Quiet transformers - Page 1
Forum section: electronics / projects

author: Rachie5272
author_rank: Regular Contributor
timestamp: April 22, 2020, 12:51:00 am
content: My latest project requires custom transformers, and we're currently using standard E-cores. It works fine, but it buzzes a bit louder than I would like. It's probably silly, but I'd like to make things a bit nicer with a quiet transformer. It's an audio transformer roughly 1cm cubed, being fed with square pulses.Are there any manufacturing techniques to prevent vibrations, and thus noise? Maybe dipping the whole thing in epoxy?

author: schmitt trigger
author_rank: Super Contributor
timestamp: April 22, 2020, 01:06:28 am
content: Did you actually built the transformer?If so......EI laminations indeed rattle, if they are not impregnated with the heavy varnish specifically designed for that purpose.If it is a commercial transformer you purchased and is varnished and still rattles, you may be over driving it.

author: thermistor-guy
author_rank: Frequent Contributor
timestamp: April 22, 2020, 02:06:34 am
content: Quote from: Rachie5272 on April 22, 2020, 12:51:00 amFor telecom applications, we used to glue the cores and the windings, to stop them from moving. That was enough to meet acoustic emissions spec of telephone exchange equipment.There are still some potential acoustic emissions from magnetorestrictive effects on the core. I have no experience with this; maybe a sound-deadening mounting of the transformer will help. You may not need it.So treat the cores first, then the windings, then the mounting.

author: coromonadalix
author_rank: Super Contributor
timestamp: April 22, 2020, 02:31:08 am
content: better go with toroids xformersbut in your case yes dipping it in epoxy should do the trick

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 22, 2020, 02:48:02 am
content: Epoxy covers a lot of sins. I can't recommend a special type, but it will have to be a slow cure, low viscosity resin to wick into the cores and provide the needed sound control. You might find it easier to do some research on the varnish which was traditionally used and may well still be available. Tar has also been used for this in the long ago past. It works but is messy, tends to drip out if you get the core warm and smells bad. Not recommended.

author: WattsThat
author_rank: Frequent Contributor
timestamp: April 22, 2020, 04:20:02 am
content: Vacuum impregnation with an appropriate varnish is the easiest way fill every conceivable void. Standard practice for motor stators since forever. Material choice is everything, something chosen willy nilly can lead to flaming examples of transformer how not to.

author: schmitt trigger
author_rank: Super Contributor
timestamp: April 22, 2020, 03:15:46 pm
content: Now that someone has mentioned tar:In the 1990s, I worked for a company which manufactured, among other things, traditional (magnetic) fluorescent light ballasts.Because of their embedded air gaps, those transformers would buzz like crazy.Those were enclosed in sand-filled tar. The best sound deadening compound you can find.That was applied at a very high temperature with specialized equipment. Because the high temperature and that the tar will strongly adhere to the skin, which would cause extensive third-degree burns, THIS IS VERY DANGEROUS to do it manually.

author: Rachie5272
author_rank: Regular Contributor
timestamp: April 22, 2020, 03:57:31 pm
content: I had custom samples made by the factory. I'll ask them if they can do epoxy impregnation.The transformers are being driven pretty much to the edge of their capabilities. The sound they make it pretty low, but I'd still like to minimize it as much as possible. I'm not sure we have enough room for an additional enclosure though.How do toroids compare to E-core transformers? Physical volume is a driving factor in this case.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 22, 2020, 04:57:01 pm
content: At least with mains frequency toroidal transformer can be smaller than conventional EI cores. However I am not absolutely sure this is also true for the very small size in question here.One difference is that the toroidal cores can use better grain oriented material that can support a higher field (may not work well in small size) and has less magnetostriction in the low field range. If money is not a big issue, one could go with a relatively expensive noncrystalline (Nanoperm) core: they have even lower magnetostriction and less loss and magnetizing current. With the small size the extra prize tag may not be so bad. The point is more how well ring core winding work at the very small end.