Hello
I need your help. I have next problem. When I turn on the light and put it at 30, 50,75…% it always happen next: after 5 secondes light flashes 3 times and lumens are reduced, this is repeating every 5 secondes and lumens are again reduced. This cycle is repeating few times till FL reach 1 lumen or very small amount.
Do you maybe know what is wrong? Do I have defect FL?
Thank you
What batteries are you using and are they fully charged?
Man this data is really making me reconsider my change to a FET + n + 1 driver…
It doesn’t seem like it would actually be much more efficient, but I guess the regulation would at least be nice.
The problem is not at all the amount of regulation but the sheer output: you want 4000 lumen?; then your pour single battery is sucked dry in 3 minutes! You want 4 lumen to read your book? (The beam is great for reading a book) You have 50 hours, enough to finish half the Potter series.
I’m actually not too interested in the 4000 lumen output, but I was hoping to be able to get say 1000 lumens of stable output with significantly longer battery life at ~300-400 lumens.
Looks like the 7135s may put out too much waste heat unfortunately.
What D4 does now puts out even more heat at the same lumen output.
Right I’m aware that a FET + 1 is horrendously inefficient at medium modes, but it looks like a FET + n + 1 isn’t that much better.
I was hoping to jump from 67 lm / W to around 110 lm / W at ~400 lumens, but it looks like it’s going to be more like 80 lm / W.
I guess on the plus side, efficiency will improve as the battery drains. Maybe I should look into IFR batteries?
I have not checked that (I suppose you have?), but does that really happen? I understand the theory: PWM-ing 15A output to get the medium modes has the potential to get under LVP voltage early because of the voltage sag under that load, but has anyone checked that this really happens at the point that the battery still has a significant charge?
I don’t think this will happen. I don’t think it will draw 15A. Theoretically if you want half the output using PWM, it should draw about half the amps, so about 7.5A (slightly non linearity). At least, that’s my guess.
Edit:
- 200 lumens with FET drive using PWM means you’re getting the low efficacy of the led at the max output of ~3500 lumens. Efficacy of the same led at 200 lumens using current control is much better.
- 200 lumens with FET drive using PWM means you’re getting the tint that you get at max output of ~3500 (which could mean bad news). Tint of same led at 200 lumens using current control is “regular” tint.
Well that’s how I see it. Ok maybe I’m not understanding something?
I have not tried, will later today.
No. It will keep shifting between 350 mA and 15A.
Exactly. But this occurs so fast, that what the battery actually feels is the effective value. So when the FET is 50% open, then the draw will fluctuate between 350 mA and 15A, but effectively will be around 7.5A. And this value determines voltage sag, and not the value at 15A.
Ok, started a check.
D4 set at output 200 lumen (leds are 219C 3500K 90CRI so the current is a bit higher than with stocks leds at 200lm), on a 30Q battery starting at 3.54V (so well over half drained). No protections kicking in yet, waiting for things to happen 
I just found out that all my INR18650-30Q cells have only around 3,40-3,50V. Now they are all in charger.
Will report back if this will fix the problem. Most likely it will.
Thank you for your help.
Another way of looking at this phenomenon is by analysing what exactly current is. 1A = 1 Coulomb of electrons/sec, which is an amount of particles per unit time.
This should mean that if the FET is opened 50% of the time, then only half the amount of electrons pass through. This should result in half of the current, hence 7.5A, hence voltage sag when 7.5A.
Edit:
Analogue. It’s actually the same thing with why PWM is used in the first place. Max output of let’s say 1000 lumens, and if we use PWM to reduce output to 500 lumens, then the max output is still 1000 lumens, except we see only 500 lumens. 500 lumens is the effective value, although max output is 1000 lumens.
Therefore max draw with PWM is 15A, but it alternates between this and 350mA so fast that the effective valuer is 7.5A.
You are right, sadly buck drivers all have big inductors, I don’t think it is possible to replace the driver with a buck in D4, unless putting shorter batteries in tubes meant for longer ones.
Current is instantaneous, PWM is to trick our eyes, not making the circuit “feel an averaged current”.
This makes sense. But even if current is instantaneous, the amount of electrons passing through the circuit is the average value.
BTW, who’s gonna be the first to run the emitters 2s2p with a pair of 18350? :smiling_imp:
Half hour into the test, output is back to 175 lumen, resting battery voltage is 3.27 V now.
I have reset the output at 210 lumen (sorry, setting an exact output using ramping is not easy).
I have to leave in 10 munutes (family related stuff: dinner in restaurant ) so next report is then. Further testing later this evening.