[TowerTalk] Array Solutions AS 8 SP

[Roger (K8RI) on TT]

It's true a lot of little events will cause an MOV to eventually fail 
shorted, except where it's on a line supplying power,  a  a direct hit,  
or even a close strike.    In the case of the line supplying power, it 
depends on how that line is protected.  A 50 A buss, or even 10 A buss 
may clear the short in the time it takes the fuse to open. Except for a 
really close strike or direct hit, signal lines such as position 
indicators on rotators, the odds are far in favor of it failing 
shorted.  A direct hit, or the induced voltages from a close strike will 
likely open the MOV and take out from a few to many associated components.

It doesn't have to be lightening.  Motors, relays, arcing connections, 
or anything that can cause voltage spikes may cause an MOV to fail.  
It's the energy in the spike that does the damage.  As the MOV ages 
while in service it takes less energy to do damage to the MOV.  The MOV 
is really nothing more than many thousands of very tiny diodes.  Look up 
their construction with a search. Years ago, GE had a very nice manual 
devoted to the construction and use of MOVs.  It's still relevant today. 
http://pml.nist.gov/spd-anthology/files/GEMOV_saga.pdf   I have or had 
one of those first edition manual;s listed as a collector's item.  Hope 
it didn't get thrown out,

73

Roger (K8RI)





On 8/27/2015 8:31 PM, john at kk9a.com wrote:
> MOVs degrade with each lightning event and will eventually fail. Typically
> they fail shorted. I have had many PolyPhaser rotator protectors fail or
> start to leak.  Often the MOV damage is visible when you open the cover.  It
> is certainly easy to disconnect the device to test the rotator and MOVs.
> The MOVs inside the Array Solutions NEMA enclosure are easy to replace.
>
> John KK9A
>
>
> To:	TowerTalk at contesting.com
> Subject:	[TowerTalk] Array Solutions AS 8 SP
> From:	Joe Feustle <jafeustle at outlook.com>
> Date:	Thu, 27 Aug 2015 17:00:15 -0400
>
> Does anyone on the list have any experience with this rotor control line
> device going bad? I'm working my way through a process of elimination to
> find out why my TailTwister no longer indicates direction nor will turn my
> beam. I've replaced the auto-start capacitor (no change) and hooked my box
> up to a known, working rotor. That works just fine: releases the break and
> turns the rotor. The surge protector is the next item in the line of
> inquiry.
>
> Thought I'd post this before disconnecting all the wires from the SP and
> reconnecting them in their proper order of color coding.
>
> TIA and 73
>
> Joe Feustle, N8JF
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk


-- 

73

Roger (K8RI)


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus