Our jewelry is solar powered AND will blink for hours after dark.  Neato!

When we tell customers there are no batteries, this is the response we often get:

Customer: “So if there are no batteries, where is the power stored?”
Us:  “In the capacitors.”
Customer:  “Oh, so then it does have a battery?”
Us:  “It has on-board power storage in an electrical component called a capacitor.  Capacitors store power in an electrical field rather than a chemical reaction like a battery.  You don’t have to replace or worry about the capacitor wearing out, unlike with a battery.”

Most people have never heard of a capacitor.  Their only experience with power storage is with batteries, and many people understandably assume “battery” means any type of electrical power storage device.

They can even look similar.

Capacitor

Battery

However the distinction for us engineers is about more than nomenclature.  There are fundamental differences between how a battery and a capacitor function.  These differences have implications for how our jewelry performs as well  as the future of electric cars.

*So far.  GO SCIENCE!!!

Batteries

In a battery the electrical power is stored by a chemical reaction.  When the battery is connected to an electrical device, energy from the chemical reaction is converted into electrical energy.  The name of the battery type states what elements are involved in the chemical reaction; lead-acid, NiCad, Lithium, polymer, etc.  More can be found here in the Wikipedia entry.

The chemical reaction is a slow process and often irreversible.  Hence why there are rechargable and non-rechargable batteries.

In a non-rechargable battery the chemical reaction is irreversible and the chemicals inside would have to be physically replaced in order to recharge the battery.  Standard disposable alkaline batteries are a good example of this.

With a rechargable battery the chemical reaction can be reversed by applying an electrical current to the battery.  However there is a limit to the number of times the reaction can be reversed.  Eventually the battery will begin holding less and less charge and develop a “memory” of a lower charge state.  We’ve all probably had this happen with cell phones, which after a few years don’t hold a charge all day and need a new battery.

Capacitors

Capacitors on the other hand store electrons directly in an electrical field.  This is the same process as static electricity.

With static electricity electrons are stored on the surface of your body, a balloon, or in your hair.  When you touch someone the electricity is (almost) instantaneously discharged into the other person.  It hurts!  In this case you have become a capacitor.

In a capacitor electrons are stored on two parallel plates separated by an element called a dielectric (insulator).

These plates are often rolled up inside a component that looks a lot like a battery.  More can be found in the Wikipedia Entry.

Capacitors have a lot of advantages over batteries, as the chart above shows.  They can charge and discharge very quickly. They can also be used millions of times without developing a memory or needing to be replaced.  Because of these two properties they are a common electrical component in computers and phones.

They have one big drawback though, and that is current capacitor technology cannot store as much energy as a battery.  This is perfect for our jewelry though because it is low power, less than a watch battery.  You couldn’t get a shock from it even if you licked it.  Honest, we’ve tried.

As science advances we hope one day capacitors will hold as much energy or more than batteries, possibly making electric cars that can be charged in minutes rather than hours.  Rock!

Made it this far?  Aw shucks, you like us, you really do.

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