The Celtic Engineer is a weekly newsletter produced by Celtic Engineering Solutions. We hope you enjoy it. If you have any suggestions for topics, would like to give feedback or want your email added to the distribution list please send an email to [email protected].
It’s a Battery. Are we at war?
An early use of the term ‘battery’ was a number of pieces of artillery used together. As early as 1748 Benjamin Franklin used the term to describe a series of early electrical devices called Leyden jars (really more of a capacitor than a battery) hooked together. Today we refer to a device as a battery if it is an electrochemical device, either a single or a series of cells hooked together.
A cell is a single electrochemical device. What we call a flashlight batter AAA, AA, C and D are cells. They are a single unit, not made up of smaller units. On the other hand, a 9V is a number of smaller cells wired together in series. The battery in your car is made up of 6 cells, each having a potential of 2.1 volts.
It’s all about energy
Batteries produce an electrical voltage that can be used to power our devices. They have a limited life span that is based on how much energy they start with. The device is labeled with its capacity in Amp-Hours (A·h). Roughly speaking a 20 A·h battery could be expected to put out 1A for 20 hours. That really isn’t true in practice. First of all, the battery may have an upper limit on the current that it can, or should, put out. Just because a battery can put out 1A doesn’t mean it is safe to do so. A batteries data sheet will explain the maximum current is should be allowed to source.
Additionally, the output of a battery is not regulated. The values of 9V and 1.5V are nominal values. They are approximately what you will see in a fresh unloaded device. As energy is removed from the cell its ability to deliver current decreases. The result is a discharge curve. It simply shows that if a constant current is drawn from a battery, the battery voltage will decrease over time. Discharge curves look very different for batteries of different chemistry. For example, an alkaline battery voltage drops off almost linearly with time. While a lithium or nickel-cadmium is flat for most of its life and then drop in voltage rapidly near the end of its useful life.
Chemistry – Mad Scientist
The term chemistry brings to mind the mad scientist in his lab with glass vessels filled with brightly colored liquids (Hollywood indeed!). Each and every battery is a small chemical device. Early batteries were called wet cells because they were made of liquids. In fact, the lead acid battery in our cars is still a wet cell device. It wasn’t until the late 1800’s that the first dry cell, made with a paste, was invented.
These early cells were a zinc-carbon battery. They consisted of a carbon rod surrounded by a paste of ammonium, or zinc, chloride. Today there are many types of battery chemistries. The most popular are the lithium. The lithium battery is actually a family of batteries. There are various chemical reactions that can be used. For example, lithium cobalt oxide (many handheld devices), lithium iron phosphate, lithium nickel manganese cobalt oxide, lithium titanate and lithium sulfur barely scratch the surface. Each type has different characteristics.
The number of types of batteries is staggering. I could never mention all of them in a newsletter. If you are going to use batteries in your design you will have to do a bit of research. I also suggest you get in contact with your local battery distributor. They can answer many of your questions and help steer you in the right direction for your specific application.
Is it safe?
It is highly desirable to have a high energy density. That is, a lot of power in a small volume. Lithium batteries (lithium cobalt oxide) have a very high energy density, but that characteristic comes with a risk. They can discharge rapidly, providing a large current, but when the do so, they also generate heat. If you will remember your HS chemistry, the rate of a chemical reaction is proportional to its temperature. As the battery heats it can react faster and the reaction can run away. The battery becomes hot, expands and eventually it produces enough pressure to burst the housing. Lithium is also flammable in air, hence all the YouTube videos.
As I researched batteries there was an alarming number of warnings about ingesting them. I don’t know why anyone would eat a battery, they are very bad for you and my advice is – Don’t.
Types of batteries
There are two main divisions among batteries: Primary and secondary. Primary batteries are single use devices. Secondary batteries are rechargeable. Great care needs to be taken when recharging Lithium batteries. There are precise protocols that need to be adhered to in order to safely recharge them. In some cases, a temperature sensor is needed to monitor the battery temperature during the recharge cycle.
This newsletter is sponsored by Celtic Engineering Solutions LLC, a design engineering firm based out of West Jordan, Utah, which can be found on the web at: www.celticengineeringsolutions.com. You can find the newsletter on the company blog, LinkedIn or by subscribing. Send your emails to The Celtic Engineer at: [email protected].