thoughts & comments on high voltage Cree XM-L?

[Steve K]

hi gang,

I may be behind the times, but I just recently became aware of the high voltage version of the XM-L. It's similar to the Bridgelux in that it is an array of dice wired in series, producing a Vf of around 45v. Seems very well suited to working off of mains voltage.

http://www.cree.com/products/xlamp_xml_hv.asp

The main benefit is in the design of a driver.. it is easier to wire up a few in series in order to produce a Vf for the string that is close to the mains voltage, making it simpler to convert the voltage and reducing the output current required. Overall, this should make the converter simpler and more efficient and probably cheaper.

There is probably some impact on reliability, if only because of all of the interconnections inside the LED itself, but I would assume that this should be a minor consideration.

regards,
Steve K.

 

[DodgeyDIY]

BUMP! i was going to ask the same thing.

 

[Steve K]

well, I still haven't heard much about it. My attention is currently on the Seoul Acriche 2 for projects powered from 110vac. There is a thread with WSJ in the title that touches on it. Essentially, the Acriche 2 has a chip onboard along with a number of LEDs wired in series. As the AC voltage increases and decreases, the chip changes how many LEDs are wired in series so as to keep the LED current in the correct operating range.

This scheme strikes me as rather clever and efficient! Using a handful of mosfets to constantly adjust how many LEDs are in the string makes a lot more sense than processing a lot of power through a switching power supply in order to regulate current. It also gets rid of the heat and reliability issues of the switching power supply.

The downside of the Acriche 2 is that the luminous efficacy is around 70 lumens per watt. It's probably acceptable for applications where you don't have a convenient place to install a switching power supply.

 

[Marcturus]

My attention is currently on the Seoul Acriche 2 for projects powered from 110vac.

Does the Acriche 2 display line frequency flicker?

 

[Steve K]

.... Does the Acriche 2 display line frequency flicker?

I wish I knew... funny, but the datasheet doesn't mention this.
Since it should be flickering at 120Hz, it doesn't seem like it should be visible. Did the Acriche 1 have any problem with this?

 

[slebans]

There is a good article on flicker here:
http://www.led-professional.com/tec...to-avoid-stroboscopic-effects-in-ssl-lighting

If I remember correctly, there are perceiveable stroboscopic effects visible at 120Hz.

 

[SafetyBob]

Been awhile since I have been on, but just completed refurbing a 3 light halogen under counter light from Lowes with 3 of the 4 watt Acriche 2 lights. Specifically, since I don't have the exact model number with me, I used the 4 led light version. Mouser only carries the 3000K version (you may see it listed at 2900K).....warm white for sure.

I bought at least one of each model all the way up to the 16 watt version. The small versions come with their own resistor and varistor board that you can use to wire up protection if needed. I was surprised the little boards came with each Acriche 2 setup. I was having and am still having a not so nice time trying to figure out exactly what sized resistor and varistor I need for the 8 watt and 16 watt versions to keep them protected. The small boards that came with the smaller boards had 220 on the SMD resistor and the varistor was around a 1/4 of an inch in diameter, smaller than I would have expected. Anyone having specific recommendations for parts needed for the 8 and 16 watt parts, please tell me. I would appreciate the help.

Be warned for the past number of years most of the interior LED lighting I have built or modified has been in the 4000K range. To "brighten" up the kitchen, all my fluorescent tubes are 6500K or 5500K, I simply can't remember which. My wife and I find the "brighter" light easier to work and read cookbooks and such in. When I turned on the Acriche 2 LED for the first time, oh boy was it MUCH yellower in color than I am used to. I moved it to another area in the house and although the color temp is much warmer than I would like, I would just like to state for the record, I like these Acriche 2 LED lights very much.

