Hi there,

I'm currently in the process of winding a transformer and want to pot just the bobbin in epoxy resin (bobbin in attachments) for better insulation. I've already wound the primary, but haven't done the secondary yet.


Transformer Specs (Approx):

Vin = 12-20V
Pmax = 70W
Vout (@20Vin) = 2500V max
Frequency = 73.5KHz
Duty Cycle Max = 50%
Primary: 6 Turns (1 Layer)
Secondary = 700 Turns (12-13 layers)

What I was thinking of doing was putting some kind of material around the entire bobbin except for the top so I can pour the epoxy resin in once I've wound up the transformer. Ideally I would have liked to have done this approach and vacuum it but I don't have a pump. Another idea I had was to do this approach but instead try to get rid of the air bubbles in the resin before I pour it in. If I were to use this approach, would it be a good idea to use kapton tape to insulate each layer before I pour the epoxy, or would it be better to just use epoxy? Or if you have other idea's please share.

 

Welcome to AllAboutCircuits!

In case your mind was running in this direction: Potting the transformer will not increase the breakdown voltage of the enamel coating on your wire. That was just in case.

I designed the power supply for a television studio camera viewfinder. Since they are most often used in studios they cannot be adding background noise. The solution was to hang the inductors (pot core and E-I) from a "clothesline" In the lab, and during the day I would pour Varathane onto the bobbin every hour or so, making sure all of the windings were covered. The acoustic noise problem was solved. Next was filter the supply to keep the switching transitions from getting into the picture.

 

Welcome to AllAboutCircuits!

In case your mind was running in this direction: Potting the transformer will not increase the breakdown voltage of the enamel coating on your wire. That was just in case.

I designed the power supply for a television studio camera viewfinder. Since they are most often used in studios they cannot be adding background noise. The solution was to hang the inductors (pot core and E-I) from a "clothesline" In the lab, and during the day I would pour Varathane onto the bobbin every hour or so, making sure all of the windings were covered. The acoustic noise problem was solved. Next was filter the supply to keep the switching transitions from getting into the picture.

Yah I wanted to epoxy the transformer to increase the breakdown voltage. It’s not so much for between each wire, but to add extra insulation between each layer so the wires don’t short.

All I have right now is epoxy resin.

The max voltage/ turn is 3.5V so i assume side by side windings will be fine, but not each layer.

 

hi rw,
Have you considered that the inter winding layers, 12 off could have 2500/12 = ~200Vac RMS or double that depending upon how you do the start and finish of each layer.
I would use an interlayer insulation method.

E

 

hi rw,
Have you considered that the inter winding layers, 12 off could have 2500/12 = ~200Vac RMS or double that depending upon how you do the start and finish of each layer.
I would use an interlayer insulation method.

E

Yes I have, that's why I'm more worried about insulating each layer

how would you interlayer insulate? I don't have varnish. What I do have is Kapton Tape, Teflon Tape (Plumbing Tape), glue gun, and epoxy resin.

 

Epoxy resin is undoubtedly much too viscous to flow within the windings and provide insulation. Vacuum penetration does not require high vacuums, just repeated enough times is the requirement.

 

Epoxy resin is undoubtedly much too viscous to flow within the windings and provide insulation. Vacuum penetration does not require high vacuums, just repeated enough times is the requirement.

good to know, thx. Another reason to get a vacuum pump.

 

…and a bell jar!

Every so many layers add a layer of Kapton or Mylar tape. (Or masking tape if it is a week-end and no one will know.).

While winding an early transformer I found that occasionally a winding would slip over the end of the bobbin, causing shorts. The solution was for to keep moving the start of each high voltage winding layer would be further and further towards the coil, and the other end of the winding would end further from the edge of the winding, thus adding the benefits of increased creepage distance to those benefits of enamel selection and all that taping etc.

 

…and a bell jar!

Every so many layers add a layer of Kapton or Mylar tape. (Or masking tape if it is a week-end and no one will know.).

While winding an early transformer I found that occasionally a winding would slip over the end of the bobbin, causing shorts. The solution was for to keep moving the start of each high voltage winding layer would be further and further towards the coil, and the other end of the winding would end further from the edge of the winding, thus adding the benefits of increased creepage distance to those benefits of enamel selection and all that taping etc.

that totally makes sense. What I try to do is when I wrap tape, also try to get the tape to also stick to the top and bottom of the inner part of the bobbin so the windings cant slip under and short. But yah that definitely seems safer to just start and end the windings sooner.

 

A bit of brushed on varnish or adhesive can also hold turns in position. My dad always would add sides to the wood core when winding transformers. That was a lot more work, but it avoided a lot of problems.

 

Yah I wanted to epoxy the transformer to increase the breakdown voltage. It’s not so much for between each wire, but to add extra insulation between each layer so the wires don’t short.

I would suggest Kapton Tape. A Google will bring up plenty of suppliers and you really don't need much.

Ron