Luxeon K2 problem

Gomer

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This isn't quite a flashlight project but rather an aquarium lighting project. I figured that some of the brains here may be able to help though.

I am using the Xitanium 700mA driver ( LED120A0700C24F ) to power six K2's ( LXK2-PW12-R00) in series. In practice, the diver powers 1-3 drivers to full brightness, but after that the LEDs are dim. This driver should be able to drive them all to 700mA.
LED
http://www.luxeonstar.com/item.php?id=1810&link_str=330&partno=LXK2-PW12-R00

Driver
http://www.luxeonstar.com/item.php?id=395&link_str=240::242&partno=LED120A0700C24F

Any comments/suggestions?

Thanks for your help
 

freerdr17

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Sorry, I cant give you any suggestions on the LED Setup. But I am Curious on what type of Fish Tank set-up your doing? I am very new to this whole flashlight thing. But I am no NOOB to Reef Keeping, and im sure that is what you are using the K2's on. I currently have a 55AGA with 2-250 20K MH's, and a 15G AGA with a 150W HQI MH 20K as well. Both are LPS/SPS tanks...
What can you keep for livestock under the K2's LED lighting?
 

Gomer

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700mA constant current
7.8-24.6V

Here are the LED's before soldering (I solder together and jumper the two together (each LED side has a non conducting "dummy" leg".
K2x12_1.jpg
 

Gomer

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freerdr17 said:
Sorry, I cant give you any suggestions on the LED Setup. But I am Curious on what type of Fish Tank set-up your doing? I am very new to this whole flashlight thing. But I am no NOOB to Reef Keeping, and im sure that is what you are using the K2's on. I currently have a 55AGA with 2-250 20K MH's, and a 15G AGA with a 150W HQI MH 20K as well. Both are LPS/SPS tanks...
What can you keep for livestock under the K2's LED lighting?

I actually have numerous FW planted tanks.
 

Gomer

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That picture has 2 strings. Each string has an independent 700mA driver.
 

Gomer

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I don't know how it works electronically, but it is a constant current source. It will adjust the voltage to maintain a constant current within the allowable voltage range.
 

McGizmo

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Gomer,
I would be suspicious of the high Vf of the K2 LED's and assume that this would approach the max power of the driver prematurely in comparison to the Luxeons that were around when the driver was designed. Your problem with more than 3 in series though sounds too low even for the K2's. Have you measured the voltage across the individual LED's?
 

VoiToi

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Stupid question: The driver and LEDs are drowned in the water?

Serious questions:
- Do you have isolated the heatsink and the bottom of the led? With Luxeon K2 you must do that, slug of the device is not electrically neutral.
- What is the temperature of LEDs? Are they well clamped to the heatsing (over the isolating film), and is the heatsink sufficient?
- Is the driver connected directly to the 120V AC? Otherwise, check if the source can handle the power of 20W per one driver (6 LEDs).

I don't know about any other possible issue.
According to specs, this Xitanium driver can handle 1 to 3 Luxeon V (700mA) LEDs, so it can handle also 2 to 6 Luxeon K2 at 700mA (the Vf is 7V for LuxV and 3.5V for K2).
 
Last edited:

Gomer

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- Do you have isolated the heatsink and the bottom of the led? With Luxeon K2 you must do that, slug of the device is not electrically neutral.
Really? I thought the slug was neutral. Is the slug connected to the annode or cathode?

- What is the temperature of LEDs? Are they well clamped to the heatsing (over the isolating film), and is the heatsink sufficient?
Thermal Epoxied to the HS, but I can remove them given the info above and rethink the project.
- Is the driver connected directly to the 120V AC? Otherwise, check if the source can handle the power of 20W per one driver (6 LEDs).
Yes and yes.

Thanks for your help. I think you found the reason but now I need to find a solution.
 

yellow

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if the K2 stats even mention them not being electrically neutral, then it is for sure teh reason.

I had the same problem with normal 1 Watters some time ago, 3 in Series worked great, 4 was impossible.
 

Gomer

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Thanks. That really helps a lot and explains a lot of the problem...now..time to find some thermally conductive, electrically isolating films LOL.
 

PhotonFanatic

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Gomer said:
Thanks. That really helps a lot and explains a lot of the problem...now..time to find some thermally conductive, electrically isolating films LOL.


From the K2 datasheet:



Electrical insulation between the case and the board is required—slug of the device is not electrically neutral. Do not electrically connect either the anode or cathode to the slug.


Why not just use some thermal adhesive to isolate the slug? The trick is to precoat one surface with a very thin layer, let it thoroughly dry, then join the emitter to the heatsink with the adhesive, being careful to not put so much pressure on the emitter that you drive the slug into the heatsink.



 

3rd_shift

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So K2's have the same issues that the red, red orange and amber Luxeons do? :poof:

Uh-oh. :eek:oo:

I'm glad I only had time to build one light with a K2 thus far.

I have some electrically isolated stars to try out a few K2's with.

Member Litemania has electrically isolated stars for sale cheap in the dealers corner part of the forum. ;)
 

evan9162

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No, they have the same issue that all other luxeon emitters have - that you must isolate the slugs if you're running them in series.
 

IsaacHayes

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3rd, the k2's and luxeons(1,3,5) that are white/green/blue/royalblue/cyan have the same charicteristics on slug isolation. If running in paralell, or single, no problem. They have no problem with one led connected to a negative heatsink. The amber/red/red-orange have a much greater problem since their postive bondwire/lead is connected to the slug, so if the slug touches negative, then it shorts the bondwire and melts it open. The amber/red's don't have ESD diodes AFAIK because their material seems to be more resistant to ESD natrually IIRC.
 

Gomer

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Where can you get thermally conductive yet electrically isolating films?
 
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