I always disconnect my feed lines and rotor cable when a storm threatens or I am away from the shack for an extended period. Just in case I am not around to do the disconnections I have polyphasers in the feed lines to provide reasonable protection.
How can I protect my my rotator and cable in a similar way? I have seen some comments about using "MOVs" but I don't know what they are and how to use them.
73
Wayne VK4WDM
1 MOV coming up -
https://www.jaycar.com.au/460vac-4500a-m...v/p/RN3416
Various ways of using them, most common is across feed lines and from each line to a ground.
The linked one is a 460v 4500A one, but there are lower voltage (275 & 100V) ones.
For lightning protection, personally, I would opt for the heaviest current version possible.
Assuming for a moment you have three control lines to the rotator, you will need 6 MOV's - imagine the three lines as the corner of a triangle with an MOV joining each of the corners, plus an MOV from each of those corners to ground.
This configuration will vary depending on how the position information is fed back to the controller.
An addition to Terry's comments:
A MOV will effectively go short-circuit when tripped (i.e. conducts the peak current once the rated voltage is exceeded, some recover & some don't) so make sure that the rotator power supply is properly fused.
I guess also protecting the rotator is dependent on how it is mounted, and how the supporting arrangement is grounded. I have towers that have bases go 1.8 metres into the ground in what is typically damp soil with 600Kg of concrete around the 150mm NB galv mounting pipe. The Yaesu G800 rotators are mounted in a U-shape arrangement on its side (1m high) so that the GS050 thrust bearing takes a lot of the mechanical load. The rotator body is mechanically grounded to the tower to the base by what should be an effective connection, a direct strike excepted.
That all said, a direct lightning strike to your antenna arrangement is not going to be overcome easily. It will pulverise any feeder and rotator cables, and gear remotely connected together in the shack. Your rigs will likely die unless they are stored away in their boxes and not connected to anything. Consider it mass destruction.
A nearby lightning strike may cause some damage and this is the case where MOVs might help. I have my doubts about what voltage the MOVs should be because the likes of a 3-wire rotator run from about 24VAC so the suggested 460V one won't conduct until the rotator's voltage ratings are well and truly exceeded nearly 20 times. I would suggest double the typically applied voltage eg 50V for a 24V circuit. Even that might be too high.
Actually the best form of protection from lightning as far as an amateur station is concerned is a good household and contents insurance policy. Make sure all of your gear (including power supplies and accessories) is covered for replacement under the policy, ditto antennas and cabling.
Touching wood here : I have had antennas up in the air for over 50 years and no really near misses by lightning. Storms with winds strong enough to fracture a rotator housing and having the top of it plus the HF tribander fall to the house roof - that would be a yes to that. (That is why I use the U-support arrangement these days, to avoid rotator failure.)
My coaxes remain connected during storms but feed via in-line coaxial arrestors to the radios, their earth path being a very direct RG213 outer/braid to the aluminium bus bar along the back of the operating table and then to the 1.8m 'shack' earthing rod via some LDF4-50 outer (slight flexibility requirement) to get there.
PS There are 13 coax feeders coming into my shack - disconnecting all of those simply is not going to happen.
Next on the list would be TVS (Transient Voltage Suppression) Diodes.
Used in much the same way and less likely to go short circuit (except in the case of a direct hit).
Available in a much wider range of trip voltages, so, as Doug, says, you can get closer to the operating voltage of the rotator.
http://www.littelfuse.com/~/media/electr...og.pdf.pdf <- the two .pdf in the link is correct, I checked.
The above is a catalogue/design guide and shows how these things are used.
The only thing to remember about either of these methods (MOV or TVS), is that you need to check that they are still working at regular intervals, like say just before each storm season.
Hey Wayne,
the other way to do this is a traditional surge arrestor:
https://www.jaycar.com.au/passive-compon...ity-desc&q
you will see lots of these in traditional telephone exchanges and from what I understand can take a pounding and still provide protection. Never the less you need to keep up some regular maint each season
Regards
Peter, vk5pj