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How to test DC adapter for reliability and performance?
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Zero999:

--- Quote from: wraper on July 31, 2021, 05:26:19 pm ---
--- Quote from: Zero999 on July 31, 2021, 04:45:08 pm ---i.e. winding  the transformer on a double section bobbin,

--- End quote ---
Does not eliminate assembly defect where single wire gets into both sections.
--- End quote ---
Yes it does. I should have been more clear. By double section bobbin, I meant two bobbins: one for the primary and a separate one for the secondary, so there's no chance that can happen.
Gyro:
Unfortunately you don't get double bobbin transformers in smps mains adaptors, the leakage inductance is too high. To make matters worse, the primary and secondary are usually interleaved.

I very much doubt the OP would be sourcing traditional 50/60Hz transformer ones.
TimNJ:
At my first internship, for a new project, the company sourced around five (somewhat dodgy) power adapters with similar specs. The lead engineer had me open all of the units, apply polyester tape to the transformer winding, output cap(s), output diode, and primary-side switching transistor. (This was to give each component roughly the same emissivity, around 0.95-0.99.) Then, I ran each power supply at the same load for about an hour each. After one hour, I checked the temperatures of each of the aforementioned components with an IR gun. We compared the temperatures of the five units and the chose the power adapter with the best overall temperatures.

If testing at room temperature (25°C) like this, with the power adapter housing cracked open, I'd suggest to ensure that following temperatures are met:

Transformer: 85-90°C (max.)

Output diode, primary-side transistor, bridge rectifier, etc: 85°C (max.)

Output capacitors(s) and primary bulk cap:

Should be 105°C rating on the label. If it's 85°C, don't even bother. Check the manufacturer datasheet to find the endurance rating (as below):

~50°C  (max.) for 2,000 hour rated cap
~60°C  (max.) for 5,000 hour rated cap
~70°C  (max.) for 10,000 hour rated cap

These temperatures would give you about 30,000 - 35,000 hours life at full load and at max ambient of 40°C. Obviously, it's up to you to determine what is "reliable enough".


Those are just ballpark suggestions. And again, the temperatures above are assuming you are measuring component temperatures at room temperature ambient. Safety-wise, the transformer is most critical. Temperature testing won't tell you if the transformer is constructed correctly, but the farther away the temperature rating is from the enamel rating of the wire (usually 130°C), the better. The components will probably run at least 10°C hotter in the enclosure, plus add another 15°C to account for a typical worse case ambient of 40°C.

Also check that the Y-caps (usually blue ceramic disc capacitor) are Y1 or Y2 type. It should be printed with various symbols like VDE and other agencies. If it just says "102 1KV" that's probably not a safety rated capacitor.
wraper:

--- Quote from: Zero999 on July 31, 2021, 07:14:10 pm ---
--- Quote from: wraper on July 31, 2021, 05:26:19 pm ---
--- Quote from: Zero999 on July 31, 2021, 04:45:08 pm ---i.e. winding  the transformer on a double section bobbin,

--- End quote ---
Does not eliminate assembly defect where single wire gets into both sections.
--- End quote ---
Yes it does. I should have been more clear. By double section bobbin, I meant two bobbins: one for the primary and a separate one for the secondary, so there's no chance that can happen.

--- End quote ---
I know what it is. And there is a chance that something goes awry during winding (like a few turns going into a wrong section) or bobbin being defective and quite likely nobody will notice it visually.
Zero999:

--- Quote from: wraper on July 31, 2021, 09:13:41 pm ---
--- Quote from: Zero999 on July 31, 2021, 07:14:10 pm ---
--- Quote from: wraper on July 31, 2021, 05:26:19 pm ---
--- Quote from: Zero999 on July 31, 2021, 04:45:08 pm ---i.e. winding  the transformer on a double section bobbin,

--- End quote ---
Does not eliminate assembly defect where single wire gets into both sections.
--- End quote ---
Yes it does. I should have been more clear. By double section bobbin, I meant two bobbins: one for the primary and a separate one for the secondary, so there's no chance that can happen.

--- End quote ---
I know what it is. And there is a chance that something goes awry during winding (like a few turns going into a wrong section) or bobbin being defective and quite likely nobody will notice it visually.

--- End quote ---
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.
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