Knowing the possible reasons as to why a capacitor might explode will save you stress and money (as you won’t have to keep replacing blown capacitors). 

So, what would cause a capacitor to explode? The main two reasons that would cause a capacitor to explode is Reverse polarity voltage and Over-voltage (exceeding the voltage as little as 1 – 1.5 volts could result in an explosion). Electrolytic capacitors are more susceptible to explode as opposed to other types of capacitors. 

This article will dive deeper into Reverse polarity voltage and other possible reasons as to what can cause a capacitor to explode. 

Deeper look at the capacitor

Understanding the construction of the capacitor will give us a better insight into the question at hand, as to what could possibly cause it to explode. 

A capacitor is an electronic component designed to store energy in an electric field. 

Capacitors are constructed with a Dielectric that is sandwiched between two Conducting plates.

The dielectric is an insulating material. Materials used for a capacitor’s dielectric can range from glass, ceramic, plastic film, paper, mica, air and oxide layers.

A conductor is needed for the two plates which can range from; metals, thin film, foil, or an electrolyte. 

Capacitance of a capacitor

How much energy a capacitor can store is determined by its Capacitance which is measured in Farads (F).

A capacitor with a higher value of capacitance can hold much more charge than one with a smaller value. 

The magnitude of capacitance of a capacitor is largely influenced by its physical construction. So, the larger the area of the plates the higher it’s capacitance. 

Other factors that influence the capacitance of a capacitor are;

• Separation of plates (the closer the plates the higher the capacitance)
• Dielectric material ( the higher the Dielectric constant the higher the capacitance

Capacitor voltage

Another important parameter of a capacitor is its Voltage.

This value of a capacitor defines the maximum voltage it can withstand without any failure. It is a measure of the strength of its dielectric insulation. 

Every capacitor has a voltage rating which is printed on the capacitor.

If it is not printed on the capacitor, it can be found on its datasheet. 

Different types of capacitor

When it comes to capacitors, there are many different types available, with each being beneficial for different electrical and electronic applications. 

Again, the type of capacitor is largely influenced by how it is constructed and what kind of dielectric it uses. 

Below are some of the most common types;

• Electrolytic capacitor 
• Mica capacitor 
• Paper capacitor 
• Film capacitor 
• Ceramic capacitor

Polarized vs Non-Polarized capacitors

Another distinction between different types of capacitor are their polarity. 

Capacitors can either be Polarized or Non-Polarized.

A capacitor that has no polarity (non-polarized) can be wired up in a circuit either way.

However, a polarised capacitor can only be wired one way. 

It has one positive terminal and one negative terminal.

So, connecting a polarised capacitor requires more care as its terminals need to be connected the right way right in a circuit. 

What type of capacitor is more likely to explode?  

When it comes to a capacitor exploding, the electrolytic capacitor is the most likely type to cause a spectacle compared to its counterparts. 

Other capacitors will not explode, but rather burn, crack, pop or smoke. 

The main reason why an electrolytic capacitor might explode is due to its construction.

As we saw earlier, the bigger the capacitor the more capacitance it will have. But, sometimes this is impractical, as you might require a smaller sized capacitor with high capacitance. 

One way of doing that is to bring the conducting plates of the capacitor closer together. But, again we encounter another problem in that the voltage rating gets a bit impractical.

Electrolytic capacitors were developed to combat this issue. 

Internal construction of electrolytic capacitors

They are designed to achieve high capacitance in smaller packages, with small separations of plates as well as reasonable voltages.

Rather than using an insulating material for the dielectric, the insulating layer is created by an oxide layer that is formed through a process known as anodization of the anode (positive plate) of the capacitor.

The oxide layer ends up being a thin film and is how both the plates can be closer together. 

This process is repeated for the cathode (negative plate). 

The electrolytic capacitor has an anode and cathode as it is polarised. 

Between the two plates is a paper separator soaked in a water based solution. The solution (also known as an electrolyte) has an alkali added to it to make it a conductor. 

So why does an electrolytic capacitor explode?

When an electrolytic capacitor breaks down (due to factors I will discuss below), the oxide layer breaks down.

This causes high amounts of current to pass through the electrolyte. 

High amounts of current will result in high amounts of heat. This high heat will vaporize the water into a  gas which causes a build of pressure in the capacitor causing it to explode. 

For this reason, electrolytic capacitors are created with a fail safe which is a split in the capacitor that helps vent the gas in a more controlled manner. 

Factors that would cause a capacitor to explode

Let’s dive into the factors that can cause a capacitor to explode.

Note, as mentioned earlier, electrolytic capacitors are more likely to explode. But, these factors will still cause other types of capacitors to fail as well, only with no explosion.

Factor #1 that would cause capacitor to explode: Reverse Polarity

The first factor that is most common and likely to cause a capacitor to explode is, Reverse Polarity.

Reverse polarity applies for components and devices that are polarised. 

As you saw earlier, an electrolytic capacitor is a polarised component that has a positive and negative terminal which means it needs to be wired the right way in a circuit. 

Reversing the polarity of a capacitor means that you wire it the wrong way in a circuit (the positive terminal gets connected to negative, and the negative terminal gets connected to positive).

If you happen to wire it the wrong way and apply a voltage for a very short amount of time, it shouldn’t be much of  a problem. 

However, longer durations when exposed to reverse polarity will cause an electrolytic capacitor to explode. 

Factor #2 that would cause capacitor to explode: Over voltage

The next factor that might cause a capacitor to explode is Over voltage.

A capacitor is designed to hold a certain amount of capacitance as well as withstand certain amounts of voltages and currents. 

The voltage of a capacitor is usually displayed on the outside of its packaging. 

Exceeding these voltages can cause the dielectric to fail which results in large currents flowing.

These large currents cause large amounts of heat and thus destroy the internal structure of a capacitor.

As we saw earlier, with electrolytic capacitors, the water boils turning into steam which builds up pressure resulting in an explosion. 

Over voltage or current might be caused by human error. Where the person might supply voltages past the capacitors limit. 

Or, it could be caused by a power surge. 

Factor #3 that would cause capacitor to explode: Storage

This next factor pertains more to electrolytic capacitors and comes down to their storage. 

Electrolytic capacitors do not store very well.

Their voltage rating drastically reduces the longer they are stored for as their internal chemistry deteriorates.

This could cause a capacitor to explode as it might display a certain voltage, but its actual voltage has reduced. So when you apply a voltage as displayed it will be higher than the actual voltage causing it to explode. 

Can a capacitor that has exploded still work?

Unfortunately a capacitor that has exploded will not work.

The internal composition of a capacitor is designed specifically to store an electric field.  

An explosion would  ruin the internal composition thus rendering the capacitor useless. 

How to prevent a capacitor from exploding

A capacitor that explodes can be a frightful experience!

So, the less explosions the better. Also, this will save you a lot of money not having to constantly replace them.

Below are some things you can do to prevent a capacitor from causing destruction.

Reverse Polarity – If you are using polarised capacitors (like an electrolytic capacitor), double check, no triple check that you have wired it the right way before applying a voltage.

Over voltage – This might be a simple solution be it’s worth noting, stay within the limits of the capacitors voltage ratings. 

Storage – Avoid storing electrolytic capacitors for long periods of time. If you are going to use one that has been stored away for a long time, test that it can still withstand the voltage it was designed for.

The post What would cause a capacitor to explode? appeared first on Electronic Guidebook.