I need to get the 8 and the 16 watt setups into some temporary heat sinks and see just how wonderful these things are. I can report my heat sink for the 4 watt setups were 2" x 5" x 1/8" thick aluminum screwed using thermal grease to the thin sheet metal of the 24 inch halogen light, then another piece of the same thing with wings bent up 1 1/2 inches on each long end greased and screwed on top of that. The Acriche 2 unit was then thermally epoxied to that "heat sink". Again, not much if any calculations were done for this...it was very much a blind stab in the dark and truly an experiment to see if it would work. 1 hour later, the back of the lighting assembly was slightly warm to the touch. I need to get the laser thermometer on the junctions and the heat sink areas to get some real data.

So those of you wondering how the new Acriche 2 LED lights are, wonder no more. The are very acceptable and it makes need for a AC to DC driver a thing of the past. For modifying accent lights, I would 100% recommend these little lights. Until I get the 8 and the 16 watt models operating, I would hesitate recommending them for a "real" light total replacement. My goal IS to totally replace under counter and eventually overhead fluorescent lighting in my house with modified housings or totally custom housings.

Wish me luck.

Bob E.

 

[Steve K]

Good to hear that you've had good results!
I've got a tasklight that I made with Cree XP-G's that I think were a neutral white, and I'm pretty happy with that color in the kitchen. It is indeed helpful to get a clear look at the color of your food when making critical "should I throw it away, or is it safe to eat?" decisions!

I've had my eye on the 8W modules for use as a bathroom light. Heatsinking will be a challenge, as I'd like to keep the temperature of the LED down to 55C or so. My assumptions are that I would have one heatsink per LED, and the numbers came out to needing a heatsink with a thermal resistance of around 3 deg C per watt. I'm not sure I have enough space available, so I was going to see how things work out with a heatsink from Wakefield that is 5.5 deg C per watt. These are from Mouser, p/n 518-95AB. The catalog says 2.2 deg C per watt, but if you look at the datasheet, you'll see that it is for forced air only.

As far as MOVs, I was thinking about a part from Bourns, the MOV14-D201K. This is rated for 130vac operation.

I hadn't picked out a 22 ohm resistor yet. The Acriche datasheet (or app guide?) mentioned something about a fusible resistor, which I assume means one that will open up if it is carrying too much current. I was figuring on including a small fuse in the light, just in case.

edit: how's the flicker?? Have you noticed it yet? That's about the only think I'm still concerned about.

edit #2: I was digging around and found the Acriche 2 application note. Couldn't find it on the Seoul site, but did find it on Mouser's site:
www.mouser.com/pdfdocs/Acrich2_Application_note.pdf

 

[SafetyBob]

Steve, good to know someone else is actively making their own lights too!! I was considering getting some XP-Gs in the 3 up style from ledsupply mainly because I love the 4000K range of color too and who knows when the Acriche 2 will be available in the higher color temps.

Let's talk about cooling with the 8+ watt models of anything. I am currently on the search for a small, reasonable, slow speed AC fan that I can mount on top, to the side, or where ever I can for additional, reliable cooling for these higher powered units. A massive heatsink will probably be unaceptable for most people (think wife here), so some sort of fan cooling is necessary......not a problem with 12 or 24 VDC feeding an LED driver, but 120 VAC.....there's the problem. It appears there are very few options when selecting AC fans, especially smaller ones. I guess I could experiment with a resistor to slow the AC fan down.....

Flicker does not appear to be a problem from what I can tell. I have NOT installed the light, only sat it on the kitchen table and let it run for 6 hours at the most so far. I got alot of initial smoking off of one of the units that I believe was my fault when soldering. I need a new soldering iron....or at least a new tip!! The smoking did go away after an hour of operation though.

Thanks for the parts leads, I will give those all a good look.

I looked for HOURS at the fusible resistors that Mouser had. My problem is since I am not Mr. EE, I am basically lost as to the actual size and specifications needed for a Acriche 2 unit that maybe pulls 0.03 amps.....I am afraid of picking a larger resistor that would not let enough juice through for proper operation.

Bob E.

