Stacking chips is proving to be rather difficult… :_(
And how many amps do you think I should run (without heating issues)? Its in a Convoy C8 host. Any idea on amps vs runtime with a Pana 18650B (3400mah)
Use your trusty HP-547A current tracer probe (you do have one, don’t you?) to find which chip does not have current flowing into it… no need to cut traces/unsolder anything.
Yeah, like there’s ever enough output… the poor boy will be stackin’ chips ’till the cows come home.
I don’t know what a current tracer probe is…
The Convoy C-8 has a decent pill and connection to the host and since you have the emitter on a Noctogon there’s no reason you couldn’t safely double stack one side and get closer to 4A. The head will get hot but you won’t have the emitter desoldering and slipping off as with old aluminum stars. If you were planning on running it full blast until it starts to dim then consider a larger host but for some minutes at a time high shouldn’t be a problem. This is why there are now drivers with a turbo mode with step down after a short period, so that you can have the wow mode and stable operation at a more reasonable level. With the light in hand it’s easy to tell when it’s time to throttle back so maybe don’t sit it on a table and leave it on high untended. Be sure the thermal adhesive between the Noctogon and pill is a thin layer(press and twist then check for coverage and clamp in place). A P60 light with it’s smaller head, smaller pill, and poor thermal connection can handle 3A without a Noctogon. FWIW I generally don’t use high for extended periods on any light. As far as run time goes the higher the current the higher the Vf of the emitter and the more voltage sag of the battery so it’s starts to dim sooner. It’s hard to say exactly when that will occur since there are also small voltage drops in the switch, springs, driver, and wires(why we do spring mods and use fat wires) as well as variations in cell capacity. If you were to compare the Discharge curve of that cell (sorry link isn’t working but google discharge curve of NRC 18650b) with the Current vs Forward voltage (scroll down to graphs)curve of your emitter you can see that a tenth of a volt either way makes a big difference. At 4A an XM-L2 is close to 3.5V(maybe less on a Noctogon) and that crosses the discharge curve(between 3A and 5A) somewhere around 1.25 Ahr which figures to about 20 minutes or so. That’s just based on graphs though and again doesn’t figure voltage losses in the light but that’s how you guesstimate it.
Oh, Hi Mark, figures you would know all about probes.
You hold it over a trace and if it is carrying current a light comes on. There is a sensitivity adjustment knob so you can set when it comes on.
Yup, been probed by the Little Green Men lotsa times… and them critters know their probes.
Wow, only $150. Guess they probe your bank account too.
I think they were over $500 new. For some tasks they can pay for themselves in a couple of minutes…
I’m not going to ask.
Thanks for all that info Rufusbduck, very helpful!! 
So I have added 4 chips which should give me around 4A in the real world… So I hooked it up to a battery (at 4.17v) and it only gave me 3.25A… Hooked it up to my psu and gave it 5v and it pulled around 4.2A. Shouldn’t it pull roughly 4A with a fully charged battery??
I only skimmed the rest of the thread. I’ve bolded and underscored your problem. The XM-L2 U3 bins are known to have a high Vf, you should expect this kind of problem.
I’m just shooting from the hip here, but switching to 4.35v cells might help.
EDIT: your post #33 supports this conclusion 100%. The 7135’s are unable to maintain regulation due to the high Vf of the LED. Increased input voltage will help at least a little.
Well, the good news is you are up over 3A no matter what. The fact that you got 4.2A at all tells me that either you fixed the bad chip or it wasn’t bad to begin with. 7135’s are current limiting and 4.2A is spot on the max for 12 x 350mA bin chips. 4 350mA chips added to your original 2.44A should have given you ~03.8A in a perfect world but I think between sag of the cell, wiring losses, and as wight says the higher Vf of the U3 bin emitter it might be time to call it good. It should still be quite a bit brighter than before at the very least. If run time is a concern then in this case less is more. If you are going for a true hot rod then you would need a higher drain cell like the 20R or Efest purple and one of the BLF DD drivers. What you will notice though is that all of the modes increase in brightness as more chips are added and in your case possibly proportionately more than high because it’s easier for the cell to supply the lower mode currents. In any case would you care to post a pic of your efforts? If nothing else it will serve as a benchmark for future attempts.
Well that sucks… So with the U3, the vf is higher so the current ends up being lower but it is supposedly a more efficient LED. Would I get more lumens with the U3 LED (lower amps) or a different LED with the same 4.2A driver (LED with not so high vf)? Say an xm-l2 U2 or what about an XPL??
Last night I also wrecked my LED, I scratched some of the phosphor off and now it has a rather blue tint… All part of learning :bigsmile:
U3 is only a few percent brighter than U2. You’d get more light out of a U2 driven at 4.2A than a U3 driven at ~3A.
That said, I think I heard that whatever they’re doing to U3’s is trickling down to U2’s as well, so watch out for that. If you can ensure that you are purchasing U2 stock from before the U3 was released you’re probably fine.
As I said earlier, using LG D1 cells charged to 4.35v may help a little bit. RMM sells them and he’s got screenshots of HKJ’s 3A discharge compared to an NCR18650B
http://www.mtnelectronics.com/index.php?route=product/product&path=59_88&product_id=191
Unfortunately the difference is even less pronounced at 5A than 3A. See HKJ’s comparator for more info.
If I got those I would need a new charger too wouldn’t I… I might just settle with 3.2ish amps 
Unfortunately yes, and not a cheap one. I’m not saying it’s a great idea - I don’t even think it will be that good a solution to be honest. I’d shoot for the older XM-L2 U2 if you can get your hands on one. You might also get good results with an XP-L, I do not know. Finding an LED with low Vf is the key.
I have a XM-L2 U2 here, but its on aluminium… I put it in place of the U3 and got 4.13A 
what the hell? That much of a difference??