If you’ve ever lost gear to lightning or power spikes, you know what a pain they are. Out in rural Arkansas, where [vinthewrench] lives, the grid is more chaos than comfort – especially when storms hit. So, he dug into the problem after watching a cheap AC-DC module quite literally melt down. The full story, as always, begins with the power company’s helpful reclosers: lightning-induced surges, and grid switching transients. The result though: toasted boards, shorted transformers, and one very dead Raspberry Pi. [vinthewrench] wrote it all up – with decent warnings ahead. Take heed and don’t venture into things that could put your life in danger.
Back to the story. Standard surge suppressors? Forget it. Metal-oxide varistor (MOV)-based strips are fine for office laptops, but rural storms laugh at their 600 J limits. While effective and commonly used, MOVs are “self-sacrificing” and degrade over time with each surge event.
[vinthewrench] wanted something sturdier. Enter ZeusFilter 1.0 – a line-voltage filter stitched together from real parts: a slow-blow fuse, inrush-limiting thermistor, three-electrode gas discharge tube for lightning-class hits, beefy MOVs for mid-sized spikes, common-mode choke to kill EMI chatter, and safety caps to bleed off what’s left. Grounding done right, of course. The whole thing lives on a single-layer PCB, destined to sit upstream of a hardened PSU.
As one of his readers pointed out, though, spikes don’t always stop at the input. Sudden cut-offs on the primary can still throw nasty pulses into the secondary, especially with bargain-bin transformers and ‘mystery’ regulators. The reader reminded that counterfeit 7805s are infamous for failing short, dumping raw input into a supposedly safe 5 V rail. [vinthewrench] acknowledged this too, recalling how collapsing fields don’t just vanish politely – Lenz makes sure they kick back hard. And yes, when cheap silicon fails, it fails ugly: straight smoke-release mode.
In conclusion, we’re not particularly asking you to try this at home if you lack the proper knowledge. But if you have a high-voltage addiction, this home research is a good start to expand your knowledge of what is, in theory, possible.
Danger Will Robinson! That layout is no good!
Way too close a gap where the component leads poke through the GND plane!
Looks reasonable otherwise (on first glance), but you have to heed those isolation clearances.
What works now might smolder tomorrow as the pcb material ages, gets dusty or moist, etc.
thank you, I’ll fix that
There is one point in this circuit I would suggest to improve:
There is a MOV in the circuit. As explained this ages when it catches surges. Once it got too many, it’s resistance in off-state lowers, making it constantly conduct and heat up, further accellerating aging. This can cause fires.
The solution to this problem is to take a thermal fuse that is in series to the whole circuit (MOV and protected device) that cuts out power should it get too hot (like in the ballpark of 180 °C ). This thermal fuse is then thermally coupled to the MOV, usually by a heatshrink tube around both.
Good points. There are also some industrial strength MOVs as well.
https://www.littelfuse.com/products/overvoltage-protection/varistors/industrial-high-energy
This is true. Every MOV in my 30 year career has self destructed within 20 years, sometimes with an explosion if it didn’t trip the substation breaker needlessly. They make the old famous selenium rectifiers look good…
After having the VFD card in my washing machine die, possibly from a voltage transient, I installed a whole house surge protector. I haven’t had a repeat.
Whole house surge protectors come in several varieties. From those that require being hung off the side of circuit breaker panel to ones that can plug in just like a circuit breaker. Assuming you have the space in the panel.
I mean, if you really want to isolate it, connect it to the network via a fiber link and power it via battery. There’s your electrical isolation.
Good idea, but I’d like to see some evidence that it actually works.
Keep in mind that lightning can completely vaporize the heavy duty and thick copper bus bars in industrial grade high voltage electrical systems and I’ve seen the before and after pictures. What he did is far better than nothing, and certainly better than those cheap power strip “surge protector”s, but if lightning really wants to get at any of your wired and plugged in stuff, it will do it.
Back in another life I used to assemble boards for Transtector…they made surge suppressors.
There was an entire board of MOVs which IIRC had over 20 of them on it…then there was an SCR that had it’s gate tied to the Ground plane…If the ground plane went above 0v it started to turn on which shorted the breaker (IIRC) while shunting through the MOV board.
There were some cabinets that came back that took a direct lightning strike (radio tower) and the entire MOV board was cooked…every single one. But the devices being protected survived and they were replacing the destroyed surge suppressor with a new one.
Was interesting to see the results of the direct strike. Made what we were doing make more sense.
You would not believe the damage I have seen at mtn. top repeater sites when working for a Motorola dealer. LARGE copper ground bars that were vaporized!! Stunning damage.
This was a site done “by the book” (grounding wise)
We lost duplexers and a rack FULL of repeaters.(And almost everything else in the building)