noob buckpuck question

[crx2ner]

Ok, so I have some of these "high power 3w" leds I ordered a long time ago. I got them on eBay for 99 cents plus a few dollars for shipping; it was like 4 bucks for 7 leds. They say "3V" on them.

 

I know you can only run 6 Crees on a buckpuck. But why? The XR-E's have a forwarding voltage of 3.3V's so six of them would be a total of 19.8Vs plus 2V's for the buckpuck. I wasnt able to find the official voltage usage of the buckpucks, but everything I seen noted about them people said it was 2v.

 

So, with Crees adding a 7th led would equal to more than 24vs.Is this the reason your limited to 6?

 

Basically what Im getting at is, would it be possible to run all 7 of these 3v leds on 1 buckpuck, off a 24v PS? If a buck puck really only takes 2vs, that would be a total of 23v between it and the 7 leds.

[doctaq]

i dont know if it is the maximum wattage rating but they seem to fail by the 7th led although thier datasheet has an application of running in series and parallel which adds up to more than 6 leds.

 

i suggest do not do more than 6.

also cree xr-e vf of 3.3 is at 350ma, at 1000ma it is 3.7

[nickijon]

The fragile pucks will fry. Just by testing my LED's, I found that they were not exactly 3.7, but all were in the low-mid 3.7's. It's something to do with quality control for different batches. Even running it at 3.3 + some headroom is pushing the fragile driver's past its limit.