Potting EQ inductors

[ed rees]

I'm thinking of getting a small vacuum chamber to do this to my pot core inductors.

Is it really necessary? Does it help temp. stability and hum? What varnish should I use?

Perhaps just brushing some varnish on the finished coil would be good enough?

 

[shabtek]

i would guess Henry would change after the chamber... and may be more stable

these are for audio freq. no?

I've seen em in wax but are any current products potted?

as far as emi hum: no benefit. microphonics maybe, but is that a problem?

temp stability, maybe due to increased thermal mass coupled to core.

 

[CJ]

just heat them up to 220 F for a few hours to dry it out then drop them in  a can of Minwax Verathane and wait till the bubbles stop,

 

[ed rees]

Doesn't get much easier than that. It wont hurt the plastic bobbin? Looks like I'll be getting a toaster oven from goodwill rather than a vac chamber. ;D

 

[CJ]

plastic or nylon? have not tried plastic,

when you drop the heated coils in the can, the air bubbles inside the windings will contract as the coil cools down, this creates a vacuum which pulls in the  verathane,

if doing high voltage stuff, then you need to pull a good vacuum, but then you need a air tight tank that will not implode, a hose with a looking glass on the oil end, and a gauge to tell when the tank is full, otherwise the oil will get pulled into the vacuum pump, oil does not compress like air, so the piston tries to come up against that oil and you bend the crank shaft of the vacuum pump, sometimes this takes a few seconds for the cylinders to fill with oil, so when we heard that vacuum pump start knockin, we ran over there and shut it off,

this was usually after lunch time if you catch my drift,  8)

now when you pull a vacuum on a huge xfmr tank, something maybe 10 feet high by 12 feet square, like the twelve we made for the Fusion project for the Lawrence Liverpool Lab, then you have to make sure the tank is strong otherwise the roof of the building caves in due to all the air getting sucked out of the room in ten nano seconds when the side seams cave in,

they use whats called Kinney Oil for vacuum pumps, if you use regular oil, bad things can happen like maybe an explosion and if your lucky, an oil fire,

 

[ed rees]

The ELNA part number for the bobbins starts with CPV, so I assume CPVC?  I read CPVC's melting temp is around 200F.  I'll try one at 180- 190, if it melts I'm only out $1.

I might find that simply brushing some thinned down varnish on the finished coil will do the trick. One I tried earlier with some really thin shellac looks pretty good. Oil vacuum pumps are sweet. I'll need one whenever I get around to metallizing my DIY mic capsules.  :


Lately I've been throwing a 100 wind 'test-bobbin' in each core set, and plugging the recorded inductance value into here: http://powermagnetics.co.uk/calculator.html

Gets me within 1% the first time around, usually closer!

 

[gyraf]

If you have pot cores with an air gap of some sort, potting is no real problem.

However, if you use ungapped pot cores, your inductance will most often end up much lower after potting, if and when potting material capillars in and expands the gap while hardening.

There is some specialized Epcos potting laquer that supposedly does not suffer from this - but it's prohibitively expensive.

Jakob E.

 

[CJ]

you will change the high end also as any liquid that gets into the windings will act as a dialectic which will increase leakage C. this is why certain McIntosh outputs have no varnish or other compounds between the turns, however, these same models tend to break more often as the wires can rattle around at certain frequencies.

heat will dry out the moisture inside your coil,

if you do not dry out the coil but paint it with varnish, you are sealing in the moisture forever which can damage the windings over a long period of time,

what Jake said about the price of good transformer resin, 50 bucks a quart for the good stuff,

here is info on the different types of processing if you are interested>

http://www.temcoindustrialpower.com/product_selection.html?p=insulating_resins_guides