I have 10 pc fans running in my indoor. All of them wired with 3 AC-DC 12V transformers (each one cost me 3â?¬). Each transformer has polarity selection button and voltage output regulable (from 3 to 12V). Wiring in very simple.

I have 4 8cm fans conected to a transformer (it gives 1,2A, and each fan uses 0,2A). Works with lights, to cool them.

Another 3 to other 1,2A transformer (one 12cm fan running at 0,4A and two 8cm running at 0,19A). They work 24/7.

And other 3 running with lighs on, 2 12cm and 1 8cm. This transformer become very hot, because the load is similar to the output. I would prefer to use a 1,5A transformer, but i was unable to find it cheap.

DC fans RPM (=noise and air flow) are easily dimmable, selecting the output V. Aditionally, i have a regulable bay for computers wich can regulate the speed of 4 fans (i have it near the thermohygrometer, so i adjust fans speed according to temp and humidity, specially the one i use as humidifier). I bought the 2 packs of 4 thermaltake fans (2 12cm and 2 8cm) with the regulating bay for 20â?¬ in a local computer store.