From: <hvanesce@comcast.net>
To: <rsgb_lf_group@blacksheep.org>
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Date: Thu, 29 Dec 2016 16:07:55 -0500
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Subject: RE: VLF: New coil for 8270 Hz
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Hello Stefan,

The process is public information but in a niche area so there is probably
no online link. Friends and I spent a year or so developing it, so we
remember all of the fine details; I will document them and post to the
group.

Solutions of this sort (high voltage environmental hardening) are always
somewhat application specific so this method may not be the best for you,
but to cover that possibility I will include three additional items (in
addition to the process description):
a) A description of a quick/easy means of life testing an expendable small
sample (a very short coil using your PVC, wire and ferrite). Just a few
labor hours (and 3 days hands-off on the workbench) provides a reliable
indicator of 10-year life for HV devices encapsulated with this process.
This simple test is one of the best parts of the process; accelerated life
tests are legendary for irrelevance, but this accelerated test originally
made root-cause isolation of the primary failure mechanism possible, and as
a result is sufficiently correlated with 10-year life to remain as the
process-validation standard for millions of fielded devices with compliant
life history.
b) A summary description of: advantages (life, cost, weight); harsh
environment specifications; and disadvantages:
  (20g shock is OK but a large coil will not survive a 3-foot corner-impact
drop to concrete unless RTV coating, thin pads or equivalent are added;
fielded units made with this process are dropped onto rock and concrete
regularly but they usually have a thin RTV layer inside of a thin plastic
case for shock spreading); also encapsulant is hard, so coil cannot be
reworked after encapsulation.
c) A description of the primary life-failure mechanism of encapsulated HV
devices in harsh outdoor/mobile/portable environments, and the physical and
chemical properties of this process that enable a low-weight solution. 

The documents in (a), (b) and (c) may help determine if this solution is
useful to you; for instance: document (a) will show a quick high-confidence
pre-test procedure, but document (b) will show very limited ability to
rework the coil after encapsulation. Another example: document (b) will show
that a key requirement for this process was: minimal added weight (for
10-year HV life in harsh outdoor/mobile/portable environments); much heavier
solutions such as some used by electric utility companies withstand repeated
high impact and may allow some rework. You might also find something in
document (c) that shows incompatibility with your environment or
application. 

If the process is not right for the ULF coil, I hope that it will find
ongoing use in other high voltage areas. The recipe has no fancy
ingredients; just the appropriate ingredients, steps and sequence for its
application; if it's not right for the ULF coil perhaps posting it will keep
it in good service somewhere, hope it works for the ULF coil or other group
applications .

73,

Jim AA5BW  

         

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of DK7FC
Sent: Thursday, December 29, 2016 1:21 PM
To: rsgb_lf_group@blacksheep.org
Subject: Re: VLF: New coil for 8270 Hz

Hi Jim,

What is the link for that information? Share it with us.
Sounds like the perfect solution but i have my doubts with such perfect and
easy solutions.

73, Stefan

Am 29.12.2016 11:24, schrieb hvanesce@comcast.net:
> Stefan,
>
> If you ever become interested in encapsulating an HV coil, I can send 
> details for a straightforward process for low-cost/lightweight 
> encapsulation that gives 10-year life in harsh outdoor environments 
> with 10kV per inch across the problematic smooth surfaces. The 
> dielectric is 450V/mil but the issue for lightweight long HV life in 
> harsh outdoors is smooth interfaces between dissimilar materials, and 
> this straightforward low cost process solves the problem. No special 
> equipment needed. Decades of good field history with this process, no
issues.
>
> 73,
>
> Jim AA5BW
>
>
> -----Original Message-----
> From: owner-rsgb_lf_group@blacksheep.org
> [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of DK7FC
> Sent: Wednesday, December 28, 2016 4:00 PM
> To: rsgb_lf_group@blacksheep.org
> Subject: Re: VLF: New coil for 8270 Hz
>
>
>
> Am 28.12.2016 19:00, schrieb jcraig@mun.ca:
>    
>> PS Stefan's coil is very compact.  0,4 mm wire?  Hope it can take the kV!
>>      
> Hi Joe,
>
> Yes, 0.4mm wire. The voltage is not the problem for the wire. But the 
> tube is out of PVC and the length of the winding is about 0.3m. So it 
> will be about 1kV/cm which could be problematic if the inner side of 
> the tube becomes wet, inhomogeneous wet. This could cause strong local 
> E field strength which leads to arcing on the surface. Arcing on the 
> surface makes the surface conductive, a self accelerating process that can
be repaired.
> This is the high risk of this construction! It has its advantages and 
> disadvantages. It will handle 700 mA RF current, at least now in 
> winter :-) But i should take care to keep it as dry as possible.
> We will see what happens.
>
> 73, Stefan
>
>
>