SMPS inrush current - Page 1
Forum section: electronics / repair

author: charlyd
author_rank: Frequent Contributor
timestamp: October 19, 2020, 09:54:01 am
content: Hello last week i repaired the SMPS for my roof cylinders. the power supply needs to deliver 12v and about 40 Amp or more.. but after repairing i discovered that it too easily triggers my surge protector. i assume this is because of the "inrush current". but when i looked at the schematic i couldn t find a protection like a NTC or something. the only thing i found was RTH1.any ideas what can be the course of my high inrush current in the attached schematic.

author: George Edmonds
author_rank: Frequent Contributor
timestamp: October 19, 2020, 10:13:12 am
content: HiFirst it may not be a faulty power supply, it could be your "surge protector" going faulty.RTH1 is an inrush current protector, the way that the schematic is drawn is mad.Check all CYx capacitors.George G6HIG Dover UK.

author: Alti
author_rank: Frequent Contributor
timestamp: October 19, 2020, 10:18:39 am
content: Quote from: charlyd on October 19, 2020, 09:54:01 amHow could SMPS trigger asurge protector?One device has nothing to do with the other.

author: charlyd
author_rank: Frequent Contributor
timestamp: October 19, 2020, 11:29:10 am
content: @George thanks for you reply, i will check all those CYx. yes indeed a chinese schematic ..pfff my surge protector is the one from my bench, but when i put a switch in between the contacts gets burn really (too ) fast.@ALti: how do you call a surge protector in the house. ( maybe i choose the wrong word) if so please let me know so i correct it.But it is the fuse in my workbench 10Amp which goes out from time to time.When i put lamps in series my psu is working fine. (btw sometimes it sparks a lot only on the AC connectors. ).

author: Alti
author_rank: Frequent Contributor
timestamp: October 19, 2020, 11:41:43 am
content: Quote from: charlyd on October 19, 2020, 11:29:10 amSurge protector in a house is calledsurge protector, or surge protection device, SPD.QuoteThen most likely the inrush current of this device wears out the fuse. Use a proper fuse and she'll be fine.Linkto fusology.Or the SMPS is overloaded or damaged or the supply voltage is too low...

author: George Edmonds
author_rank: Frequent Contributor
timestamp: October 19, 2020, 11:57:39 am
content: HiBy and large fuses are no longer used in domestic premises, now days devices called MCB's (Magnetic Circuit Breakers) are used and these WILL trip on an inrush current as they are designed to do. Alternatively devices called RCD's (GFI in the US) sense out of balance phase/neutral currents produced by the Y rated RFI capacitors.George G6HIG

author: charlyd
author_rank: Frequent Contributor
timestamp: October 19, 2020, 02:52:40 pm
content: Hi george i will believe you but this SMPS is from 2016. and had no inrush protection at all. the schematic i uploaded in this topic was even better then the psu i have here. My unit only has the 3 caps. like CY1, CY2 and CY3. two over the rectifier to earth and one at the other end of the power supply.no NTC or what so ever. i changed the schematic on the primairy site. I took the soldered fuse out of the board and installed a fuseholder. On the fuse place there is now room for a NTC-5D15 Thermistor.let s see how that works out ;-)