Improvised surge protection

[evilkitty]

Last Friday my raspberry pi zero took some damage from what i believe to have been caused by lighting
The damage appears to have been minimal considering
I lost a DS18B20 sensor, an led, and 2 GPIO pins
the system did not even power cycle
i would just plug a surge protector up to it, but i do not have space for a proper outlet
are there some parts i can just use to add surge protection o should i just mod a surge protector in the attic on to the primary circuit that power my pi
this box gets its power from the attic from the same box as the transformer for the doorbell, so i could slap a surge protector up there
but i think i can crap a few small parts in there, any sugestions

[stj]

Re: Improvised surge protection

you cant stop the emp from lightning, it will destroy mov's and spark-gaps that are fast enough to respond.

[kaboom]

Re: Improvised surge protection

Other than power, what is the RPi connected to?

[redwire]

Re: Improvised surge protection

I think it's best to know where the surge came in- between which two points the surge occured. Then you can plan where to put a surge arrestor.

I don't know all the stuff you have connected. Two relays but more I/O?

Mains -> 5V PSU -> RPi -> HVAC

With things turned off, take an ohmeter from RPi GND to earth ground, and Rpi GND to HVAC thermostat lines.
To see if the RPi is isolated from the Air Con. It should be, the relays are supposed to isolate but a solder bridge or tiny gap can make incoming (mains) HVAC spikes jump to the RPi and kill it.

I'd guess the lightning surge came in between the air con and the RPi power supply (usually ungrounded 5V PSU).

The DS1820 might have been part of the loop the surge took.

Most lightning damage I've seen is between Ethernet (DSL/Cable modem) line and other gear, but WiFi is used on the RPi Zero.

[kaboom]

Re: Improvised surge protection

Most lightning damage I've seen is between Ethernet (DSL/Cable modem) line and other gear,

When it involves comms, either POTS or CATV and other equipment with a three wire cord, and there's no bonding jumper (NEC 820.100, 250.94 and related), these independent common points (NOT grounds in this sense) pick up unequal voltages during nearby strikes or line faults.

You've essentially got one "rod" in the ground for the elec service, and another for the telco cable shield and arrester (and CATV shield, if present).

These lines will be at different potential without the bonding jumper.
In that case, guess where current from that difference of potential (caused by step event) is going to equalize thru?

But with the jumper, this current is essentially bypassed around the computer, TV, etc, and, as a bonus, everything rises and falls together.

[stj]

Re: Improvised surge protection

emp is absorbed into coils and converted into current.
that's why the most common victim is the network controller - it has the transformer in it's i/o

if you want to put spark-gap's across the transformers windings then go ahead, but i suspect the energy will just blow the tracks off the board when the spark-gap triggers.

[evilkitty]

Re: Improvised surge protection

Mains AC-> MFM-05-5 -> Rpi
this is my control board
https://i.imgur.com/YBiU6mV.jpg (sensor is in the lower left)
This board receives +5 to control the relays, the pi uses a pair of massive overkill darlington TIP120 transistors that control the relays, each relay poll has a snubber
the board receives +3.3 to power the led and the sensor
*the led control pin survived the senor, led, and sensor GPIO pin (GPIO 4) were not so lucky
i also lost GPIO 5 which was a OPEN circuit (momentary toggle switch)
the relays have a flywheel diode and a indicator led to show if the col has power (on the right side of the relay in the picture)

I am assuming the LED protected the LEDs control pin

*The networking is done via wifi

[stj]

Re: Improvised surge protection

wifi is irrelevent, you still have the ethernet on the pcb even if you arent using it.

think of a cloud of energy looking for a place to go.
long wires or coils act like an antenna and absorb some of the energy - then you have to deal with it.

mov's and spark-gaps work by going short circuit if the voltage across them is above a set level.
the problem is they have an energy rating in amps or juels - go over that and boom.

[evilkitty]

Re: Improvised surge protection

As far as i know the Raspberry pi 0 v1.0 does not even have a Ethernet controller much less a jack

[budm]

Re: Improvised surge protection

So did you have anything connected to the HDMI and the USB ports when the fault occurs?

[evilkitty]

Re: Improvised surge protection

No HDMI, infant that circuit was powered off

/usr/bin/tvservice -o

as for the USB port, that has my wifi adapter (using a Pi 0 v1.0; so no bluetooth or wifi onboard)

Bus 001 Device 002: ID 7392:7811 Edimax Technology Co., Ltd EW-7811Un 802.11n Wireless Adapter [Realtek RTL8188CUS]

[redwire]

Re: Improvised surge protection

For the LED and DS18B20 GPIO to fail, the spike must have arced from the relays over to the RPi side.
Either across the relay (coil-contact) or there is a close spacing on your protoboard between the two sides. One solder pad on the relay contacts, close to a solder pad on the RPi side would do it.

That would be a transient (potential difference) between the RPi 5V side and the air conditioner 24VAC controls.

It's hard to tell if it came in on earth-ground bouncing up at the air conditioner (ground strike) or it came in on mains (powerline strike) to the Meanwell 5V PSU.

Anyway, one problem is your RPi is floating, it's not earth-grounded, but the air conditioner is. I'm not sure if the 24VAC side is earth-grounded on the air con. Have to check with power off and ohmmeter.

You could add a MOV or GND wire between the two to prevent large potential differences between them.

MOV's+fuse across line-gnd and neutral-gnd I think would have helped. Not Line-Neutral. Anything else get damaged in the home?

Air conditioners are weird for lightning because they are usually outside on a concrete pad (sorta grounded) and connected to lots of tubing/sheet metal ductwork as an antenna.

[evilkitty]

Re: Improvised surge protection

As far as i am aware this was the only damage
none of the components around the relay were damaged (did not test the flywheel)
I have been using this for around 2 years and never had a issue, well until a relay failed so i added snubbers recently
I did not notice any sings of a arc anywhere on the board
the power company recently changed the polls and made them taller so more likely targets for strikes
i have not looked at the power adapter thought i should have but i did not