Using PIR sensor unconventionally for controlling bathroom extractor fan

[Johnnz]

I have to install an extractor fan above the shower cubical in our bathroom this coming week and am thinking about how to control it. Since there is already wiring in the wall to have it powered by the light switch I will be using that, however since I dont want it to come on and create a draft everytime the bathroom is used I am thinking of placing a PIR sensor against one of the hot water pipes leading to the shower (only have shower and hand basin using hot water in this bathroom). The fan will be low (12vac) voltage since it is in a wet zone, so I am thinking of having the light switch power up the transformer(s) to power a low voltage pir sensor that will in turn switch on the extractor fan when hot water runs through the pipe it is pointed at.
Think it will work? only thing I am worried about is that I notice a lot of sensor lights always come on immediatly when you switch them on whether or not there is any source of heat moving in front of them.

[blanco]

Seems to me that you need to use a simple temperature sensor
and not a PIR sensor which detects body heat AND movement.

[blanco]

Better still, why not keep it simple and instal a
ceiling pullswitch for the fan ? that gives total
control to the user without any pipe attachments
and additional cables. - Sorted!

[godfather]

The PIR may come on for a brief period when the hot water heats the pipe up, but unless there is then a constant movement of that heat it will turn off.

As above, they trigger on moving heat, not static heat.

[rob_on_guitar]

Unless you set the PIR to activate on the shower door.

[Jester]

I can just imagine the comments:


"Oooooh look, an alarm in the bathroom!"

or

"Uuuum, Is there a hidden camera in here somewhere ....?"

:D

[PaulD]

I dont want it to come on and create a draft everytime the bathroom is used

Try it first, you might be disappointed about the lack of draft :D

[Graham L]

PIRs don't work very well when turned on and off as you propose. They are very sensitive heat detectors, and take a while to thermally stabilize themselves when first turned on. The PIR is best left turned on., then it could detect the warm moving body in the shower.

I suppose a real geek would have a web camera, connected to a computer with software for detection of motion in the shower. You could have a pay per view web site. :)

A thermocouple fixed to the hot pipe might work, but would take some development. (I suspect the necesssary amplifier would swing a bit when turned on -- like the PIR system).

A thermostatic switch like Jaycar's ST3831 might do the job, if the pipe will get to 50 degrees C.

A real switch is the simplest solution, and it will work reliably.

[rob_on_guitar]

You can set them to either heat or movement or a combo of both.

Lol! at the 'is there a hidden camera...'

[Johnnz]

Good point about the possibility of being checking whether or not the fan will create any noticeable draft, I have been disappointed before...

Hm, just looking at Jaycar website - seems that this kitset will do the trick: cat number KC5381:


"Economy Adjustable Temperature Switch

Ref: High Performance Electronic Projects for Cars - Silicon Chip Publications.
If you don’t need the display, or the huge operational range of the High Range Adjustable Temperature Switch with LCD, then this unit is a great alternative. It has an adjustable switching temperature up to 245°C, and it can be configured to trigger with rising or falling temperature. It has adjustable hysteresis (the difference between on/off temp) which is a great feature many other units do not possess. It can be used to operate cooling fans on a radiator or amplifier, over-temp warning lights or alarms, and much more. The small temperature sensor reacts quickly to temp changes. Kit supplied with PCB, NTC Thermistor, and all electronic components."

Only thing is whether or not it will trigger the relay upon power up?

Back to PIR sensors - the one I installed for the lights in the hallway isn't sensitive enough to activate the beyond about 3.5-4 meters. Is it likely there will be a trimpot inside the sensor that can be adjusted? There isn't anything on the exterior that can be adjusted.

[Agent_24]

Why not just have a separate switch for the fan? everyone I know with one just does that...

[Johnnz]

Now where's the fun in that? :nerd: :D

[Graham L]

"Keep it simple" is a very good rule.

A simple switch that an electrician can understand will work. Every time.

A simple thermostatic switch fixed to a hot water pipe should work every time.

The PIR won't work without a lot of work. It probably won't ever work properly pointed at the pipe. It's designed to do a completely different task. All the movement detection PIRs I've seen need the moving of the target to create the signal which is amplified to produce the required action.
The pipe doesn't move. If you must use a PIR, point it so it sees the moving body in the shower.

Silicon Chip had a project a while ago which detected the noise of the water and turned it off after four minutes or so for power (and water) economy. That would work better than the PIR.

I still think I'd use a switch to activate a fan. If I wanted to impress the natives with technological magic which worked, I'd use a thermostatic switch on the pipe. I would not use a PIR, even to impress the natives with technological magic which didn't work.

[Johnnz]

Thanks for the tips about PIR's being unsuitable. I have just completed the installation of the extractor fan this afternoon (currently just wired into the light switch) and tested it having a shower. It certainly does the job - it felt really quite drafty in there and the vanity mirror never fogged up which is a first. Walls dry too. Although the outside temp was a rather mild 7 degrees there was a lot of condensation dripping down inside the grill, so all in all it is very effective. (positioned on the wall inside shower cubicle about 50mm below the ceiling). By the way this is a Manrose 150mm 12vac fan.

Although this is a pretty good system as is, I still plan to make up the kitset I posted early (temperature switch). Although it isn't necessary of course, I haven't done a kitset for ages and it should help to refresh and expand a bit of my electronics knowledge. I ordered it yesterday from Jaycar and it turned up today! Record time for anything i have ever ordered. Only paid for parcel post too.

Will update this thread when I get it done.

[PaulD]

By the way this is a Manrose 150mm 12vac fan.

Glad to hear that it does shift some air. What sort of price is the 12vac version?

[Agent_24]

I ordered it yesterday from Jaycar and it turned up today! Record time for anything i have ever ordered. Only paid for parcel post too.

Sounds right to me, if you paid the same day you ordered (eg: credit/debit card) and parcelpost is now done via courier anyway.

[Johnnz]

Glad to hear that it does shift some air. What sort of price is the 12vac version?

Got it for $133 from Redpaths. Outside grill was half the price of Placemakers there too.

Yes, I am pleased about the result too. We have 100mm 240v Manrose fans through the rest of the house and they don't do jack.

[BobM]

[QUOTE=Graham L;698476]"Keep it simple" is a very good rule.



. . . . . . . . . . . . . . . . .detected the noise of the water and turned it off after four minutes or so for power (and water) economy. That would work better than the PIR.

But every time you went to the toilet,the shower would come on! :D :D

[godfather]

I use 10" 230v fans from Bunnings, under $25...

[R2x1]

. . . But every time you went to the toilet,the shower would come on! :D :D

With a Northern Hemisphere shower, you may produce a bidet.