Rewinding a shorted SMPS transformer
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From: Tim Williams on 18 Feb 2010 00:28 "Robert Baer" <robertbaer(a)localnet.com> wrote in message news:4MGdnTLON4AsKOHWnZ2dnUVZ_tidnZ2d(a)posted.localnet... > <varnish> more insoluble than the core itself. Been there. Hmm, I'm willing to bet 70% nitric acid would do a number on it. It might not eat away the core too quickly, but it will certainly be etched. Of course, you won't have any turns left to count, as the copper will disappear before anything else. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: JosephKK on 18 Feb 2010 01:11 On Wed, 17 Feb 2010 17:24:39 -0500, Jim Flanagan <jflan(a)tampabay.rr.com> wrote: > >I have a defective SMPS transformer which I cannot replace and >am contemplating rewinding the primary which has shorted >internally. I've rewound 60Hz power transformers in the past with >no problems. What are some pitfalls that I might run into when >attempting this. > >Any help is appreciated. >Thanks >Jim It is important to know why is failed. You are not ready to rewind until you know why and how to prevent recurrence.
From: pimpom on 18 Feb 2010 07:40 Jim Flanagan wrote: > I have a defective SMPS transformer which I cannot replace and > am contemplating rewinding the primary which has shorted > internally. I've rewound 60Hz power transformers in the past > with > no problems. What are some pitfalls that I might run into when > attempting this. > For someone with experience in winding mains transformers, the only major problem is taking the core apart without breaking the brittle material. Some time ago, I had to build an SMPS from scratch for a client. The original was badly burnt and the company quoted >$2000 for a replacement. I designed a new one to meet the specs and at first thought I'd wind the transformer on the core of a transformer from an old computer SMPS. Taking it apart proved to be more of a hassle than I anticipated, so I just bought a new core and used that. I didn't have to count the turns or measure the wire gauges as the new one was my own design. But if I had to, I could have done it by unthreading the windings through the core window or simply by breaking the core first. (I felt adequately compensated by the $800 I charged my clients, and they appreciated the >60% saving in cost. A satisfactory deal all round).
From: life imitates life on 18 Feb 2010 08:30 On Wed, 17 Feb 2010 23:28:54 -0600, "Tim Williams" <tmoranwms(a)charter.net> wrote: >"Robert Baer" <robertbaer(a)localnet.com> wrote in message >news:4MGdnTLON4AsKOHWnZ2dnUVZ_tidnZ2d(a)posted.localnet... >> <varnish> more insoluble than the core itself. Been there. > >Hmm, I'm willing to bet 70% nitric acid would do a number on it. It might >not eat away the core too quickly, but it will certainly be etched. Of >course, you won't have any turns left to count, as the copper will disappear >before anything else. > >Tim The best way to determine winding construction on a vacuum impregnated pot core transformer is to source and buy a new core and bobbin, and then destructively dissect the old one. A cros-sectional cut through the bobbin of the old core will allow one to examine winding layers and get turns count and wire gauges from that.
From: life imitates life on 18 Feb 2010 08:33
On Wed, 17 Feb 2010 22:11:17 -0800, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Wed, 17 Feb 2010 17:24:39 -0500, Jim Flanagan <jflan(a)tampabay.rr.com> wrote: > >> >>I have a defective SMPS transformer which I cannot replace and >>am contemplating rewinding the primary which has shorted >>internally. I've rewound 60Hz power transformers in the past with >>no problems. What are some pitfalls that I might run into when >>attempting this. >> >>Any help is appreciated. >>Thanks >>Jim > >It is important to know why is failed. You are not ready to rewind >until you know why and how to prevent recurrence. Many transformer failures are due to poor or improper construction choices made either by its designer or by its builder. The failure mode is usually in the form of an arc-over event. If a transformer gets driven to failure through current, then the drive side of it was poorly designed, or the transformer itself was poorly designed electrically speaking. This is, of course, a reference to small form factor pot core transformers. |