Dry Contact input relay

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joshv

New member
Location
Cincinnati, OH
I really need some help with a home automation project. I am looking for a relay to fulfill the following requirements and need some recommendations. I have searched all over and I must be using the wrong terminology for this relay, because I can't find what I am looking for.

I need to use a dry contact closure to activate the relay (input). I have taken measurements and it is truly dry contact, not low voltage. I have seen suggestions that require me to add a voltage source to input and I'd like to avoid this because I am not confident that the source can handle the additional voltage.

On the output side, I would prefer SPST Type C (both NO and NA options - if I am using terminology correctly). But a NO (type A I think) would suffice if type C is not possible given the input requirements. I am controlling 12V DC load, but would be happy if it could handle 5V DC as well for future use.

Price needs to be sub $20 each as I need 6 of these relays.

As far as form-factor, I am wiring this up to home security type devices (16ga wire in most cases) - so something that is either pre-wired or has a plug in option might be best. But I can work with anything that I can solder to or use crimped wire connectors, etc. Price and function are more important than form to me in this case.

TIA if anyone has ideas!
-Josh
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
150331-2010 EDT

joshv:

I can not understand your post.

Your have a "home automation" box you want to connect to. I have to assume that you want to connect to what I would can an "input". That means that by some action at that input the "home automation" box will take some action in response to your input. This is to be contrasted to an output from the box.

Based on this assumption what are the specifications for the input? If the specification says that a "dry contact" input is required, then that simply means you need some switch contact that opens and closes, and that there is no voltage or current supply in the switch. It is just a switch, nothing else.

This also means that if nothing is connected to the two input terminals that you should read a voltage between the terminals with a high impedance meter. Also if you connected an ammeter (probably a milliammeter) across the terminals you would meaesure current. You need to know the maximum input short circuit current of the input before you select a meter range.

Your input device can be a relay contact pair, a reed switch, a toggle switch, a pushbuttion, and certain solid-state switches.

Do you need a relay input? Possibly not. But you need isolated contacts from ground or anything else.

The choice of a suitable input switch will depend upon the source voltage and current from the "home automation" box. For example you almost certainly do not want to use silver-cadimum-oxide contacts as I assume the input source voltage will be low.

.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
I'm going to assume the home automation has a dry conduct output and you wish to activate a relay. Go look at a Newark, Mouser catalog. P&B K series, octal sockets maybe is a choice. However, as don said, you will have to pass some current through the dry contacts to pull in the relay. You could get cute and use some opto-isolated stuff and the current /voltage through the dry contacts would be really low. Again Mouser/Newark.

Usually commercially available Home Automation systems have a plethora of add-on auxilliaries. So, I'm guessing this is an engineering project and you will be hiring a card carrying electrician to do any work subject to the NEC.

As for the relay contacts, you listed the voltage as 12VDC now, and maybe 5VDC later. That's good, but you also need the current draw and load type: Load Amps, inductive, incandescent, resistive. And if the current is really low as in sub-milliamp, that takes a different type on contact chemistry.

ice
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
150331-2337 EDT

joshv:

ice caused me to reread your first post.

So it appears you want to use a "home automation" output to control something. What are the specs on this output? Is the output a normally open relay contact or some kind of solid-state switch, and is it isolated? The ratings on the output will determine what kind of load you can connect (your relay), what supply voltage, and isolation you need.

What do you want to control and how rapidly with your relay?

.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
I am closing this thread in accordance with forum rules. Since you are not an electrician, we are not allowed to help you perform electrical design or installation work.
 
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