New Q5 and existing drivers

[RV7]

Has anyone measured the Vf of the new high bin Crees? I haven't got any Q5's yet myself. But I heard the Vf of the new Crees is pretty high. At 1A the Vf of a Q5 can be as high as 4V.

If that's true, most existing buck drivers for single li-ion and many boost dirvers won't work well with the new Crees. We may actually see lower output after upgrading to Q5. Especially, those LDO type linear drivers will work in direct drive mode most of the time. Also, a higher bin doesn't necessarily mean higher efficiency, if it's measured by lumen/watt, instead of lumen/amp.

 

[legtu]

http://www.candlepowerforums.com/vb/showpost.php?p=2170040&postcount=141

 

[RV7]

Thanks for the link. What a relief... and let's keep upgrading!

 

[RV7]

Just saw that some of the Q5's StefanFS got have a 3.9-3.99V Vf at 800mA! Doesn't sound great...

 

[acourvil]

I did a 5 Cree Q5 mag mod. Using a shark driver, I was seeing 19.6v at 980mA, implying an average Vf of 3.92

 

[StefanFS]

Just saw that some of the Q5's StefanFS got have a 3.9-3.99V Vf at 800mA! Doesn't sound great...

That's correct, but it only applies to half of my first shipment from earlier this summer. Two Q5 were over 4 Volt @ 1 A, the others were between 3.57 to 3.68 Volt if I remember correctly. In my last two shipments in September & October all Q5's are 3.50 - 3.57 Volt @ 1 A. To me that implies that CREE has been refining their product, and that they had problems with the first batches. I wasn't pleased with the first shipment of Q5 emitters.
Stefan