Inrush current of multiple Switch Mode PSUs for LED lighting - Page 1
Forum section: electronics / beginners

author: Daz
author_rank: Contributor
timestamp: July 20, 2015, 12:08:04 am
content: Hi,Can anybody help me understand if I have a problem here or if I am worrying needlessly?After watching Dave's recent video on LED lighting I thought I'd better get on with installing my LED lighting strips (the flexible reels of LEDs). I will be using 3 separate switch-mode power supplies to power LED strips in 3 separate areas of the room:- One of these PSUs is a small cheap wall-wart, which I can't find inrush current specs for. It's 12 volt 1 amp, and it only needs to supply 0.3 Amps.- Two of these PSUs are some generic Chinese thing, model YU1206, 12 volt 6 amp, but they will only need to supply 2 amps each (they're over-spec'd for what I need but I was given these PSUs for free). I found the spec online for the YU1206, which says:Inrush Current: COLD START 40A /220VACInput surge: 50A@120VAC, 50A@ 230VACThese 3 PSUs will be switched on simultaneously from one domestic 240v (UK) wall light switch and my concern is the total inrush current, which could be 100 Amps (40A each for the two YU1206, and an estimated 20A max for the wall-wart). This seems like a lot for a lighting circuit, and the standard domestic lighting switch on the wall is only rated at 10 Amps!Will any arcing age the switch contacts prematurely?Or is 100 Amps an acceptable inrush for domestic lighting circuits?I found some specs on proper LED drivers that showed inrush current to be up to 70 Amps, which for 3 drivers would give an inrush of 210 Amps! So my case isn't that bad, but it might be for somebody out there.Thanks for your help,Daz.

author: Cliff Matthews
author_rank: Unknown
timestamp: July 20, 2015, 11:57:11 pm
content: Wall-warts are typically dumpster trash and the other units are over-kill for the job. If you must, use one of them and maybe switch the outputs instead. Even with all LED strips on, the SMPS efficiency will be low (the best numbers are typical at > 50% load without PFC).

author: Daz
author_rank: Contributor
timestamp: July 21, 2015, 02:14:03 am
content: Thanks for responding, Cliff, and for the info on efficiency. You're right, using just one of the 6 Amp PSUs for all 3 LED strips would be a better option... less inrush and more efficient.The reason I mentioned 3 separate PSUs is that the LED strips are for under-lighting on kitchen wall units, and the kitchen already has mains wiring buried in the 3 walls from the old flourescent under-lighting on the old kitchen units, all connected to one light switch. So 3 PSUs on 3 separate 240v points seemed like the obvious way to go at first.If I do use just one 6 Amp PSU then I'd probably have to use some of the mains wiring in the walls as 12volt wiring... shouldn't be a problem, so long as I label the wires clearly! Alternatively, I could stick to 3 separate and more suitable power supplies and live with the high inrush current.

author: Cliff Matthews
author_rank: Unknown
timestamp: July 21, 2015, 11:54:26 am
content: I doubt those unrush specs are normally as high. Perhaps that's worst-case full-load with the on-board inrush limiter (NTC thermistor) shorted, or maybe you'll need to install one? For the wall-wort, the pip-squeak primary cap inrush might only be a micro-blip by the time it reaches the mains panel...

author: Daz
author_rank: Contributor
timestamp: July 22, 2015, 01:19:42 am
content: I've been looking at other switch mode power supply specs and inrush always seems to be really high, between 40 and 70 Amps at 230v. I checked the specs of proper 'LED Drivers', and they are just the same. Surprisingly, even a tiny 12v 1 Amp driver has an inrush of 70A at 230Vac (spec says "twidth=120?s measured at 50% Ipeak")... that's this little driver here:http://export.rsdelivers.com/product/mean-well/apv-12-12/constant-voltage-led-driver-12w-12v-1a-mean-well-apv-12-12/7381577.aspx?query=MEAN+WELL++APV-12-12http://docs-europe.electrocomponents.com/webdocs/135f/0900766b8135f5b2.pdfOh well, I'll do a bit of trial and error and if it doesn't work out I've got a couple of options now. Thanks for getting back to me, Cliff.I think inrush current problems with LEDs on mains lighting is definitely a 'thing' though... a bit of internet searching showed up a couple of products to help with the problem. One is an inrush limiter especially for LED lighting on 240v circuits:http://www.cooper-ls.com/sites/cooper-ls.com/files/products/datasheets/cooper-ls-datasheet-inrush-limiter_0.pdf... and the other is a relay to limit arcing on the light switch:http://www.flexconnectors.co.uk/special-relay-for-high-inrush-currents.html... so I'm surprised there's not more info out there on the subject.