Photo Relays: A Beginners Guide

Contents

1 What are Photo Relays?
2 Photo Relays versus Mechanical relays
3 Benefits of Photo Relays
4 How to make a portable photo relay
5 Summary

What are Photo Relays?

To understand what photo relays are, it is essential you first have a clear understanding of what relays are.

Put simply. Relays are switches used to provide both high-power and low-power outputs in electrical circuits.

Relay models are into two groups;

Semiconductor relays, also known as contactless relays.

Electromagnetic relays. Primarily known as mechanical relays.

Now Photo relays are a type of contact-less relays that use light as the impulse signal. This means that, unlike the mechanical relays, they do not require contact to switch current to a load.

Photo relays work by releasing light once the current goes through the LED.

The released light then falls across the isolation boundary onto the PDA chip light sensor, which powers a connected MOSFET pair.

Once the MOSFET pair is turned on, AC/DC flows through its power terminals.

Photo Relays versus Mechanical relays

In the table below, the features of photo relays are compared against those of mechanical relays.

Photo Relay	Mechanical relay
Uses Light	Uses movable contacts
Fast and quiet switching	Slow switching and produces a loud clicking sound
Long-lasting as there are no contact parts	Shorter lifespan due to pressure resulting from the movable contacts
Low input power consumption	High input power consumption

Benefits of Photo Relays

They have longer lifespans since they do not have mechanical parts. Hence, slower degradation enhances their reliability.
Photo relays have reduced power consumption. Relay photo relays require as little as 3 to 5mA level current. To give you a clear perspective: contact relays consume about 100 mW, whereas photo relays consume 0.5mW
Smaller due to their package style.
Faster switching speeds.
They are affordable as they don’t require mechanical relay replacements.
Enhance device functionality.

How to make a portable photo relay

Items you will need to make a portable photo relay.

Transformer
NE-2 Neon Lamp
Plastic Case preferably 12cm*8cm *3cm
Light-dependent resistor
A receptacle
7555 CMOS timer
A solid-state relay; item model 2 Amp
Tip Jack
Bottle top
Silicone rubber Sealant
Tip Jack
LED mounting Sleeve

Procedure

Place the SS relay, LDR leads, and the transformer onto the plastic case. Using silicone rubber sealant, secure them on the plastic.

Place the small parts, such as the diode, capacitor, and integrated circuit, onto the circuit board.

Circuit Board

After which, mount the circuit board onto the plastic case. Place the circuit board between the SS relay and the transformer next to the LDR leads.

Now connect the 2-pin header to the LDR.

Wire the SS relay to connect to the circuit board, and then wire the transformer to connect to the circuit board.

Place the output receptacle onto the SS relay while installing the transformer wiring and inputting the line cord.

Finally, install the neon lamp and ground terminal connecting it to the transformer. Your portable transformer is now complete.

Below is a circuit diagram to provide direction:

It is worth noting that there are three variations of a photo relay, and they include:

240 VAC single pole version
Weatherproof version
High Current Version

Let’s have a closer look at each and learn how you can make them.

240 VAC single Pole Version

Making the 240 VAC single pole versions is relatively easy. All you have to do is use a 230V/6v×2 transformer in place of the 240VAC and remove the neon lamp and resistor (150k)

Resistors

Weather Proof Version

By removing the light sensor using low voltage wiring, you will have created a weatherproof Photo relay version.

However, you will need to enclose part of the Light sensor in a translucent waterproof tin to place the remaining circuit parts in a covered location. As shown by the circuit diagram below

High Current Photo Relay Version

For a high-current photo relay version, you will need to replace the original resistors. That you used when making the initial photo relay with more powerful resistors to handle the high current.

This system is preferred as it provides enhanced nighttime security.

Similarly, you can follow the circuit diagram as shown below to pilot a 240VC relay.

Safety Precautions to follow when making a portable photo relay

Whenever dealing with any digital device, you must adhere to safety regulations to prevent you and the electronic item from harm or damage.

Some of the precautions include:

1. Work on a dry surface and environment to avoid electric shocks.

2. Ensure you have turned off any power source linked to the device before working on it. You should also disconnect all the wiring attached to the photo relay.

3. Conduct a polarity check to ensure all the conductors are de-energized. A polarity test will also prevent your device from short-circuiting and also improve your device’s functionality

4. Only use a voltage that the system can handle, as a higher voltage may lead to an explosion once you connect the photo relay to power.

5. Double-check the wiring on your digital device to ascertain you linked it correctly before connecting the photo relay to a power source.