if you do the sums with a 1hp electric motor, 1hp = 750w (ish)

Now as power = current x voltage

so lets say that you are running a 12v system with a 750w motor.

750/12 = 62.5A - far more than a sabretooth can handle.

Another thing you have to bear in mind with electric motors is that when they are stalled they will draw far higher currents. 1hp motors can draw as much as 200amps when stalled before they burn out. For a split second before the motor starts to rotate it is effectively stalled. Now it won't quite draw the huge 200amps or so but it still will draw more current than its regular running current.

You haven't said what you are going to be running with the fan motor so I am going to assume either electronic axe or spinning disc?

If you are looking for on/off control then using one of these relays

http://www.jaycarelectronics.co.uk/prod ... BCATID=754

along with a battleswitch (see technobots) will give you on off control of a motor. I have used these relays with magmotors and they have handled them even when stalled!

Proportional control gets a bit trickier and more expensive. The victor as Jamie mentions would do the job along with a number of other controllers.

But whatever you do, please don't wire a sabretooth to a fan motor!!! They are nice speed controllers when run within their range. I ran one towards its limits and smoked two of them and that was only with drill motors.