Hi Guys
I am still pretty new to flashlight modding and tried 7135 stacking today. I used an 8*7135 driver and added another 6 to it, because I couln’t fit the other 2. I knew, this might be a little too much and I might kill some part, but I wanted to try it and learn from the results. Now to my problem. I finished the light and compared it to a stock 8*7135 light with the xp-l v5 I already had and didn’t see a huge difference. Then I measured the current at the tailcap and got 2.7A for the stock light and only 3.3A for the 14*7135 light. As far as I know this should be at about 4.5A. Can somebody tell me, what might have gone wrong?
I checked all my solder connections with a multimeter, so this shouldnt be the problem
What was your cell voltage under load, and the LED voltage? Could be the battery wasn’t able to push any more juice.
7135s are linear regulators which means they will supply up to the 4.5A, but the actual current you get can be limited by the resistance in the circuit, the cell voltage, and the LED Vf. That is likely what is going on with your light, especially if you measured with a DMM which adds resistance to the circuit.
If you really want to get the 4.5A the best way is to get a lower Vf emitter like the SST40 or SST20 or luxeon V.
I dont know how to measure the cell voltage u der load
I didnt measure the led voltage, but i can Do that when i am at home tonight.
Are there any compromices with takeing one of the other emitter you mentioned @EasyB
It’s difficult to measure the cell voltage under load. What battery are you using?
The SST40 will give you a very similar beam to the XPL. The SST40 comes in 6500K and 5000K. The SST20 will make a smaller and more intense beam (and a bit fewer lumens). The luxeon V also will give a pretty similar beam to the XPL.
I am unable to measure the voltage at the moment, but the other emitters seem promising. Where can I buy them?
I looked on fasttech but didnt find any of these there. I am living in germany, if that helps.
kaidomain has them.
Thanks
I just ordered a sst40 and a luxeon v
You would need a good low resistance cell like a 30q to make it happen. I can remember trustfire cells not even making 3 amps if driven direct drive to a xml.
I did the same thing you did and added more amc7135’s and the current never moved. Then I got a icharger and tested the capacity at a 3 amp discharge. The cell wouldn’t even make 3 amps before the cell voltage droped below 3v. The cheap cells we used back then were crap but we didn’t have lights than ran much over a couple amps.
Anyway its a matter of having enough cell voltage overhead versus the led vf at the current your running at.
Find a led test of your particular led and note the vf at the current your planning on. Then look up a battery test of your particular battery used and match the current of the led to the current discharge of the cell. That will give you a curve of when the battery voltage is above the vf of the led at that current and a rough estimate of about the time it will be there.
The driver, wires and switch will eat a little voltage but the curve should be close.
I used these batteries in today.
Sanyo/Panasonic NCR18650GA 3,6V - 3,7V 3500mAh
I dont know, if they are good, but I think they are optimised for high current, but for high capacity.
Battery discharge test by HKJ
Xpl v5 led test by TA
Looks like at 4.5 amps you would need 3.8v plus voltage losses so around 3.85 to 3.9v from the battery. Looking at the 5 amp discharge curve the GA cell would be close to that from voltage sag right from the start of the discharge if fully charged. Your basically running direct drive with that cell.
Try charging the cell up completly then as soon as it finished charging, try it in the light. It should be brighter for a few seconds reading a higher current. Also make sure your using a heavy guage wire to test with. They are also voltage losses in the tailcap current test wire. The bigger the wire the less loss. If you had a way to measure the light it be pretty simple to see. Eyes are not a real good at judging lumens.
Thanks for that @moderator007
I will swap the emitter for one of the others when they arrive and check how much current I will get then. I didnt really know about Vf before and just used the xpl because they were cheap and had ( at least in my opinion) a decent efficiency. Now that I know about Vf, I will still use them, just that don’t need a lot of amps
If I swap the xpl v5 to a xhp50.2 3V I should be able to get the same result, shouldn’t I.
Are the LEDs I orderd better than the xhp50.2 3V or would I have any advantage in taking the xhp50.2?
Yes, XHP50.2 will have an even lower Vf. It will give you a wider, less intense beam than the SST40. It will have a bit more lumens but not much more.
If you prefer the 3535 led then use a xp-l2 they have a low vf. Cree XP-L2 V5 5000K LED - Bare
TA’s test from xp-l2. XP-L2 V5 Output & Death test by Texas_Ace Over 2200 lumens! Still worked after 15 Amps!
Looks like it needs about 3.35v or so at 4.5 amps.
There is also a chance the vf could be a little lower or a little higher. Vf lottery 
.
True, if you use the SST40 you will need a different centering ring made for XM sized LEDs. What host are you using?
I am using a convoy c8.
Nothing special, but I like it. If you have any other good recommendation for hosts, just leave them in the comments