12V RELAY operating with arduino

Other Hardware General Electronics
1

I just made a project in which i am using Bluetooth module hc-05, Arduino Uno and Relay of 12 V.
It is not working properly when connecting relay to 220V appliance.
As RELAY is of 12V and supply from Arduino Uno is 5V.
Connection for Relay is:
NO to Appliance and C to main
and another wire from appliance to main.
Can anyone tell me how to give external supply to Relay?

2

Fist of all, a Arduino can only supply limited power on a pin. So driving a relay directly is a bad idea anyway.

To fix that and the 12V problem, just use a NPN or N-mosfet to drive the relay. Just Google "Arduino relay" or "Arduino NPN" or "arduino mosfet".

Also place a diode (simple 1N4148 will do) in reverse over the relay coil to act as a fly back diode to catch voltage spikes.

3

As RELAY is of 12V and supply from Arduino Uno is 5V.

I know it sounds silly to say this, but, it's actually called a "12V relay" for a reason, that being, that the coil requires 12V to energize, so it will never work with only 5V. That should have been obvious.

As stated, connect one end of coil to 12V, the other end to collector of NPN transistor or drain of N-channel Mosfet, and drive the transistor through a 470 ohm resistor or drive the mosfet directly.

4

It is not working properly when connecting relay to 220V appliance.

If you've already got it connected correctly and its powered by a separate supply and it always works fine except when the 220V appliance is connected, then EMI created by the 220V load and contact arcing is the issue.

Conductive EMI on the power rails and control signal can all be eliminated if an opto-isolator is used.

Emissive EMI can be reduced by (in no particular order):

  • Using a suitable MOV (rated for at least 275VAC)
  • Using an RC subber circuit (instead of the MOV)
  • Increasing the distance from the relay board (or relay circuit) and 220V load from the Arduino
  • Using a 12V zener diode in series with the fly-back diode. This speeds up the contact-break, thereby reducing the arcing and EMI. It also increases the relay life. The fly-back spike will still be adequately clamped.
  • If opto-isolation is not used, then using a suitable ferrite core with 3-5 turns through it on the AC load wire to the relay's NO contact will reduce EMI
5

If you've already got it connected correctly and its powered by a separate supply and it always works fine except when the 220V appliance is connected, then EMI created by the 220V load and contact arcing is the issue.

I beg to differ, but a 12V relay is not going to work from a 5V source no matter how you connect it.
The OP already admitted powering it with 5V so why would you expect it to work ?

6

I beg to differ, but a 12V relay is not going to work from a 5V source no matter how you connect it.
The OP already admitted powering it with 5V so why would you expect it to work ?

After the 12V problem is resolved ...

If you've already now got it connected correctly and its powered by a separate supply and it always works fine except when the 220V appliance is connected, then EMI created by the 220V load and contact arcing is the issue.

7

I am using 8 channel 12 V ULN2803 based relay module board and i dont want to give supply it externally not from Arduino. I know it never give supplies using Arduino 5V.
Tell me please How to power Relay module Externally?

8

With a 12 V power supply.

9

Always on the money ...
That one had me stumped.

10

i have completed this project and its working properly... thanx for help