Should not be any limit at all.
There is, however, a very severe limit on having the download interrupted in any way whatsoever, power outage, cable slipped out, etc., if that happens during the process you have a door stop, a paper weight, useless lump of metal.
I'm guessing that is what happened to you. Be more careful next time, cause this is a fairly expensive mistake. You will need a new controller, and to install it.