Inrush Current limiting - Page 1
Forum section: electronics / general

author: Veketti
author_rank: Regular Contributor
timestamp: February 08, 2025, 08:40:26 pm
content: Dear All,One thing that has been annoying me for a long time is plugging laptop chargers to wall outlet. Depending on the phase angle at the time of plugging you either get pop and flash, nothing or anything between those, eg. 0° & 180° nothing and close to 90° & 270° biggest arc. I thought I found perfect product to prevent these current spikes:Mean Well ICL-16R. According to datasheet it directs the current through resistor for 300ms and then relay bypasses the resistor. This sounds perfect to pre-charge the large capacitors and prevent the short like situation. So, I added dedicated socket connected to this current limiter and switched power on. Heard the relay pull and realized I had misunderstood the working principle of this unit. I thought that the datasheet “control circuit” sniffs the current through the phase and once sensing load will bypass the resistor after 300ms. But no, the timer starts immediately when the device is energized.So, the question is, is there a readymade device for this purpose that would work like my initial expectations were, like sensing the load and only then start working? Or some other device like maybe zero-crossing sensing thingie?

author: Siwastaja
author_rank: Super Contributor
timestamp: February 09, 2025, 07:06:36 am
content: Maybe instead try to find inrush-free laptop supply. Now with all laptops transitioning into USB-C, it is easier to find alternatives.For example, my Dell's USB-C supply from three years ago has internal inrush control (of some sort, did not look further into it). Never any sparks.Though, I have no idea what search terms to use.

author: benseno
author_rank: Regular Contributor
timestamp: February 09, 2025, 09:33:32 am
content: I recall, long time ago, soft Switch ON circuits for tungsten wire incandescent lamps made of diode bridge and BJT with cap between BE and its charging resistor were popular.Not sure if dropped input voltage (due to switchable 300 Ohm) falling outside of adapter permissible input range will not create a problem on the longer run.

author: JohanH
author_rank: Frequent Contributor
timestamp: February 09, 2025, 10:08:25 am
content: These kind of inrush limiters are common in audio gear and such that use large transformers. I built one for an amplifier a long time ago. Note that there are designs also involving transformer secondary, but the design I used is a simple device for 230/230V.https://www.eevblog.com/forum/beginners/simple-amplifier-soft-start-for-inrush-protection/msg3774620/#msg3774620You can find ready made such modules (typically plain circuit board modules) on e.g. Aliexpress and Ebay. They aren't supposed to be mounted in an electrical cabinet and are not certified for such things. But if you put it in a plastic box with proper grounded input lead and output socket, it's probably fine for the purpose.You could also mount the device you bought in a box with a power-on switch in addition. Not the best solution, though.

author: Veketti
author_rank: Regular Contributor
timestamp: February 09, 2025, 10:30:10 am
content: Unfortunately older laptops don't have USB-C charging possibility and not even all newer ones.. Have at least four types of laptops of various ages so looking for new chargers for each is not an option.Next best thing was to circulate the Mean Well ICL-16R input through a switch but like JohanH said, not the best solution.. Need to make sure it's off when plugging the charger and only then switch it on. Not a big deal but still something automatic would be wonderful..

author: Siwastaja
author_rank: Super Contributor
timestamp: February 09, 2025, 11:50:53 am
content: May I ask, why are you concerned about this? They were designed to handle the inrush, and zillions of people use them as designed every day. The sparking is more like an aesthetic problem.Series NTC is the classic solution (simpler than fixed resistor + timing circuit + relay), but it needs to be correctly dimensioned for the charger so maybe not a generic solution inside a socket (risk of connecting something else than suitable adapters).

author: ledtester
author_rank: Super Contributor
timestamp: February 09, 2025, 01:08:41 pm
content: Quote from: Veketti on February 09, 2025, 10:30:10 amCrazy idea: Permanently wire the Meanwell to the charger so that when you plug in the "charger" you are plugging in the series combination of Meanwell+your charger.Advantages: No switch to worry about and you'll get the protection regardless of what outlet you plug it into.2nd crazy idea: Put the Meanwell in a box with a line cord and a socket so you can insert it between an outlet and any device that needs inrush limiting.

author: 5U4GB
author_rank: Super Contributor
timestamp: February 09, 2025, 01:49:30 pm
content: Quote from: Veketti on February 08, 2025, 08:40:26 pmThis problem is common for any number of external soft-start devices (which also act to limit inrush current), you need to switch the power before the soft-start device, not at the device being soft-started. So it works for something like a pump that's controlled by switching external power on and off but not for machinery where there's an on/off switch on the machine itself.