 

[Steve K]

..A massive heatsink will probably be unaceptable for most people (think wife here), so some sort of fan cooling is necessary......not a problem with 12 or 24 VDC feeding an LED driver, but 120 VAC.....there's the problem. It appears there are very few options when selecting AC fans, especially smaller ones. I guess I could experiment with a resistor to slow the AC fan down.....

I don't know what to suggest regarding fans. My personal feeling is that I try to avoid fans because they are just one more thing to break. Noise is a secondary issue, although they do get much quieter when they quit working! A search for "low-noise AC fan" might be the best option. Clearly, if you don't use a fan, you'll need a much larger heatsink, or have to accept much hotter LEDs. My strategy is to try to hide the heatsinks behind a diffuser or lamp shade.

..
I looked for HOURS at the fusible resistors that Mouser had. My problem is since I am not Mr. EE, I am basically lost as to the actual size and specifications needed for a Acriche 2 unit that maybe pulls 0.03 amps.....I am afraid of picking a larger resistor that would not let enough juice through for proper operation.

Did you find a fusible resistor at Mouser? Nothing comes up with a simple search. I did find a few fusible resistor families from Vishay, but they don't show up at Mouser. The other big resistor manufacturers should have something too, but finding someone who sells them might be the hard part. It might be easier to just add a small separate fuse instead of relying on the resistor to act as the fuse.
As far as the other issues, you can calculate the current in the LED and resistor : I = P/V
For a 8 watt LED running from 120vac rms, the current is 0.066mA (also AC and rms). The power dissipation in the resistor is then P = I^2 x R, or roughly 100mW. A resistor rated for 200mW would be fine.
edit: Digi-key has the Vishay NFR family; p/n PPC22ACT-ND. $0.39 each.

 

[AnAppleSnail]

Let's talk about cooling with the 8+ watt models of anything. I am currently on the search for a small, reasonable, slow speed AC fan that I can mount on top, to the side, or where ever I can for additional, reliable cooling for these higher powered units. A massive heatsink will probably be unaceptable for most people (think wife here), so some sort of fan cooling is necessary......not a problem with 12 or 24 VDC feeding an LED driver, but 120 VAC.....there's the problem. It appears there are very few options when selecting AC fans, especially smaller ones. I guess I could experiment with a resistor to slow the AC fan down.....

I'm interested in these as well. I have found an 80mm fan (Square, 23db, 23 CFM) that runs at 13W, and have trouble locating smaller ones. It'd be a heck of a thing to have the fan consume more power than the light, right?

How about this fan?

It's true that fans are "just one more thing to fail." But until your ceiling is a metal plate for LED heatsinking convenience, pretty retrofit light fixtures are likely to be large or fanned. Guess which is an easier sell to wifey?

 

[Steve K]

the suggested fan has a longer life than I expected... 60k hours. Not that much less than the LEDs, really. The price isn't too bad either... $16. It would be a good exercise to see how the cost, size, etc., compare for an active vs passive design. As the light's power increases, the fan is certainly going to look better and better.

How loud is 23 dB?? (the Mouser page says 19dBA). Seems like it would be not much more than a background hum.

 

[AnAppleSnail]

the suggested fan has a longer life than I expected... 60k hours. Not that much less than the LEDs, really. The price isn't too bad either... $16. It would be a good exercise to see how the cost, size, etc., compare for an active vs passive design. As the light's power increases, the fan is certainly going to look better and better.

How loud is 23 dB?? (the Mouser page says 19dBA). Seems like it would be not much more than a background hum.

Audio 'loudness' page says it's rather quiet. I think my aquarium motors are 20 and 25 dB respectively. The crickets outside are louder most nights. I used a 12VDC fan on a couple ohms resistance and it was quieter than the aquarium, so it didn't add much noise. Generally if there is one 30 dB source (TV, AC blower, kids or a mower outside) then another won't be too terrible, and you wouldn't notice a 23 dB source easily.