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Re: Unpotting techniques...



Original poster: "Mike Novak by way of Terry Fritz <twftesla-at-uswest-dot-net>" <acmnovak-at-email.msn-dot-com>

I'd like to make an addition to this post that will save some secondary
windings.

If there happens to be some "stubborn" tar which you're not going to wait to
dissolve, the best tool is NOT a toothbrush!!! Toothbrushes  should be used
only on the core and shunts. What works best, and is least messy, is a
spnoge brush. They can be bought for $.50 at your local hardware store .
When removing tar directly from the windings, here's the best technique i've
come across:
Take the NST out of the solvent and place it in an empty bucket of whatever
to catch the tar. Place a small roll of coarse screen ( cookie rack, heat
sink, etc...) to keep the transformer from sitting directly on the bottom.
Now, using a second bucket of CLEAN solvent, use the brush to gently wipe
the tar away. Again here, if you want a clean working NST, TAKE YOUR TIME!!!
I spent 2 hours doing this step on the core of one of my NSTs, because I
didn't have a aquarium pump at the time



*Note*- All methods presented on this post are TESTED SUCCESFULLY, for those
of you who are inquiring...

Safe coiling!

-Mike Novak


> Original poster: "Mike Novak by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<acmnovak-at-email.msn-dot-com>
>
> Hello Everyone,
> I thought I'd take a moment and share with you some of the little secrets
> that I found make unpotting MUCH easier.
>
> 1.)Modified Freeze and Chip Method:
> The original "Freeze and Chip" method was NOT as easy as everyone claimed.
> It's dangerous for the windings and extremely messy as well. Here's what I
> did; First, chizel off the case using a good sharp chizel and an angle
> grinder to weaken the corners so they break easiily. Unclip the insulators
> and disconnect their wires before removal. Then place the transformer
> outdoors to aquire a good freeze (or in a freezer if you live in a
southern
> climate). Next, Using a chizel (or sharpened screwdriver in my case:) chip
> off the thin layer of tar on the top to reveal the core. This IS as easy
as
> it sounds because the transformer's silicon steel doesn't bond with the
tar
> too well. Now that you've revealed the top of the core, locate the two
pairs
> of hot wires and the GND wire. Hook the input and the GND to a grounded
> plug, and hook both HV leads to the core or GND connection. Once plugged
in,
> use a plumber's propane soldering torch to heat the core. If you use a
fine
> point flame, and stay to the center of the core, you can unplug it and
turn
> off the torch when the tar nearest the core melts to a real thin liquid
(and
> I emphasize THIN liquid, if you just soften it, it won't work as well).
With
> everything unplugged, use that sharp chizel and start removing chunks of
> tar. It should come off real easily, and you should be able to pry off
LARGE
> sections at a time. If it didn't cooperate, just plug it in and apply heat
> for another 10 mins of so, then try again. Now that you're done getting
all
> the tar goblins off your beautiful NST, we're ready to throw her in
> solvent!!!
>
> 2.)Solvent Secrets:...
> I've had a bit of troubles with solvents in the past. For instance, I
always
> have tar left in every crack which must be tediously removed by hand, and
> when I'm done, there's a big old pail of  solvent which must be disposed
of
> :( If you're using solvent to get rid of the entire block of tar, you'll
> have a REAL hard time getting rid of it. The best way to minimize the
amount
> of dirty solvent is to use the smallest possible container. What I suggest
> is a 1-2 gallon rubbermaid container with a really tight fitting lid (i do
> all my unpotting indoors during the winter so the lid is a MUST).
Completely
> disassemble the core before soaking, as It will save you time later. After
> you've removed the bulk of the tar from the core and coils, you should be
> able to put it in the sovent right away, just as long as the transformer
is
> cool enough to touch, although a warm transformer helps the tar dissolve,
> you don't want it *too* hot because of the low flashpoint of pretty much
any
> solvent. If you have access to a heated garage, then here's one thing you
> can do to speed up the process: Cut holes in the top of the container to
be
> used, place a couple peices of some kind of metal (must be at least 1"
> thick) in the bottom of the container followed by a coarse screen. In the
> space created beneath the screen, place a "bubble stone" (the kind found
in
> aquariums to add oxygent to the water) and run the tubing through the lid
to
> an elevated position in respect to the container so the solvent won't
> "crawl" up the tubing. This bubbling action will act as a automatic
stirrer
> (if you can't afford a refugee from a third world country to do it for you
> :).
> Now that you've got a relatively clean transformer, you *could* immerse it
> in oil. However, the oil will inevitably turn a lovely mud brown colour
due
> to the tar hiding in the cracks in the laminations. Of course, in a
acrylic
> enclosure, that gets quite unsightly. So, we're going to take the solvent
> process  one step further. Get yourself a new gallon of solvent and
transfer
> the contents of the used container to a milkjug using a big funnel. Now,
> take apart the core from the coils. Separate the shunts and the
laminations
> into piles to be cleaned. Aquire a bit of coarse sand (or maybe even
> aquarium gravel might work). Start stacking alternating layers of a single
> lamination, and some sand. You'll only be able to do half of the
laminations
> at a time if you've got the "optimal" sized container. If you've made the
> bubbling assembly (or the heatless boiler as i like to call it:) you can
> just turn it on and wait. However, if you didn't see the necesity of doing
> so, you will now because you'll have to sit and stirr it for an hour or so
> before the laminations are thoroughly cleaned. Repeat the process using
the
> other stack of laminations and the shunts as well. Once they've all been
> cleaned, wipe the excess solvent off with a terrycloth rag ( paper towel
is
> just a total pain here).
> Re-assemble the transformer the way you found it (minus about 6 leaves per
> packet of shunts) and you've got a spotless transformer that's ready to be
> mounted in any kind of enclosure you desire. I suggest HV oil, but
Vaseline
> is the next best thing.
>
> Hope that helped you brave souls who dare to venture into the dark black
> sticky depths of your NSTs...
> Good Luck!!!!
>
>
> Safe coiling !
> -Mike Novak
>
>
>
>
>