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Input Relays

Posted: Fri Mar 15, 2019 11:23 pm
by walterwoj
I'm looking for a suggestion for where to get (which ones to get) multiple relays (4) to use for power sensing inputs. I'm looking for 110vac input relays that can close a 3.3/5vdc circuit. preferably 4+ on one board or at least easily connected to the pi and wire used in pi projects. You thought are welcome!

Background:
I am going to wire my pi with a 8 channel relay board (already acquired) to control my garage. I will be controlling my furnace, 3 overhead light circuits (led lights, so low load), garage door (with input to tell if it's open) and my air compressor (I'll use a second heavier duty relay to keep from overloading the main relay). This question pertains to the overhead lights. I want to use the relay board in conjunction with 3 way switches so I have a fail-over way to switch the lights if there are issues with the pi. Because of this there would be no way to know if the lights are on or of when the relay switches (without knowing the position of the other switch on the circuit) I need to 'input' the light's state (powered or not). I've looked at CT type clamps and detectors but they are: 1.) Overkill, I don't need to know how much energy is flowing just weather it is or not: and 2.) too sensitive and probably prone to false positives without sufficient space between all the wires.(might detect flow in nearby wires) I'm open to other ideas for this solution but I think a 110v relay that closes an input on the pi to tell it if there is power is the best (so far).

Re: Input Relays

Posted: Sat Mar 16, 2019 11:16 am
by boyoh
walterwoj wrote:
Fri Mar 15, 2019 11:23 pm
I'm looking for a suggestion for where to get (which ones to get) multiple relays (4) to use for power sensing inputs. I'm looking for 110vac input relays that can close a 3.3/5vdc circuit. preferably 4+ on one board or at least easily connected to the pi and wire used in pi projects. You thought are welcome!

Background:
I am going to wire my pi with a 8 channel relay board (already acquired) to control my garage. I will be controlling my furnace, 3 overhead light circuits (led lights, so low load), garage door (with input to tell if it's open) and my air compressor (I'll use a second heavier duty relay to keep from overloading the main relay). This question pertains to the overhead lights. I want to use the relay board in conjunction with 3 way switches so I have a fail-over way to switch the lights if there are issues with the pi. Because of this there would be no way to know if the lights are on or of when the relay switches (without knowing the position of the other switch on the circuit) I need to 'input' the light's state (powered or not). I've looked at CT type clamps and detectors but they are: 1.) Overkill, I don't need to know how much energy is flowing just weather it is or not: and 2.) too sensitive and probably prone to false positives without sufficient space between all the wires.(might detect flow in nearby wires) I'm open to other ideas for this solution but I think a 110v relay that closes an input on the pi to tell it if there is power is the best (so far).
This project is not for one with very little knowledge of mains electrical work, There are too many variables ( IFF’s or BUT’s) in your project
There must be total isolation between mains and low voltage (Safety)
The Pi programming must be fail to safe, ( Garage Door’s( ect)

Re: Input Relays

Posted: Sat Mar 16, 2019 12:12 pm
by Burngate
Why not use a light sensor?

Re: Input Relays

Posted: Sat Mar 16, 2019 4:23 pm
by walterwoj
boyoh: I agree with you about safety and the requirement of mains knowledge. I would say my knowledge of mains power is excellent as I have several house re-wires and entrance cable/service panel/meter socket installs under my belt. I'm not an electrician but I'm as close as you can get without the licence (IMHO). For what I am doing the required mains knowledge is well within my body of knowledge. :ugeek:

Burngate: A light sensor was considered but the distances involved (30+ feet to the farthest light) would require running a LOT of extra wire and would be very 'in-elegant'. I think having some way of sensing the circuit's status from the wires themselves (because they will be inside the project enclosure already) would be most efficient. So far, relays would appear to be the best way. :D


So does anyone have a type of relay that they have used and would recommend for this use? :?:

Re: Input Relays

Posted: Sat Mar 16, 2019 5:06 pm
by drgeoff
I suggest optocouplers. For each, use a capacitor as the major part of the voltage dropper.

Re: Input Relays

Posted: Sat Mar 16, 2019 5:35 pm
by walterwoj
drgeoff: Generally optocouplers are low voltage and DC. I need 110vac on one end and 3.3/5vdc on the other. Also relays are by nature isolators for stepping up/down voltage or changing types of power (ac/dc)

All I'm really looking for is some recommendations on RELAYS, please? 110vac coil designed for project/maker work.

Re: Input Relays

Posted: Sat Mar 16, 2019 5:42 pm
by drgeoff
walterwoj wrote:
Sat Mar 16, 2019 5:35 pm
drgeoff: Generally optocouplers are low voltage and DC. I need 110vac on one end and 3.3/5vdc on the other. Also relays are by nature isolators for stepping up/down voltage or changing types of power (ac/dc)

All I'm really looking for is some recommendations on RELAYS, please? 110vac coil designed for project/maker work.
Optocouplers give kilovolts of isolation.. Yes you need to add a diode or use an opto that has an AC compatible input. The capacitor I mentioned is to drop the voltage. Similar to a resistor but doesn't get hot.

Re: Input Relays

Posted: Sat Mar 16, 2019 5:56 pm
by walterwoj
drgeoff: Can you point me towards some 110v optocouplers then? My google-fu is failing me and I'm not finding any rated for that input. I did find this one but it's rated for 220v and in don't know that it will work on 110v

Re: Input Relays

Posted: Sat Mar 16, 2019 6:08 pm
by drgeoff
walterwoj wrote:
Sat Mar 16, 2019 5:56 pm
drgeoff: Can you point me towards some 110v optocouplers then? My google-fu is failing me and I'm not finding any rated for that input. I did find this one but it's rated for 220v and in don't know that it will work on 110v
No, I have not suggested 110 volt optocouplers. You don't appear to understand the use of a capacitor as an AC dropper. Try googling that.

