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Re: [TowerTalk] Rotator Lightning Protection

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Rotator Lightning Protection
From: "Bry Carling AF4K" <bcarling@cfl.rr.com>
Reply-to: bcarling@cfl.rr.com
Date: Sun, 17 May 2015 09:03:04 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
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@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@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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>     >
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