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USB air pump power supply tear down.


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disclaimer: I'm not a certified PE, nor do I specialize in consumer electronics safety.  I'm also not a lawyer, or your mom, so take everything I say with a grain of salt.  I'm just some dude on the internet.

TLDR: Its not marked by a US test lab but seems like its actually designed well, safe, and usable.

I decided to take apart the USB power supply that came with my air pump.  It didn't have a mark from UL or intertek and the CE mark looks suspect (the C and the E are too close), so I was a little worried about it.  Below you'll see my photos.PXL_20210514_215653292.jpg.707908f4a984ba3db6f4e18eb7847ee7.jpg

It's got a 1 sided PCB with Chinese electrolytic capacitors.


Inside it looks like a standard flyback topology used with most low power AC to DC supplies.  I can't identify the exact controller IC (it's marked FT8378A), I assume its some Chinese chip not indexed by english speaking google.  The mains voltage seems well isolated from the low voltage side and the noise suppression cap is a proper Y rated capacitor, meaning it's unlikely to fail shorted and connect mains power to the output.  There's also proper separation between the high and low voltage side with a cutout in the PCB near the two closest high and low voltage points.PXL_20210515_013939311.jpg.fc74b9dcf7b075af1f8034085fb2ab81.jpg

There's a disc punched out of steel taped to the top.  I have no idea what this is for but I assume its to make it feel heavier and higher quality.  It sits right above the transformer so I guess there's a possibility its there to lower magnetic interference (??).



The two colored outputs are identical and have their D+ and D- lines connected together.  This should make any USB power delivery compliant device take up to 1.5A from the socket, which makes it a pretty decent phone charger too.  I don't have a good load tester so I can't verify the 2.1A rating on both outputs but 4.2A total seems like a lot to me.  I also didn't take the transformer apart to verify that the primary and secondary windings are properly isolated, this could be another possible path from mains to the USB output.


Over all this is clearly a cheaply made power supply (which isn't a bad thing, especially to run a motor) but for what I assume is a 1-2$ price point it seems properly designed and built.

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1 minute ago, Fish Folk said:

 were you experiencing any troubles? Or were you just concerned by the near proximity of the "C and E"??

I was mostly concerned about safety.  I didn't have any issues.  Most big stores (target, walmart etc) won't sell things that don't carry the UL or intertek (ETL) mark, because they haven't been tested to meet safety standards and in some cases (i think?) people can sue them for selling unsafe products.  A lot of stuff out of china thats REALLY cheap and connect to mains voltage are death traps waiting to happen, this can be especially true for USB chargers where either they weren't engineered with enough isolation or they cheaped out on components that may kill you when they fail.


24 minutes ago, Fish Folk said:

Not sure how you came by your price point estimates at the end,

Partly because of the cost cutting measures that were there.  A one sided PCB, and a third coil on the transformer for feedback rather than an opto-isolated feedback, smt components glued and wave soldered instead of reflowed.  And partly because cory said they added a dollar or two to the pump. 

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