What Is A Short Circuit And Why Do You Have It?

A short circuit is a connection that was not meant to be there. For example, if you accidentally connect the plus to the minus of a battery, you have a short circuit between the plus and minus of the battery. Which is not good.

You can use it as a verb as well:

“I accidentally shorted the battery and it exploded!”

(Yes, some batteries can really explode if you short-circuit them.)

This is a very important concept to understand because it’s used a lot in “electronics language”.

What Causes A Short Circuit?

If you built the circuit, the most probable is that YOU caused the short circuit.

I know that’s hard to accept.

I never accept it…

…until I find the error and realize there’s no way I can blame this on someone else.

Connection Error

Every time I build a new circuit I check if I have corrected everything in the correct place before I connect the power.

This way I can make sure I haven’t created any short circuits from connecting something in the wrong place.

I go through each connection on my circuit diagram, then check if I have this connection on my board.

For larger circuits, I like doing this with a friend. For example like this:

My friend looks at the circuit diagram and says: “One side of the photoresistor should be connected to the plus, and the other side to the 33k resistor”

I look at my board to check this and reply: “Yep, that’s correct.”

Then my friend says: “The other side of the 33k should be connected to the base of the transistor”

Then I say: “Oooooops. I’ve shorted the 33k resistor.”

This means I’ve found the error: An unintentional connection between the two sides of the 33k resistor.

Solder Bridge

If you are a bit uncareful when you solder, you can get something called a solder bridge between two pads on your board. For example, if you add too much solder and the solder flows over to a pad close by.

Pieces Of Metal

Another reason for having a short circuit could be that a little piece of metal fell onto your circuit. For example, when you cut the legs of a component, the piece you cut off can easily go flying off in an unknown direction. If it lands on your circuit, it can give you a short-circuit.

Conducting Surface

This is an embarrassing error to do. I’ve done it a few times. It’s when you place your circuit onto something made of metal.

If you’re using a breadboard, it’s not a problem. But if you have a circuit board with connections underneath your board, a metal surface will of course create a lot of short circuits for you.

It doesn’t have to be a surface either. Maybe you placed it on top of a screwdriver, some pieces of metal after clipping component legs, or something else.

Damaged Components

Another reason for short circuits can be a damaged component.

I had this happen to me a couple of weeks ago to my drone. It was a damaged transistor that created a short circuit between two of it’s pins.

You can read the whole story on how I repaired my drone here.

How To Find Short Circuits

The best way to find short circuits is to use a multimeter with a continuity checker.

This tool will beep every time there is a connection between its two measurement probes. So, if you touch the tip of one probe to the other, it will beep.

You can use this to check if there is a connection between two points in a circuit. Touch the tip of each probe to the two points you want to check. If it beeps, you have a connection. And if these points were not supposed to be connected, you’ve found a short circuit!

Do You Understand What A Short Circuit Is?

Let’s say you have a circuit that doesn’t work, and you ask me for help. Would you know what the problem was if I told you:

“Ahh, I see the problem. You’ve shorted the battery.”

If the answer is yes, then I think you got it. If the answer is no, read through the beginning of this article again, then let me know your questions below.

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