[TowerTalk] Rotator Lightning Protection

ve4xt at mymts.net ve4xt at mymts.net
Sun May 17 17:39:44 EDT 2015


I guess the moral is, if you think disconnection is a guarantee, you're wrong. Unless you can anticipate every path and diligently disconnect everything every time. Of course, you can't ignore the potential for airborne paths inside the home, either. If it jumped thousands of feet through the air, it will have no objection to jumping from your disconnected coax or CAT5.

Of course, easier said than done if you're in Jacksonville and your station isn't. 

How much you spend is a function of risk vs. need: if you can't guarantee access to the station, need it to be operational despite weather or just have a large enough budget it doesn't matter, then read up on, say, N3RR and his protection scheme. 

For most of us, there's insurance and whatever minimum standard you need to satisfy the adjuster of reasonable steps to mitigate damage. 

73, Kelly
ve4xt 

Sent from my iPad

> On May 17, 2015, at 10:56 AM, "Roger (K8RI) on TT" <K8RI-on-TowerTalk at tm.net> wrote:
> 
> If you are going to disconnect, disconnect everything.  Remember that 1000 volts per meter of wire from a lightening strike a mile away and there are how many meters of wire in the house?
> 
> In my case I had the stations disconnected from the computers, but I failed to disconnect the computer network and it sure made an expensive and time consuming mess in the network and computers. The CAT-5 went through protection at each computer's UPS, but it welded the contacts  together in one and melted the plastic RG-45 plug and socket together. It also took out 3 of 4 NICs. and one motherboard.  The only things left were the 850 W PS, the video card and the hard drives. It also wiped out the 8 port smart switch and a 4 port router which also had dual channel wireless. Fortunately my wife's computer is wireless as is the printer.
> 
> The UPSs are under warranty, but weigh around 40# each.  So there's the cost of shipping both ways, plus the down time.  I'll probably just purchase the stock parts and DIY.
> 
> Had this computer and the one in the shop been hooked into the rigs using  HRD it could have been much more expensive.  I now have two servers in the den so I can leave the two computers in the shop, off line "most of the time" although I'm working toward remote control of both stations.
> 
> I have a 30 A 120 VAC line conditioner that I have to hurry and run a new circuit for.  then the computers and rigs in the den will be on a regulate 120 VAC that is a clean sine wave.  That does not include the amps that run on 240 VAC.  In the early days computers ran on line conditioners, but the expense brought about simple UPSs.  Like many things we become accustomed to, UPSs are now thought of as normal and line conditioners a gimmick, but in many areas with wide variations in line voltage, the line conditioners with a clean, regulated 120 VAC is good protection and a good investment even if a bit pricey compared to a UPS.  If you can find one.
> 
> 73
> 
> Roger (K8RI)
> 
>> On 5/17/2015 9:03 AM, Bry Carling AF4K wrote:
>> I guess the moral of this story is don't connect your phone line to your amplifier?
>> 
>>>> On 16 May 2015 at 17:26, Chuck Dietz wrote:
>>> 
>>> I used to pull all plugs and disconnect all antennas but had a problem because I left the
>>> equipment grounded and strike came over phone line through an amplifier to ground. Now I have
>>> an equipment ground disconnect too.
>>> Chuck W5PR
>>> 
>>> On Saturday, May 16, 2015, Bry Carling <bcarling at cfl.rr.com> wrote:
>>>     My solution is to pull all AC plugs from the wall and disconnect all antennas whenever a
>>>     storm is coming. That pretty much takes care of most problems.
>>>          My ground system is going to be improved from the current setup but I'm not going to the
>>>     kinds of extremes that some people have, and assuming that will be a perfect system of
>>>     protection.
>>>          Best regards - Brian Carling
>>>     AF4K Crystals Co.
>>>     117 Sterling Pine St.
>>>     Sanford, FL 32773
>>>          Tel: +USA 321-262-5471
>>>                         > On May 15, 2015, at 9:11 PM, Roger (K8RI) on TT <K8RI-on-TowerTalk at tm.net> wrote:
>>>     >
>>>     > Having worked with literally thousands of MOV,s from little ones up to 50,000 Joul ratings,
>>>     They will typically fail shorted, BUT I have seen many fail open.  It depends on the power
>>>     contained in the "final spike" that causes them to fail.  From power line spikes and nearby
>>>     lightening strikes the ODDS ARE it/they will fail shorted.  If enough power/energy is
