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GDT surge life question.
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SiliconWizard:

--- Quote from: Electr0nicus on October 25, 2018, 12:50:26 pm ---I have a special problem designing a product.
The product itself will be used in a very harsch environment where 50 lightning- induced overvoltage occurences are possible per week.  :o Also the customer wants the device to last for at least 15 years, which means 39000 overvoltage events in total.
(...)
So i need to use a GDT. I've searched Littelfuse's homepage, but all their products have a way to low surge life. Mostly 400 shots. The pulse in Littelfuse's datasheet is a 10/1000us, which is longer and has more energy. Does that mean, that this particular GDT can handle more overvoltage events, due to my shorter pulse.

--- End quote ---

You may take a look at the Bourns 2027-xx-SM or 2027-xx-XX series which are heavy duty GDTs.
A GDT would have to be complemented with additional protection means (current limiting, TVS diodes...) IMO.

Still, with your possible number of strikes...


--- Quote from: Electr0nicus on October 25, 2018, 12:50:26 pm ---How fucked am I?

--- End quote ---

You are. ;D

I wonder what kind of environment that would be?
Seaside? Or mountain tops?

coppercone2:
Won't movs need to be balanced too? Some might end up getting insane peaks.

Do they kinda wear out evenly or something? (like sanding metal or wood). Even if they wear down to trigger at the same voltage, won't the leakage of the worn ones be much higher?
jmelson:

--- Quote from: BravoV on October 25, 2018, 01:35:57 pm ---There is no ABSOLUTE 100% guarantee when it comes to protection from the wrath of mother nature, as simple as that, period.

Just tell your customer the story on Japanese Tsunami walls, there were built with centuries of wisdom & experiences, still, the last 2011 great earth quake wiped off thousands of human lives there, turned those walls useless, just google it, plenty of it.

--- End quote ---
Tokyo Electric knew about tsunamis, and CHOSE to just IGNORE all the centuries of experience.  They KNEW that they'd get hit with a Tsunami EVENTUALLY, but just didn't want to deal with it.  Incredibly, the Japanese government just let them do something WAY stupid.

As for GDTs, there is NO WAY you can have a tube survive 39000 events without failure.  I use them on my incoming phone lines, and every ten years or so, they get "leaky" and have to be replaced, when they hold the lone off-hook.

Jon
floobydust:
Engineering always gets silly requirements and demands from customers or product management.
You have to push back, say "no" and explain the cost/design time required to implement the silly feature.
A product in a perpetual lightning storm? Maybe on Mars or Jupiter.

For an ignitor application, I needed 100K lifetime with low current <0.1A discharges.
I talked to Bournes and they advised, for low current discharges, that the GDT aging mechanism is electrode etching.
You can't get long life with high discharge currents, something about the plasma reacting with electrode metals.

OP is better off to "ride through" the surge instead of hard clamping it entirely.
Add series resistance or inductance (good for HV), then clamp that lesser current with MOVs, or something without negative resistance.
BravoV:

--- Quote from: jmelson on October 25, 2018, 08:23:00 pm ---
--- Quote from: BravoV on October 25, 2018, 01:35:57 pm ---There is no ABSOLUTE 100% guarantee when it comes to protection from the wrath of mother nature, as simple as that, period.

Just tell your customer the story on Japanese Tsunami walls, there were built with centuries of wisdom & experiences, still, the last 2011 great earth quake wiped off thousands of human lives there, turned those walls useless, just google it, plenty of it.

--- End quote ---
Tokyo Electric knew about tsunamis, and CHOSE to just IGNORE all the centuries of experience.  They KNEW that they'd get hit with a Tsunami EVENTUALLY, but just didn't want to deal with it.  Incredibly, the Japanese government just let them do something WAY stupid.

Jon

--- End quote ---

Jon, its not the nuclear reactor I was talking about, its the tsunami barrier walls that were built at many of the coastal cities, and the wall's height was considered safe or good enough according to their knowledge gathered thru centuries of experience + from ancient geological water flood markings caused by ancient tsunamis, yet, they were breached big times at almost all cities, killing so many humans.

The moral story, don't underestimate mother nature, thats all.
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