Can I use a BB1000 with 3 x Lux3?

[KevinL]

I have a spare Badboy 1A converter sitting around and I was wondering whether I could drive it off a couple of lithium ions (7.4V nominal) powering 3 Luxeons in series (J Vf, 3.3V each).

According to my calculator:

Output voltage 9.6 V
Output current 1 A
Output wattage 9.6 W

Input voltage 7.4 V
Converter efficiency 0.85
Input current 1.526232114 A

Would mean that the BB is still within its nominal input current. Any forseeable issues?

 

[HarryN]

Maybe. The J bin range is actually 3.27 - 3.51 V (according to LL data sheet AB21). I could not find the reference in the data sheets, but I remember somewhere that the Vf is measured at 700ma, not 1000ma, and there is a fairly steep Vf vs ma curve at that point (almost vertical).

I usually assume closer to a nominal 4 V for 1000am, but this might be overly conservative.

I looked at the Sandwich Shopped FAQ on the converter boards, and the V out limit is set by the voltage limit of the output capacitor, which is stated as 10V - and a suggested derating of 9 V.

If you end up with an effective Vf of 3.5 V for each Lux III, you will be just outside of the rating of the board. I have no idea if that will ultimately mean sucesss or smoke.

According to a post in the electronics section on Vf, you could somewhat lower the Vf of the Luxeons by running them at a nominal 1 amp for 48 hours (on a heat sink). The effect was to reduce it by approx 0.2 V IIRC. I think the post was by evanxxxx or at least he posted info in it. Might be just enough.

Georges80 (taskled) sells a similar board (cc5wb) with a higher V out rating, but it is not round so you may or may not be able to get it to fit in your setup.

 

[McGizmo]

I think the BB is now good to higher voltage out, 18 or 20?!?!

I did a 4xLuxIII with a BB and it's running just fine. Granted I set the current at 500 mA but I think as long as your anticipated I-in is within reason, you should be OK. /ubbthreads/images/graemlins/icon3.gif With I-out at 1000, you better be darn near V-out with your V-in; don't think you are there. I agree with HarryN that your Vout will likely be higher which will force a higher I-in and I think the I-in will be your stumbling block but I admit to electronic illiteracy! /ubbthreads/images/graemlins/blush.gif

 

[HarryN]

That is a nice build Don. Thanks for the correction on the BB Vout - nice to know.

 

[dat2zip]

Yes, the BB now can go safely to 16V on both input and output.

As for worst case computations, compute the low end of your battery life. If you still make the numbers and are withing the operating range of the Badboy then you are good to go.

Even if the converter hits the ISW limit, it will still be putting out max power which could still be plenty bright.

I would also suggest using 3.8-4.0Vf for a J bin 1A. That puts the Vf around 12V for three of them at 1A.

A fresh battery under load sags, so I rarely use the fully charged voltage in any of my calculations.

For example: A 123 sags ~0.5V/A. So, in a NG driving a Lux3 at 700mA the converter draws close to 1A to maintain regulation and with a fresh 123 the starting voltage is around 2.5V and drops from there.

Wayne

 

[KevinL]

Thanks for the info guys, it is appreciated. Maybe I should stick to using this in its original application - for a R/O Lux3. Didn't know that the Vf rises so drastically as current goes up!