Benefits of Potted Output Transformers

[dsavitsk]

I have some James transformers that have cases around them, which I guess means they are potted. Does this mean I can not worry about their proximity to chokes and power transformers, or perhaps worry a little less, or is this not the benefit of potting them.

Thanks

[jarthel]

Originally posted by dsavitsk
I have some James transformers that have cases around them, which I guess means they are potted. Does this mean I can not worry about their proximity to chokes and power transformers, or perhaps worry a little less, or is this not the benefit of potting them.

Thanks

runs cooler I believe

and looks sexy that than using "end bells" (typo?)

[SY]

Neither. The potting has no/very little effect on magnetic fields. And it actually can decrease cooling. It's done for better environmental isolation (particularly moisture), lower vibration, and because it looks and feels cool. Sexy indeed!

[HollowState]

Actually I believe the most important benefit of potting is preventing moisture from getting in the windings as well as physically sealing it against vibration. Yup, it also looks nice too. Unless there is a mu-metal shield inside, there's often no better shielding then a regular end bell. And call me cynical if you want, but it also helps deter getting at it to reverse engineer it.

Victor

[dsavitsk]

Originally posted by SY
Neither. The potting has no/very little effect on magnetic fields.

Is there a good way to determine optimal direction vis a vis the power transformer/chokes. or is it a matter of bread boarding one way, and then turning 90 degrees to see which is better?

[anatech]

Hi dsavitsk,
That's about it. Low tech, but it works.

-Chris

[EC8010]

Originally posted by dsavitsk
Is there a good way to determine optimal direction vis a vis the power transformer/chokes. or is it a matter of bread boarding one way, and then turning 90 degrees to see which is better?

You can be a bit theoretical. Think of the mains transformer as having the coil that is the primary of a transformer and the output transformer as having the coil that is the secondary of that same transformer. You now want to make the coupling of the notional transformer as poor as possible. Orient the coils at 90 degrees to one another and get as much distance between them as possible. Fine tweaking when you've made it may help.

[NickC]

Potting has its pro and cons

When you pot it looks nice
it prevents high tension build up and prevent corona discharge
No moisture can build up within the coils.
Helps to slighlty reduced vibrations as the epoxy acts as a dampener


Cons
The trans runs hotter as there is no air flow
For audio trans the potting materials will act as a dielectric
most potting material like james is epoxy which is bad for sound. The good sounding potting material which wax on the other hand melts at 60-90 C depending on wax types

[EUVL]

According to my very limited understanding, all potting compounds, polyurethane or epoxy based, shrink when they set (ca. 3 vol %). The shrinkage inevitably put the core/winding under stress (deoends on construction, elastic modulus, .... ). Stress in laminated cores reduce their saturation level, by as much as 30% if I remember correctly. Epoxy is worst than varnish in that respect.

But of course you can design for this, by using a larger core.


Patrick

[SY]

Orient the coils at 90 degrees to one another and get as much distance between them as possible.

True, but how do you know the coil orientation when it's all buried in a chunk of polymer and metal?

most potting material like james is epoxy which is bad for sound.

Having built my first amps using James iron, I can attest that there's nothing whatever wrong with the way they sound. Superb transformers.