need to learn, interesting questions

Ok all u gurus can hopefully start “taking me to school” on modding drivers.

Here’s my current question:

I have a driver for headlamp that factory is set for 2 emitters in series. Its with the coil (buck?). 2 xm-l2 with 8.4v battery pack. (using my kd2 driver as example basically)

Besides obviously the sense resistor, 1 alone, won’t handle it (my new ss x3 has 5 for a 3x parallel) so multiple paralleled would be needed for idea below:

What other factors of the driver would stop me from running total 4x emitters, 2 parallel strings of 2x in series? ( hope I explained that right)

Based on what ive learned so far: Series= amps constant, voltage drops per emitter. Parallel is vise versa. So parallel strings would get half the amps but maintain voltage, each set in series would keep the emitters operating at the drivers set output voltage. 2 emitters produce more light at half the current than 1 emitter at twice the current.

Besides keeping heat in check, multiple parallel sense resistors to spread the load, what else would be needed to make this work? Not looking for “not an efficient way” and all the more in depth to make it function amazing (not yet), just looking at the basics.

Other question, can u run 2 drivers parallel with one switch that operates both drivers? As in the momentary switch for mode selection? Trying to sort out a monetary switch that would operate both but separetly (so their own switches could be used to program/change mode separately too)

Running paralleled mcu’s from one switch doesn’t work because small differences in internal clock cycles mean the modes don’t stay synced. Led drivers are current regulated rather than voltage regulated. The voltage drop across sense resistors is used by the mcu to maintain set current. Lowering the sense resistance will increase the current to the point the voltage drop across the new R value is the same as before but other components on the driver might not be able to handle the added load. It’s a pass fail test to change Rsense. You can often boost current some but at a certain point operation becomes iffy or something burns up.

For the 2 drivers parallel it isn’t so they can run same set of emitters, but 2 separate sets. Say 1 pair xm-l2 for flood, 1 pair on xp-g2 for spot. Each set on its own driver nut a single switch to operate modes on both. Sorry should have clarified that. That was meant to be a completely separate question. My thought process was 4 xm-l2 being pushed at less current since 2 at same current is more than 1. So four instead of 2. Driver pushing 1.5a across 2 parallel sets of 2 emitters in series.

If your just doing 2s2p with the same current as 2s alone then no change to the driver is needed, it will correct for the lower Vf of parallel sets of LEDs. One switch - two drivers will not stay synced. Would need a separate switch for each driver.