Relay Ratings and Limits
Relays often have two ratings: AC and DC. These rating indicate how much power can be switched through the relays. This does not necessarily tell
you what the limits of the relay are. For instance, a 5 Amp relay rated at 125VAC can also switch 2.5 Amps at 250VAC. Similarly, a 5 Amp relay
rated at 24VDC can switch 2.5 Amps at 48VDC, or even 10 Amps at 12VDC.
Volts x Amps = Watts  Never Exceed Watts!
An easy way to determine the limit of a relay is to multiply the rated Volts times the rated Amps. This will give you the total watts a relay can
switch. Every relay will have two ratings: AC and DC. You should determine the AC watts and the DC watts, and never exceed these ratings.
Example Calculations
AC Volts x AC Amps = AC
Watts 
DC Volts x DC Amps = DC Watts

Example: A 5 Amp Relay is Rated at 250 Volts AC. 5 x 250 = 1,250 AC Watts 
Example: A 5 Amp Relay is Rated at 24 Volts DC. 5 x 24 = 120 DC Watts 
If you are switching AC Devices, Make Sure the AC Watts of the Device you are Switching DOES NOT Exceed 1,250 when using a 5A Relay. 
If you are switching DC
Devices, Make Sure the DC Watts of the Device you are Switching DOES NOT
Exceed 120 when using a 5A Relay. 
Resistive and Inductive Loads
Relays are often rated for switching resistive loads. Inductive loads can be very hard on the contacts of a relay. A resistive load is a
device that stays electrically quiet when powered up, such as an incandescent light bulb. An inductive load typically has a violent startup
voltage or amperage requirement, such as a motor or a transformer.
Startup and Runtime Loads
Inductive loads typically require 23 times the runtime voltage or amperage when power is first applied to the device. For instance, a motor
rate at 5 Amps, 125 VAC will often require 1015 amps just to get the shaft of the motor in motion. Once in motion, the the motor may consume
no more than 5 amps. When driving these types of loads, choose a relay that exceeds the initial requirement of the motor. In this case,
a 2030 Amp relay should be used for best relay life.
Induction Suppression Capacitors
Controlling
inductive loads requires the use of induction suppression capacitors. The purpose of this capacitor is to absorb the high voltages
generated by inductive loads, blocking them from the contacts of the relay. Without this capacitor, the lifespan of the relay will be greatly
reduced. Induction can be so severe that it electrically interferes with the microprocessor of
the board possibly requiring the board to be power cycled.


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