Re: {Collins} 30L-1 MOV question



Ah yes Dale, You missed my email to the list where I owned up to using the
wrong nomenclature. I really meant a Clamp diode or Transzorb kind of
device. Vishay just calls them Voltage Transient Suppressors.

I stand corrected and I am sorry if my use of this "historic" term has
confused anyone.  Years ago, we started using MOVs for the application that
we are using the clamp diodes for today. The technology has improved
(bunches) and the user has remained (apparently) frozen in time......happens
when you are 72...  Ha! At least the part I recommended is the correct one
for the application on the 30L-1 bias line.


Bill

-----Original Message-----
From: Dale Svetanoff [mailto:svetanoff@xxxxxxxxxxxxx] 
Sent: Saturday, February 25, 2012 9:47 AM
To: Bill Carns; frank hughes; COLLINS@xxxxxxxxxxxxx
Subject: Re: {Collins} 30L-1 MOV question

Bill and All,

I was reading the overall thread about MOVs in the 30L-1 and then got
confused.  The problem?  Are you talking "MOVs" or "Transzorbs(R)"?  

These two devices are NOT alike.  MOVs ("Metal Oxide Varistors") were
developed by General Electric back in pre-historic times (1970s, maybe even
earlier).  They are not polarity sensitive and have response times usually
measured in microseconds.  When an MOV is triggered into action by an
applied voltage that exceeds its knee region, it then clamps that voltage at
some specified level, it does not produce a near-dead short across the
protected line.  Further, MOVs have 2 other characteristics that make them
unique (in a way) and also a potential for future failures.  They all
exhibit a given leakage current (shunt current, if you will) that increases
as they absorb more energy.  (One PhDEEE I worked with referred to MOVs as
"Coulomb counters".)  When used in AC line applications, the leakage current
will slowly increase over time until the device fails  When an MOV has
reached end-of-life, it usually fails open - meaning, you have no more
protection.

Because of the leakage currents and failing open, many military procurements
prohibit the use of MOVs in all but a few applications because they are
considered to be reliability risks. The most common MOVs are in disc-type
packages with radial leads, but the higher energy ones tend to be "blocks"
with screw or tab terminals.  They can be used on AC or DC circuit
applications, but are most often found in use as SURGE protection on AC
power applications (such as power strips).  Note that MOVs are rated by
Joules and voltage.  The typical power strip will have 3 MOVs inside, each
rated at about 90 Joules.  One is applied across the hot and neutral,
another between hot and ground, and the third between neutral and ground. 
This provides a minimum level of both differential mode and common mode
protection to whatever is powered by the strip.

Transzorbs(R) were, I believe, introduced in a similar time frame by General
Semiconductor.  (The trademarked name "Transzorb" is now used by Vishay
Semiconductor.)  These true semiconductor devices are known generically as
"transient voltage suppressors" ("TVS").  They have response time in the
nanosecond region, are rated by power capability (watts) and nominal
hold-off voltage, and they do provide a near-total short across the
protected line when activated.  They respond well to fast rise time
TRANSIENTS.  They are made in both unipolar and bipolar configurations, and
are marked accordingly.  They are usually made in axial packages, thus
looking a lot like regular diodes.  

Bill, with all due respect, the part number you cite below is not an MOV,
but a Transzorb(R).  It should work well on the DC keying line.  BTW - The
"1.5" part of the device number means that it is rated for 1.5 kW!!! 
Beware, however.  That sounds huge, and it is, but these devices are not
made for sustained conduction of high currents.  Also, when they fail, they
frequently fail open, unless things got so nasty inside the junction area
that it becomes a fused device and is now a dead short.  Again, some
military procurements either prohibit or limit use of these devices. 
Special ultra-low capacitance versions of TVSs are now being used as ESD
protection for the zillions of ICs that are used in portable and hand-held
devices to protect them from static charge buildup of their users.  

As an aside, I'll mention that I have equipped all of my 12V equipment
(meaning "13.6 VDC") with a 1.5KE20A (or equivalent) connected across the DC
power lead, usually right at the piece of equipment.  This serves 2
purposes: 1) The Transzorb(R) guards the equipment against transient and
impulse spikes, which are common in automotive systems; 2) By using a
unipolar device, it acts like an ordinary polarity protection diode and will
shunt the DC line, blowing the line fuse, if polarity of the applied power
is accidentally reversed.

So, pardon my intrusion into the thread, but I really did wonder which
device was intended.  I have to believe that you do want the Transzorb(R),
and if so, it needs to be IDed as such, not as its slower, leaky distant
cousin, the MOV.      

73, Dale
WA9ENA
CCA Member


> [Original Message]
> From: Bill Carns <wcarns@xxxxxxxxxxxxx>
> To: frank hughes <fsh396ss@xxxxxxxxx>; <COLLINS@xxxxxxxxxxxxx>
> Date: 2/19/2012 10:02:12
> Subject: Re: {Collins} 30L-1 MOV question
>
> The part I recommend is a Vishay Part.
>
> Mouser catalog - last page of the semiconductor section.
>
> P/N   625-1.5KE300CA-E3
>
> This is the part that is shown in the Signal article that includes 
> install of this MOV.
>
> Regards,
>
> Bill
>
> -----Original Message-----
> From: frank hughes [mailto:fsh396ss@xxxxxxxxx]
> Sent: Sunday, February 19, 2012 8:14 AM
> To: COLLINS@xxxxxxxxxxxxx
> Subject: {Collins} 30L-1 MOV question
>
> Hi,
> The 30L-1 discusson has been very informative!
> If anyone has a P/N for the correct MOV, I would really appreciate it, 
> as there seem to be a bewildering (to me) number of options/values for 
> selecting an MOV.
>
> 73
> Frank
> KJ4OLL
> _______________________________________________
> SHARE THE FUN: JOIN THE COLLINS COLLECTORS ASSOCIATION TODAY !
> http://www.collinsradio.org/membership/
>
>  NETS: Tues & Thur: 3.805 MHz-2000 Central + Fri: 3.895 MHz-2000 Pacific
>   SUNDAYS: 14.263 MHz-2000 UTC  +  AM Net: 29.050 MHz-1200 Central
>   1st Wednesday AM Net 3.880 MHz-2000 local (ET, CT, MT, PT)
>
> The Collins Reflector reserves the right to refuse access to anyone.
>
> LIST HELP?  ADMIN EMAIL:  collins-owner@xxxxxxxxxxxxx This ONLY goes 
> to
the
> list admins and does not post to the group!
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 10.0.1424 / Virus Database: 2112/4819 - Release Date: 
> 02/19/12
>
> _______________________________________________
> SHARE THE FUN: JOIN THE COLLINS COLLECTORS ASSOCIATION TODAY !
> http://www.collinsradio.org/membership/
>
>  NETS: Tues & Thur: 3.805 MHz-2000 Central + Fri: 3.895 MHz-2000 Pacific
>   SUNDAYS: 14.263 MHz-2000 UTC  +  AM Net: 29.050 MHz-1200 Central
>   1st Wednesday AM Net 3.880 MHz-2000 local (ET, CT, MT, PT)
>
> The Collins Reflector reserves the right to refuse access to anyone.
>
> LIST HELP?  ADMIN EMAIL:  collins-owner@xxxxxxxxxxxxx This ONLY goes 
> to the list admins and does not post to the group!




-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 10.0.1424 / Virus Database: 2113/4831 - Release Date: 02/25/12







This archive was generated by a fusion of Pipermail (Mailman edition) and MHonArc.