AN EFFECTIVE AND ECONOMICAL WAY OF PROTECTING ELECTRONIC EQUIPMENT, INCLUDING COMPUTERS, MODEMS, FAX-MACHINES ETC, FROM STORM GENERATED LINE-BORNE STATIC HITS, BY PRE-EMPTIVE, AUTOMATIC DISCONNECTION, FROM EXTERNAL POWER AND TELEPHONE LINES.
AN EFFECTIVE AND ECONOMICAL WAY OF PROTECTING ELECTRONIC EQUIPMENT, INCLUDING COMPUTERS, MODEMS, FAX-MACHINES ETC, FROM STORM GENERATED LINE-BORNE STATIC HITS, BY PRE-EMPTIVE, AUTOMATIC DISCONNECTION, FROM EXTERNAL POWER AND TELEPHONE LINES.
PREFACE
For several years, I resided on the Mediterranean island of Majorca.
Majorca frequently suffers, in the latter part of the year, from sub-tropical storms, which can be very static-intensive Lightning and weather research.
Any electronic equipment which required connection to either the mains electricity supply and/or a telephone line(modems, fax's etc), were vulnerable to damage. The problem was compounded by the fact that in the rural area where I lived, the electricity and telephone networks were, with the odd exception,' over-head', both networks acting like a huge antenna to static, during a storm. Also, the local strata was solid-rock and a good 'earth' was very hard to find. The net result, therefore, was a situation, when, in the event of a storm, a lightning hit, even several miles away, on the electricity or telephone network, would send very high voltages coursing around these networks, causing untold damage to any connected electronic equipment. In the absence of a good 'earth', the static energy would be 'attracted' by any capacitance it could find. So, for example, if we take say, a television receiver, which is disconnected from the electricity supply, but has its antenna connected. It may be thought that the television would be safe in the event of a lightning-strike in the vicinity of the antenna, (i.e. the static has 'nowhere to go'), but this is not necessarily the case. The television by nature of its construction, i.e., its internal circuitry, the tube, even its case, combine to form a capacitor, which the static will attempt to 'charge', this surge of static can cause damage to sensitive components in the television set.
PROTECTION
Items such as spike suppressors etc, only provide very marginal protection in the event of a storm, due to the very high voltages encountered. The only certain way to protect equipment in the event, is to completely disconnect it from all external sources. This may not always be possible, i.e., one might not be 'at home' when the storm arrives, etc.There are, of course, commercially available products APC protection devices which can provide effective protection against all but the most severe static hits, but these items, if at all effective, tend to be very expensive, at least several times the cost of the average PC. Also, most of these units do not work by pre-emptive disconnection, i.e., they stay connected to the external lines, during a storm and any protection that they may provide to the installation would be normally at the expense of their own destruction!.
The 'home-made' unit described, will, in the event of a storm, disconnect automatically, the equipment from its external lines, monitor the lines for harmful static while disconnected), then, reconnect the equipment, again automatically, after the storm has past.
While living in Majorca, I noted, that, on the approach of a storm, as the static levels were building up, P.I.R.(passive infra-red) automatic security light installations in the neighborhood, were being triggered, this gave me the original idea for the unit. I needed a proprietary item which could be easily modified for my purpose, i.e., would detect static before it reached harmful levels, be readily available, be-able to trigger relays, have a 'timing' facility, be cheap(around £10).The P.I.R. detector had it all!.
THE UNIT
The following, is a description and circuit diagram of a unit suitable for the protection of a typical computer/modem installation. Of course the basic concept can be modified to protect any number of eventualities, even a whole premises!, by using it to trigger the differential breaker [RCD] on the main fuse-panel, of course, this would have to be manually reset, after the storm has past).
The standard proprietary P.I.R. detector consists of an infra-red sensor, a high-gain amplifier, with a gain control(marked 'sensitivity', or 'range'), an adjustable timer(usually adjustable between approximately 1-45mins) and a photo-electric-cell which is used to inhibit the detector during day-light hours. Basically, the unit is modified, to be able to monitor static-noise on the incoming lines. If the noise reaches certain pre-set levels, the unit will trigger, releasing relays to disconnect the lines, for a pre-set period(say 5mins).Then,to continue to monitor the lines, during this period, resetting the timer continually for further periods, if more noise of a dangerous level is detected. After a period(5mins in this example), that no further noise of a dangerous level has been detected, to reset, thus re-operating relays to automatically reconnect the lines.
ITEMS REQUIRED(Including possible U.K. stockist). (N.B. The component list is for the construction of a unit suitable for 240volt u.k. use, but the unit can be adapted for any supply voltage, by adjusting the p.u., relay and v.d.r. working voltages. The v.d.r. trigger value should be chosen, to be about 5-10% above the normal local supply voltage ).
