Primair fan controller

[lightsout]

hey guys

i've bought a primair fan controller, with a thermostat and speed control for 2 fans. My problem is that my filter/fan combo is meant for a much larger room. My room has (and can only have) one vent for air in. so when the temp gets above what i've set on the dial and my exhaust fan comes on full power i can hear the motor strain as the room is under negative pressure.

 

Before i bought the primair controller i just had my fan on a fan speed controller i borrowed off an old ceiling fan. Can i some how wire that in to slow down the fan when it comes on full power? or, as i'm not using the 2nd fan dial, can i wire that up to control the speed of fan1 when the thermostat temp is above what i've set? any electronics gurus out there?

 

I have experimented with a few different cheap intake fans but none of them could match the airflow of the exhaust, so i've just got passive air in at the moment

[Innocent criminal]

There are a couple of peeps here that really know their stuff when it comes to electrickery, one of them may have an idea of the best way to go about this...

 

My understanding is you should be able to run a speed controller inline between the thermo switch and fan, that way only affecting the fan not the primair unit.

Also beware of running your fan on a speed controller, some fans burn out very quickly when run at lower current, this will be worse if the fan is running under heavy load.

 

IMHO you would have been better off simply buying a smaller exhaust fan and fixing the problem that way.

 

Edited August 30, 2009 by TheHeadCing

[chuffer]

You can use the fan speed controller if its got a Triac circuit (sometimes called a chopper), but absolutely NOT if its just resisters or you'll burn out the fan. Wire it in same way as you did with your last fan, and leave it set on the level that seems to be right.

However this is not a good fix for a number of technical reasons. I would be recommending that you get yourself a lower powered fan instead, and you'll avoid a lot of nasty problems

[lightsout]

ok, bit strapped for cash at the moment so i'll have to be using this fan at least until the end of this crop. if i wired the controller in (not sure whether it has a triac circuit or not, i'll check it out tomorrow) i'm guessing it would also slow the fan down when it is on idle speed? what sort of nasty problems am i likely to run into?

[chuffer]

If its got a Triac it will most likely be in a standard black plastic block, rectangular shape about 1cm long, with a metal back and 3 leads coming out the bottom. One will go to the speed controlling dial which will be a pot or a series of switches with resisters on each one.

 

Running a motor at below full speed when its working against a load (like restricted air in the pipe) can make it try to draw more current than is intended, which can burn it out (sounds back to front I know). Chopper circuits should prevent this, but I'm uncomfortable recomending much without being there to see what you've got.

 

Still, smoke test thinking says just run it for a while and monitor the temperature of the motor to check if all is ok. Also smell it before and after a run, looking for the distinctive smell of burning insulation, you'll know it if its there. If you get that then stop the experiment. If you don't get the smell, and the motor doesn't get hot, then maybe you are ok.

 

Don't touch any wiring when any of it is live - ever !!!

[lightsout]

ok thanks alot for your help chuffer. i had a look at my speed controller (pic attached) it kind of fits your description. can you tell from the pic? sorry shitty phone quality. Do you reckoin there would be any way of wiring the idle speed controller, on the primair unit, meant for an intake fan, in to control the max speed of the exhaust fan?

 

Edited September 1, 2009 by lightsout

[chuffer]

fraid I cant tell from the picture. You could try it, wired in between the timer and the fan, give it the smoke test as I described before. I'd be happier hearing you get yourself a lower rated fan