# Electrical Relay Fun

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## Introduction: Electrical Relay Fun

A relay is a switch that is electrically operated with the switch being isolated from the power that causes the switch to operate. The relay I am going to show is operated by low DC power. The switch is capable of handling high voltage AC power. In other words you can turn on and off a 110 volt appliance with a 5 volt power source. But in the interest of safety I am only going to explain how to use the relay to turn on and off low power LEDs.

## Step 1: Parts Used

Here is a list of the components I will use in this demonstration.

Mini Relay SPDT 5 Pins 5VDC 10A 120V Contact

2 - Resistor 30 uF

2 - AA Batteries

5 volt power supply

1 Red LED

1 Green LED

Jumpers - Clips -

## Step 2: The Relay

The relay has 5 pins. It is a SPDT relay. SPDT means single pole double throw. Pins A and B are the pins where you apply the 5 volts. The other three pins make up the two switches. 1 and 2 make up one switch and 1 and 3 make up another switch. Even when no power is applied to pins A and B, pins 1 and 2 are connected. They are Normally Closed or NC. When you apply the 5 volt power source to pins A and B the connection between 1 and 2 opens and 1 and 3 connect. You can set the polarity of the 5 volts to A B either way, when the power is applied the change will occur. The connection between pins 1 and 3 are Normally Open (NO) meaning no connection exists between those two when the relay is unpowered.

## Step 3: Power!

In the photo where the green LED is glowing the circuit has 5 volts of power being applied to pins A and B from my 5 volt regulated Altoid power supply. The power from the two AA batteries is flowing to pin 1 and 3, then through the LED and back to the batteries.

In the photo where the red LED is glowing no change has taken place in the circuit with the AA batteries other than the connection change in the relay. There is no longer any voltage being applied to pins A and B. This closes the connection between pins 1 and 2 and opens the connection between pins 1 and 3. The connection between pins 1 and 2, or 1 and 3 are capable of handling enough voltage to turn on a 110 volt alternating current (AC) light or appliance. But the voltage that operates this relay should not exceed 5 volts. So you can turn on and off a household appliance with a 5 volt power source. But please leave dangerous voltage alone if you are not absolutely sure you know what you are doing because that is easily enough voltage to kill you.

Thanks for looking at my Instructable and if I can answer any questions please feel free to ask.

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## 12 Discussions

I would like to control a ac aquarium pump with arduino. Can i know the connections??

At first I was going to suggest insulated rubber booties for your alligator clips, but then I thought that hook clips would be even better. Although I use alligator clips a lot myself for bigger lash ups. I've even a picture of that on this site

https://www.instructables.com/files/orig/FEF/7GNU/G...

But the relays I'm using have the larger Stacon tabs. You can see that a few of my alligator clips sport rubber booties themselves. The final circuit ended up looking a bit better than that I hope.

https://www.instructables.com/files/orig/F0D/HU6I/G...

That control box operates my table saw. It works good too, honest! I love that thing.

I corrected the part about which LED is glowing when power is applied to pins A and B. I had it backwards when originally published. The connection between pins 1 and 2 is made without power to the relay. I hope the mistake didn't cause anyone trouble. Also I ordered the minigrabber jumpers today (as suggested by phred2) which should be a huge improvement. For some time now I have had minigrabbers for my DMM so I know what a wonderful improvement is in store. Now if I can just get a solder sucker the volthaus electronics lab will be totally equipped! Well that may not be exactly true. I don't have a scope yet. Or a lighted mag lamp on an articulated arm. But I hope to muddle along as time goes by and do my best. Thanks again to everyone who has taken the time to read my Instructable.

An oscilloscope is like having sight in an obstacle course as far as working with electronics goes. Without one you have to guess often what is really going on. It sucks that scopes can be so expensive, but if you can manage to swing one, and you're serious about electronics, then I say go for it.

I'll add that it doesn't cost anything to look. So even if you're not ready to buy now it might still be a good idea to begin looking. Just so you get more familiar with the marketplace. Who knows, you might find something cheaper than you think eventually too.

Be careful about buying a scope without probes though. While you're learning about scopes spend some time learning about probes too. Then you might figure out why I say be careful about buying a scope without probes. It'd have to be really cheap for me to buy a scope with no probes. Plus you can tell a lot about what kind of life a scope lead by just looking at the probes.