bam@PRC.Unisys.COM (Brian A. McCreadie) (09/27/89)
Does there exist a method of protecting emp sensitive components from lightning, short of putting them in a Faraday cage and unplugging them? I have an Adcom pre-amp that has twice been killed by a nearby lightning strike. It uses IC's to select between sources rather than mechanical switches. It turns out that these IC's are super sensitive. The mains power cable for the unit is a two-prong polarized plug. It has a ground for the phono input and also one for the AM antenae. The first time it got nailed, the pulse also took out the surge protector. I discovered (too late) that surge protectors can only deal with the first 200-300 volts of a spike. I didn't bother buying another one. The local TV cable enters my house close to the power for the preamp. Is it possible that the cable picks up the pulse from a nearby strike and since the preamp isn't grounded, has no place else to go once it is in the preamp? Could I rig up something with BIG caps to absorb the energy before it does damage (assuming BIG caps are cheaper than preamps) Thanks in advance.
dag@hp-lsd.COS.HP.COM (David Geiser) (09/28/89)
In hp-lsd:sci.electronics, bam@PRC.Unisys.COM writes:
b>
b>The first time it got nailed, the pulse also took out the surge
b>protector. I discovered (too late) that surge protectors can only
b>deal with the first 200-300 volts of a spike. I didn't bother
b>buying another one.
Cheap ones, yes. I've seen used better ones.
b>Could I rig up something with BIG caps to absorb the energy
b>before it does damage (assuming BIG caps are cheaper than preamps)
I would guess you're talking about using a cap to filter HF noise
on the power line to ground?
Use small caps. Ten in parallel are more effective than
one ten times as big.
You might consider a ferro-resonant power conditioner such as is
sold for computer equipment.
dag
"You pay for what you get.
Sometimes, you get what you pay for."lkraft@hpccc.HP.COM (Lyle Kraft) (09/28/89)
On a related note, does anyone know what to do about ungrounded wood stoves? You know, the kind that sit exposed in a room on top of some kind of bricked-in area. I conducted an experiment during a recent thunderstorm and found that a nearby lightning strike would cause a pretty hefty arc to a ground wire held near it. Doesn't seem very safe for a fixture that features a few feet of stovepipe sticking above the roof. Specifically, are there any building codes regarding the grounding (or ungrounding) of woodstoves, fireplace inserts, etc.?
morris@jade.jpl.nasa.gov (Mike Morris) (09/29/89)
(David Geiser) writes: >In hp-lsd:sci.electronics, bam@PRC.Unisys.COM writes: >b> >b>The first time it got nailed, the pulse also took out the surge >b>protector. I discovered (too late) that surge protectors can only >b>deal with the first 200-300 volts of a spike. I didn't bother >b>buying another one. > > Cheap ones, yes. I've seen used better ones. Read Jerry Pournelle's column in the August Byte, somewhere around page 100. Some clown hit the power pole that feeds his house and dropped a 16kv feeder into one side of the 220... "Incandescent light bulbs exploded"... Anyway, due to his experience, I compared the guts of a Tripp-Lite Isobar, and the common "surge supressed" outlet strip. There are several heavy-duty toroidal chokes and capacitors in an Isobar, vs 3 metal-oxide-varistors in the cheapies. in fact, I recently found a bunch of 140v MOVs in surplus and added them to the standard strips I already had. The Isobar is also built with good components, and put together like the proverbial tank - no snap-together plastic here - it's all metal and screws. Due to the above, I've bought 3 of the 8-outlet Isobar units for my computer room (IMSAI, DG Nova 4, PClone, Kaypro, LAN Server, four printers, three terminals, two modems, speakerphone, 12v power supply for the ham radio and packet unit, etc. I have an additional two cheap strips (with the added MOVs) plugged into the Isobars - one switches the IMSAI and it's drives on and off, the other handles the DG Nova 4 and it's peripherals. The PClone, modem and two printers are plugged into a Computer Associates Power Director/surge supressor, and the modem line is too - I've got the model with the supressors for the phone line. The CA Director is the first one I purchased, more for the switching than for the supression. One switch is very stiff, so I use it for the external hard drive box, so it gets left on, but I now try 'em before I buy 'em. If I could find the paralell printer spooler for the CA Director at a good price... Another 8-outet Isobar is going on the TV/stereo system RSN. I don't need an exploding TV, or VCRs, or ... One gentleman I know has a CA Director on his stereo system - the switches make it very nice... Mike Morris UUCP: Morris@Jade.JPL.NASA.gov ICBM: 34.12 N, 118.02 W #Include quote.cute.standard PSTN: 818-447-7052 #Include disclaimer.standard cat flames.all > /dev/null
kencr@haddock.ima.isc.com (Kenny Crudup) (09/29/89)
In article <1827@jato.Jpl.Nasa.Gov> morris@jade.Jpl.Nasa.Gov (Mike Morris) says: >Anyway, due to his experience, I compared the guts of a Tripp-Lite Isobar, >and the common "surge supressed" outlet strip. There are several heavy-duty >toroidal chokes and capacitors in an Isobar, vs 3 metal-oxide-varistors in the >cheapies. What are "Heavy duty toroidal chokes and caps" are going to do for you extra when given a large power hit? Tell me.... They may supress some mediocre spikes better than an all MOV approach, but when the shit hits the fan.... >The Isobar is also built with good components, and put together like >the proverbial tank - no snap-together plastic here - it's all metal and >screws. And....? -- Kenneth R. Crudup, Contractor, Interactive Systems Co.(386/ix), Cambridge MA Don't worry- I haven't lost my mind....its backed up on tape *somewhere*.... Phone (617) 661 7474 x238 {encore, harvard, spdcc, think}!ima!haddock!kencr kencr@ima.ima.isc.com
bam@PRC.Unisys.COM (Brian A. McCreadie) (09/30/89)
