Inrush current limiter for PC - Page 1
Forum section: electronics / projects

author: LukeW
author_rank: Frequent Contributor
timestamp: September 04, 2018, 08:22:45 am
content: A powerful desktop PC is designed to accomodate several powerful GPUs, and uses a Silverstone ST1500-Ti 1.5kW power supply.https://www.silverstonetek.com/downloads/Manual/power/en-st1500-ti-manual.pdfResistance measured looking into the AC input is about 20Mactive-earth, and about 5Mneutral-earth and 5Mactive-neutral. Earth continuity to exposed areas of the metal case is good.The Silverstone manual specifies a maximum input draw of 8.8Arms at 240V.(It would be expected to maybe be a bit higher if the line voltage here is not truly 240V, but I haven't measured it.)The PC immediately trips the breaker when plugged in (there is no power switch on the PSU). Removing peripherals such as the graphics cards on the DC output side doesn't make a difference. You don't have to wait until you actually press the PC power button.It's a brand new PSU, and there are no shorts or obvious issues with the output wiring. (You would expect the PSU's internal overcurrent protection to catch this.)It's plugged into a standard 10A domestic circuit. I've removed other loads from this circuit as far as is practical.I think this is an inrush current issue into the active PFC system, input capacitors etc.Is there any device you can get as an off-the-shelf "soft start" system to limit the current draw?

author: mikerj
author_rank: Super Contributor
timestamp: September 04, 2018, 09:34:42 am
content: If it's the current breaker that has tripped rather than a ground fault breaker then it may well be inrush causing this, though that does point to a pretty crappy PSU design to not take care of inrush limiting internally.You can buy specialNTC thermistorsdesigned for exactly this kind of application, but they are supposed to be integrated into the PSU. You could mount one in a suitable enclosure with IEC connectors etc.

author: David Hess
author_rank: Super Contributor
timestamp: September 04, 2018, 10:09:23 am
content: Active PFC should *prevent* high inrush currents because input capacitance is only high enough to filter the high frequency ripple current of the active PFC stage.Are you sure you are not tripping a ground fault interrupter? This can happen if too much Y capacitance is added between hot and ground even if it is on multiple devices.

author: LukeW
author_rank: Frequent Contributor
timestamp: September 04, 2018, 10:18:28 am
content: I have a bank of individual breakers for each circuit at the distribution board and only the one for that GPO circuit trips. I wouldn’t expect them to all be individual RCDs, I’d usually expect a single RCD.

author: LukeW
author_rank: Frequent Contributor
timestamp: September 04, 2018, 11:03:23 am
content: Tom'sHardware reckons the inrush current is 76A at 230VAC, which does seem high.https://www.tomshardware.com/reviews/silverstone-strider-titanium-st1500-ti-psu,5324-4.html

author: Ice-Tea
author_rank: Super Contributor
timestamp: September 04, 2018, 11:10:21 am
content: Maybe have a look at the characteristics of the breaker? You may be able to get one which takes a bit longer to react perhaps? I would very much prefer that instead of twiddling around with the PSU itself (putting any current limiting device in series witht that PSU qualifies as such).Also: why 10A? Most outlets are good up to 16A, 1.5mm² can handle it,... So...?

author: LukeW
author_rank: Frequent Contributor
timestamp: September 04, 2018, 11:33:32 am
content: I don't think it's faulty, it just needs moar powa. I've never seen a PC do this before, including other high-end machines with 1500W PSUs.The fact is it's reliably tripping circuits (in a typical office in 230V Australia) and I'm not sure if I'm barking up the wrong tree or not and whether I need to find a completely unused circuit or get a 15A outlet

author: Messtechniker
author_rank: Frequent Contributor
timestamp: September 04, 2018, 12:23:51 pm
content: Get yourself a "Schalk EBN2 inrush current limiter".Had to install one for my workbench. Too manyPCsand equipment with switching power supplieswould trip the circuit breaker when operarating themain mains power switch for the workbench.Works reliably every time upon switching on. yay!How to wire up:On the distribution board:Automatic circuit breaker - Main switch - EBN2In your room:Your equipmentFor convenience, the main switch may be replaced with a power relay (impulse switch) where the corresponding actuating switch is located near the PC.

author: SparkyFX
author_rank: Frequent Contributor
timestamp: September 04, 2018, 01:24:54 pm
content: I am using a BLOCK inrush current limiter for my 1,5kVA isolation transformer. It consists of a resistor that will be shorted after a certain amount of time and maybe has overtemperature protection and some more features. Seems relay operated. It was needed as 16 Amp B-characteristic breakers would react when switching it on.Other options could be staggered switching on of components.The PSU may also simply be faulty - with a short behind the first switching component. Can you try connecting it without any load?