How to Protect Electronic Devices from Voltage Spikes

What are we considering here: single family dwelling, multi family apartment, large industrial facility, agricultural concern of some type, government office complex…

Is the problem too large for a common power strip type suppressor, or some transient voltage surge suppressors in the panel?

Sir,

This refers to a single family dwelling and at the time of transient voltage surge.

Thanks.

There are many options from simple MOVs to PI networks of MOVs and inductors, through to MOVs, and an inductive snubber in both the active and neutral lines, some have capacitive filtering added and you can advance to full UPS system, it all depends on the depth of your pockets.

You might consider an isolation transformer. They are wound 1:1 but become a heavy inductive load when presented with high frequency transient spikes. Getting one that can handle a house is not budget friendly but making one that can handle a single non inductive load, like say a single outlet that feeds a TV or computer is dirt cheap. I have made them from microwave oven transformers (2) by cutting them open (grinding the welds) and putting only the primary windings back into a single core. Put a plug on one winding and an outlet on the other and stick it in a nice box.

When you grind off the weld, you are breaking the magnetic circuit, and the transformer will have a shorter life than normal. I have found the best way is to cut the unwanted winding out using a sharp wood chisel very carefully on one side and the pulling it out from the other. I have made a spot welder like this.

I removed the secondary winding, and replaced it with two turns of #02 cable for the output.

I used the copper contacts from an old golf cart reversing switch, ground to a point, for the contact points.

Here is a link for new studs of you don't have an old golf cart laying around.

A local golf cart repair center will probably give you an old reversing switch for free because they do not bother with repairing them.

https://golfcartrentals.com/shop/p/ezgo-11903g1-copper-contact-stud-for-forward/reverse-assembly-gas-2-cycle-electric

Works great.

I've done the same thing several times, making a spot weld transformer from a microwave oven transformer. I carefully used a bandsaw to cut off one side of the secondary winding, then a hammer and punch to knock out the remaining parts of the secondary winding.

Same here. only I grind the welds and then clamp it back together after rewinding. I made my point contacts out of copper pipe. Hell I make my own end grommets out of copper pipe flattened at one end and drilled.

What does SDSI stand for? I couldn't find a good match using a search engine.

SDSI--I should have said SDSA for Square-D Surge Arrester. Find them under Square-D.

My error, sorry. --JMM

I did see the Square-D website, so I thought that might have been the case, but thank you for clarifying. Cheers !

Voted GA.

To the OP: A properly sized surge arrestor from any reputable company will work, but it is crucial to install them properly, and to the code for your country. It is worth getting a version that indicates when it is not functional, as they may fail after particularly intense surges in a way that is not easy to observe and is then useless. I would not try to save money on either the surge arrestor or the installation electrician's costs if at all possible. Surge arrestor design and installation is one of those areas where more detailed knowledge is often required.

Friend,

Good advice regarding GDT's. Because MOV's are very inexpensive and are available in a wide range of peak energy (in Joules) they can discharge without failure, they are the typical first and often the only choice in surge arresters. Because they must remain passive in ordinary use, their breakdown (or whatever it is called) voltage has to be higher than the peak voltage of the incoming power's sine wave, plus a reasonable allowance for times when the power supply has an occasional variation of +/- 10% or so. Multiply that by 1.414, so a typical 120VAC circuit would need an MOV rated over 190V. Leave the designing to the engineers and buy the commercial product rated for your circuit voltage, but get the largest one you can afford.

GDT's are very good, but more expensive. Anything that increases the impedance and can filter out the very high frequencies associated with a lightning strike or switching transient is often useful and cost effective.

I had a brand new Variable Frequency Drive in a pump station, but it failed within one month, as did the two replacements. We put an analyzer on the incoming 480V line and saw spikes well over 1500 volts, both positive and negative. Because we had a 3% choke on the line these spikes were not the cause of the problem--it was a bad manufacturing design, which they corrected, and gave us the next larger size VFD for our job. Never had any further failures. Baldor was good.

--JMM

Chokes are good, no doubt. Impedance works almost like magic. Size and cost can be an issue, depending on the application. I am familiar with line reactors for VFD's.

Sizing GDT's is not easy, because often times it can be difficult to quantify lightning strikes. But I'd rather blow apart a GDT and save the rest of the system.

Surprisingly, there are some rather large units at fairly reasonable prices. The link below is for a 20,000 Amp GDT with a spark-over voltage at 800 VDC for less than US $30 from DigiKey (in-stock). Not sure of the mains voltage for the OP so this may or may not be a good choice.

https://www.digikey.com/en/products/detail/epcos-tdk-electronics/B88069X9170B152/3502960

The newer TVs have surge protection built into the plug. The older tv's could be given a partial protection by tying a couple of knots in the flat power cord. A crude but effective choke.

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