lsusb -v | less
#or
ls -l /sys/bus/usb/devices

echo -n 0 > /sys/bus/usb/devices/<device>/power/state

#from manual (hdparm -help)
 
#-S
#    Set the standby (spindown) timeout for the drive. This value is used by the drive to determine how long to
#wait (with no disk activity) before turning off the spindle motor to save power. Under such circumstances, the
#drive may take as long as 30 seconds to respond to a subsequent disk access, though most drives are much quicker.
#The encoding of the timeout value is somewhat peculiar. A value of zero means "timeouts are disabled": the device
#will not automatically enter standby mode. Values from 1 to 240 specify multiples of 5 seconds, yielding timeouts
#from 5 seconds to 20 minutes. Values from 241 to 251 specify from 1 to 11 units of 30 minutes, yielding timeouts
#from 30 minutes to 5.5 hours. A value of 252 signifies a timeout of 21 minutes. A value of 253 sets a
#vendor-defined timeout period between 8 and 12 hours, and the value 254 is reserved. 255 is interpreted as 21
#minutes plus 15 seconds. Note that some older drives may have very different interpretations of these values.
 
#A simple example
#I would set a timeout of 5 minutes
#5 minutes = 5 minutes * 60 (seconds / minute) = 300 seconds
#300 seconds / 5 seconds (the multiplicator in the manual) = 60 (the final value)
#
#I would set a timeout of 10 minutes
#10 minutes = 10 minutes * 60 (seconds / minute) = 600 seconds
#600 seconds / 5 seconds (the multiplicator in the manual) = 120 (the final value)
 
#set the spindown-time of 5 minutes
sudo hdparm -S 60 /dev/sda