CC.Otken@UTEXAS-20.ARPA@sri-unix.UUCP (08/03/83)
From: John Otken <CC.Otken@UTEXAS-20.ARPA> Has anyone had any experience with lightning protectors for computers/ terminals/modems? -------
Seiler@mit-xx@sri-unix.UUCP (08/04/83)
From: Larry Seiler <Seiler@mit-xx> DEC sells a lightning protector that you can plug your terminal or PC into. Look in the DECdirect catalog - the price is $134. They also sell voltage conditioners (starting at $500) that take garbage and convert it into the right frequency and voltage. I own one of the lightning protectors. My terminal used to flash occasionally (overvoltage?) but now it doesn't. My dad (who is an electrical engineer) owns one of the voltage conditioners and thinks that the price is awfully low for how good it is (mostly his job involves designing power stations). Larry -------
dya@unc-c.UUCP (08/06/83)
References: sri-arpa.3798
Full-Name: David Anthony
Location: The University of North Carolina at Charlotte
Lightning surges really come in two varieties. The first is almost
invariably destructive; if your home mains should suffer a truly direct
hit, there isn't much one can do except call the insurance company.
Fortunately, this is not the usual case. The best el-cheapo way
to deal with this probelm is use of a GE-MOV **WIRED AT THE POINT OF
ENTRY INTO THE WALL OUTLET** or similar device. What a GE-MOV does is
essentially the equivalent of two back-to-back zener diodes, so when
the voltage rises above ~ 160 volts (on 117 v mains), the voltage is
effectively clamped.
On my sensitive equipment (i.e. Accuphase amplifier, tuner,
and various computing devices) I have acquired a 3000 kv-a Sola constant
voltage transformer. It seems that the biasing circuits in my amplifier
didn't like all those air conditoners starting in my apartment complex. (i.e. Pouf ! and $ 45 of outputs gone). It also
saves my computing equipment from errors of the same kind.
Telephone circuitry is usually very well protected, with all
kinds and manner of gas arrestors, etc.
The Sola transformer is a bit extreme, but you might find one
surplus somewhere for $ 100 or so. Be sure to get the sinewave kind,
the square wave outputs are for driving rectifier stuff only (either
directly or through another transformer).
Most surges from lightning can be controlled, and I highly reccomend
the GE-MOV first. We have had them in service on several satellite receivers
connected to a dish which scores many near- and direct-hits for some reason.
No lightning damage to date.
GE-MOV is a trademark of the General Electric Company
> From the Home of the Video Wizards
unc-c!dyaciaraldi@Rochester.ARPA@sri-unix.UUCP (08/06/83)
From: Mike Ciaraldi <ciaraldi@Rochester.ARPA> I have an Isobar 8-outlet power strip (about $65 from Priority 1) which provides 4 filter banks and some overvoltage protection. Since putting it on a year or so ago, my system has been more stable. I doesn't flinch when tthe furnace comes on and the voltage dips and spikes appear. I don't know how well it would stand up to lightning, though.
hsplab@tucc.UUCP (08/07/83)
David Anthony's remarks about GE MOVs do deserve some caution. We have been having some problems with high voltage transients produced during the testing of emergency power generators in the hospital (NC Memorial Hospital/Univ of NC-Chapel Hill). The GE MOVs which I put into several of these terminals failed to provide any protection. Upon inquiry with several engineers, it was concluded that the MOVs are relatively slow. In order for them to be effective in removing short duration spikes (or all of longer duration spikes), it is necessary to have a series resistor (low ohmage), parallel capacitor network to swamp out the spikes until the MOV has time to react. This is because of the varistor action of the device itself. A similar solid state device made by Panasonic call Transorbs are considerably faster. In our case, the Trans- orbs were effective without any additional swamping circuit. They are some- what more expensive, however. Finally, some of the noise reduction filters, such as the Corcom, can be extremely effective in reducing line spikes of short duration. To my chagrin, the protection of computer systems from line transients is not as trivial as I had initially imagined. Although many manufacturers are in- stalling Corcom type filters into computer devices (mostly for FCC certifi- cation and/or DIN approval for sales to Europe), I have seen almost no MOVs in computer equipment. Although this may be due to costs, I am also beginning to suspect that the overall benefits of the MOV are somewhat marginal. A direct lightning strike will destroy everything anyway, and the amount of protection provided by most devices may be not be useful except in cases such as ours where the equipment is subjected to repeated and regular high voltage spikes. David Chou Univ of North Carolina, Chapel Hill
Fbrown%Micom%udel-relay@sri-unix.UUCP (08/08/83)
If you have access to back issues of Radio-Electronics, you might want to check out the Summer 1982 Special Projects issue. On page 21 is a description and set of plans for a "Surge Stopper" which consists of a GE-MOV Varistor, a neon lamp, a fuseholder, a metal box and an outlet strip. I ordered the Varistor, it cost ~$5.50 and took a week to arrive. Haven't got it put together yet, will be a couple of weeks before I get around to it. It appears to be simple enough that anyone could build it. Frank Brown <fbrown.micom@udel-relay>