I really dont want to take the chance. I ideally need a 1.5a buck driver that can except running 2 18650’s stacked. They used to make such a driver, but it appears to be obsolete.
Actually most of LEDs are based on GaN,not silicone semiconductor. LEDs behave like a non-linear resistor,so voltage and current are strongly dependent on each other,how can you put too much voltage without putting too much current also?
My deepest apologies. I mean, I know so little about anything I’m still happy with stone-age direct drive PWM open-source drivers, for cryin’ out loud! I’ll try to remember not to butt in to highly advanced technical discussions like ‘can I run this 3v LED from 8volts???/’, I’ll just wait for you to show up and handle things. 
What’s wrong with my suggestion? http://www.mtnelectronics.com/index.php?route=product/product&path=67_115&product_id=521
Not a thing
More arguments(currently: 0),less whining please.
The lowest drop is 5v, and correct me if I’m wrong, thats still to much voltage for an XP-E2. Plus it would be triggering the low voltage protection way to premature.
Your reply makes no sense. Rest assured that finges/Rufusbduck are correct. I’m not certain what you mean by “The lowest drop is 5v”, but the only mention of 5v on that page is the input range in the title so I’m going to assume that you’ve misinterpreted that. Please look through the “Available Options” and “Description” sections. I think you’ll quickly see that this is a very good match for what you want to do.
The input range is 5-15v. I am running an emitter that can only handle a range of about 4v and some change. Usually i would use a driver set up to handle 1 18650, and wouldnt trigger the low voltage protection until it drops to about 1 volt, I believe. Using a driver between 5-15v, its going to trigger the low voltage protection much sooner than 1v, right? Therefore i would not get as long of a runtime as you should having the advantage of running 2 18650’s. Please correct me if im wrong. If i knew what i was talking about, i wouldnt be posting on here.
- Yes, you are wrong.
- LVP should be setup to kick in when each cell is in the 2.8v to 3.5v range, not 1v (someone else can get more specific about voltages if you need them to).
- Yes, normally a DD or Linear driver for a “3v” emitter like the XP-E2, XP-G2, XM-L2, XP-L, etc would be used with a single Li-ion cell. LVP would be setup to correspond to the voltages of the single cell.
- I recommend doing a little background reading, it seems that you are way out in left field currently. Lagman wrote a pretty big post a while back on the topic of “Understanding the difference between Linear, Buck, Boost and Direct Drive drivers”. I later revised that post significantly and posted it further down the thread: Understanding the difference between Linear, Buck, Boost and Direct Drive drivers - #56 by wight
Frankly I’m unable to understand your post #17 very well at all. It may be a communications failure, but it looks like you are under some serious misconceptions - maybe just about how LVP works? Unfortunately I’m not certain that the post I linked to will help out with that. Generally speaking in a flashlight with removable cells which are in series, LVP works by simply measuring total battery voltage and comparing that against a value which is known to be “low” for that number of cells. The primary shortcoming of this method is that it assumes that all cells are around the same voltage when they could actually be seriously imbalanced.
EDIT: Or maybe you are simply confusing the words “input” and “output”? (sorry, I simply do not know where the confusion stems from)
It’s a buck driver so input voltage is greater than led voltage. Some of the extra power is stored in the inductor and converted to current. The driver senses battery voltage and indicates when it is low for the number of cells used.
Appreciate the help, but no need to be kind of insulting about it. Sometimes, you got to put it out there in the simplest form to make sure every concern is addressed, even if you already have a general idea. I think I understand now. Thanks.
Sorry, didn’t mean to be insulting at all. Now if I’d said” It’s a buck driver, you idiot.” Then it’s pretty clear I would be trying to demean you. I generally don’t do that sort of thing unless I’m writing to Steve. In this case I’m pretty sure you’re just projecting. I’ll let you know when it’s serious. 
I wasnt referring to you. Sorry for the confusion. Should have quoted it.
Yoke’s on me then.
I’m not as bad as I was once. 
Maybe I took it wrong. Its hard to tell peoples tones when typing. I appreciate the help. I think I was overthinking it. My downfall is im not a risk taker, so I want to be positive I know exactly what Im doing prior to the build. This is only my 2nd multiple cell light Ive done, other than a couple of headlamps I did where the batteries run parallel so the voltage is the same. I do appreciate everyone’s input. I think I’m good on the matter.
Definitely not intended as a slight hemimike. Any tone is from good honest frustration. I don’t know where some of your numbers/figuring came from. That makes it hard to set you straight without writing long essays and/or potentially telling you a lot of things you already know.
I settled for covering the two most important topics and being explicitly clear that you were way off base.
All good. Thanks for the help. Unfortunately, Mountain is out of that driver. Anyone know where I can get a similar one from?
Do you definitely have to have 17mm? If you can go bigger there are some good alternatives. IIRC the LD-29 has some form of LVP but the mounting board is ~21mm in diameter. In fact, MTN carries this driver! IIRC it has configurable modes like the LD-25, but I am not sure and there may be a special trick. convoy-flashlight - video of LD25 output current setting ,wish you success!
Otherwise if you need 17mm and LVP I think you’re stuck either (a) waiting on RMM to restock [which means build more himself] or (b) posting in the WTB section asking someone to build you one since RMM has posted all the information needed for a driver modder to build their own.