Electrical Conductibility of varnish

[davidmoul]

Hi guys,

I was wondering how to measure the electrical conductibility of a varnish? My problem is that we would like to estimate is the conductibility of a varnish we would like to use in a magnetic application.

Can anyone give me a link to references / norms or something else?

Thank you for your help!

 

[jedward]

Vanish was used as an insulator for wire and transformer winding for many years and should be an excellent electrical insulator. Do you need the actual value for conductivity?
A modern equivalent material used on wire is "formvar".
Is it really the dielectric constant or breakdown that are more important?

 

[davidmoul]

oops, my english is not so good... I was talking of a protective painting (Interplus 256, which contains Al and Mica).

In fact we said "it's conductive", but we would like to quantify for the internal report, in a correct way.

it is really important for our application that no conductive material is used (because of high magnetic fields)...

 

[tomwalz]

Why not just paint a strip and do your own measurements?

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[IRstuff]

If neither the varish nor the magnetic field is moving, why is there a problem with conductivity?

What do you mean by "correct way?" One method is to use a Vander Pauw test pattern.

TTFN

FAQ731-376

 

[davidmoul]

Both are turning (paint on a rotor, magnetic field is alternative...)

 

[IRstuff]

I haven't seen anything on the IPC website to suggest that the resultant coating is conductive. 256 contains micaceous iron oxide, not mica.

What exactly is the concern about conductivity, given that you're painting a conductive rotor?

For sheet resistivity see:

http://en.wikipedia.org/wiki/Van_der_Pauw_method.

I would start with a high-end PC board with 4 symmetrically placed electrodes, mask off the center and the external contacts, and coat and cure per your procedure. Get a high end, Kelvin-connected resistance meter and have at it.

TTFN

FAQ731-376

 

[davidmoul]

in fact the rotor is not conductive at all... and it must be insulated because of the technology used. So I have to be sure that the corrosion protective painting is absolutely insulative and not conductive...