When choosing electric fans an important consideration is CFM as related to amperage draw and the alternator capacity. As a general rule of thumb for every 90 CFM you're going to pull one amp and the highest draw is on start-up of the fan.
As an example I run two engine radiator cooling fans drawing 20amps each and a transmission radiator cooling fan drawing that draws 15amps. All are installed with ignition on relays with two temperature senders; one engine, one transmission. That's 55amps of draw without temp sensors, ignition, stereo, lights or other electrical requirements.
For that reason, after watching the lights seriously dim way down at idle when the fans went on with the stock 60amp alternator, I went to a 140amp alternator that puts out 90amps at idle.
