Thank's for your help, you are very informative.
One more question, the BLDC controller I am going to use for testing is this :-
http://grauonline.de/wordpress/?page_id=3122This BLDC Controller is rated for use with a maximum 36V supply so it says but the MOSFETs used (NCE6690) on it have an absolute Vds of 69V, so what would happen if you run it with a 48V supply?
I want to use the 48V supply so it is the same as the product I am back engineering, is it the back EMF that is the problem here not the 48V supply? if so changing these MOSFETs to 150V (IRFI4321PbF) with similar Id would be a good way to go so it can then be operated from 48V supply with less likelihood of any problems due to back EMF?
Thanks in advance.