[TowerTalk] Rotator Lightning Protection

[john at kk9a.com]

Physically unplugging things on a remote station is not a practical
solution.

I believe that MOVs typically fail shorted and actually they start to leak
voltage after some use.  This can affect the ramping on some controllers. I
would either use a Green Heron controller or duplicate his isolation relay
circuit to minimize the chance of free spinning.

John KK9A


To:	"Roger (K8RI) on TT" <K8RI-on-TowerTalk at tm.net>
Subject:	Re: [TowerTalk] Rotator Lightning Protection
From:	Bry Carling <bcarling at cfl.rr.com>
Date:	Sat, 16 May 2015 01:59:14 -0400

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 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