Fan speed controllers?

Firstly, ....Silly question i know, but ''WHY'' do you want to run two fans off a single speed controller??

Large rumpus room 2 fans haha

Then you'll need two controllers, one for each fan!!

Bugger

What type of fans are they? I assume single phase but are they pedestal fans, ceiling fans, toilet type extract fans?

Ceiling single phase

If it looks like this type then they often don't follow the usual motor speed control methods. These things are usually between a 10 and 16 pole external rotor motor and they run with massive slip to the point of being close to stall. They often use varying the capacitance to achieve different speeds rather than a PWM controller you'd see on most motors. In theory you might be able to run two of them from a single control but I wouldn't advise it unless it's a project in your own house, it would be too unpredictable to do it in a customers place.

It is my own place they are both running off 1 controller but seem to be running very slow! Not sure if its just because of fan quality, im about to isolate 1 fan to see if it makes a difference

They're generally PSC configured motors and if they're capacitor speed controlled then to run two fans off one controller you'd probably need to replace the cap with a highr value component.

The capacitor they use are actually a 3 in 1 and usually have 5 wires like this one
Please note that this one has a discharge voltage of 250v so it's suitable for an American 110v fan.

Here's a website that has some info on how these fans work.

Cheers marvo the fans came with 2 identical capacitors would paralleling them work?

Capacitors work the opposite way to resistors when it comes to parallel and series arrangements. If you connect two 10uF caps in series you end up with 5uF in the circuit whereas if you connect two 10uF caps in parallel you end up with 20uF. So if you parallel two multi value capacitors you'll get roughly double the original capacitance at each speed setting which will give you a higher rotation speed.

I'm not sure how much electronics experience you have but would be best to find a supplier and buy a similar 5-lead multi capacitor that has higher values with the same discharge voltage or even better buy several packets of polypropylene or polyethylene foil capacitors of the correct discharge voltage and that way you can experiment easier by making up different capacitor networks of varying values for testing purposes. These capacitors are cheap to buy and easy to source at places like Farnell or RS Components or even Maplins

As to whether it will work or not I'm afraid you're in the twilight zone with this kinda thing. Because of the way these particular motors are designed to be practically running in constant stall and with high 'slip' changing the capacitance is not going to produce an easily predictable outcome. The motors are impedance protected usually so it will be difficult to destroy them by experimenting with different capacitances (within reason) so I'd suggest trial and error would be the way to go but please be aware there is always a chance you could damage one beyond repair even though it's a slim chance.

**Edit**
If you do some experiments let me know how you get on, I have about 10 ceiling fans in my house and 3 of them run very slow even on high speed. It's been on my list of thing to do for a year or two to actually try and get them running faster and with our temperatures being in the low 40's over the last week I'm getting earache from the family so it's become more urgent I get around to it. Mine are also controlled by a 5-lead capacitor but each one has its own speed control.

Awesome right up im going to experiment with paralleling the current capacitors i have to see if it helps otherwise ill try chase down higher value ones!