| Electronics > Projects, Designs, and Technical Stuff |
| GDT surge life question. |
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| Electr0nicus:
Hi 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. The overvoltage pulse is defined by the customer as follows: 1,2kV superimposed on the AC sine wave. 500A surge current 1,2/50us surge duration. 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. Also the overvoltage protection circuitry is not servicable, because the whole electronics will be potted and can not be accessed later. Is there a possibility to design a overvoltage protection circuit which can last that long, and for that many overvoltage occurences? Are there mayby other devices which are better suited for my application? How fucked am I? Cheers |
| IconicPCB:
There is no protection from lightning strike. Renegotiate the clients specification. Use a GDT in combination with a bit of series inductance and a MOV |
| BravoV:
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. |
| capt bullshot:
There's more than the GDT / MOV way to deal with overvoltages. GDTs reflect the pulse energy back to the source (by creating a short) and so they have to stand the surge current and suffer from electrode degradation or whatever. MOVs partially absorb and partially reflect the energy by limiting the voltage (but do not short the line). They suffer from repeated absorbing the pulse energy and somewhen explode. If you find a clever way to not have to absorb or reflect the energy (e.g. by shortly opening the circuit by an appropriate switching device), one can create a protective device that can stand way more usage than a GDT / MOV. If your device is low energy itself, an appropriate series impedance and a TVS (these don't degrage as long as you don't exceed its ratings) may work fine. In the end, usually some combination of these techniques does the job. Maybe you go research telecom subscriber line interfaces and railway power supplies, those usually have to stand a lot of "abuse". |
| Miyuki:
There are some huge TVS on market rated even for kAmps surges, but prices are rather high Depend of what they want to pay |
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