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How to test DC adapter for reliability and performance?

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Zero999:

--- Quote from: TimNJ on August 02, 2021, 03:44:28 pm ---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.

--- End quote ---
That must explain why I normally see such a construction used for mains frequency and large SMPS transformers.

I have seen a much smaller transformer using an intrinsically safe constuction, with separate bobbins for the primary and secondary, except they're inside one another. It was used inside an SMPS in an old TV. I'll see if I can find it, so I can take and post a picture.

Intrinsically safe transformers are also common in electronic halogen lamp transformers, except a toroidal transformer is used, with the primary encased between two, thick, double insulated plastic cups.
https://320volt.com/en/electronic-transformer-circuit-schematics-12v-halogen-lamp/

I generally prefer to design things which are intrinsically safe. If people need to perform tests, they can, but I certainly don't like relying on them.

wraper:

--- Quote from: Zero999 on August 02, 2021, 03:25:24 pm ---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.

--- End quote ---
Those pictures have nothing to do with transformers used in SMPS. If you try to make them like that, performance will suck. Not to say they are not inherently safe. Crack in the bobbin, and you may have mains voltage on the core.

wraper:

--- Quote from: Zero999 on August 02, 2021, 04:04:49 pm ---I generally prefer to design things which are intrinsically safe. If people need to perform tests, they can, but I certainly don't like relying on them.

--- End quote ---
You are checking for possible insulation defects as safety test. Not relying on it while ignoring the rest of production.

Zero999:

--- Quote from: wraper on August 02, 2021, 05:32:26 pm ---
--- Quote from: Zero999 on August 02, 2021, 03:25:24 pm ---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.

--- End quote ---
Those pictures have nothing to do with transformers used in SMPS. If you try to make them like that, performance will suck. Not to say they are not inherently safe. Crack in the bobbin, and you may have mains voltage on the core.

--- End quote ---
The core is normally earthed, or in a double insulated enclosure. Either way, choose a material which isn't brittle and it won't crack and it's a non issue.


--- Quote from: wraper on August 02, 2021, 05:37:58 pm ---
--- Quote from: Zero999 on August 02, 2021, 04:04:49 pm ---I generally prefer to design things which are intrinsically safe. If people need to perform tests, they can, but I certainly don't like relying on them.

--- End quote ---
You are checking for possible insulation defects as safety test. Not relying on it while ignoring the rest of production.

--- End quote ---
True, I jut was pointing out that is isn't always necessary to perform a hi pot test. I can think of plenty of electrical items which meet, or exceed the safety standards and haven't been subject to such a test. It's definitely mandatory in something like a transformer, with the primary and secondary on the same former, where there's the potential for a wire to be in the wrong place, or the tape to fail, but in other instances it's debatable where's there's any point, or not.

Anyway, it's off-topic. If it needs to be hi pot tested, it's the manufacture's job. I suggested the original poster test a small sample, as due diligence.

And here's a picture of the transformer I was talking about before. It came from an SMPS. The primary is on the outside and secondary in the middle. The two coils are on separately on a material which isn't brittle and won't crack.

Surajg:
Hello Everyone,

Thanks all for replies  :)
I have this DC electronic load tester. Can this help for basic test during sampling?
Like I keep it set for 12V and 2A and keep adapter ON and see if heats or any abnormal thing happens to adapter?

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