It should be doable, but choosing the epoxy might be important.
I had a fiasco of that sort some 15 years ago because I used some
general purpose epoxy, dual syringe just bought some place.
We were making some tiny HV transformers - 5kV flyback, no
multiplier. We used - still do - to make them on RM8 but then
we tried something much smaller, RM6 if not even smaller....
(the core was about 10mm high on the PCB).
Now winding this so it can withstand the voltages, having all
the 1000 or so windings is very hard; and we had quite a few
attempts and they were just all too lossy - as if they had
a shorted turn but not quite so bad.
It took me some torture and time wasting until I realized it
was the epoxy I was pouring inside the core which was conductive....
Some part of it remained liquid and well, conducted.
In another life, some 25 years ago, I used to pot RM8 cores
(5kV again) using a special - can't remember the brand etc. - epoxy,
it was very low viscosity and using vacuum it penetrated
virtually anywhere (some colleagues were worried it did not
penetrate between the windings, 1000 turns x 0.07mm.... they
had cut one open to look at :D ). Now this had no problems at
all, the epoxyd became as hard as glass. [Nowadays I have
mastered the process a lot, just a few drops of the right
silicone in the right places, no vac etc. do the job].
Not so sure this is very helpful to your case as your speeds
are much higher than in my 5kV flyback (still the 5kV excursion
upon switch open is quite a thing) but it might ring some
bell at some point. I guess trying things out would be best.
Dimiter
------------------------------------------------------
Dimiter Popoff Transgalactic Instruments
http://www.tgi-sci.com
------------------------------------------------------
http://www.flickr.com/photos/didi_tgi/sets/72157600228621276/
From: Krunal Desai <movax@xxxxxxxxx>
Date: Thu, 16 Jul 2015 18:10:52 -0700
Subject: [SI-LIST] Effect of Epoxies on Ethernet Magnetics
To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
Hi all --
Please let me know if there's a better place to ask this question, but
I figured someone here might have run into this before.
I have an application that is in a very tough vibration / shock
environment, and I've got the Pulse HX1188FNL in my design -- a
single-port, non-PoE, 100Mbit Ethernet transformer. Looking at the
part, there's some kind of basic epoxy holding the cores in place, but
my mechanical folks and myself would feel more comfortable if we could
just fill the rest of the space with epoxy and essentially pot the
transformer cores.
100Mbit is fairly "slow", but I was wondering if the addition of epoxy
fill to the part would affect the dielectric / gapping of the
transformer considerably enough to affect performance of a 100Mbit
Ethernet link.
We have a list of candidate epoxies, but as a first-order question,
will the addition of /any/ epoxy-like material affect SI performance
to the point of making it unusable?
Thanks!
--khd
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