didn't have any isolation from the line voltage, either, so I'm actually not overly concerned here. Chances are good the current sense resistor would burn itself open if any serious current started to flow. Even at 5 amps, it would be dissipating 60+ watts. I doubt two little SMD 1206 resistors in parallel could handle that for more than a millisecond.
 

brickbat

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Looks like you did your homwork, JTR. I was too lazy to check and made an (incorrect) assumption.

BTW, light doesn't scare our raccoons off. Bottle rockets do, however.... ;)
 

BirdCelebration

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Hey JTR1962,
You seem to know a thing or two about circuitry. I bought 1 cxa2540 and 2 cxa2520's. The 2540 is 37V 1.1A, 2520 is 37V 0.55A. Could I wire the 2540 in parallel with two 2520s in parallel. This would keep the voltage at 37V and create the equivalent of two 1.1A 37V lights. Could this be powered by a 2.2A 36V led driver?

I have a few 12-35V boost converters for some cheap ebay 100w leds, can this be modified? Is There any way i could build some new constant current source for these lamps? I'm more willing to learn and tinker than just buy a power source.
 

jtr1962

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Hey JTR1962,
You seem to know a thing or two about circuitry. I bought 1 cxa2540 and 2 cxa2520's. The 2540 is 37V 1.1A, 2520 is 37V 0.55A. Could I wire the 2540 in parallel with two 2520s in parallel. This would keep the voltage at 37V and create the equivalent of two 1.1A 37V lights. Could this be powered by a 2.2A 36V led driver?
Yes, that would probably work provided both the 2540 and 2520 have the same number of dies in series (they should based on the fact that they have the same forward voltage).

I have a few 12-35V boost converters for some cheap ebay 100w leds, can this be modified? Is There any way i could build some new constant current source for these lamps? I'm more willing to learn and tinker than just buy a power source.
No idea here as I'm not familiar at all with the type of converter you have. I have noted that most of these eBay converters have an adjustment pot, so you might be able to tweak the output to match what your CXAs need.

As for designing a constant current source from scratch, that's not for the faint of heart. Even for an experienced EE like myself sometimes problems arise.
 

Mkala

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Nice work jtr1962 ! Cree really make great LEDs.

I like the simplicity of overall, especially the driver. And this with a thermal foldback, please ! :)

Apart the CCT temp I would have chosen more in the 3000-3500°k range (but as you say it's truly personal), no earthing for the fixture is the only thing I not agree with you.
Yes, it's not really risky, and you know what you are doing. But the rule is simple, conductive case without double insulation = earthing. Even if LED insulation is rated at 4kV, a metal core PCB is made with some micrometer of insulation. Transistor insulation can fail, moisture can be inside, etc...

But nice work again, and thanks for the pics :)
 

jtr1962

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Apart the CCT temp I would have chosen more in the 3000-3500°k range (but as you say it's truly personal), no earthing for the fixture is the only thing I not agree with you.
Yes, it's not really risky, and you know what you are doing. But the rule is simple, conductive case without double insulation = earthing. Even if LED insulation is rated at 4kV, a metal core PCB is made with some micrometer of insulation. Transistor insulation can fail, moisture can be inside, etc...
Actually, the conduit is grounded and that's connected to the metal case, so if the LED insulation fails you wouldn't get a shock touching the fixture.

Yeah, CCT is a personal thing. I already had the halogen lamps in the 3000K range and didn't care for them. 5000K makes the grass and plants look more natural in my eyes. And since it's 90+ CRI, I didn't have to compromise in that area, either. In fact, that's the reason I choose the CXAs. They are one of the few emitters with a 5000K, 90 CRI option.

But nice work again, and thanks for the pics :)
Thanks! Glad you liked my work!
 

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