- Aug 25, 2007
- Lake Zurich, Illinois, USA
I am looking to run 9 xp-g off of 2 AW black C cells (8.4V) by direct drive and I always get confused by this, can anybody can help?
9P configuration using whacking great resistor
Sorry, I totally disagree. IF he's using 2 cells in series (8.4v) you'll be hitting each led with 8.4v if you wire the emitters in parrallel. This is far above the usual 3.5v. I have no idea what you're seeing that makes this seem like a good idea.
That's what the resistor is for. I see steve6690 beat me to it.
The 3S2P or 3S3P configuration is maybe possible, at least initially before voltage drop kills you. If you assume no voltage drop at all for your 8.4V power source, then 3S (assuming electrically identical LEDs) means 2.8V Vf for each XP-G. Looking at the datasheet, that corresponds to about 150mA drive current. That looks like about 40% relative luminous flux, or about 50 lumens per XP-G R4 bin. If you have 9 XP-Gs wired in 3S3P, then that could theoretically mean 450 lumens. However, if you suffer any voltage drop at all (which you undoubtedly will for a battery source for the current draw required to power 9 XP-Gs at 150mA per XP-G), e.g., to 7.6V or 7.4V, then your output could plummet. The problem is that the XP-G datasheet for If vs Vf stops at 2.75V. However, extrapolating to 2.5V Vf, I think you are going to get very little output. With 4S2P, you are looking at a Vf of 2.1V and I doubt that the XP-G will light up at all.
That's what the resistor is for.
It doesn't, because the resistor is a current limiting device, so the LED(s) would not be running directly from the battery. I'm going to go out on a limb and claim 3s3p is the only safe genuinely direct driven option that would actually make some light. :nana:-minor follow-up: I didn't know use of resistors qualified as direct drive.
-minor follow-up: I didn't know use of resistors qualified as direct drive. As such, was trying to think of viable set-ups. Thus 3s2P, yes which isn't 9 xpg's, is atleast a config that doens't . Same as 9s, while 9 won't work, I did instruct that the series xpg's be reduced down until a feasible set-up is discovered. In short, with my initial assumption that direct drive meant no resistors as well as no boards, I was hinting that 9xpg's off 2s C batts was a challenged format.