Help interpreting schematic with relay

In summary: The schematic attached shows a connection to the 5V and GND on the Arduino board. The CN024D05 SSR will be able to source or sink up to 40 mA, so no transistor is needed, it can drive the SSR directly. The SSR output can switch a current up to 3.5A at 24VDC. If you are driving an inductive load such as a motor, you will need to use a flyback diode to protect the SSR output.
  • #1
LickMyEyeball
23
1
Hi, thank you for your help.

I am having fun experimenting with an arduino. I have a solid state relay (SSR) which I am learning to use for the first time. I have found things sort of confusing, but have found the following image at the Arduino playground useful: Image here

Here is what I have so far.

The problem is that it tells me connect relay power + and relay power - at certain points in my network. What exactly does this mean? I would like to power a servo motor through my relay for fun, using the relay to provide some degree of electrical isolation. Does 'relay power' refer to the power which will drive this motor, or something else entirely? Can I just connect these points back to the 5V header and GND on my arduino board?

As well, my actual SSR is the CN024D05. If I can figure out how to wire this up properly, does the motor--side of the relay need anything? I've seen some documentation warning about inductive loads: would a servo motor be a problem? I have some fuses since I had a feeling it would be a good idea.
 
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  • #2
A resistor and transistor is used when the digital output cannot handle the current needed by the relay coil. A relay coil is inductive so it needs a flyback diode to catch the voltage spike that occurs when it turns off.

But, you are using a semiconductor relay; CN024D05. Look at the “INPUT SPECIFICATIONS for CN024 (1)” on page 2 of the data sheet. It shows that the SSR will draw typically 10mA when driven with 5V. The SSR will turn on when a voltage of more than 3V is available. The SSR has an LED and current limiter on it's input so you need no resistor or flyback diode there.

I believe the Arduino digital output can source or sink up to 40 mA, so no transistor is needed, it can drive the SSR directly.

The SSR output can switch a current up to 3.5A at 24VDC. If you are driving an inductive load such as a motor, you will need to use a flyback diode to protect the SSR output.

Schematic attached...
 

Attachments

  • SSR schematic.png
    SSR schematic.png
    15.9 KB · Views: 855
  • #3
Thanks I really appreciate you taking the time to do that!
 
  • #4
LickMyEyeball said:
Here is what I have so far.

did you reconfig your circuit to match that shown by Baluncore ?
 

Related to Help interpreting schematic with relay

1. How does a relay work?

A relay is an electrically operated switch that is used to control the flow of electricity in a circuit. It consists of an electromagnet and a set of contacts that open and close when the electromagnet is energized. When the relay is energized, the contacts close and allow electricity to flow through the circuit. When the relay is de-energized, the contacts open and stop the flow of electricity.

2. What is the purpose of a relay in a schematic?

A relay is used in a schematic to control the flow of electricity in a circuit. It acts as a switch that can be controlled by a smaller electrical signal, allowing for the control of larger electrical loads. This is useful in situations where a low-power control signal is needed to operate a high-power device.

3. How do I interpret the symbols on a relay schematic?

The symbols on a relay schematic represent the various components of the relay. The coil symbol represents the electromagnet, while the contacts represent the switch. The normally open (NO) and normally closed (NC) contacts indicate the default state of the switch when the relay is not energized. The switch may also have a common (COM) contact that is used to connect to the power supply.

4. How do I know which relay to use for my circuit?

The type of relay needed for a circuit depends on the voltage, current, and type of load that the circuit requires. It is important to select a relay that can handle the appropriate voltage and current ratings for the load. Additionally, different types of relays may be better suited for different types of loads, such as AC or DC circuits. Consult the relay's datasheet for specific information on its capabilities.

5. Can a relay be used for both AC and DC circuits?

Yes, there are relays that can be used for both AC and DC circuits. However, it is important to select a relay that is specifically designed for the type of circuit you are using. AC and DC circuits have different characteristics and require different types of relays to operate safely and efficiently.

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