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View Full Version : VFD's and surge protection



QSIMDO
08-16-2007, 05:50 PM
We got thwacked with a bit of lightning recently and the results has me thinking of installing a "whole house" surge protector (cheap from our utility company) but I thought I should ask first if VFD's have any problem with devices like that?

BadDog
08-16-2007, 07:01 PM
Seems to be a lot of that going on lately, just that time of year I guess.

We had some bad storms here in Phoenix and I also go "thwacked" for the first time in MANY years. My professional computer (and supporting systems) are on a nice UPS with decoupled power supply. Other systems are on mid/low range surge suppressor systems. But we got (what seemed to me to be) a major strike right behind my shop. Even with dedicated suppressors, my 2 remaining CRT (not flat panel) CRTs (son and daughter's machines) had to be degaussed, lost a router that was plugged into my main UPS, lost a NIC in my daughters machine, and my son lost his switching box (multiple game systems, audio, DVD, VHS, etc.). All of these were plugged into "Woods Wireworks" suppressors (a few years back when bought, consistently ranked among the better consumer grade suppressors) or better. No suppressor "popped", but one breaker was thrown for the circuit our main entertainment center is on.

BUT, my VFD and mill DRO in the shop less than 20 feet from the strike seem to have escaped unharmed. Though the DRO did act a little flaky at first, it settled down and seems ok now. And neither of them are on ANY type of surge suppressor.

Very weird all around and I can't explain any of it.

J Tiers
08-16-2007, 08:50 PM
The "whole house" surge protector sounds like a good idea.

BUT, I very much doubt that it really is a cure-all.

I have seen equipment zapped quite thoroughly despite the existence of a GOOD surge protector. There are bad ones, that essentially do nothing, and I do NOT mean those.

My suggestion is that you UNPLUG sensitive equipment during storms.

If that sounds impractical and unworkable, well, too bad........ I will offer my condolences on your lost files and fried drive, but I will still say "I told you so".

Now, I fully expect lots of "I never do that and I never had a problem" replies. I'm Ok with that too. One day it will happen to those folks too, and I don't expect them (macho folks) to 'fess up about it.

I just finished setting up my in-law's computer. it worked fine for a week. Then they IGNORED my advice to unplug......

Yep, two weeks into having the new computer, there was a storm, and it got zapped.

So if you think it is a bunch of bull, dream on, or accept the risk.

tattoomike68
08-16-2007, 09:12 PM
My suggestion is that you UNPLUG sensitive equipment during storms.




Phone lines are bad news too , not just power lines.

J Tiers
08-16-2007, 11:57 PM
The intent was unplug from everything.... But that is an EXCELLENT reminder for folks.

The phone line is probably what zapped the in-law's computer.

Just as a point of information, they live across the road from a pretty good-sized cornfield, at least a quarter mile across, probably more. An old locust tree is the first thing sticking up as you come from the field, and it is near the phone and electric wires.

When the tree was struck, the phone line probably got a zap, and the zap went through the DSL modem and into the computer through the ethernet port.

Of course if the tree were not there, the lines, or the house might have got it. I did suggest they not cut down the tree, or if they did, to put up a BIG flagpole.....

nheng
08-17-2007, 12:17 AM
Often lax at this end when it comes to unplugging but JT is correct. Only unplugging will give you near 100% protection. Equipment switched off or on switched off surge strip will not take a heavy hit.

Use a cordless phone, stay off the sh-tter and avoid showers, baths, etc. during heavy lightning ... it can and has found all of those. Open windows are also an attraction when conditions are right.

C - ROSS
08-17-2007, 02:26 AM
The only way to be 100% sure is to unplug everything.

Old wives tale.-- Tie a knot in every power cord. The only things that I have lost to elec surge did not have any knots. Some in the same room and on the same circuit as more sensitive equipment. Does it work, who knows, do I do it yes.

Ross

BadDog
08-17-2007, 02:45 AM
My power cords (and Cat-5, etc.) tie themselves in knots. Didn't seem to help this week. :D

lynnl
08-17-2007, 02:17 PM
I gotta agree with Ross. I had never had any lightening surge damage to any devices until moving here some 17 years ago. Since then I've probably suffered 10 or 12 damaged TV's, modems, phone answering machines, computer devices, etc..
And every single instance could be traced to a knotless power or phone cord!

...plus, an added benefit of knotting the power cord is reduced power consumption.

tattoomike68
08-17-2007, 02:41 PM
Knotting the power cord Sounds like a job for Mythbusters.

New chips
08-18-2007, 03:29 AM
I do a lot of work on communications equipment on towers. The basic theary on Lightning is as follows. When Lightning hits it follow all conductor paths to ground but the speed that it travels veries on the conductors. Steel ,copper conduct the strick energy faster than the earth. The stick energy for example hitting a tower goes fast down the tower and into the earth and then slows down. At the same time the energy moves along the cable into the building and out the elecrical ground at a fast speed and then slows down in the earth. This sets up a wave action simular to droping two stones into a pond at diferent spots and time. Depending on the propigation speads and distances you can have worst case double the potential energy at your equipment groung. So the best thing is to tie every thing together. Your electrical ground ,phone line ground, building bround , tower or tallest structure , lightning rods. What then happens is the energy is evenly distributed and your ground acts like a capacitor bilds up a charge and disipates it. Had one tower with this setup take a direct hit. The antenna disapered and the line down the tower was blown open every three foot but computer and phone equipment
just had fuses blown. equipment worked good for year after. As to unpluging is best but unplug every connection not jest power. We carry a AC suppeser that garenties $10,000 max on equipment pluged into it.
Costs about $100.00 for duplex outlet unit, thay allso make phone and mane braker box equipment.

J Tiers
08-18-2007, 11:41 AM
IF you have a lightning rod system, electrical code requires that it be bonded to the electrical grounding system. In fact ANY available conducting objects are supposed to be bonded to the lightning rod system.

That is pretty standard.

Not sure that the "speed of travel" theory is quite right, BUT there can be very large differences of potential along ANY conductor which is carrying strike current. A peak current of 100,000 amps can produce a voltage of 100,000 volts with just 1 ohm resistance (actually impedance, in this case, as lightning is high frequency pulsed current).

Considering that the low voltage measured resistance of a ground rod may be as high as 25 ohms and still be considered "OK" by the electrical code, you can easily see that the ground rod might be at a rather high voltage relative to nearby earth. A few feet up the rod conductor adds more voltage...... That is despite the possibility that the impedance of the earth at high voltage may not be the same as that at low voltage.

Net result is that during the strike, the electrical system might easily be a half million volts or so below the voltage on the rod conductor. Not good, might draw a side arc.

Bonding reduces the chances of that, but does of course not 100% eliminate them.

And, any sharp turns of the rod conductor may produce a local impedance sufficient to have a large voltage drop and potentially produce side arcs.

If I were designing a rod system, I would be tempted to use sheet conductor and not wires. That would have very substantially less inductance, and as a result would be a better conductor of the HF pulse current. Parallel wires spread out in a line would also be better.

ckelloug
08-18-2007, 06:58 PM
Whole house surge suppressors are a nice first line of defense especially for devices without their own protectors but from what I've read, the Metal Oxide Varistors in them are typically set to a relatively high voltage such that they'll keep the spike down to less than a few 100 volts above the line but won't necessarily keep the spikes small enough to prevent damage to the most sensitive equipment. MOV's are an electronic component that behaves as an open circuit below a set voltage but they are subject to burnout if they take a big surge. MOV's work by shunting the big surge to ground.

Lightning struck my neighbor's tree some weeks ago and that's when I wished I had replaced the whole house surge suppressor that had a bad MOV on one of the 120 V channels. Note to self replace surge protector before the lightning strike as after only saves you for the next one. I lost one port of a 24 port ethernet switch that for some dumb reason wasn't plugged into the UPS. . . The VFD for my Bridgy was safe due to its position in a cardboard box far away from electricity on the floow of the kitchen. . .

For the most sensitive equipment, there is a company called brick wall that uses diodes and inductors to clamp surges at only a few volts above line voltage. These brick walls claim to be certified to the highest UL rating for surge protectors. On their web site over at http://www.brickwall.com they have ocilliscope traces on their site to back up their claims. The huge inductors also mean that brick walls block line noise. The only downside is that they aren't cheap. I've got one on my stereo.

--Cameron