Friday, 8 April 2016

Charging your smartphone via subwoofers USB port?

Last Friday will be a day I'll never Forget.I had just bought a subwoofer and was enjoying the output when suddenly it stopped working.(After 6hours of Use).My panic button got activated.I tried troubleshooting but all in vain.I couldn't believe it
I went on a Google search spree and came across people who were experiencing the similar problem.After a tiresome digging ,I came up with 2 theories;
1)My subwoofer had switched to auto-standby because of lack of an audio signal and the remedy to this was to Set my receiver base higher
2)A Fuse had blown and also the ic had been damaged.This was my worst fear.So I leant towards the first theory.
So today,I went to try my sub on a
Friend's house and was disappointed.

My sub couldn't work.My friend called on a qualified technician who came and opened up the sub and after careful examination Located a burnt I.C.This confirmed my worst Fears.Then it dawned on me .
Flashback,during the 6 hours I was playing music,I had my phone charging using the USB port while at the same time using it.I plugged into the Port while at 12% ,as time went by there was surprisingly no change .It stuck at 12%.Did I overdraw more power from the port that led to the damage of the IC?
With 5V , the USB bus can charge a

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small single-cell Li-ion pack, but there is a danger of overloading the USB hub . Charging a device that draws 5V together with other loads(in my case using the phone while charging) connected will exceed the port’s current limit(5V) leading to a voltage drop and a possible system damage. To prevent overload, some subs contain current-limiting circuits that switches to Auto standby mode when overdrawn.Now ,Charging my 3.7V Li-ion began by applying a constant current to a voltage peak of 4.2V, Where did the (5.0V-4.2V)?Read on the Attrition power .Once it reached the peak voltage,the voltage started plummeting.Due to the voltage drop,as well as losses in the charging circuit and the fact that I was using the phone while charging,this might have led an overdraw lets say 2 times my 3.7V(7.4V) which exceeds the circuit limit by 2.4V (thereby charging circuit loss) and this led to the ic damage.
The Ic was replaced and all is good.Just Learnt my lesson.

 Read on the attrition power