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USB Micro Power Enough to Start a Fire

I had a scary incident this weekend that I want to share with readers in hopes of avoiding a catastrophe. I plugged my USB micro in backwards to a point where it got so hot that it melted out of both the cord and the device it was charging.

This concerns me greatly as USB is supposed to be limited in current to 2.5 amps from the data I found. Also, I never should have been able to plug this in backwards like I did. This is what we have standards for. Finally, there should be options that limit current when plugged in backwards. None of this seemed to work in this case.

I have had trouble with the fit on the USB headphone jack from day one. Even when oriented correctly it doesn’t seem to be an easy fit. On this particular day I was seething from a bulged disk and throbbing from an intense upper body pounding from my fitness routine. Suffice it to say, the pain offset my attention to detail. I was beyond my usual bonehead self and somehow plugged this in backwards. I don’t remember forcing anything. I remember the usual fit that didn’t seem right.

Luckily, I felt the heat of the current being dumped into the headphones and tried to pull the cord out. The entire connector came out of the headphones having been fused by the heat to the USB micro connector from the cord. Then the combination of connectors fell out of the USB cord end (light blue in the picture) onto a paper that could have easily caught fire from the heat.

Rounding out this collection of components was the USB jack that provided the power. This was a simple combination of two USB jacks with a cigarette lighter plug that is wired for 12 VDC automotive systems. I surmised there is a voltage down converter to the USB five volts. I wonder if the converter limits current as per USB specs. Apparently, it didn’t or otherwise, 2.5 amps causes great amounts of heat.

During all of this, the 12 VDC to USB plug kept sourcing current (it’s fused by the way at the car harness) and the headphones kept playing as the battery was still charged. Therefore, it was business as usual at the source and the load. The source has a lithium based battery, by the way. That’s even more cause for concern.

All ended well although there was a potential for a catastrophe yet I discovered and fixed the situation in time. If you have a USB charger, check the plug for heat right after plugging it in. I was lucky and found the problem immediately. I hope this blog saves you as well.

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