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About Relays:

  • - Relays are just switches that are electrically (magnetically) operated, often by a computer. Find one. Take it apart.</span>
  • - Relays have ratings for the voltages and currents they can switch. For example the relay boards we typically sell have voltage ratings of up to 230 volts AC or 30 volts DC, and current ratings of up to 10 amps.</span>
  • - Multiple relays on one board provide the ability to control multiple independent devices. Their ratings are not additive for any one device.</span>
  • - You need to compare the voltage and current requirements of the device(s) you want to control against the relay ratings. For example, a solenoid valve that is operated by 24 V AC and draws a current of 1 amp would be fine with a relay rated at (up to) 230 V AC and (up to) 10 Amps.</span>
  • - Reality Check: Solenoid coils have Inductance and therefore store some magnetic energy when activated. When you switch them OFF they can output an "Inductive Kick" voltage that might affect the long-term life of the relay contacts inside the relay.</span>
  • - Reality Check: These "Inductive" effects that happen when a device is turned off MAY cause ElectroMagnetic Interference (EMI)to computers and other electronic devices. </span>

Some approaches to help this are shown here:

- Reality Check: An Arduino powered from USB or wall wart will only provide enough current to operate 1 or 2 relays. A separate 5V supply for the relay boards is suggested. Or consider the YourDuino RoboRED which is an Arduino UNO compatible board which has a higher-current capability when operating from a 9 to 12 VDC source and can drive several relays without added power supplies.