Sorry for the newbie questions, just trying to get my head round all the terms and things again after my injuries.
I won’t be using my S2+ on 100 unless I really need to see something after testing in the dark. 50 is bright!
My question is as it has 8 7135 things (drivers I think they are called) using it at 50 will it be as efficient as 4 on Max, or does it not work that way?
I’ve seen mention of PWM, which I remember from my vaping days. I can’t hear the typical PWM hum though when it’s on 50/mid.
So is there a big difference in battery life there, or am I misreading how 50 and 100 works I. A torch?
Wasted power in the 7135s should be more or less constant. I’m deliberately neglecting voltage-sag of the cell at higher current, and higher forward voltage of the LED at higher current, so this is only a 1st order approximation.
If the “excess” voltage is 1V (nice round figure), total waste should be 1V at 1A at 100% (ie, constant), vs 1V at 2A at 50%. So 1W vs 2W/2.
The only real difference is the efficacy of the LED at different currents. Again, it drops off at higher currents.
Solution would to be to use a triple or quad, so that each LED sees only 33% or 25% of the total current, putting it in a higher efficiency range (say, 130lm/W in my first example).
So how close are we talking. What excess power is needed to be dissipated by the 7135? The LED’s loss of efficiency with the PWM is there with 8 at 50% vs. 4 at 100%. But is it really worth consideration for practical purposes?
Back to the original post. So is there a big difference in battery life, no. Difference should be very slight. And welcome back I noticed you’ve been gone for awhile.
Thank you for the welcome back . I had some issues going on and ended up being attacked with a baseball bat, orbital, skull and jaw fracture, all over my stolen phone. Nearly killed me and my memory isn’t as it used to be, but I am trying to re learn things I enjoyed.
I’ve got back into my mods and vaping collection, and saw a flashlight on sale which reminded me at one point I was getting into this as a bit of another hobby.
I didn’t really understand the maths posted and I do apologise, let’s say I’m using a Samsung 30q , is it really worth having an extra with 4x7135 or is the loss minimal at 50 percent using the 8x7135? As in are we talking a few minutes difference?
If the math could be explained as if to a total new person to flashlights , how would you explain it? I’ve manahed to get my head round regulated boards for mods, efficiency etc- and it was me that wrote the actual guide on a big forum before what happened so I feel a bit silly.
As in with PWM? I really am a beginner again trying to re learn. Is PWM used to step down voltage to reduce the output to 50 , or are 4 drivers just bypassed to get that level?
Thank you for your answer. I gather the 8x7135 does use PWM then to step down to 50 percent?
Also in a previous answer it was mentioned at 1A and 2A- what should that flashlight be pulling from the cell? Also I gather the amp load is reduced when on 50 and it isn’t a constant draw on 50 percent compared to 100 percent? As if the components are still drawing the same load then I would understand a big difference in battery life between 8x7135 vs 4x7135 due to the way cells work, let alone the sag going on.
If it’s only a few percent though then it’s not much at all- even though I plan to add a few more to my house for different uses. That’s unless there is something better than the Convoy S2+ for value.
I am interested in trying a few different lights as well though size wise, even one that has USB charging for a change.
It’s not worth having an additional light with 4x7135. The efficiency of the 8x7135 light at 50% will not be that different.
A lot of that drop in efficiency at constant current is due to increased temperature. So for this situation where the average current is the same, the temperatures will not be very different. So there wool be some efficiency drop due to the higher pulsed current, but not as much as you would expect just looking at the lumen vs current plot.
Here is a chart I use often http://pct.cree.com/dt/index.html On the line marked “Compare” I only use “Current range”. On the line “Model” you click to select the LED. Then the line “Flux” you select the LED rating.
In another thread you said you got a Convoy S2+ with 8×7135 XML2. So on the chart we select “Coarse current range (0.35A - 4.0A)” On model we select “Cree Xlamp XML2 {White}”. Guessing the bin/Flux we’ll go U2. Chart automatically fills itself. So lets read it now. At 1.400 amps your getting 623.8 lumens. With 8-7135 same level your PWM is at 50% so it’s on at 2.800 amps half the time and off half the time. At 2.800 amps your getting 1067.3 lumens half the time so it becomes 533.65 real lumens.
Going with this chart, minus the slight percentage of driver efficiency you get the same run time but 17% more lumens in this case. 4-7135’s at 100% give you an output of 623.8 lumens, 8-7135’s at 50% give you 533.65 lumens. This is not 100% accurate as 2.800 amps at 50% on/off generates less heat the 2.800 at 100% on. So it’s even closer between the two outputs. For practical purposes it’s the same output as side by side you would hardly notice any difference. Using a Samsung 30q cell as you noted will give you at least 2 good hours of output.
Typically no PWM is used with the 7135. It has been tried but has issues with the boot-up of the 7135 chip every time the power cycles.
Think of PWM like making a light dimmer for your room by repeatedly flicking the wall switch on and off.
If you could do this fast enough you might not notice the off period. FETs can be driven at a high frequency with no delay due to any boot-up time, but not the 7135.
. I had some issues going on and ended up being attacked with a baseball bat, orbital, skull and jaw fracture, all over my stolen phone. Nearly killed me and my memory isn’t as it used to be, but I am trying to re learn things I enjoyed.