LED Driver Wiring: Help a newbie be less unclever? - Page 1
Forum section: electronics / beginners

author: Fawlty
author_rank: Newbie
timestamp: March 16, 2021, 05:40:45 am
content: Greetings all,So I've got some Mean Well LED PSUs in 30 & 60 watt flavors, along with some CREE CXA3070 COBs.I wanna wire each COB to a pair of the two power supply models, essentially in parallel, but only one of each pair of PSUs would be connected to the mains at any time. The object is to run the LEDs sometimes at 30 watts, and sometimes at 60.What I'm looking to find out is how much the +V and -V outputs of the PSU pairs need to be kept apart. I've drawn three diagrams to illustrate...A: The +V and -V lines are both tied togetherA1: PSU 1 is connected to mainsA2: PSU 2 is connected to mainsB: The +V lines are separated, and the -V lines are tied togetherB1: PSU 1 is connected to mains, and terminal blocks 1&2 are bridgedB2: PSU 2 is connected to mains, and terminal blocks 2&3 are bridgedC: The +V and -V lines are both separatedC1: PSU 1 is connected to mains, and terminal blocks 1&2 and 4&5 are bridgedC2: PSU 2 is connected to mains, and terminal blocks 2&3 and 5&6 are bridgedShould scenarios A or B be avoided?I've attached the specsheets for the PSUs (in case there is a need).Thanks in advance for your help. :)

author: Terry Bites
author_rank: Super Contributor
timestamp: March 16, 2021, 01:57:08 pm
content: Avoid putting drivers in series or parallel. It can lead to unpredictable current and if one is on and the other is off you'll probably kill one or both of the drivers.I recommend just using a pair of mains switches, one for each driver and string. Keep it simple.

author: madires
author_rank: Super Contributor
timestamp: March 16, 2021, 02:08:47 pm
content: Better solution: one LED PSU with dimming control

author: mvs
author_rank: Frequent Contributor
timestamp: March 16, 2021, 02:25:18 pm
content: Quote from: Fawlty on March 16, 2021, 05:40:45 amThis PSUs are essentially current sources and should work quite well in parallel. You can make OR-ing with Schottky diodes to be sure, but most probably it is not needed in this case. You can also use two 30W units at the same time to get 1400mA current.

author: RJSV
author_rank: Super Contributor
timestamp: March 18, 2021, 10:25:33 pm
content: Yes, the suggestion, to simply wire-or through diodes in each of two 30 watt supplies. Then, having one supply, on an AC mains switch, and, again, a second 30 watt supply, turned on with a second mains switch.Question is: I am guessing, you maybe have remote handheld control of each mains plug outlet? Does it hurt anything, suppose someone does the two power options, by switching in 'wrong' order... Or, with manual old-school mains switches, you do a 'two switch, two hands' coordinated switch over, going to 60 watts from 30, or reverse.?Interesting question, in parallel current sources, why no problems? Seems like each (supply) might put out additional current, making the other supply 'want' to put out additional, as it sees itself putting out 'too little'.Kind of a reverse stealing, from each other. But I'm only of moderate skill, so...

author: ledtester
author_rank: Super Contributor
timestamp: March 19, 2021, 12:53:05 am
content: Your option "C" looks like a DPDT switch:https://www.electrical4u.net/switch/dpdt-double-pole-double-throw-working-circuit-diagram-application/which might be more convenient than bridging terminal blocks.

author: Fawlty
author_rank: Newbie
timestamp: March 21, 2021, 12:40:39 am
content: Quote from: RJHayward on March 18, 2021, 10:25:33 pmThinking at the moment is to attach mains plugs like NEMA 1-15P to each power supply. I've got a bunch of power cords with receptacles like NEMA 1-15R and IEC C13s on em. One cord per pair of PSUs. When I'd switch the outputs of a power supply going to a COB, I'd unplug the PSU from mains, move the terminal bridge(s), and then connect the appropriate PSU to mains.I've already got most of this stuff on hand — accumulation from other projects. Enough PSUs of each wattage to run 4 COBs in a combo like I laid out in the drawings. So it's a matter of finagling all the junk to do a job that could be better served by variable PSUs, as user madires suggested, but using what I've got is a lot cheaper.The reason for not just running more COBs, and each have a dedicated PSU, as Terry Bites recommended, is due to the heat sinking required. The LEDs are efficient, but the heat sinking they need is still non-trivial. I'm drilling and tapping PC CPU heat sinks in order to mountIDEAL 50-2234CCOB holders to them. One COB holder per heat sink/fan combo. Don't wanna do any more of that than I really need to.What I'm putting this together for is supplemental lighting for plants to extend the growing season, start seeds, etc. In the case of starting seedlings, less light will be needed; in the case of fruiting, or fast vegetative growth of large plants, you need more. You can fruit tomatoes, peppers, etc. under these COBs.The whole kit needs to be (more or less) portable, or least not a permanent fixture, so the power supply and distribution components are going to be mounted on a board. That can be hung on a wall, and moved and revised as needed. Seems like the most practical approach at this point, I think.edited to add: I didn't comment on the potential pitfalls regarding paralleling of PSUs you questioned 'cause that stuff's well out of my league. Interesting questions, though. Be cool if someone answered, or recommended a good article. What discussion I've found regarding the paralleling of PSUs wasn't targeted toward dummies, and it was all treated very briefly — didn't delve into hows and whys.