[AMRadio] High Voltage Power Supplies - varistors


Jim Candela jcandela at prodigy.net
Sun Oct 30 15:36:42 EST 2005


Brian,

   Littlefuse has a whole line of varistors. Go to
www.mouser.com, and enter the following part numbers:

v130LA10a
v130LA20a
v250LA20a

The 10, or 20 in the p/n specifies the diameter in mm
for the part. The 130 or 250 is for the rated RMS
voltage the varistor is designed to protect. The
larger diameter has higher Joule capability. Look at
the data sheets relating clamping voltage versus
current through the device. 

These items offer some protection for your equipment,
BUT these are only one component towards protecting
your equipment from power line transients. They are
intended to suppress the once in a while transient,
and are not intended to be working repetively since
they will warm up, and eventually be another toasted
charcoal brick. 

Other things to consider are ferrite beads, common
mode transformers, feed through capacitors, bypass
capacitors, etc. Most if not all of these items are
used on computer power supplies where the input 120
vac is converted to DC. Sometimes you can "saws-all"
the filter off a computer power supply, and use that
for protecting ham gear of similar power ratings (<
250 watts).

Jim


--- bcarling at cfl.rr.com wrote:

> Noit sure Don - a fellow ham traded these to me.
> They are black disks and look pretty much like a
> large 
> ceramic capacitor, if you can imagine...
> 
> They are marked:
> STM  and  CL-30
> 
> I think the resistance at rest is about 3 to 5 ohms.
> 
> On 30 Oct 2005 at 9:24, Rev. Don Sanders wrote:
> 
> > OK Bry, You got my interest. What is the part
> number and are they from
> > Mouser? I know I need several for my boatanchors
> and my 2 Astrons(20 and 35
> > amp).
> > 
> > Healthfully yours,
> >                           DON W4BWS
> > ----- Original Message ----- 
> > From: <bcarling at cfl.rr.com>
> > To: "Discussion of AM Radio"
> <amradio at mailman.qth.net>
> > Sent: Sunday, October 30, 2005 7:27 AM
> > Subject: Re: [AMRadio] High Voltage Power Supplies
> > 
> > 
> > > On 30 Oct 2005 at 9:08, Ed Swynar wrote:
> > >
> > > > Is this the reult of transients / voltage
> spikes somehow "overwhelming"
> > > > the diodes...?
> > >
> > > Probably - why not try one of those transient
> suppressors (varistor I
> > think)
> > > on the primary side of your power tranny?
> > > I just put one in my Astron 35M and it
> eliminated the "THUNK!"
> > > at power-on.
> > >
> > > A number of guys have put them into Johnson
> xmtrs with similar
> > improvement.
> > > Maybe it could save your diode strings.
> > >
> > > Do you have a capacitor-input filter on the
> p.s.u.?
> > > Choke input filters tend to be a bit kinder to
> the rectifiers.
> > >
> > > 73 de AF4K, Bry
> > >
> > >
>
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