I was just explaining to someone how to calculate cob voltage and current with chips in parallel on a constant voltage meanwell so i figured id copy it here for reference
cob= Luminus CXM22 gen 3
driver= MeanWell HLG-600H-54B
lets revisit out voltage/current curve for the chip
just like the chip above can only operate on the curve provided, the same is true of the driver. it has its own graph on its datasheet
in the graphs below 100% of Vo is 54V, 100% of Io is 11.2A
Case A: 12 cobs = 11.2A/12= 933mA > look up voltage of chips at 933mA, it is 50.75V, that is the voltage all cobs and drivers will be operating at
that would be 'constant current' mode like this (full current, reduced voltage)
Case B: 10 cobs = 1.12A > look up voltage at 1.12A, it is 51.75V
that would be 'constant current' mode like this (full current, reduced voltage from 54V but slightly higher than the case above)
Case C: 5 cobs = 2.24A each >>TRICK QUESTION!!!! in this case 2.24A to the cobs would require 57V which is above 54V so, you guessed it, driver operates at 54V ("constant voltage area") and reduces current to what the cobs can take, something less than Io. in this case looking up what current corresponds to 54V in the chip graph we see 1600mA x 4 cobs = 6.4A
no matter if you hook up 1,2,3,4,5 or 6 chips to the driver, in no case can the driver deliver more than 54V to a cob so it will never go over ~1600MA per cob. if you design your cooling solution to handle 85W (really a 120mm passive would do this.. it wouldnt be ideal but the chip wouldnt burn up) you will never have an issue with "thermal runaway"
54B (or 48A) is a good match for the luminus cxm22 since it limits the voltage to an appropriate range within the voltage/current curve of the chip. wanna blow a chip up for fun? throw a single 36V chip on the same driver and watch sparks fly as it will give it all 11A and blow up instantly
you could however hook (5) 36V chips up and let them take 2.24A each and they would run fine. however if one or more chips in that array get disconnected or burn out, the driver will make short work of the rest. so you can see why that's not recommended (in either case a 36B,36A or even 42A or B would be a better match as in a given driver series the current is higher for lower voltage models. "A" models have the additional feature of adjusting voltage down so going back to the 50V luminus chip say you built a rig with a 48A or 54A you can dial the max voltage down to whatever is a safe match for your chip/heatsink combo