Thermal runaway : Print fan trigger

Hi there! I have a problem with my printer.
I couldn't print overhangs very well so I decided to print myself a printfan mount for a 40mm fan.
The problem is that my print fan now triggers the runaway protection. The temperature drops from 205 to 195. I don't want to disable it. I also set in slic3r maximum fan speed at 70%. I also did a PID autotune.
Also, my ATX power supply voltage drops down when it heats the bed, maybe this is why it can't keep up the temperature? Or is there any other problem. I'd like to keep my ATX like this because at lower voltage the bed takes lower amps, at full voltage I don't think my power supply will keep up (350W total, 16A on 12v rail).
Other information :
Prusa i3 rework - standard Wade extruder
E3D V6lite with 40W chinese cartridge (the original one burned out, but this chinese one heats faster and so far it's good).
Pictures of setup

Edited 1 time(s). Last edit at 08/01/2015 01:08PM by icamaster.

insulate the hot end.

I insulated the hotend with kapton tape, same thing, it drops 10 degrees.
I also used a different power supply for the Headbed, so I think that this isn't the problem.
Maybe I didn't insulate the hotend good enough. Can i use teflon tape (like in plumbing), I can't find fiberglass insulation here.

Edited 1 time(s). Last edit at 08/02/2015 12:08PM by icamaster.

Use a duct - a layer fan should put little to no air on the hot end. If not possible, slow it down some more!

- Tim

You can see in the picture, it has a duct, maybe the design isn t good?
I turned it down to 50%. It is a larger 40mm fan, like really thick and draws 0.1A.