Toroidal transformer potting [thermal issue ?] - Page 1
Forum section: electronics / projects

author: Coordonnée_chromatique
author_rank: Frequent Contributor
timestamp: November 03, 2020, 04:30:30 pm
content: Hello all,i expect that you've had a good day.I’m searching for a material in order to dope my transformer potting sauce.I was looking at some marble granules because of the good thermal effusivity but this material is also paramagnetic.My question is, when immersed into the intense transformer magnetic field the marble granules will start to be polarized by the Xformer, will they heat ?

author: coppercone2
author_rank: Super Contributor
timestamp: November 03, 2020, 05:24:48 pm
content: i don't like the idea because they are abrasive anyway, they would need to be stone polished, not just chipped, meaning rotary tumbler and sieve, then acid etch and to increase porosity for adhesion then ultrasonic cleaning to get rid of residual dust (will form a poor bond) and then heavily rinsed (possibly multiple ultrasonic cycles), dried and potted. I don't think you are saving yourself money compared to buying thermally conductive epoxy.Also those epoxys are weird, you need to bake them, or they have a very long cure time (some don't cure). I think its because epoxy is thermally activated to some degree and if you add thermal conductor to it and decrease the epoxy per unit volume the reaction does not occur. It would be difficult to tune this yourself for reliable service. Otherwise it can delaminate and you will have a strong insulator form (it needs to adhere properly to work as a heat sink). Also to get very good thermal conductivity they are expenisve and it does not appear you can easily jury rig similar parameters.Also for whatever reason, some of the epoxies become glass-hard and are prone to shattering after a natural cure, so you need to bake them afterwards to get it to a potted consistency, meaning the addition of thermal modifiers causes weird changes to resin that you are not familiar with as a typical glue user. I would hate trying to figure out a new glue mixture..I have made mixtures with sand and epoxy before and it works more like cement then epoxy, difficult to fill and degas in tall structures, etc. What you want to do might be a good bet with hot tar. Also, it seems that conventional mold release is effected by the addition of particles (my mold release totally failed with a strong bond to the area that was supposed to release)

author: Gyro
author_rank: Super Contributor
timestamp: November 03, 2020, 05:26:28 pm
content: Toroidal transformers don't have an intense external magnetic field - it is contained within the core.

author: Coordonnée_chromatique
author_rank: Frequent Contributor
timestamp: November 03, 2020, 06:24:31 pm
content: Quote from: coppercone2 on November 03, 2020, 05:24:48 pmThe epoxy is great but too expensive for my application since i need 6 liters of sauce. I'm finally envisaging to use some calcium aluminate cement, the thermal conductivity is around 1.2W/m.k, the density is very high 2100kg/m3 and it is very cheap.Quote from: Gyro on November 03, 2020, 05:26:28 pmWill you use some another paramagnetic material for the doping granules, like the aluminium in order to raise the thermal condictivity ?

author: coppercone2
author_rank: Super Contributor
timestamp: November 03, 2020, 06:37:28 pm
content: have you considered making a more advanced mold to reduce the amount of glue you are using, i.e. formed doughnuts, to reduce the amount of glue and allow you use to use a proper glue? I would put it in a mold and give it only a mm or so layer. I am not sure drowning it is a good solutionI would make a mold and use a grinder flap wheel to make it smooth

author: Coordonnée_chromatique
author_rank: Frequent Contributor
timestamp: November 03, 2020, 06:50:48 pm
content: Quote from: coppercone2 on November 03, 2020, 06:37:28 pmThe thickness and the mass is required to muffle the magnetostriction noises, i'm on the way to NC15.https://www.plitron.com/news/low-noise-toroidal-technology/"But, because of the their highly efficient nature, standard toroidal transformers become noisy under adverse line conditions, such as overvoltage and DC offset, (and tend to draw high inrush currents during start-up). With increasingly deteriorating power lines over the years, these adverse conditions are becoming more prevalent""For reference, a good recording studio’s noise level is typically NC 15 to ensure a virtually silent noise floor, while in offices NC 30 is usual. LONO™ transformers measured in our Noise Test Chamber under adverse mains conditions produce less than NC 19 at 1 metre distance. At 2 metres they produce less than NC 13"

author: coppercone2
author_rank: Super Contributor
timestamp: November 03, 2020, 07:02:05 pm
content: oh, then this is normal, noise proofing something is really expensive if you do it rightnot sure where additives will get you, you need to do some small scale experiments (1/10th at least).What I did with one of my prototypes with a E-core is I put it over a steel plate, and to attach it to the steel plate, I used loctite glue to glue rubber strips to the bottom of the plate, then I glued the microwave transformer on top (already very strong with loctite prism glue and proper surface prep, I was unable to remove it with a maul), then I made holes in aluminum flat bar, glued rubber strip to that, then put the flat bar over the transformer flange and then I put bolts into it (not through the transformer flange) so it was being braced by 4 bolts from the top on 2 strips of thick aluminum and glued to aluminum on the bottom (as you would with a bar to press a TO-package to a heat sink on both sides without using the screw hole on the To-220 so you get even pressure.WIth this heavy fixture I was able to put the transformer on a thinner sheet metal table and it did not make much noise.in short, pro audio is expensive. people will be happy to pay

author: Coordonnée_chromatique
author_rank: Frequent Contributor
timestamp: November 03, 2020, 07:38:12 pm
content: Quote from: coppercone2 on November 03, 2020, 07:02:05 pm"proaudio is expensive"Quietaudio is expensive IHMOYou are reading my mind, Pilton is very expensive, i've got a lot of EI transformers and recentely buyed a lot of NTC sensors that will be glued on the transformers before the casting process in order to validate the thermal aspect. The calcium aluminate cement and the sanding granules are very cheap.The transformers sound pollution is awfull :https://sndup.net/9b6g/pollution.flac