pir..110v or 12v?

[Lucie99]

Hello everybody

I wish to make a simple circuit, motion sensor to turn heaters on in my home, to help save funds during the cold winter months, and for a bit of fun to learn. I am a newbie, I know this is very very simple for most of you but it would be my most complex project so far

Goal: to build a simple motion sensor/pir circuit, to turn a relay on, with adjustable timing. e.g so I can adjust heater to stay on between 30 minutes to 3 hours, after motion is detected. I understand standard max heater draw is 1500 watts, so I will want a 15A relay?

I am trying to build this project from scratch, as opposed to picking up a cheap pir sensor from an old alarm system, even though that would be easier? My reason for doing it that way is simply I figured I would learn more...

Question one: Is it possible to keep the whole circuit 110v? e.g use a 110v pir instead of a 12v pir?
I dont know if its simple to include an onboard 110-12v converter? I wish to install this "inline" as my current heaters are hard wired. i.e I wish to avoid need to plug a transformer into an outlet, for space and simplicity and cosmetic reasons.

Question two: Adjustable timing: would I use an adjustable capacitor to get that sort of time range, or is there a better way?

Question three: am I better going with a solid state or mechanical relay? I estimate the relay would get tripped maybe 5 times a day, and be in the on position 10 hours a day.


Thankyou!

Lucie

 

[davenn]

hi there
welcome to EP

I am trying to build this project from scratch, as opposed to picking up a cheap pir sensor from an old alarm system, even though that would be easier? My reason for doing it that way is simply I figured I would learn more...

and if you screw up your 110V work, it might be the last project you ever work on
Do you really think you are skilled enough to work on mains voltages with high current ?

 

[Lucie99]

Yes I do, and thankyou for checking. Appreciate the safety concern.

Many years experience with fixing mostly 220v but also 110v electrical appliances, washing machines, dryers, stereos etc (mostly just finding and fixing faulty contacts, not "advanced repair" i.e I have only replaced individual faulty components on a handful of occasions).
Am comfortable rewiring houses (to the switchboard) and installing all the outlets and lightswitches etc.

Understand safety protocol in handling mains voltage electrical appliances, no safety issues to date. I am an advanced computer programmer by trade and very good with computer hardware as well, but understand that is an entirely different area, but I do possess the logical mindset. Also have done a bit of arduino programming, which was very easy, but I really lack the electronics knowledge to go with it.

I do wish to move more towards Ardunio/micro-controller work, however as I am already competent at programming, but possess very little electronics knowledge, I thought I would focus on improving my electronics knowledge, by trying to build a few micro-controller-free basic electronics projects. This is my first.

Where I lack knowledge, and am a complete beginner, is in circuit design etc. This is something I would like to fix
This is my very first post, and I am just starting out.... any help or steering greatly appreciated.

----

As a starter project, I simply wish to build, from scratch, devices to automatically turn on my hard-wired heaters when motion is detected, with some form of adjustable timed latch - so they turn off 0.5 to 3.0 hours after the most recent trigger.

--

I guess my first question is: can (and should) I build this as a pure 110v circuit? or should I step it down to 12v and just use a 12v/110v relay? Are there pros and cons to each path?

 

[davenn]

I had to ask

yes you should be using low voltage control, after all your timing and PIR circuitry will need low voltage/current
and it can be used to switch the SSR ( aka contactor relay)

 

[cjdelphi]

circuitry will need low voltage/current
and it can be used to switch the SSR ( aka contactor relay)

A contactor relay? Would imply contacts are made via mechanical action from an energized coil, that's not an SSR...

 

[Lucie99]

I had to ask

yes you should be using low voltage control, after all your timing and PIR circuitry will need low voltage/current
and it can be used to switch the SSR ( aka contactor relay)

Really Appreciate you asking

Thanks for the tips I now have a good starting point!

Question 1: Does it really make much of a difference if I go for a mechanical vs solid state relay for home usage like this? SSR is more expensive. Expecting ~50% of time on @ 1500watts.
Question 2: Would it be more standard to aim for 12v or 5v? Is there any real-world practical difference in using one or the other?

Thankyou

 

[cjdelphi]

For a heater stick with a mechanical relay as you won't need to worry about over heating, SSR's are better suited lighter loads but obviously an SSR could be used...

 

[Gryd3]

Instead of even touching the HV lines, why not just interrupt the signal between the controller and heater?
That is usually a LV line isn't it?

 

[Lucie99]

Good question, hadn't thought of that.

I'll share my reasoning, please do let me know your thoughts.

Its for an old Montreal apartment, with 5 old hard-wired wall-mounted heaters, each with just a simple thermostat dial.

For simplicity, the idea of being able multiple "motion sensor switches", and install them effectively inline on each heater was appealing, because:
1) When I move out they are easy to remove and take with me - the heaters are fixtures that belong to the building/landlord.
2) Trivial to transplant to any other device, such as lamps.
3) Attaching the motion sensor to the heater itself is not ideal - physical placement means the sensor would better placed "inline" on the mains cable to the heater, about a meter or two away, rather than on the heater itself. I also had heat concerns about having the pir/circuit too close to the heater.


Thankee

 

[CDRIVE]

Some Motion Detector Stuff to get you going...

Chris

 

[CDRIVE]

Oops I forgot to include Timers With Integral Relays too.

Chris

 

[Alec_t]

After the heater has been off for a time when the room is unoccupied, how long does it take to bring the room up to a comfortable temperature, bearing in mind that the heater is only 1500W? If the time is excessive, then power reduction, rather than switching off the heater completely, might be advisable.