Batteries: The Shocking Truth
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Project Summary
| Difficulty | 5 |
| Time required | Average (about one week) |
| Prerequisites | Some versions of this idea require a voltmeter or multimeter |
| Material Availability | Readily available |
| Cost | Low ($20–$50) |
| Safety | No issues |
Sponsor
| Sponsored by generous support from AMD |
|
Objective
The objective of this project is to investigate the performance of batteries in a scientifically valid way.
Introduction
Studying batteries involves more than turning on a battery powered device to see how long it runs. Different types and sizes of batteries have widely varying characteristics, so there are many interesting experiments you can perform to make for an excellent science fair project. We'll suggest a number of possibilities for your experiment below.
Terms, Concepts and Questions to Start Background Research
To do an experiment in this area, you should do research that enables you to understand the following terms and concepts:
- Electromotive force (EMF, or voltage), measured in volts
- Electrical current
- Current drain
- Terminal, electrode, anode, cathode
- Electrolyte
- The history and operating principles of batteries
More advanced students will want to study:
- Ohm's law
- Series and parallel circuits
- Duty cycle
- Ampere-hours
- Internal resistance of a battery and how it changes with usage and temperature
Bibliography
Here are some resources to get you started:
- How Batteries Work: http://electronics.howstuffworks.com/battery.htm
- Energizer Learning Center (you can also find technical information on this site): http://www.energizer.com/learning/default.asp
Energizer's Technical Information site has a wealth of information about batteries for more advanced students. Check out the application manuals (which include excellent cut-away drawings) and the product datasheets: http://data.energizer.com/Default.aspx
Materials and Equipment
To do this project, you will need the following materials and equipment:
- a voltmeter or multimeter; notes:
- Most, but not all of the projects described below require a voltmeter or multimeter.
- You will need a meter that accurately measures voltages between zero and two volts. Radio Shack carries a variety of multimeters. You can get a basic one for about $20 or borrow one from a friend.
- You can also purchase a basic, inexpensive multimeter online from Jameco Electronics, part number 318781 (about $10 plus shipping, May, 2007).
- batteries,
- one or more battery-powered devices (for example, a flashlight, a portable radio, or a portable music player.
- (Optional) You can buy or make a battery holder to make it easier to capture your readings; however, a battery holder is not required. A variety of battery holders (for different battery types and various numbers of batteries) are available from either Radio Shack or Mouser Electronics.
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Experimental Procedure
As one uses a battery, its voltage drops until eventually it falls so low that it can no longer operate the device it powers. At that time we say the battery is dead.
Consequently, one good way to measure the performance of a battery is to operate a device using the batteries you want to test, then measure (and plot) the batteries' voltage at regular time intervals, say every half hour. Be sure to start with fresh batteries, or if they are rechargeable, make sure they are fully charged.
The best way to measure the voltage is to do so while the battery is under load, in other words, while it is still installed and powering a device. However, that can make the experimental setup more complicated than you want. Quickly removing the batteries and measuring the voltage with the batteries outside the device is a workable alternative for carbon zinc (sometimes called "heavy duty") and alkaline batteries. Measuring the voltage outside the device may or may not work for other battery types.
If you measure the voltage with the batteries outside the device, try to be quick and consistent in your measurements (don't take 30 seconds to measure the voltage one time and 5 minutes another time). You'll find that the voltage "recovers" slightly, more so the longer the battery is no longer powering the device. Thus, consistency is an important part of your experimental technique or you won't have measurements that are comparable to one another.
To measure the voltage, simply place the red wire from the multimeter on the positive electrode and the black wire on the negative electrode. If your multimeter has different "scales," make sure to use one that is close to voltage of the battery (for example, a 2 volt scale for a 1.5 volt battery).
Variations
There are many different types of batteries: carbon zinc (sometimes called "heavy duty"), alkaline, lithium, nickel-metal hydride rechargeable (NiMH), nickel-cadmium rechargeable (NiCad), lithium ion, lead-acid, and many others. And, each of these types come in different sizes. The properties of these different types of battery vary widely, making each one better for powering different kinds of devices, for example a constant load for a long time versus an intermittent peak load. This makes for some interesting project possibilities, and here are some ideas:
- Batteries lose capacity when operated at cold temperatures, and some battery types lose much more power than others. Do research to find a type of battery that you believe will have easily measurable loss of capacity at the temperature in your home freezer. Select an inexpensive device such as a flashlight to use for this test (DO NOT use something like a CD player). Measure voltage versus time as described in the Experimental Procedure above for your device when it is operated in your home freezer. Repeat your experiment at room temperature and compare the results. You can also compare different types of batteries.
- Different sizes of battery (AAA, AA, C, D) of the same brand and type have a different capacity. (Your grandmother might say, "Big batteries have more juice!") Build or buy battery holders for different sizes of battery so that you can power a device with batteries of a different size than it was designed for. Measure how long the device works with each size of battery. (You don't need to measure the voltage of the batteries for this experiment.) Create a graph plotting the time until the battery can no longer power the device on one axis and the physical volume of the battery on the other. Create another graph with time on one axis and the weight of the battery on the other. Explain what is happening. Why did engineers pick the size of battery that they did for the device you chose? (Advanced students might want to measure the current draw of the device so that they can calculate the ampere-hours of each battery.)
A more precise version of this experiment would define and measure what it means for a battery to be "dead." For example, you might say that the battery is dead when the voltage decreases by xx volts or yy% when some heavy reference load is put on the battery.
- For different battery types, the slope of the discharge curve (a graph with voltage on the y-axis, time on the x-axis) will be quite different. One possible experiment would be to compare the shape of the discharge curve for different battery types; comparing any two of carbon zinc (sometimes called "heavy duty"), alkaline, and NiMH would be a reasonable choice. For example, carbon zinc batteries have a strongly sloping discharge curve, alkaline batteries have a less sloping curve, while nickel-metal hydride rechargeable batteries (NiMH) have a flat curve. In other words, NiMH batteries stay at a relatively constant voltage until they are almost dead, then the voltage drops very quickly. This explains why the battery indicator on some devices seems so poor, reading full, then quickly changing to half full . . . empty. Such devices are probably using a battery with a flat discharge curve.
- Different types and sizes of battery have different costs. For any of the above possible experiments where you are comparing different batteries, you can also examine which battery offers the best value. For example, if one battery has half the life of another, but costs only one quarter as much, it offers a better value.
- For more science project ideas in this area of science, see Electricity & Electronics Project Ideas
Last edit date: 2007-05-14 15:00:00
