[paulgato]

26w wastage isn't too bad. That's less than half of what mine wastes. What wattage is your motor at full speed?

At 12.4v mine wastes around 50w (50w, 53w or 46w) at all speeds apart from full speed. (At 14.4v it wastes 66w, 74w or 62w at speeds 1, 2 and 3 respectively.)

To be honest, I don't really know what these PWM's look like. I only know what I've read online myself. I think the one you linked to is probably the kind of thing to use. PWM motor controllers I've seen online look similar and cost a similar amount. However, a 15A rating would not be enough for my blower motor, and even if yours is significantly smaller I still don't think a 15A rating would be enough. Motors can sometimes take a surge of power when they first start which is much higher than their sustained current draw. This isn't normally an issue with simple resistors, as they would take a while to overheat anyway, but I think you'd need to over-specify an electronic controller by quite a wide margin to avoid problems. In theory, a nice big capacitor across the windings of the motor would supply the start-up current boost required but it's better to get a controller you are sure is big enough to start with. But I don't really know any of this from first hand experience. Maybe these controllers have large enough output capacitors built in to them anyway. Doesn't look like, but maybe.

One thing (as far as I have read) that you need to be aware of is the frequency at which the PWM switches. If that frequency is within the audio range then the motor can end up audibly humming. 20+KHz should apparently be OK unless you've got ears like a bat. ;-)

But do your own research and don't rely on what I say. I've only recently looked into these things since I realised how much power those resistors are wasting.

If you fit a PWM before I do let us know how well it works.