I want to be able to automatically switch on an AC-DC power supply edit for clarity: it's a constant current LED Driver [edited again for further clarity- the driver won’t actually be driving LEDs- this is just a cost effective off-the-shelf option for my specific task] (or potentially multiple supplies and a peripheral). While my steady state current draw will be quite low the supplies have a very high maximum AC inrush current of 50 A. There are a couple potential switching mechanism I might use, but they're all essentially simple mechanical relays, and of course are NOT rated for 50A AC current, and certainly not rated for 130A or so of the maximum inrush I might throw at the system if I switch everything all at once with a single relay. So I will need to mitigate this inrush or I'll most likely fry some components.
I've ruled out using simple resistance to limit inrush. Mostly because I think I need a relatively high power resistor, and to do that cheaply means wirewound, which has some inductance. I think that would be fine for limiting the in inrush but could pose some issues to then bypass the resistor after inrush with another relay since on an AC line I can't just use a simple freewheel diode. A simple solution that immediately gets complicated and requires several components. Correct me if my thinking is wrong here and that a wirewound resistor in series with a LED Driver should not be considered an inductive load and is thus nota problem to switch. Late Edit: I suppose I could use several 10 watt ceramic resistors in series so that there isn't any inductance making relay bypass after inrush unproblematic. This might be viable, and perhaps preferrable to using a SSR, but is definitely clunkier than an NTC Thermistor.
Question 1: I've read a lot of conflicting information about Zero Crossing Solid State Relays. If I can figure out what is and isn't true I feel confident I could make a good selection for my application. So, which of the following statements are true for why these might be a good choice for high AC inrush currents?
a) They dampen inrush by switching near the zero point.
b) They can handle short overcurrent events because there's no contacts to weld.
c) They can be found rated for 100 amps+ so most inrush currents won't exceed their rating.
d) Whether it is AC control or DC control the inrush current handling of the AC output side will be the same.
Question 2: Say a you have a 100 watt power supply that's about 90% efficient. Does this mean that the total power consumption during inrush is about 110 watts? The reason I ask is that I noticed that something like a 5V 1A wall wart supply can have an inrush over 20 A as well, but surely there must be much less power being drawn, right?
Now let's look for an NTC Thermistor! I think these would be my preference as I won't be doing any rapid switching on and off. I'm just a bit lost on sizing. My concern is that I get one that can't handle the load and I blow it up.
On the left is the power supply I'd like to use. On the right are specs for a thermistor I think might be suited for my task. I chose it based on it's max current and steady state conditions, obviously, but it also seems to be able to handle a lot of energy, which seems like a good thing! I've just been ignoring the capacitance specs. There's a note elsewhere in the data sheet that these figures aren't absolute. I also have no idea what the bulk capacitance of these power supplies is. So I'm trying to tackle this through power/energy rather than capacitance, hence question 2.
For this scenario, let's say we are trying to switch on two of the pictured power supplies plus one unknown 5v 1a wall wart and we want to limit the AC inrush to 10A or less. We need to allow a steady state current of around 3A.
Question 3 Does it seem to be adequately sized? And if a smaller currents are applied, am I correct that the main difference would be that the thermistor won't heat up as much, leading to a bit higher resistance, causing a small voltage drop between AC mains and power supply input, but otherwise doing no harm?
Alternately, I could use separate NTCs for the supplies and use separate relays to switch them on if necessary. I'd still like to cap inrush current to 10A or less per relay though.
I think that's all of my questions for now, trying to keep this as brief as possible and not meander too much. Thanks.
Late edit post note: I'm on 120v mains power. I'm not terribly concerned with tripping breakers but that's another perceived benefit of limiting inrush rather than simply withstanding it. I'm pretty unlikely to ever see the maximum inrush currents given the usage pattern I'll be following, but I'd still like to size everything for the extremes.