Protection Circuits (Home) - Page 1
Forum section: electronics / projects

author: GoatZero
author_rank: Regular Contributor
timestamp: November 03, 2013, 07:01:52 am
content: I know this is more like an electrical question however i must knowHaving fuses, circuit brakers and grounded earth, all correctly instaledIs it possible for any kind of sensitive electronic to still get fried?

author: tsmith35
author_rank: Frequent Contributor
timestamp: November 03, 2013, 07:22:18 am
content: The answer is YES. A friend had all of his home electronics on surge protectors or UPSes. Lightning struck the gutter on the corner of his house and fried all of his electronics: TVs, computers, stereo equipment, and so on. Fortunately, he had replacement cost insurance, so he actually got all new equipment (and the corner of his house repaired).Another way for electronics to get damaged is due to blackouts or brownouts. You wouldn't think a brownout or voltage sag could cause damage, but just Google forbrownout inrush currentand you'll find that they can be tremendously damaging.

author: GoatZero
author_rank: Regular Contributor
timestamp: November 03, 2013, 08:22:28 am
content: So lets assume i also have a lighting rod on the roof connected to my ground earth .... does that mean i would only have to worry about brownout inrush currents?And even if i put an UPS in every single thing in my house the UPS`s might still die to these brownouts?sorry, im about to read about these brownouts so i dont really know that to expect

author: JohnnyGringo
author_rank: Regular Contributor
timestamp: November 03, 2013, 09:57:22 am
content: Quote from: GoatZero on November 03, 2013, 08:22:28 amBad idea, they tend to attract lightening and would have to be HUGE to be useful and not attached to any structure.I've lost more stuff from brownouts than ever from lightening. Buying replacement insurance is your best protection.

author: tsmith35
author_rank: Frequent Contributor
timestamp: November 03, 2013, 12:12:26 pm
content: Quote from: GoatZero on November 03, 2013, 08:22:28 amHere's information from Georgia Tech about CVSS vs TVSS relating to brownouts:http://innovate.gatech.edu/entrepreneurs/innovolt-atdc/I can't find the original article about CVSS technology (might've been in a Power Electronics mag article), but it detailed how transient current inrush following a brownout can reach 5-10x the normal current for a device during a very short period of time. Since the voltage during a brownout doesn't fall below a level that would normally cause current-limiting circuits to be pulled in, the excess current can cause a tremendous amount of damage. Here's an article from EDN that may help you out:Circuit protection basics - Part 1: Issues and design solutions

author: DL8RI
author_rank: Regular Contributor
timestamp: November 03, 2013, 12:27:28 pm
content: QuoteThats not so easy. Lightning-Protection is not just the rod on your roof. Thats a whole lightning-protection-System to prevent pontential lift, backfiring and so on. Very complex and expensive.A company, Dehn&Söhne, has written a book about this topic which is of very high quality. Their US-Branch has a english version of the "Blitzplaner":http://www.dehn-usa.com/dehn-Lightning-Protection-Guide-pubcid4.htmlHave fun

author: Whuffo
author_rank: Regular Contributor
timestamp: November 03, 2013, 01:22:39 pm
content: I've seen lots of lightning damaged equipment; the most common is when lightning hits a power line somewhere in the vicinity; a big voltage surge is applied to all the lines simultaneously and when it gets to your house ("the target") the nominal voltage is correct - but it's also a few thousand volts above ground potential. This is hard on equipment - and if that equipment has a connection to ground through the phone lines, TV cable, water pipes, etc. then it's going to die a horrible death. Keep in mind that sparks will jump about 1 inch for each 40Kv; lightning strikes can be a couple of orders of magnitude more so just being sort of close to a ground is a bingo.Direct hits are fortunately rare - and also very devastating. The only protection against these is to be somewhere else when they happen. Close by hits can be protected against (mostly) with spark gaps at the meter base followed by big beefy MOVs in the breaker box - immediately following the main breakers. Those spark gaps and MOVs must be connected not just between the hot wires, but between any and all combinations of hot, neutral, and ground wires. And make sure you've got at least one ground rod sunk fully into the ground; three are better. Connect a nice HEAVY conductor between your earth ground and the breaker box ground.This will substantially reduce your exposure to lightning damaged equipment. If you want to be fully protected - buy full replacement value coverage insurance. Lightning is a force of nature that laughs at the puny humans; search for images of houses that took a direct hit and you'll see what I mean.PS: MOVs self sacrifice as they burn up the unwanted joules. When they've dissipated all the joules they can, they're no longer effective. One big zap or a bunch of tiny zaps will use one up. If the protection they offer is important to you, you'll need to replace them on a regular schedule.

author: GamerAndds
author_rank: Regular Contributor
timestamp: November 04, 2013, 04:33:51 am
content: So do mov's act quick enough to save from lightning? Could I put it on my main AC plug or on the breaker output to ground? Reason im asking is cause i ran one specific circuit to my home server and all my Home Theater equitment, including my amp i just made?

author: tsmith35
author_rank: Frequent Contributor
timestamp: November 04, 2013, 05:25:52 am
content: Quote from: GamerAndds on November 04, 2013, 04:33:51 amYes, though lightning may jump right past it due to the extremely high potential (it can jump the small gaps in typical home surge protectors easily or may simply vaporize MOVs in its path if the lightning hits nearby). This may help explain it:What is a Lightning Arrester? (PDF)Also, don't forget that lightning is very opportunistic: it will find and follow the path of least resistance (or multiple paths). For example, you may have a fully capable lightning protection system on your home power lines, but nothing on your cable TV coax and nothing on your phone line. Lightning can pass through the coax, through your cable modem, then on into the home via ethernet wiring. Or it may go through your phone line, jump across to power or ethernet wiring (often located in very close proximity) and continue on to your home electronics.If you have some time (61 pages worth), you might want to read this:How to Protect Your House and Its Contents from Lightning: IEEE Guide for Surge Protection of Equipment Connected to AC Power and Communication Circuits (PDF)

author: DL8RI
author_rank: Regular Contributor
timestamp: November 04, 2013, 07:25:54 am
content: Hi,if you're talking about your AV-System, most likely you will also have inductive coupling into your speaker-wires.A MOV is just one step Normaly you must have at least a two-step-protection: First a Spark-Gap/Gas-Discharge-Tube(*) (High-Voltages but slow), then a MOV (faster, but lower voltages) and for lower voltages a Zener diode. They have to be designed to handle the current until the next greater device "fires". The Zener will be first and has to handle the increasing-current until the isolated areas of the MOV have made connection and the MOV has to withstand the Current until the (stochastic) ignition of the Gap.(*) This are not just some wires, it's a dedicated part (filled with Gas) you can solder on your PCB. Maybe it has a proper english name, but I don't know it, sorry