The above shows the basic circuit diagram of the unit and the following is a description of its construction.
Remove the P.C.B. from the P.I.R. detector case, retaining the cables connected to the P.C.B.(usually 3, :-live, negative and switched-live output). The only modifications required, will be to 'blank' the infra-red sensor window(usually a round component, approx 1cm in diameter with a small 'window', approx 2mm square), by gluing to it, the head of a standard drawing-pin(the 'upright-pin' forming a convenient 'bobbin', for use later). Also, to inhibit the photo-electric-cell(usually a small clear-glass component about 2mm in diameter), by covering it with black insulating tape etc. Glue the various items into the plastic case, the lay-out is not critical. The static-noise-coupling, is accomplished by taking four pieces of the fine insulated wire, wrapping it about six or so times around each incoming 'leg' of the power and telephone lines and then once around the pin(of the drawing-pin) then finally to earth. This would appear somewhat 'crude', but it works and avoids modification[i.e.,., 'hard wiring'] to the P.C.B..Note, the only point that the insulation is removed from the wires is at the point where they are connected to earth. A bead of glue is then added to the 'pin' to prevent the four loops of wire from coming-adrift. The V.D.R.s should be connected at a point, where the incoming lines(telephone/mains) first enter the case. It is their job to 'fire-off', any incoming high-voltage 'hits', to either earth, or, back out on the other lines(hopefully!).It will be noted that I have not included any fuses on the unit. Fuses of say 5amp rating could be included in each line if so desired(In the event of a power failure, the unit releases to its 'dis-connect state').
TESTING AND CALIBRATING THE UNIT
Before powering-up the unit, set the sensitivity control(formally range-control) to maximum and the timer control to just above minimum. The day/night control can be set anywhere(it is now ineffectual). Power-up the unit. On initial power-up, you will notice that the unit goes into 'trigger' condition, it will reset, after the time set on the timer control has expired. You will now require a source of static-noise to test the unit. A piezoelectric igniter is an ideal source, either a piezoelectric cigarette lighter, or better still a piezoelectric gas-oven lighter. Take the telephone-line input cord and wrap it several times around the end of the gas-oven lighter(in close proximity to the spark point), operate the igniter, the unit should 'trigger' immediately. In the 'triggered' condition, any subsequent operations of the igniter will reset the unit timer to the beginning of the start period.(With the sensitivity of the unit set to maximum, its possible that the unit will 'trigger' to other nearby sources of 'normal' static-noise[A.C. units, refrigerators etc], so the trick is to continue to decrease the sensitivity, until the unit no longer "triggers" to normal local static-noise sources,[a good extra margin should be allowed to prevent false triggering]).Once satisfied with the sensitivity setting, the timer should be set for between 10-15 minutes, this should ensure the storm has past to a safe distance, before the unit re-connects your equipment.
CONCLUSIONS
For the periods when the unit was in place, no loss of equipment to lightning damage was experienced(not so for my immediate neighbours!).To an electronics engineer the units adaptation will appear 'crude', but it works!, its cheap(around £30 in total), has readily available parts, is very fast-build, even for a person with no experience in electronics. Also, to my knowledge, there is nothing available commercially, which gives the 'automatic dis-connect, re-connect' feature and is in the price-range of the average private PC user. The unit, of course, could be simplified, using the detector only, to provide a storm-warning receiver, or more sophisticated, to provide a prior shut-down-before-disconnection condition to the computer, in the event of it being switched-on, at the time(this would require an additional 'timer').
OPINIONS
It was interesting, the reaction, when, the news of this unit was received by certain 'friends', one owned a computer store, who always made 'bumper sales', after a storm?, the other, who had suffered several PC 'fatalities', always received a new PC, courtesy of his 'new-for-old' insurance policy??........Still, I think there may be a few of us out there, who may not be in a position to enjoy such 'fortunes'!. I hope this 'idea' has been useful to you.
TELL ME
If you have any problems obtaining components or constructing the unit, please contact me and I will do my best to help you. Also, if you have any good ideas, especially any involving the adaptation of existing equipment for other purposes, I would be pleased to here from you(Much of the time, its a lot easier to adapt existing gear, than to start from scratch, quicker and cheaper too!).
If you do not feel inclined to construct the unit yourself, then it might be possible for me to construct one for you, for a modest fee. However, if this is the case, please give me plenty of notice, as I have other commitments.
Email me.(jeff@jeffreycsmith.flyer.co.uk).
Last updated ,11.8.00,1553 hrs.