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Wednesday, 03 October 2012 16:26
8 Channel Relay Box
This is a 8 channel relay box that the input connect to a controller allow it to control large loads like home appliances.
I'm using this relay box for a snooker centre to control snooker table lamps. The lamps consists of 6 pieces 20W and 3 pieces 10W fluorescent lamps, total of power consumption is 150W per table. Picture below shows the snooker table lights for the snooker centre.
As shown in figure below, the Omron DC12V DPDT Relay (MKS2P) is using in this projects. According to the specification, the relay can handle 10A for 250V AC or 5A for 30V DC.
The max power (P=IV, P=10A x 250V) for the relay is about 250W per contact which is more than enough to handle 150W snooker table lamp. For this project, the relay contact is connecting in paralle in order to handle higher power in the future.
In parallel configuration all relays contacts will close at the "same time" (I know this is physically impossible). I think it should work since all the fluorescent lamps will not turn on at the "same time" (most probably few milliseconds or more than one second different), by the time all fluorescent lamps is turned on, both the relay contact is already closed . Please correct me if I'm wrong.
Working with high voltages is extremely dangerous. Use this information at your own risk.
This article explain how to connect a ULN2803 to the Arduino. As shown in figure below, I'm using Swiss machined socket for the ULN2803 line driver since the ULN2803 can generate heat & require more current on it especially on pin9 (Gnd), but I agree the best thing is a solid soldered connection. Always remember stay away from using standard IC socket.
To turn on relay manually, on/off switch must connect between the output of ULN2803 and relay coil. See figure below on how to adding on/off switch and indicator to the circuit. This is very useful when the controller is not able to control the relays while still want to turn on the lights.
Figure below shows 10 units on/off switch fixed to the cover, I'm using only 8 of them, the other two is reserved for future use. A key switch is use to prevent manually turn on the relay.
As shown in figure below is the final product of the Relay Box. An Arduino is use to control the relay.
This project hab been using for more than 20 months without major problem, the only problem I'm facing is the light inside the on/off swith getting too hot that cause the swith mul funtion. I suggest to use LED for the indicator instead of built-in light from on/off switch.