for a while i've had a b&q fan controller, similar to the dimmer switch type, linked with my rts5 thermostat.
its worked well, but when the thermostat turns off the fan is buzzing coz of the fan controller.
i've had it wired like this

i've got this ATC controller which is variable.
when i connect it up to the thermostat, the fan controller works with no buzzing on lowest setting, but when the rts5 kicks in, it blows the fuse in the ATC controller.
is there anyway i can work around it so it does'nt blow the fuse???

heres a few pics of the controller.

n e suggestions plz?

it's a transformer, you can't just go and short out the output of a transformer. you're trying to put 240v on the output of the transformer, so rather than your transformer being a step down transformer, i.e. 240v on the input, say, 170, on the output, your putting 240v on the out (which now becomes the input) and are getting something like 340v on what is now the output!! the lower the setting you have the transformer set to when the stat shorts it out the higher the voltage is on the input terminals, you could be getting over a 1000v on those terminals!!!! very dangerous!!

this isn't whast popping the fuse though, just highlighting how dangerous whats happening is to yourself!


because the output of the transformer m beay only halfway down the length of the coil, or possibly even further, unlike the input which is all the way at the top, you're putting 240v onto only half the resistance, which means a lot more current flows, and your fuse pops.

you can get round this though, with just a bit of rewiring, i'll need to see a diagram of the thermostat wiring to check if you can use that stat though, as you can't use some electronic types, because they need 240v on a certain terminal

check this link. see the picture of the transformer diagram.... when your stat switches over it's putting 240v to your fan, but at the same time it's taking the 240v off the input to your transformer and putting on the output, which is further down the coil, meaning less resistance (reactance) to neutral, which in the end is where the current is trying to flow, less reactance means more current, = poppy poppy fuse


http://en.wikipedia.org/wiki/Autotransformer


what you need, is the fan to be connected to the common terminal. the output of your transformer going to the terminal of the stat that is connected to the common terminal when the stat is happy with the temperature, and your 240v goes to the terminal that only connects to common when the stat is calling for cooling, when this happens the output terminal that was connected tothe common is disconnected......... meaning, that the output of the transformer is isolated from the circuit, and the 240v now being directed towards your fan, can't back feed through the transformer and pop the fuse

hi scraglor, thx for the info, i'll try it the way you suggested.

although i no longer have the diagram for the thermostat, coz i've had it a while.
the bridge between live and common is to enable the thermostat to output 240v through terminal 2 when the thermosat kicks in.
calling for cooling is terminal 2 on this stat, and terminal 3 is calling for heating so not used.

hope this helps.
cheers

yeah i know, that's the usual way for electronic controllers, because you can just stick 240v on the output, and all that'll happen is the voltage will be = on both sides of the controller, so it ceases to operate. an autotransformer has a neutral connection connected to the output though, so sticking 240v on it, means current flows. and blows the fuse.

you need to use the call for heat, because for the stat to work with a transformer you need to disconnect the output of the transformer, so the common needs to go to the fan, variable output to the call for heat, and 240v on call for cooling. this way you cant have both the variable output and 240v on the same terminal at the same time......

because your stat has a seperate live, AND a common terminal, it should be ok, because the electric feed needed for the stat to work is seperate from the switching circuit.

thx dude, i sort of get it, but a little confused now.

any chance of a simple diagram on how to wire it all up?

thx again

im on a mac, don't have any kind of drawing program on this crappy thing, but it's pretty easy, look in the variac thread, think it's sticky'd in the diy forum

yeh i had a look, so is it basically like this scraglor?
there is a fourth terminal, but its not connected in any way to the stat.

yeah, you got it, except the thermostat still needs 240v on the L, as this turns the thermostat on, so link 2 to L

ok cheers m8, will give it a try now.

cheers

just wired it up, and its working perfectly scraglor...nice one m8, thx m8.

scraglor...it is a 5amp fuse i use with this setup right?

cheers
m8