And you need to understand that the on input side of an opto the primary consideration is current not voltage.

Re: Input Relays

Posted: Sat Mar 16, 2019 7:02 pm
by NGC6543
Check out the RM84 series relays, for instance: RM84-2012-35-5110.

I've not used that particular one but it seems to fit your requirements, and is quite small and inexpensive (for an AC-coil relay).

A relay does seem the simplest solution. As to the optocoupler method, there's a page explaining how to power the optocoupler's LED here: http://www.turbokeu.com/myprojects/acled.htm

You still have to then interface the output to the Pi of course, and maintain proper separation of AC/DC sides on the PCB. Another option is a common 110V neon indicator lamp and a phototransistor, etc.

Re: Input Relays

Posted: Sat Mar 16, 2019 9:00 pm
by walterwoj
NGC6543: Thank you! A recommendation like that is what I was looking for. :mrgreen:

Re: Input Relays

Posted: Sun Mar 17, 2019 10:32 am
by boyoh
If you want to monitor mains power using a opto isolator
back to the Pi, why not use a 5vdc power adapter plugged
In to the circuit you want to monitor, Use the 5vdc to switch
The opto isolator IR transmitter then use the opto transistor
To switch 3.3v to a Pi in/put, this will give you total isolation.
(The Raspberry Pi is Not Plug & Play)
Regards BoyOh Retired Electrical / Electronics Technician

Re: Input Relays

Posted: Sun Mar 17, 2019 11:31 am
by Brandon92
You could also buy for example this kind of relay. This allow you for a easy connection and are reasonable small. And they have other types as well (and there are other brands as well)

Re: Input Relays

Posted: Sun Mar 17, 2019 11:57 am
by rpdom
NGC6543 wrote:
Sat Mar 16, 2019 7:02 pm
As to the optocoupler method, there's a page explaining how to power the optocoupler's LED here: http://www.turbokeu.com/myprojects/acled.htm
I note that on those diagrams the discharge resistor is directly across the mains input. On pretty much every other circuit I've seen for a capacitive dropper, the discharge resistor is connected across the capacitor.

Re: Input Relays

Posted: Sun Mar 17, 2019 12:10 pm
by Burngate
Is there a reason behind that?
I can't see what difference it would make, given the relative sizes of the voltages involved.

Re: Input Relays

Posted: Sun Mar 17, 2019 12:19 pm
by rpdom
I'm not sure. But basically it's job is to discharge that capacitor, the diodes and other resistor don't need it.

Re: Input Relays

Posted: Sun Mar 17, 2019 4:01 pm
by boyoh
Using a 5v+ power adapter , you will be using full wave rectified
Smooth filtered 5vdc, all component parameters worked out for you
BoyOh

Re: Input Relays

Posted: Sun Mar 17, 2019 4:30 pm
by drgeoff
boyoh wrote:
Sun Mar 17, 2019 4:01 pm
Using a 5v+ power adapter , you will be using full wave rectified
Smooth filtered 5vdc, all component parameters worked out for you
BoyOh
Unnecessarily expensive and possibly bulky given that the OP wants 4.

Re: Input Relays

Posted: Sun Mar 17, 2019 7:23 pm
by boyoh
You should not attempt to build, test, or use this type of circuit unless you are experienced and competent in handling AC mains and high voltage. Do not touch this circuit. Depending on:
built either many or all points are at mains potential while powered. Further any point in the circuit can be at mains or higher voltage at any time, all it takes is a single component failing or some spike on mains. There is no transformer or other source of galvanic isolation. Even after disconnecting from mains, the dropping capacitor can hold a dangerous high voltage.
WARNING: AC Capacitor voltage dropper
Regards Boy Oh

Re: Input Relays

Posted: Sun Mar 17, 2019 7:30 pm
by rpdom
boyoh wrote:
Sun Mar 17, 2019 7:23 pm
Even after disconnecting from mains, the dropping capacitor can hold a dangerous high voltage.
That is why it has a discharge resistor. Those circuits are commonly used in LED lamps up to about 6W. The resistor has to discharge the capacitor quickly to stop people getting a shock from a bulb that has just been switched off and removed from the socket.

Re: Input Relays

Posted: Sun Mar 17, 2019 10:50 pm
by boyoh
rpdom wrote:
Sun Mar 17, 2019 7:30 pm
boyoh wrote:
Sun Mar 17, 2019 7:23 pm
Even after disconnecting from mains, the dropping capacitor can hold a dangerous high voltage.
That is why it has a discharge resistor. Those circuits are commonly used in LED lamps up to about 6W. The resistor has to discharge the capacitor quickly to stop people getting a shock from a bulb that has just been switched off and removed from the socket.
You should not encourage the untrained to build or work
On mains voltages, This capacitor mains voltage dropper is not
for the armature to build.
BoyoH

Re: Input Relays

Posted: Sun Mar 17, 2019 11:38 pm
by rpdom
boyoh wrote:
Sun Mar 17, 2019 10:50 pm
You should not encourage the untrained to build or work
On mains voltages, This capacitor mains voltage dropper is not
for the armature to build.
BoyoH
I did not.

I merely replied to your statement.