[TowerTalk] (no subject)

[Patrick Greenlee]

Something to remember on MOV's:

Every time they conduct, i.e. "eat a transient" they lose a little 
capacity.  They are being chipped away at and eventually their capacity 
is reduced below sufficiency for a specific purpose. This is true with 
power strips, service entrance sized protective units, and all other 
applications.  MOV's need to be replaced over time and the difficult 
part is knowing when.

Some electric utility companies offer MOV entrance panel protection for 
a monthly fee and they change them on a schedule.  Unfortunately most 
power strip and other users are blissfully ignorant of the fact that 
their old strips and protective devices with MOV's are probably offering 
no protection if well aged and have actually done any protecting.

Patrick NJ5G


On 7/29/2014 11:51 AM, Will Jones wrote:
> Message: 8
> Date: Tue, 29 Jul 2014 01:20:24 -0500
> From: "Matt" <maflukey at gmail.com>
> To: <towertalk at contesting.com>
> Subject: [TowerTalk] FW:  MOV's for Polyphaser Rotor Wire Protection
> Message-ID: <03d601cfaaf5$2f7db270$8e791750$@gmail.com>
> Content-Type: text/plain;    charset="us-ascii"
>
>
>
> I need to replace one that has blown. It says, 20K on one of the MOV's but I don't know what that means. I guess I would need one at about 50 volts.
> Bill, N4LB
>
>
>
>
>
> Hi Bill,
>
> Perhaps someone out there knows the specific answer to your question, but
> since I did not see a response (yet) perhaps the little info I know may help
> you in some way.  Perhaps someone knowledgeable on MOVs can add more into as
> well...
>
> I know that the peak clamping voltage ratings of the MOVs in another similar
> rotor protection device that I own are rated at ~2.5 x the maximum RMS VAC
> rating of the device (or ~ 1.7 x the PEP VAC rating).  I think these will
> deviate a little from mfg to mfg based on the service ratings in AC (or DC
> for that matter).  Also, I believe that the peak clamping voltage is some
> statistical high point for a specific device as there is some mfg tolerance
> involved, so a nominal value might be different.
>
> If you are protecting a rotor, I would suggest considering how well the
> power supply voltage is regulated and what the worst case maximum no-load
> voltage could be.  Once you have that value, you should be able to look in
> the mfg literature and select the device with the next highest service
> voltage rating.  Be sure to check if the mfg ratings are RMS or PEP and
> convert accordingly.  As mentioned above, the clamping voltage will normally
> be higher that the service rating by some margin.
>
>
>
> I need to replace one that has blown. It says, 20K on one of the MOV's but I don't know what that means.
>
>
>
> You may want to take a look at the literature and specifications for MOVs
> from a mfg (such as Littlefuse company).  The literature does a pretty good
> job of guiding one though the process of selecting an appropriate clamping
> voltage for a MOV based on the intended service.
>
> Good luck.
>
> Matt
> KM5VI
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Will
> Jones
> Sent: Monday, July 28, 2014 7:17 PM
> To: towertalk at contesting.com
> Subject: [TowerTalk] MOV's for Polyphaser Rotor Wire Protection
>
> Does anyone know what value of MOV is used in the Polyphaser rotor wire
> lightening protector model IS-RCT ?
> Bill, N4LB
> _______________________________________________
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