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I don’t think a traditional round flashlight driver exists that will do what you want. But depending on how much space you have in your light you might find a boost converter with adjustable constant current that could work.
Is the cell about 15Ah with threaded bosses at the terminals at each end?
i tested a batch for electric car application. The nominal voltage is about 3.2V, a fully charged cell of this chemistry sits at about 3.334V and they are easily damaged by overcharging. Little to no extra energy is available by operating at the bitter ends.
What is the forward voltage required for the LED that you want to use?
The circuit that you will need is called a Boost power supply, it will take your 3.3 to 3.0 VDC from the cell and “boost” it to the higher voltage needed for the LED.
The main components will consist of an inductor, a diode, a capacitor, a current sense resistor (low R) and a big-ass transistor. A control chip is needed to drive the transistor based upon the feedback signal from the sense resistor.
Example:
If you have the makin’s then you could roll your own; but there are boards already available that do this for low cost. Buy some and start playing around with that thang.
[edit] search for example boost boards.
MT3608 2A board
XL6019 5A board
What is your custom light? Can you use multiple 3V emitters in parallel instead of just one?
An LED has a relationship between current and voltage. See, for example, below link for some tests.
A rough example of how this might work is if your cell provides 15A at 3.2V, it would drive 3 SST40 LEDs at 5A each.
Like nearly everything in electronics, it depends.
Here’s a typical discharge graph for both rate and temperature.
It’s pretty obvious that at the top end there is no usable energy available above about 3.3V. The cell drops so quickly and it is easy to damage this chemistry with just a slight overcharge. In my way of thinking, going to the absolute max is not recommended unless the application is critical and the extreme is required.
Looking at the bottom end, the knee in the curve varies depending upon load (and temperature). When i was doing discharge testing at significant currents, e.g. 1/3 to 1 C, the steep slope past the knee occurs in a very short time period—it’s just a blink and nearly too quick to detect and respond manually. IMO, the amount of energy in that short time is insignificant compared to the bulk capacity of the cell, and going to the absolute min is not recommended unless critically required, i.e. a life or death situation.
That big flat-sloped region is the best part of these cells and a time history would show how long that voltage just holds and holds till it gives up. By all means test your cell and see what you get, i would be interested to hear what you think about it.
If you have 2 of these cells, you could direct drive a 6v xhp70 with no driver.