I HIGHLY recommend you use a fan controller (automatic speed controller) to save your alternator, relay, and battery.

I have a Delta Controller on my e-fan setup and I would never go electric without it: http://www.dccontrol.com Unfortunately, their seem to have gone out of business?

Here is an archived version of their site dating back to Spring 2007: http://web.archive.org/web/20070304150513/http://www.dccontrol.com/

Here is an archived page with some info on the advantages of a variable speed controlled e-fan setup:
http://web.archive.org/web/20070928193904/www.dccontrol.com/introf2.htm

Here is a pretty nice write-up I posted back in 2006 on this subject:
http://board.marlincrawler.com/index.php?topic=22660.msg243208#msg243208

Good luck!
BigMike