How easily does Enamel Wire coating cracks?

[Magnethicc]

Hello everyone,
I want to wind a 1.45mm enamel wire 39Turns on a CH46760GT core.
The enamel wire is a MW 35-C (ANSI Standard) and I don't know if the coating will hold the rather acute bending angle on the toroid core.

39 Turns with a wire with d=1.45mm makes the first and last turns to close to comfort.
I was wondering if the coating can handle such bending angles.

Would love to hear from your experience.

 

[mtwieg]

I'm assuming the angle you're talking about is the ~90 degree angles formed by the perpendicular faces of the toroid. If there's no chamfer or rounding then yes, this can cut through enamel insulation (especially if uncoated). The datasheet doesn't mention this feature though, so no idea how "sharp" these corners are.

Theoretically 39 turns of 1.45mm wire should fit as a single layer, but it depends on the equipment used to assemble it. The gap between the start and finish will affect SRF and max voltage, which may be an issue depending on your application.

I'm not sure how the winding gap relates to bending angles though.

 

[Magnethicc]

I'm assuming the angle you're talking about is the ~90 degree angles formed by the perpendicular faces of the toroid. If there's no chamfer or rounding then yes, this can cut through enamel insulation (especially if uncoated). The datasheet doesn't mention this feature though, so no idea how "sharp" these corners are.

Theoretically 39 turns of 1.45mm wire should fit as a single layer, but it depends on the equipment used to assemble it. The gap between the start and finish will affect SRF and max voltage, which may be an issue depending on your application.

I'm not sure how the winding gap relates to bending angles though.

Yes the angle I'm talking about is the ~ degree angles formed by the perpendicular faces of the toroid. the toroid corner are rounded since the core is coated too so no real concern that the core will chamfer the wire coats.

The wire has 2 coats - A base coat of polyester-imide and a topcoat of polyamide-imide.

The winding gap related to the bending angles -> since the 39 Turns fit tightly together, the first and last turns are adjacent and if the bending causes the enamel to crack that first and last turns may short under high voltage (when producing thousands of cores all of which will preform under load).

 

[Easy peasy]

What is the coating of and sharpness of the ferrite core ?

 

[aliarifat794]

MW 35-C is rated for Class 155°C, meaning its insulation is robust for typical electrical applications. However, bending stresses are mechanical, not thermal. Enamel coatings have limits to the degree of bending they can handle before cracking.

 

[dick_freebird]

Perhaps the core can be chamfered if it is not
already acceptably radiused along the edges
as-molded?

I've seen cheap sharp cores and I've seen ones
nicely radiused and coated with "something"
smooth and hard. Maybe it's worth the extra
pennies to eliminate this concern, by shopping.

 

[mtwieg]

The winding gap related to the bending angles -> since the 39 Turns fit tightly together, the first and last turns are adjacent and if the bending causes the enamel to crack that first and last turns may short under high voltage (when producing thousands of cores all of which will preform under load).

You certainly should not allow the start and finish of the windings to come into contact, even with their insulation intact IMO. If for some reason this is difficult to avoid, you can add additional insulation on the wire leads. Teflon tubing and fiberglass sleeve is sometimes used for this purpose. I would communicate your concern to the transformer manufacturer and let them suggest a solution based on their materials and equipment.

 

[cupoftea]

Use multiple thinner strands of ECW.

 

[wwfeldman]

maybe you should go up one size in the core
can you wind on a round bobbin?