Home Chapter 19 Batteries and power supplies
Batteries and power supplies

Batteries come in a variety of sizes and amperage's and are evolving very quickly as nanotechnology and the need for green technologies is permitting rapid investment in battery evolution. All batteries transform chemical energy to electrical energy.

Many kinds of batteries exist with more common types  being, electrolytic cells, galvanic cells, fuel cells, Nickel Cadmium and voltaic piles. A batteries performance is determined by a number of factors such as the current drain the battery sees, the internal chemistry of the battery and the temperature under which the battery performs.

Each battery has clear advantages and disadvantages for the artist inventor and selection of a battery is determined based on cost, environmental issues, if they are disposable or rechargeable, the AH (amp hours) you need the battery to last,the voltage you need from the battery and if the battery can travel on an airplane for example or will it be undergoing extremes in temperature or vibration. 

Remember that you can have a 12 volt battery and if your robot needs perhaps 12 volts for the motor, 5 volts for the microprocessor and 9 volts for other parts you can use voltage conditioning circuits like the 7805, 7806, 7809. Search these parts on Google for the PDF data sheets and design. You will need the TO-220 package style for this part not the D-PAK unless you are going to do surface mount parts. 

Alkaline batteries are a kind of battery that is dependent upon a reaction between zinc and manganese (IV) oxide (Zn/MnO2). They can be either disposable or rechargeable depending on their design. These types of batteries tend to have a high energy density and a long shelf life. Over time alkaline batteries can leak and these batteries are generally not environmentally friendly. Some suppliers will recycle batteries and when purchased it may be wise to ask suppliers if they have such a program. 

Galvanic cells, are batteries consisting of electrochemical cells with different metals connected by a salt bridge and a porous disk between the individual half-cells. These cells are also called Voltaic cells.

Electrolytic cells consists of three parts: two electrodes (a cathode and an anode) and an electrolyte. The electrolyte is generally water or another solvent in which ions can be dissolved.

Nickel-cadmium batteries often abbreviated NiCd is a type of rechargeable battery that uses nickel oxide hydroxide and metallic cadmium as electrodes. These batteries are quite popular with robotic artists and inventors because of their relative low cost and speed of recharge. These are the batteries you are familiar with from your rechargeable drill or RC cars and they are popular with robotics folks because they have low internal resistance and can supply high surge currents for motor applications. These batteries are a bit more expensive than other batteries and they are toxic to the environment. 

Nickel-Metal Hydride (Ni-MH) and lithium ion batteries (Li-ion) are now a bit less expensive and offer an alternative to Ni-Cds in cost. They also have a high energy density as with the Ni-CD and they are becoming increasginly the most popular batteries for robotics applications.

Battery suppliers:

At Batteries has a wide selection of batteries at a reasonable prices http://www.atbatt.com/

Power supplies

The primary types of power supply is the Linear power supply. A linear AC power supply generally has a device called a transformer (discussed in chapter 3) that converst one voltage generally 115 volts AC 60 HZ in the United States or 220 volts 50 Hz in European Community. It involves rectifying the AC voltage so that the votage stays in the positive range  and capacitors are used to smooth out the voltage from a pulsating voltage to a solid DC voltage.

Voltage produced with an unregulated power supply will often vary according to the load placed on them or based on variations in the AC voltage source. For electronics that require a stable non varying power source a linear regulator is used to add stability as well as adjust the voltage up or down.

The well afforded electronics lab should have a decent adjustable linear power supply that provides a varieaty of volages and amperages available. An adjustable supply from 0-30 volts and 1-5 amps is avisable. You can expect to spend about 100 to 200 for a new one or 50-100 for a used unit that provides adjustable voltage and amperages.