MobileRead Forums - View Single Post - PRS-650 Charging issue

elcreative · 07-17-2011, 07:24 PM

pidgeon92... don't resurrect the "too much power" story again...

it's been killed so many times... USB is 5V at 500mA as standard... the voltage is ALWAYS 5V while the current can vary (I use 2,000 mA USB PSU)... excess voltage fries things, excess current is just that - a device takes as much current as it needs - if it wants 500mA and there's 2,000 available then it takes 500mA.

Modern USB powered devices can also handle variable power and can take from 500mA upwards depending on the device, they start at 300-500mA and then query if more is available, if it is then it'll step the power draw up to the device's max (or the PSU's max if less than the device).

Bottom line: Excess voltage can wreck things but USB PSUs are a standard 5V so no excess unless PSU is totally broken. Current is taken as needed...

07-17-2011, 07:24 PM	#58
elcreative Wizard Posts: 2,888 Karma: 5875940 Join Date: Dec 2007 Device: PRS505, 600, 350, 650, Nexus 7, Note III, iPad 4 etc	pidgeon92... don't resurrect the "too much power" story again... it's been killed so many times... USB is 5V at 500mA as standard... the voltage is ALWAYS 5V while the current can vary (I use 2,000 mA USB PSU)... excess voltage fries things, excess current is just that - a device takes as much current as it needs - if it wants 500mA and there's 2,000 available then it takes 500mA. Modern USB powered devices can also handle variable power and can take from 500mA upwards depending on the device, they start at 300-500mA and then query if more is available, if it is then it'll step the power draw up to the device's max (or the PSU's max if less than the device). Bottom line: Excess voltage can wreck things but USB PSUs are a standard 5V so no excess unless PSU is totally broken. Current is taken as needed... Last edited by elcreative; 07-17-2011 at 07:26 PM.