DC fan controller modification

[t1muk4s]

Hello!
I have a problem with a fan controller. The controller is able to regulate the voltage to the fan from 7 to 15 volts DC (speed regulation).
Also the controller is switching the voltage in the output from one output to the other so that the fan is able to spin in both directions (it switches the negative part of the output).
The fan has three wires so i assume that it has two coils.
I need to connect more fans to the controller, but the controller is only able to control 50W of fans. My goal is to boost somehow it to 300 or more watts.
I added a simple sketch to show the system.
What kind of solution is for this problem (so that the speed regulation works with the new switch block)?
Best wishes,
T.

 

[chuckey]

Quite a few problems here.
First, New power given as 300W, I guess this is when the fans have 15V on them, so when the fans are down to 7V, the power will fall to 150 W (from a 15V source), so the current is = 150/7 ~ 20A, so the controller dissipates 8V X 20 A = 160 W - you will need two fans extra to keep the controller cool.
Second to reverse the polarity of the DC feed, the easiest way would be to use a relay, again a 20A contact rating relay is a big job and will need 5W of power on its coil to actuate it.
I would have a serious think about using a transformer which is 30-0-30 V and using SCRs as your controlled rectifiers. If you switch the SCRs on when the positive peak is there, you will get a pulsing positive DC, as you switch them later in the cycle, the positive voltage will fall. As you delay the switching the output voltage will go through zero then the inverse connected SCRs take over and you get a pulsing DC. Its a lot of fiddling about but your heat dissipation should go down to 20 W or so.
Frank