I still remember that many years ago I planned to build a huge microcomputer system from scratch. The processor is ready for the 68020 or 68030, and I also got the VME prototyping board and chassis (although I don't plan to use the VME bus). Like my other ambitious projects, it has not made substantial progress. But considering my new demand for power, I think of the 400 VA toroid kit that I bought for that computer project. "Ring coil kit?" Hey - you might ask what it is. At least one manufacturer at the time produced a series of such kits, in fact, with a pre-wound primary coil core. As for the secondary coil, you can wrap it according to your needs. I have been using a 14ga magnet wire because this voltage is very suitable for switching power modules. In fact, the voltage is generated by two 16V windings, producing two 21 VDC rails for the (non-isolated) module. Since the voltage does not need to be adjusted, this avoids the inefficiency of the entire linear power supply. The biggest loss is the bridge rectifier. CDEL itself also requires power: MOSFET drive requires 12V (fan relay may also be required), while other parts require 3.3V. These are fine, I just need to put a few more coil windings on this "doughnut". And the winding does not have to be 14ga. 450 mV per revolution. Potting Using a toroidal coil, I quickly built a half-wave power supply to test the DC-DC module. Under load, the transformer's chirp/beep noise is quite large. I also remembered the experience of customizing a toroidal coil for an active speaker a few years ago. There was a bit of noise (just a little bit) during the first potting, although the noise of the loop coil was not large. When the second potting was done, I told the manufacturer to use epoxy resin to pot the holes in the “doughnutâ€. There is no noise at all, this is absolutely true. Therefore, this time I also want to do the same. But this time the buzz was much louder (I guess it was because the secondary winding was too loose) and I decided to pot the entire ring. However, this can be done with a lot of expensive epoxy! It may be possible to fill it with some silicone caulking agent. Ok... I don't dare recommend this process. It's messy, any silicone area will take a long time to dry out (it's not as fast as chemical curing. Maybe it's better to fill it in 2~4 steps, let it dry for one step each time). Although it looks not very beautiful, I am quite satisfied with the results. Does it completely cure the noisy buzz? No, but the noise has indeed dropped a lot, at least 10 decibels. When I listened carefully, I realized that the snoring will gradually increase after the AC is connected. Half...wave...rect. The magnetization of the transformer is unbalanced because it is only loaded for half the time. If you use the appropriate bridge, the buzz will basically disappear. I am still very happy to make a potting for this huge monster. It is also much stronger and safer than a bare ring core. And I have reserved a large enough "doughnut" bolt hole so that additional windings can be added if needed later. In fact, I will even add some 14ga windings that are directly connected to the front panel posts of some fixed voltage (possibly 5V) power converters. There is now a third 7.8V original winding, and I will do the same for it. You can also customize your own transformer without having to buy a kit. Any existing toroidal coil can be used, but I still recommend finding a coil with a ring core that is not potted. other @Brian park commented that it is not a good idea to enclose electronic devices with “interstitial†silicone. Unless you use silica gel specifically for electronics, it will corrode copper wires by releasing acid. Silica gel cannot penetrate and fix the winding unless it is potted while winding. I have always used a little varnish to fix the windings, no matter whether it is a toroidal coil or an EI transformer, there is never noise. More important than winding is to fix the iron laminations on the EI transformer. Are you charging for that large capacitor (after the bridge)? Peak currents may be the culprit in causing noise, not half-wave rectification. Investment Casting, also known as lost wax casting, includes wax pressing, wax repairing, tree formation, paste, wax melting, casting metal liquid and post-treatment processes. Lost wax casting is the process of making a wax mold of the part to be cast, and then coating the wax mold with mud. After the clay mold is dried, melt the wax mold inside in hot water. Melt the wax mold out of the clay mold and then roast into pottery mold. Once roasted. Generally, a casting port is left when the mold is made, and then molten metal is poured into the pouring port. After cooling, the required parts are made. Investment Casting,Lost Wax Casting,Steel Investment Casting,Stainless Steel Investment Casting Tianhui Machine Co.,Ltd , https://www.thcastings.com
