[Test-Equipment] Mains protection for work bench test equipment?

[Eric Lemmon]

But, not all Sola ferro-resonant constant-voltage transformers are alike.
Sola produced at least two types:  Normal Harmonic (CVH/CVN) and Sinewave
(CVS).  The former type is not suitable for loads that don't like square
wave power, which is rich in harmonics.  These Sola transformers were
designed for voltage regulation, not for spike suppression.

It is far better to design an electrical system to avoid spikes and surges,
than it is to suppress them after they occur.  The key is to use established
power-quality design engineering practices in the electrical system design.

I completely agree with several other posters who mentioned that spikes
propagate through transformers primarily by capacitive coupling, and that is
why the really good isolation transformers have a shield between primary and
secondary windings.  It is imperative that such transformers be applied
within a properly-designed grounding system.  Moreover, a
haphazardly-designed grounding system can easily negate all other design
features and create rather than solve problems.

73, Eric Lemmon WB6FLY


-----Original Message-----
From: test-equipment-bounces at mailman.qth.net
[mailto:test-equipment-bounces at mailman.qth.net] On Behalf Of Brooke Clarke
Sent: Tuesday, February 19, 2008 11:42 AM
To: Discussion of Electronic Test Equipment
Subject: Re: [Test-Equipment] Mains protection for work bench test
equipment?

Hi John:

I think the prior post that mentioned Sola transformers was intended to
refer 
to their ferro resonant type.  These have an extra winding that has a
capacitor 
across it and resonates at the line frequency.  It's acting as a narrow pass

filter, voltage regulator and does suppress spikes.  It also fills in small 
dropouts or brownouts.

For the basic Ferro Reasonant transformer see patent 
http://www.google.com/patents?id=gAsCAAAAEBAJ&pg=PP1&dq=2143745
by Joseph Sola
and for one that also includes a spike suppression circuit around the
capacitor 
see: http://www.google.com/patents?id=gAsCAAAAEBAJ&pg=PP1&dq=3938033

Have Fun,

Brooke Clarke
http://www.prc68.com/P/Prod.html  Products I make and sell
http://www.prc68.com/Alpha.shtml  All my web pages listed based on html name
http://www.PRC68.com
http://www.precisionclock.com
http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Web Cam


J Forster wrote:
> Isolation transformers, with ultra low primary to secondary caacitance,
will
> help a lot with common mode spikes, but all transformers just pass
differential
> mode spikes. Core saturation does not help  because the the VdT integral
is not
> large enough in most spikes to saturate the core.
> 
> Best,
> -John
______________________________________________________________
Test-Equipment mailing list
Home: http://mailman.qth.net/mailman/listinfo/test-equipment
Help: http://mailman.qth.net/mmfaq.html
Post: mailto:Test-Equipment at mailman.qth.net