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Recently, I have bought this product. It is basically a USB cable, with a magnetic end, and a tiny attachment that goes into the mobile device.

I plugged it into my laptop cooling stand (which has USB hub), and then plugged the tiny "adapter" into my phone. The magnetic end of the cable was free, and it stuck onto the metal leg of my work table.

It caused short circuit and burnt the fan. I only realized this after I plugged it into my laptop, and the same thing caused the laptop to restart immediately.

Here is a photo of the gadget.

enter image description here

What is the reason behind this? The leg of my table is not connected to my computer, obviously. So, how come this USB cable was able to burn my fan, and restart my laptop?

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  • $\begingroup$ The restart is probably due to the USB crashing down. If both poles of the connector of the cable touch the table, there's a short. Shouldn't be enough for a fire, but your USB driver will probably activate some preservation mode. $\endgroup$ – Mast Dec 3 '19 at 10:08
  • $\begingroup$ Can you post an image of the product? The attached link requires authentication. $\endgroup$ – Mahendra Gunawardena Dec 3 '19 at 13:47
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I got one as well, but with a blue LED. Luckily I have very few iron stuff around, but perhaps I should tape the few exposed screws near the floor.

A better design would be: (housing and magnet not shown)

 ┃ーーーーー GND
 ︙┃┠wwwwー +5V spring
ーー┨wwwwwwx main spring, not connected
 ︙┃┠wwwwー +5V spring
 ┃ーーーーー GND

+5V connected when contact pin has passed the GND ring. Only downside is that there can not come any dust between the inner contacts. Multiple springs can be used. Of course it results in higher costs as well.

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So, the answer is obviously that the inner pin sticks out too much. I couldn't stop fiddling and I got a spark when connecting. It's also entirely possibly to reverse the polarity albeit like 0% chance of it happening with normal use.

Found a simple solution though... I cut a piece of plastic from cotton swab and grabbed a thin iron ring. I widened the plastic piece a bit with a chopstick and made sure the length mached the ring. It seems to stay in place without the help of any glue!

parts and tools assembled

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