I have a bluetooth adaptor that is not working very well. This is because its range is about 30cm, as the antenna is broken (I have checked with my phone and the bluetooth speaker). As I have had it for years, the warranty had expired, and I was going to bin it anyway, I cracked it open. Then I plugged it into my laptop. I disconnected the charger beforehand, so I couldn't fry myself with 240 volts! (I'm joking here, I know chargers have fuses and other stuff to stop this).

I got my voltmeter out and started measuring some voltages, to see if there were any problems, or if any fuses had blown. After a few minutes, I got a bit bored, and found a paper clip! As it was covered around the middle, and bare at the ends, I had an idea. I put one end on the +5V pin, and the other near the port and there was a spark. I don't mean a 1mm spark, I mean like a 2 cm spark.

Instantly Windows 7 made the disconnecting sound, and the adaptor did not work. However, I plugged it back in again, and amazingly it still worked! I did it again, and there was a spark again, I think it was to the -5v pin. This really baffled me. I mean 5 volts at 750 ma (It's a USB 2.0 port) is nowhere enough to give a spark. The battery is about 17 volts. The pc carried on working normally. This happened in November, and I am typing this question now!

I thought there were restrictions in place, so even a malfunctioning device could not use enough current to get a spark...

Why did this happen?

Is it just my laptop (Dell Inspiron 1545)?

  • I had no USB devices plugged in at the time. Also I think I have already broken the USB standards by creating a short circuit! I still have the adaptor, I will try and measure voltages on the spark sometime.
    – George
    Dec 22, 2013 at 22:39
  • Heh, 5 volts isn't enough to give a spark when you're shorting it? And 2cm sounds like static discharge. Dec 23, 2013 at 2:47
  • So is it static then?
    – George
    Dec 24, 2013 at 12:25
  • @GeorgeH - 5v is enough to give a spark. Heck, the amount of voltage in an ESD event is enough, if the component is sensitive to such an event ( most ICBs are ). Although the part would also have to be powered for that to happen. Seems like you don't understand the reason electronics "spark". You don't even know what you connected the 5v pin too it seems.
    – Ramhound
    Apr 19, 2014 at 22:43
  • @Ramhound. Thanks for the info. I binned the adaptor. It was dead anyway!
    – George
    Apr 19, 2014 at 22:45


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.