When an amperage specification is quoted about drivers - such as an 8 amp 3 volt driver - is the 8 amps the input to the driver, or is it the output of the driver?
Also wondering if the 3V 8A buck driver in my new Convoy S21B (sft40) would benefit from spring bypass? I’m thinking of doing it on both springs using copper braid/wick. FYI I’m using Molicel 42a cells capable of high current.
Also considering spring bypass on recent hot rod FET driver KR1 (sbt90) and KR4 (W2) both with high current Molicel 30b. I would do this after trying out on the convoy first.
Output. Input wouldn’t make sense, since you need the driver current to determine what your LED can take and match LEDs and drivers.
For linear regulators, output current = input current. For buck drivers, input current is lower than output current. For boost drivers, input current is higher than output current.
Rough estimate for input current on switching drivers (buck/boost):
Take the max output current, find the forward voltage of your LED at such current. Multiply V_F with I_out to get P_out. Then divide P_out by V_battery and add 10% (most drivers are probably a bit more efficient, but 10% are easier to do the math haha). I’ll make 2 examples. Let’s say we discharge the batteries down to 3.5V at most.
(All values invented and just for demo purposes - I did not look up any real led specs!!)
3V Led with 3.2 V_f, at 8A. I_in = 3.2 * 8 / 3.5 * 1.10 = ~8A at empty battwry (the buck would lower input current, but power losses in the losses in the driver offset this)
6V LED with 5.9 V_f, at 5A I_in = 5.9 * 5 / 3.5 * 1.10 = ~9.3A
Hi, the current eg. the 3v 8a is the output of the driver going to the Led. unless otherwise stated. spring bypass is easy mod to boost current. i reccomend a copper wire braid. The difference wont really be noticeable though.
What about spring bypass for these setups? They are drawing a lot of current. I’ve heard sbt90 can pull approx 20 amps, and my quad FET W2’s get very hot quickly as well.
I know Hank uses some special materiel in his springs, but has anyone experimented with bypass on these?
EDIT: my convoy S21B looks like it has the old spring. I’ll try to post a picture later.
From personal experience, use a 22 AWG or better wire. I think you’ll find concurring opinions throughout this site. Braid can’t handle high current and melts.
Do you keep the insulation on the non contact section or remove it? Removing it would give more flexibility when spring compresses or am I overthinking it?
In this case, it will maybe give you a little longer in regulation. But no more brightness. Except maybe the SFT 40. Because it has a hard time hitting 8 A on a single cell. As for a fet driver, With a W-2 swapped TS 21, I went from 2805, two 3450 lm. So a bit of a jump. That was just a bypass on the tail cap spring, As the positive positive is a button
No need to remove insulation. I think the best technique is to connect PCB to top of spring on the outside so moves up and down (spring-like) v’s, perhaps, more metal fatigue within the coil.
