Power Transformers: The Lost Art Of Custom Winding - BSFEEChannel #5

[Cliff Matthews]

Grab some old disposable SMPS pulse transfomer and pull the tape off. You'll probably see what your looking for along the sides of the bobbin where the leads come out (like double-sided sponge tape). IMO it would seal out moisture too.

[Cerebus]

Yup, exactly like that. Nomex is scarily expensive and so used for the very highest temperature classes only, you can get a 180 C rating with cheap, easy to find polyester insulation. You're looking for a creepage path of around 4mm on most common classes of transformers, so 2mm each side of the main insulating layers between the bobbin and winding for 2k5 V isolation (from memory). See standards documents for figures applicable to one's target usage (i.e. EN 90950 for computer and telecoms equipment).

[T3sl4co1l]

"Margin tape" gets a lot of hits, "filament reinforced electrical tape" seems to be a good description as well.

3M type 46 seems to be the stuff, https://solutions.3m.com/wps/portal/3M/en_US/ElectricalOEM/Home/Products/ProductCatalog/~/3M-Filament-Reinforced-Electrical-Tape-46?N=5561499+3293718001&rt=rud
and 44.  Looks like Permacel and P. Leo are also popular mfgs.

Tim

[bsfeechannel]

Grab some old disposable SMPS pulse transfomer and pull the tape off. You'll probably see what your looking for along the sides of the bobbin where the leads come out (like double-sided sponge tape). IMO it would seal out moisture too.

Yes. I have some computer SMPSs lying around here doing nothing. I think I will sacrifice one of them to the gods of knowledge. Thank you for the tip.

As a side note, SPMS transformers are subject to high voltages due to their switched mode of operation (The sudden interruption of current across its primary for each cycle produces high voltage spikes). It makes a lot of sense, now that you mentioned SMPS, to provide that kind of protection, even with the use of RC snubbers and flyback diodes.

Yup, exactly like that. Nomex is scarily expensive and so used for the very highest temperature classes only, you can get a 180 C rating with cheap, easy to find polyester insulation. You're looking for a creepage path of around 4mm on most common classes of transformers, so 2mm each side of the main insulating layers between the bobbin and winding for 2k5 V isolation (from memory). See standards documents for figures applicable to one's target usage (i.e. EN 90950 for computer and telecoms equipment).

That's what I thought. Thank you for calling my attention to that aspect. That is one technique I will try to employ on my next project.

"Margin tape" gets a lot of hits, "filament reinforced electrical tape" seems to be a good description as well.

3M type 46 seems to be the stuff, https://solutions.3m.com/wps/portal/3M/en_US/ElectricalOEM/Home/Products/ProductCatalog/~/3M-Filament-Reinforced-Electrical-Tape-46?N=5561499+3293718001&rt=rud
and 44.  Looks like Permacel and P. Leo are also popular mfgs.

Tim

Cool! Following your tip, I googled that too and found this:



Seems to go along with the lines of what y'all been trying to say.

[johansen]

yeah that's basically how every power transformer has been wound for a long time.

but not only is it for clearance and creapage but the space between the wire and the core is also there to reduce the capacitance in some cases

it may also be there to keep the wire away from problem areas, such as air gaps

for example, read here https://engineering.dartmouth.edu/inductor/shapeopt.shtml

[tautech]

I'll drop this link in this thread for the OP's reference............and others.
Practical transformer winding
http://ludens.cl/Electron/trafos/trafos.html