The problem with rheos is that when they're used in the lower range of resistance (near short), they have to dissipate a lot of power. In this particular case, the rheo has to dissipate the most amount of power when its resistance is the same as the fans.
A correction to my previous post: if the total power is halved, and the resistance of the fan and rheo are about the same, then the power dissipated by the rheo is half the total power, and since we dropped the total power by half, the rheo has to dissipate 1/4 of the fans' rated power.
So a 3 Watt rheo would work for a 10 Watt fan, since it would need to be rated for at least 2.5 Watts.
If the rheo is not sufficiently powered, it will burn up. Radio-Shack probably doesn't carry anything like that, but it might be worth a look.
I ran the numbers in an Excel spreadsheet. If anyone wants a copy, let me know.
|