HDD File Transfer Issue

I just purchased a new USB 3.0 External HDD which I want to add some files to from another External HDD.
Each one is USB connected to computer. I started to copy and paste the files until it was time to quit and turn off computer. The next day, I continued the process but ran into a problem. Each time I went to paste the file to the new HDD it wouldn't copy it and disconnected. The only way I could bring it back was to unplug it and re-connect but it continued to do the same thing each time I tried.

 

I'm sorry that is what I did. I also formatted the drive and tried to load all the files at once using drag and drop. The drive loaded about 50gb and then stopped and disconnected.

 

Would there be sufficient power available through USB to do that job in a HDD?
Is the external drive enclosure powered separately?

 

I did set the power options for optimizing the copy process. The actions of the HDD left me to believe it may have some defect. I have sent it back and will try a different approach with another HDD. Thanks for your help.

 

I set the copy process loading 658 files (706GB). The HDD started to copy fine at 76mb. At 24% the speed would drop to the 60mb range then 50mbs and slowly drop to 0 and message would say Source Drive no longer available. I should have been able to restart the process after re-connecting the HDD but it would not copy ANY files. CHKDSK did not show anything wrong with HDD but I still think there may have been . Have sent HDD back and will try again with new HDD. Thanks