my shuffle does not charge when my imac is asleep
Is there a way to keep the usb ports active when the iMac is in sleep mode?
iMac
From this page on charging your iPod
http://support.apple.com/kb/HT1384
Note: If using a portable computer, make sure it is plugged into power and that the lid or display is open because if the lid is closed the computer may go into either standby, sleep, or hibernation mode and iPod will not charge.
If there is a way of keeping them active it does not appear to supported by Apple