>>>     contained in that final spike at failure time, it becomes likely they will fail open and  that
>>>     anything on that line will fail as well.
>>>     >
>>>     > Based on experience, you can expect the MOV to fail shorted and it will PROBABLY
>>>     protect any electronic device connected to it. That being the case, the prop pitch motor will
>>>     PROBABLY need some sort of "fail safe" to prevent over rotation.
>>>     >
>>>     > That's a lot of probables, but it's unfortunately a fact of life, leaving you playing the odds
>>>     which favor the MOV failing shorted, but with no guarantee it will do so.   If the MOV works
>>>     as we all hope, then you will need some sort of "fail safe"
>>>     >
>>>     > Since the big ground system was installed my tower has been hit at least 7 times that can
>>>     be verified with nothing disconnected and NO MOVs in the rotator lines.  No damage was
>>>     seen.
>>>     >
>>>     > I can not say the same for my computers and network.  A nearby strike did nothing to
>>>     either station, but it sure cost me a lot in network and computer damage.  The CAT-5 lines
>>>     go through protection at the UPS for each computer.  The connectors were melted and the
>>>     wire contacts welded together at one UPS.  The router, 8 port switch and most NICs were
>>>     shot!
>>>     >
>>>     > So, lightening and MOVs are a crap shoot.  They will protect you from the smaller stuff,
>>>     but cause other problems. They are unlikely to protect you from the larger stuff.
>>>     >
>>>     > In the end, I'd use them, plan on the MOVs failed as a short, and hope for the best  There
>>>     is no guarantee, but you have tilted the odds in your favor..
>>>     >
>>>     > 73
>>>     >
>>>     > Roger  (K8RI)
>>>     >
>>>     > .
>>>     >> On 5/15/2015 10:38 AM, Paul Christensen wrote:
>>>     >> N4CC and I have finally completed our remote Internet station in Hilliard, FL.  Probably
>>>     half our time spent before and during construction was studying and implementing lightning
>>>     abatement.  Ground rings were created around each tower, and the communications
>>>     shelter.  All grounds, including the adjacent electrical service ground are brought together at
>>>     an external ground bus (EGB).  In total, 55+ ground rods are used with four rods each 24 ft.
>>>     Lines are bonded at the top and bottom of the towers.  We do not disconnect anything.
>>>     Everything stays up and running 24/7 regardless of the WX.
>>>     >>
>>>     >> Poyphaser rotator MOV protection devices are installed at the base of each tower.  At
>>>     the EGB, we're using an Array Solutions model. In looking at all the failure modes, I missed
>>>     one:  If the MOV on the rotator return lead was to short to ground, it creates a disastrous
>>>     situation where the prop pitch will turn freely beyond the electrical stop point.  The MOSFET
>>>     is controlled by a PWM circuit and the duty-cycle is what varies motor speed.  A shorted
>>>     MOV will cause the lines to break apart up the tower at the coax loop.  The prop pitch would
>>>     stop at nothing and keep turning.  Do the MOVs in these units generally fail open or closed?
>>>     >>
>>>     >> We're using a pair of M2 PCX2800 controllers.  To help protect the MOSFET device
>>>     from a similar "short-to-ground failure" during a lightning event, I designed a circuit that
>>>     engages a vacuum relay such that the MOSFET is only exposed to the outside world during
>>>     rotation.   It's not a 100% guarantee against MOSFET failure, but should help to mitigate
>>>     damage.  This is an add-on that's similar to what K7NV did with the Green Heron prop pitch
>>>     controller model.
>>>     >>
>>>     >> Here's my thought for a potential fix:  While another vacuum relay could be added on the
>>>     +48V supply side to the prop pitches, I could isolate circuit ground from chassis ground on
>>>     the secondary side of the controller's power transformer.  The primary would still be safety
>>>     protected and meet UL. Isolating circuit ground from chassis ground would inhibit rotator
>>>     turning in the event of a MOV failure on the return line.
>>>     >>
>>>     >> Anyone been through this?  I welcome comments on any better ways to manage this.
>>>     >>
>>>     >> Paul, W9AC
>>>     >> _______________________________________________
>>>     >>
>>>     >>
>>>     >>
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>>>     >
>>>     >
>>>     > --
>>>     >
>>>     > 73
>>>     >
>>>     > Roger (K8RI)
>>>     >
>>>     >
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> 
> -- 
> 
> 73
> 
> Roger (K8RI)
> 
> 
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