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 <javascript:;>> 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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