General > General Technical Chat

How to test DC adapter for reliability and performance?

<< < (4/6) > >>

wraper:

--- Quote from: Zero999 on July 31, 2021, 09:37:43 pm ---You clearly don't know what it is. The primary and secondary coils are wound separately, on different formers, so it isn't possible for any of the turns to go onto the wrong section. They are then placed, either side by side, or inside of one another, on the same core. I have disassembled transformers before and have been able to hold the secondary in one hand and and the primary in the other, without unwinding them. I have a small ignition transformer on my desk at the moment, which is wound using this method. The primary is wound in the middle, on a small former, then a larger former, containing the secondary is placed on top and the whole thing potted in transparent resin.

--- End quote ---
You talked about bobbins with multiple sections then about separate bobbins. Nonetheless even in that case screw up is still possible during transformer assembly. Wires still come out of bobbins and still need to be connected to terminals.

Zero999:

--- Quote from: wraper on August 01, 2021, 02:00:48 pm ---
--- Quote from: Zero999 on July 31, 2021, 09:37:43 pm ---You clearly don't know what it is. The primary and secondary coils are wound separately, on different formers, so it isn't possible for any of the turns to go onto the wrong section. They are then placed, either side by side, or inside of one another, on the same core. I have disassembled transformers before and have been able to hold the secondary in one hand and and the primary in the other, without unwinding them. I have a small ignition transformer on my desk at the moment, which is wound using this method. The primary is wound in the middle, on a small former, then a larger former, containing the secondary is placed on top and the whole thing potted in transparent resin.

--- End quote ---
You talked about bobbins with multiple sections then about separate bobbins. Nonetheless even in that case screw up is still possible during transformer assembly. Wires still come out of bobbins and still need to be connected to terminals.

--- End quote ---
And there can be no electrical connection between the primary and secondary, if the terminals are on oppisite sides of the transformer. I'll have to dig out one of the transformers I've salvaged from something to show you want I mean.

wraper:

--- Quote from: Zero999 on August 02, 2021, 10:48:19 am ---
--- Quote from: wraper on August 01, 2021, 02:00:48 pm ---
--- Quote from: Zero999 on July 31, 2021, 09:37:43 pm ---You clearly don't know what it is. The primary and secondary coils are wound separately, on different formers, so it isn't possible for any of the turns to go onto the wrong section. They are then placed, either side by side, or inside of one another, on the same core. I have disassembled transformers before and have been able to hold the secondary in one hand and and the primary in the other, without unwinding them. I have a small ignition transformer on my desk at the moment, which is wound using this method. The primary is wound in the middle, on a small former, then a larger former, containing the secondary is placed on top and the whole thing potted in transparent resin.

--- End quote ---
You talked about bobbins with multiple sections then about separate bobbins. Nonetheless even in that case screw up is still possible during transformer assembly. Wires still come out of bobbins and still need to be connected to terminals.

--- End quote ---
And there can be no electrical connection between the primary and secondary, if the terminals are on oppisite sides of the transformer. I'll have to dig out one of the transformers I've salvaged from something to show you want I mean.

--- End quote ---
There can be some manufacturing defect you cannot possibly imagine. So relying on "defect cannot possibly happen" in safety critical situation is flawed logic. For example there may be a monkey brain personnel who can assemble wrong something that shouldn't be possibly assembled wrong. For example Proton rocket with 3 out of 6 acceleration sensors mounted upside down, even though there were mounting guides which should make doing so impossible, not to say it even passed inspection.

Zero999:
You are funny the way you like to argue for no reason. Is it a hobby? Anyway, that video is completely irrelevant and off-topic, since it's a about a rocket launch, rather than a mass produced item.

Of course, there's always a possibility something unforseen might happen and no amount of testing can be done to stop it.

There are ways to design things to be intrinsically safe, with minimal testing required. Indeed, there are instances where, a high pot test won't gaurantee safety, for example if the manufacturer of the wire skimped on the insulation material, so it melts under normal load conditions. The device will pass the high pot test in the factory, but fail dangerously in the field.

Anyway, here are a couple of pictures of transformers which are designed to be intrinsicly safe, without any need for a high pot test. Note how the primary and secondary windings are on completely separate formers and the terminals are opposite one another. There is no way, a wire from the primary can touch the secondary. I've also dismantled transformer which appeared from the outset to have two coils wound on one former, but they were really separate formers, as I was able to completely remove the secondary and rewind it. They cost more to make, but money is saved with less testing.

TimNJ:
Regarding this whole split-bobbin/multi-section bobbin discussion, probably >99.9% of SMPS adapters <100W do not use this kind of transformer construction. Flyback has been the topology of choice for many years (in various incarnations) and splitting the bobbin into primary and secondary halves is a great way to reduce the efficiency by 10-20%. Of course, for high voltage transformers, as was alluded to, the multi-section bobbins are necessary to prevent turn-to-turn breakdown.

Split bobbin is useful in some resonant topologies where leakage inductance is purposefully added to create an 'L' in the resonant tank circuit. Otherwise, it's not particularly a good ideas.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod