Surge protection

[evilkitty]

I had a power surge kill a piece of low cost hardware that due to the chip shortage they are well...
My hardware is powered by a meanwell 5v 1A open board power adapter/supply, this has survived and works properly still, i assume all i need is one of those blue disk 2 pin things, what should i attach to my high power supply's input power to help prevent this from happening again

it took damage twice from t-storms, the 1st was non-fatal (the second well... RIP SOC),

the damage happened on the 3.3v, the 5v seems fine, does it seems more likely low voltage AC jumped/arked on my PCB to my data/3.3v wires based on the damage? if so i could insulate that area of the pcb with some plastidip

[pavithra_uk]

Re: Surge protection

For small power adapters or other equipment without ground connection, I use 1 varistor (470V usually) after fuse.

L ---- FUSE ----+-- To adapter
MOV
N --------------+---To adapter

if adapter have no ground connection, but it has wires long enough or connected with other ground, arcing can occur between AC input and DC low voltage rails. in this case, you must add 2 varistors and ground them.

for power adapters like you mentioned, 3 varistors to protect LN, LE, NE and make PSU case grounded properly ensures good protection.

[stj]

Re: Surge protection

when varisters fail they get very hot,
you should put a thermal fuse in series and mount the thermal fuse against the mov.

[redwire]

Re: Surge protection

OP, you have to figure out where the lightning transient got in, and where it got out. Mains, telephone, CATV, earth-ground etc.
I have no idea about the 3.3V power you mentioned, what's that got to do with the 5V Meanwell PSU that you didn't give us a model number for.

I'm using TMOV 150VAC for 120VAC mains, and they clamp to 395Vpk with a 10kA lightning strike (20mm).
For 240VAC mains, I believe suitable is 275VAC MOV clamps to 710Vpk.

I put that across the Line-Neutral and an ordinary MOV across Neutral to Ground, I don't use the thermal MOV's there.

Making a DIY thermally protected MOV by adding a thermal fuse and sock (or heatshrink) over top is fine - but not tested so it may not work as expected.
If you have it in a metal box there's likely no real harm if it doesn't work, melts, arcs etc.
I wanted to add gas-tubes but not sure what voltage to use or how they interact with a MOV.

[stj]

Re: Surge protection

gas tubes latch on until the voltage drops below that needed to sustain the arc.
great on an AC phone line,
but i wouldnt put one on mains!!!

[evilkitty]

Re: Surge protection

I have access to a ground wire
120V AC -> Meanwell 5v 1A -> Raspberry pi -> onboard 3.3v regulator

everything lives inside a 22cu in box in the wall aside from this board: https://i.imgur.com/YBiU6mV.jpg (1st time i lost a led resistor and d18b20 at the bottom and a few gpio pins)
https://raw.githubusercontent.com/GM...o_DSCI0030.JPG

my power board is inside a gutted wallwort's case in the top of the box

so for putting protection on the mains side i put this between line and ground? https://www.digikey.com/en/products/...RP150E/1154452

[redwire]

Re: Surge protection

Oh that's harder to figure out the path.
A lightning zap coming in on the home's mains, seems to be nailing (jumping) between the Pi and the air-conditioner's thermostat circuits. The lightning surge is seeking earth ground.
You can add MOV's to the Meanwell's mains input but that will not help if the surge is instead coming in to the air-conditioner and making the thermostat wiring have the spike on it, then it will still jump to the Pi.

[evilkitty]

Re: Surge protection

found the power supply, got it early jan 2018, the pi was a few years older that that (2016 at least)
https://www.mouser.com/ProductDetail...09%2DMFM05%2D5

what are the odds that everything before the SOC survived (including the 1.8/3.3v supply IC) if it came though the power adapter? is that even possible? note that that the USB wifi chip still works

the SOC was shorted on 3.3v to ground, 3.3v was at 1.1v, the 3.3v was at max current output so the SOC did not get hot, gave it 3.3v with a higher current limit and tripped OCP/SCP on my power supply and saw the SOC get hot in the corner farthest (going towards the center) from the power input plug