In article <7600025@hp-lsd.COS.HP.COM>, dag@hp-lsd.COS.HP.COM (David Geiser) writes: > I would guess you're talking about using a cap to filter HF noise > on the power line to ground? > Use small caps. Ten in parallel are more effective than > one ten times as big. Could you describe how that works? I am not sure that I understand. Do you mean: - pre-amp - | | | | | | | | | -----|(-------- | | | | -----|(-------- | | | | -----|(-------- | | | | -----|(-------- | | | | -----|(-------- | | | | -----|(-------- | | | | | | | | | Neutral Hot Ground
BHB3@PSUVM.BITNET (09/30/89)
I can vouch for the Isobar also. I was determined to be the best protector in a survey by the electrical people at the Ford Motor Research complex(note I am a Penn State student working at FOrd for a year)
phil@ingr.com (Phil Johnson) (09/30/89)
In article <1827@jato.Jpl.Nasa.Gov> morris@jade.Jpl.Nasa.Gov (Mike Morris) writes: > >Anyway, due to his experience, I compared the guts of a Tripp-Lite Isobar, >and the common "surge supressed" outlet strip. There are several heavy-duty >toroidal chokes and capacitors in an Isobar, vs 3 metal-oxide-varistors in the >cheapies. in fact, I recently found a bunch of 140v MOVs in surplus and added >them to the standard strips I already had. The Isobar is also built with >good components, and put together like the proverbial tank - no snap-together >plastic here - it's all metal and screws. > These surge supressors are intended for "surges" and will not provide the type of protection needed in "near" thunderstorms. The best protection from induced high voltage is the liberal use of gas-discharge supressors. The gas- discharge supressor consists of a gas-filled glass tube with a ground, anode, and a cathode. These three leads are connected across the source, virtual ground and real ground as shown below: ........ .............. ........ | | | | | | |120vac|------------|--- ---|-----------|120vac| | main | Cathode | | | Anode |Return| |......| (anode) |......|.....| (cathode) |......| | | | Ground ---- / / / The connection order, other than ground, does not matter. When a high voltage spike is induced on the your power grid so that the potential between the Cathode and Anode reaches the rated trigger potential of the device the gas ionizes and shorts the spike to real ground. The device dumps the voltage surge extremely fast. Be sure that you have provided an adequate ground path. I worked for a SCADA company in New Orleans and had a system with environmental sensors mounted on top of a 280 feet stack. During the storm season (July-Oct) the stack averaged two to three direct hits a month. The only device I found that prevented the data input cards from getting fried was the gas-discharge supressor. You should be able to find them in any electronics or electrical supply house that services the tele- phone industry. NOTE: We used a 3 inch diameter, 10 feet long, solid copper rod as our real ground for a number of gas-discharge tubes. -- Philip E. Johnson UUCP: usenet!ingr!b3!sys_7a!phil MY words, VOICE: (205) 772-2497 MY opinion!
davidc@vlsisj.VLSI.COM (David Chapman) (10/03/89)
In article <1827@jato.Jpl.Nasa.Gov> morris@jade.Jpl.Nasa.Gov (Mike Morris) writes: >Anyway, due to his experience, I compared the guts of a Tripp-Lite Isobar, >and the common "surge supressed" outlet strip. There are several heavy-duty >toroidal chokes and capacitors in an Isobar, vs 3 metal-oxide-varistors in the >cheapies. in fact, I recently found a bunch of 140v MOVs in surplus and added >them to the standard strips I already had. The Isobar is also built with >good components, and put together like the proverbial tank - no snap-together >plastic here - it's all metal and screws. The chokes and capacitors are for filtering, not for surge protection. They keep RF energy from getting in through the power lines. Neither one would dissipate much of the energy of the lightning strike (in fact, they would store it for later delivery :-). They might help if the strike were far away and all you got was a very short and sharp spike, but then again so would the MOVs. If you don't have MOVs in your outlet strips, you'd better have insurance. Ditto for a surge suppressor on the incoming phone line. And back up your data regardless... -- David Chapman {known world}!decwrl!vlsisj!fndry!davidc vlsisj!fndry!davidc@decwrl.dec.com
nagle@well.UUCP (John Nagle) (10/08/89)
For reference, where does one get serious lightning protection devices
today? Certainly they exist for antenna protection, but they don't seem
to be widely available for other purposes.
What you really need is as follows.
The first stage is a spark gap to ground, with large wire to ground,
perhaps 000 gauge. This is followed by a inductor composed of a few turns
of about .25 inch copper busbar. The whole unit is enclosed in a grounded
can. Heathkit used to sell such a device for antenna protection. The
device because a lightning stroke is a sharp enough rise that the inductor
blocks it, and the voltage arcs across the spark gap, ionizing the air
and providing a low-resistance path to ground until the charge dissipates.
Properly constructed units of this type can survive multiple lightning
strokes and cut the output voltage to about 400V.
Lightning arrestors aren't fundamentally expensive, but they tend
to be on the large side if they are any good, with heavy wiring and big
insulators. Properly, there should be one on every wire that goes into
a building, and in isolated structures in thunderstorm country, there
had better be. You don't need one on every outlet strip; you want to stop
the energy pulse before it gets into the interior wiring.
A second stage, useful in stopping inductive surges due to lightning
strikes near, but not on, wires, is a neon glow lamp to ground. With the
firing voltage of the lamp appropriately chosen, the unit will consume no
power until a big spike comes along.
With one of these on the front to divert the energy of the lightning
bolt, MOV-type devices can do their job properly.
John Nagle
John Nagle