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Topic: Surviving (nearby) lightning strike (Read 1 time)previous topic - next topic

MarkT

#15
Jun 25, 2018, 03:56 pm
A nearby lightening strike is similar to an EMP burst, except lightening may contain several discharges. Research how to protect from EMP.

Paul
Sorry, I have to enter pedant mode, "lightening" is the act of making something lighter, "lightning" is an electrical discharge in the atmosphere!  Noone has seen darkning though
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Paul_KD7HB

#16
Jun 25, 2018, 05:56 pm
No one has suggested burying the wires in trenches, as deep as possible. And separate the wires in the trench from each other. Conduit made for burial may be used.

Paul

JohnRob

#17
Jun 26, 2018, 05:47 pm
In my limited experience with lightning I've formed two conclusions;

1)  Nothing to my knowledge will survive a direct lightning hit.

2)  For a nearby lighting strike the considerable energy directed into the ground dissipates in a near radial pattern resulting is a voltage differential  of some number of volts / meter that drops the further you get from the strike zone.

I would look at this link http://www.surgetek.co.za/more/step_and_touch_potentials.pdf

To simplify the problem I would look look at it in with some simple assumptions ( perhaps not 100% correct but simple enough to move forward)

1) The voltage differential from the sensor(s) to the base circuit is a function on how close the lightning strike is.   For a practical number I would use 100 to 200 V of ringing AC + some DC.

2) I would assume the current capacity is very high.

So your circuit needs to be able to survive the above voltages.   OR  have some sacrificial component that is easy to replace.

Sorry I don't have an exact circuit for you but I hope this somehow helps you find it.

John

raschemmel

#18
Jun 26, 2018, 07:08 pm
That's why tge use SADs gor surge protection.
They clamp the voltage at the specified clamp
voltage but have the capability to conduct large currents. (see Joslyn datasheets ).
You need suppession at the main feed for the building and then at the local feed and last at the DC supply (input & output).
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

Smajdalf

#19
Jun 26, 2018, 08:14 pm
Sorry for not responding for long time - I wanted to write "proper answer" and a lot needs to be said.
1) I am sorry for the click bait title - I do NOT try to protect the device from direct lightning strike. I know it is nearly impossible to protect from it and I believe it is also nearly impossible for it to happen - after all our house with a lightning rod is nearby. Also as far as I know a lightning never struck "near". There used to be a charred tree nearby (~200m) likely from a lightning but it is many years ago. But on the other hand I cannot be 100% sure about this - maybe the lightning hit a nearby house's lighting rod or something else nonflammable and strikes in 100m radius are common?

@ JohnRob: thank you for the link to the document. I hoped for something like that - some (very rough) numbers to know what is likely. Do you (or someone else) have a link to some "more technical" and "less advertising" document?
Why do you assume current capacity is very high? The linked document as well as Wiki says 30 000 amperes is current of the lightning. It is roughly 1A/m^2 at 100m distance. Provided there were 2m of water in the well and it has 0.5m diameter only 1A wanted to pass via the water - and only part of this wanted to pass via my wires?

@ falexandru: the continuous measurement is the reason for the device. Disconnecting it is not an option.

Is the moment lightning strikes the only moment a harm to the device may happen? Meaning is it enough to be prepared "only" for very short pulses of high voltage and/or current? Or are there other less dangerous potentials?
My idea of lightning strike is that (positive) ions accumulate in the earth but since they "have nowhere to go" they are evenly distributed. When lightning strikes a lot of negative ions enters the earth at one spot "eating" the positive ions at the spot. So nearby positive ions "rush to fill the gap" quickly restoring even distribution. But maybe during the storm the ions slowly constantly shift around "anticipating" the strike - each time passing through my poor circuit slowly wearing down the protection diodes until something breaks?
How to insert images: https://forum.arduino.cc/index.php?topic=519037.0

MorganS

#20
Jun 27, 2018, 09:54 am
If electrical fields are surging around and into your circuit then there are 3 voltage levels that are critical:

1. Below your power supply voltage. The electrons help or hinder your power supply. This may give false readings (noise) on an analog sensor but nothing will break.

2. Within the capacity of your protection devices. The protected voltages will rise above the normal voltage to the level where the protection device becomes active. For example 1mA into any Arduino input pin wil make it go up to 5.6V and then the internal protection diode conducts to hold it at that voltage.

The capacity of the protection devices is usually related to the wasted power heating them up. A small device only takes a small amount of energy to heat it up hot enough to explode. A big one can absorb more energy. That is why they often have ratings in Joules instead of watts.

Older protection devices may wear out over time. Newer ones probably don't wear out. A TVS diode can conduct 1mA forever. That is an infinte amount of Joules, but at such a slow rate that it can dissipate the heat over time.

3. Outside the capacity of your protection, obviously you get explosions with sparks and poisonous smoke.
"The problem is in the code you didn't post."

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