KR1 output is 14V and 2A is 28W output, and must input 31W, 33W (increasing as the voltage input drops). It simply cannot have 5mm*2.5mm inductor like Lume1’s 10W if you want some constant current output for that amount of output power.
Since cell buck driver are all plagued by the same thing in single-cell 18650 lights, ICs that incorporate FETs with high RDS (ON), manufacturers use tiny inductors, weak springs, etc (so just that it fits some tiny 18mm-20mm diameter).
Otherwise something like 3A at 3VF should not be a big deal for a buck driver from a single cell, if the driver is completely different in size and price.
It’s always a compromise to fit the required space. The everyday carry size lights I’ve been most satisfied with in terms of driver performance have all used boost or buck/boost drivers. Those occasionally have efficiency issues when they’re pushing especially high max outputs, but those are essentially burst modes no matter what sort of driver is used, so I’m not too concerned with that. The Lume1 takes an interesting approach with the buck/boost through medium-high and FET for max.
If an LED has a vf of 3V at 1.5A with an input of 4.2V that is not boost is buck, pretty simple at this point.
Nobody should call that boost is my point, and I am using lower numbers example this time to attempt to be drawn into tangents.
Boosting is completely unnecessary and impossible in such conditions and if a driver has that much voltage burden that it needs to drop cell voltage from 4.2V to 2.5V to boost to 2.8V (for the sake boost argument), then that is a bad driver. That is why if it bucks it is a good driver those conditions I have mentioned, this is why Lume1 is primarily a buck driver and a direct drive driver.
I don’t think talking about what a real Lume1 will be asked to do in a real FW1A XP-L HI is a tangent. It should supply 3A@3.5V to that LED until its LVP trips with the battery around 3.0V. It has to boost to do that.
On the other hand, a very low Vf configuration, like four E21As in parallel can probably have a stable 3A with no boost within the voltage range of an 18650.
If I recall correctly, the default setting is rainbow mode, not voltage mode. So by default it’ll just cycle through the colors instead of displaying the battery level.
To change this, click 7 times while the light is off, but hold the 7th press until the aux LEDs get to the desired mode. Voltage is the one where the aux LEDs cycle rapidly during the preview, right after rainbow which cycles at a slower speed.
How about a noctigon K2 with a bigger head and more cells?
Edit: 3x 21700 seems good but I’m curious about how the reverse polarity protection will work since you can’t use the plastic things with flat top cells.
