Alright, the 9V battery is almost flat and my player only managed about 2/5 battery capacity. Perhaps it's the low capacity of the 9V cell, those cheap batteries.

Got bored while waiting for it to charge and i just finished soldering my DIY laptop cooler! :lol:
2x16cm fans! Will be doing the base tomorrow.. :D

But anyway, will be testing with other types of batteries for the charger over the next few days. Hopefully will get 1 with reasonable performance.

Re: USB Data Pins
 

The good'ol'LM7805 is an linear reg and hence very inefficient. You would get far better results from a DC-DC converter such as a switching regulator or buck converter. These will however require additional components, but will increase the lifetime of the 9V battery.

The reason for the drop in voltage when the battery is connected is that whenever you pull current from a battery, due to the electron movement, the potential will drop. As long as the voltage is above the "dropout" voltage for the regulator, the regulator will draw current and provide a stable output voltage. However, Impeeza is correct in that there is a voltage drop accross the LM7805 and this creates power loss and heat. DC-DC converters do not have this problem.

Using a series resistor to limit current is not advisable, as the resistor will drop the voltage and therefore eliminate the voltage regulation. If you want to limit the current, use a buck converter that has current limiting features. This will also improve efficiency.


Sorry for the lecture in power electronics, but it's what I do...
Oh, and Good Luck - try not to electrocute yourself by drawing 20A from a button battery :shock: