WTB 3V input 6v output 3-4A XHP50/70 boost driver

space is not an issue, it can be a large rectangular block. i’m homebrewing a light and want usb charging to 4 parallel 18650. i’d like a 3 hour duty cycle from the driver, don’t know is that possible at this amperage.

Well, it would be easier to use your batteries in a 2S configuration to reach a higher voltage and improve efficiency.
Your driver choice would be greater

I know that, but serial wiring lithium cells is a little risky and |I don’t even know is a boost charger made for charging 2series cells from 5 volt. i saw a thread here about a 3v 18650 boost driver but it was restricted to 30 seconds operation.

this on kaidomain is the closest I think I’ve seen to what you’re asking for.

thanks, that should do. 6.3v seems a little high for an xhp50, could be better to go for a xhp70 for longevity. the sos mode pisses me off though. anyone know if drivers can be seriesed or paralleled to raise voltage or current?

High current boost drivers that are compact are not really available to us as far as I know. Since you don’t require the driver to be small, you might be able to find it somewhere, but you might have to find it yourself since it wouldn’t really be a flashlight specific device and people here might not know about it.

Most likely that driver will supply a constant current, so the voltage would be whatever is required to send the 2.5A to the LED, not necessarily 6.3V. So you could use it with the XHP50 most likely with no issue.

Maybe you can use an on / off switch that puts the batteries in parallel when off, for charging, and switches them in series for your light.
This way they will always be equally charged.
But i think you’ll need a 3 pole on / on switch for that…

Maybe better to look for a 2s protection balancing PCB and a cc cv boost converter (5 V in 8.4 V out, yes they do exist) to charge it.

a constant current driver is certainly a must for any high power led.

I have seen various boost drivers on ebay which i could daisy chain together to do what i want but the inefficiencies would be cumulative so hardly ideal. the switching from series to parallel is doable but would only generate trouble down the line. has anyone seen a circuit to build a driver? I know it’s a little technical but i’ve built an rf amplifier before and know where to look to calculate inductors and frequencies.