I bought a 12 volt relay from ebay. My thought was I'd provide the back end with a 12v car battery or 12v lawn tractor battery and 1 line from the arduino to signal the LOW/HIGH trigger. Then on the front end I'd power a 12v DC device, such as, a water pump or CPU fan. Do I have the right idea for this board? How is the "COM: Common Interface Relays" used?
Module description:
the module uses genuine quality relay, normally open interfaces Maximum load: AC 250V/10A, DC 30V/10A;
using SMD optocoupler isolation, driving ability, stable performance; trigger current 5mA;
the module Operating voltage 12V;
the module can be high or low by a jumper setting trigger;
fault-tolerant design, even if the control line is broken, the relay will not operate;
the power indicator (green), the relay status indicator (red)
the interface design of human nature, all interfaces are available through a direct connection terminal leads, very convenient
IN: can be high or low level control relay
Relay outputs:
NO: normally open relay interface
COM: Common Interface Relays
NC: normally closed relay interface
High and low level trigger options:
It is low level trigger when jumper connect to LOW pin
It is high level trigger when jumper connect to HIGH pin
Great info on that page! I understand better now. In experimenting with DC power, I would connect a lamp's positive (+) side to COM and NO leading to battery's positive terminal. Then the lamp's negative (-) side to battery's negative terminal. So when does a wire get connected to "NC: normally closed relay interface"? Also, the backend of the relay would be connected to the arduino Vcc, GND, and digital output pin. It was mentioned that switching a relay off using DC power could melt/destroy it.
A DC spark / arc could continue for some time, acting like a miniature welder and welding relay contacts together.
Instead use a Power Field Effect Transistors. Since my relay says SRD-12VDC-SL-C then I should be safe using 12VDC devices, right?? 8)
The relay COIL is rated at 12VDC and when you apply 12V DC to the coil the electromagnet inside the relay switches the physical contacts.
The relay CONTACTS are rated as shown on the relay. One rating is 10 Amps (or LESS) at 30 VDC (or LESS) .
So you can switch 12V DC at up to 10 amps.
Reality Check: IF the load you are switching is inductive (Like motors, solenoids, other bigger relay coils) you need to protect the relay contacts from the dreaded
A DC spark / arc could continue for some time, acting like a miniature welder and welding relay contacts together.
For solutions see the article on the ArduinoInfo.Info WIKI HERE: (See the "Turning stuff ON and OFF).
Also, switching power loads can cause ElectroMotive Interference (EMI). See THIS about That...
Do not connect anything to anything until you draw a schematic with pen and paper and take a photo with your cell phone and post it. Repeat. Do not connect anything until you do that . You have already shown that you don't know how to wire it.
