12vdc motor speed controller question

[1971challenger]

Hi, I (will)have a 12vdc radiator cooling fan. I am using it for a different purpose. I haven't received the fan yet but the manufacturer say it draws 13 amps. I assume this is at full speed, (But I probly won't run it at full speed) but when I get it I will connect it to an ammeter to see what it really is. I kinda doubt if it draws that much. If it does I will have to get a 15 amp power supply. My question is how to vary the speed of this fan the cheapest way possible? Would a rheostat do it? and what value in ohms and watts will I need? I figure with a rheostat I may have to crank it up to get it started and then slow it down.
Thanks in advance.

 

[Resqueline]

50W, 13A, sub-10 Ohm Rheostats aren't plentiful or cheap, & neither is 15A 12V PSU's. How about an adjustable PSU to begin with? It won't run so hot either. There are also diagrams for fan speed regulators on the net, just search.

 

[fish]

You could always use a fairly simple 555 circuit to generate a PWM signal, and then connect that to a FET which can handle the current (shouldn't be too expensive if you have good sources). You can then adjust the PWM duty cycle with a pot to vary the speed.

Also, that's a 156W fan. That is one heck of a fan. Maybe the 13A is the peak starting current? In which case a hefty capacitor bank may well come in handy.