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@gmail.com>
To: <towertalk@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@contesting.com] On Behalf Of Will
Jones
Sent: Monday, July 28, 2014 7:17 PM
To: towertalk@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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