April 2006 – Page 3 – Battery Education

Battery Voltage

What is battery voltage? I think we talk around the real definition so much we actually begin to believe that we understand what it means when in reality we do not. Even I was just commenting to my wife that I wish I paid more attention while I was in my college electronic classes so that I too could understand the very basics of voltage . For my benefit as well as yours let us go back to the basics of what battery voltage really means and how the work it conducts inside your battery affects the other technical factors of your battery.

Italian physicist Alessandro Giuseppe Antonio Anastasio Volta (February 18, 1745 – March 5, 1827) grew up with a passion for electricity. In 1775 he devised the electrophorus, a device that produced a static electric charge. In 1776-77 he studied the chemistry of gases, discovered methane, and devised experiments such as the ignition of gases by an electric spark in a closed vessel.

In 1800 he developed the voltaic pile, a forerunner of the electric battery, which produced a steady electric current. Creating a cell, a wine goblet filled with brine into which the two dissimilar electrodes were dipped, Volta placed together several pairs of alternating copper (or silver) and zinc discs separated by cloth and soaked the cloth in brine (salt water) to increase conductivity, and an electrical current was produced. The electric pile ultimately replaced the goblets with cardboard soaked in brine. The number of cells, and thus the voltage the electric pile could produce, was limited by the pressure, and exerted by the upper cells that would squeeze all of the brine out of the cardboard of the bottom cell.The electric pile was the first electric battery.

In 1881 the electrical unit we know today, the volt, was named in Volta’s honor. From the first battery, mentioned above, we can derive a definition of voltage as: Volts – or V – are an electrical measure of energy potential. Voltage can also be thought of as the amount of "pressure" of electrons that pass from a negative connector to a positive connector. Or V can be defined as the measure of the strength of an electrical source of power for a given current level.

Voltage can also be defined as Electrical Potential difference – a quantity in physics related to the amount of energy that would be required to move an object from one place to another against various types of force. In the fields of electronics the electrical potential difference is the amount of work per charge needed to move electric charge from the second point to the first, or equivalently, the amount of work that unit charge flowing from the first point to the second can perform.

Mathematically voltage is commonly measured by V= I x R; where V=Voltage, I=Current, R=Resistance.

Beyond the definition what challenges many is the confusion that a battery contains four unique types of voltage measurements. Each voltage measurement type residing in a battery effects battery life.

Float Voltage – is battery voltage at zero current (with battery disconnected).
Nominal Voltage – is battery voltage range 3.7V, 5.2V, 10.2V, 12V etc that says that a voltage range exists depending on the number of cells in the battery. For example a 12 Volt battery is made of 6 cells and has a Float voltage of about 12V.
Charge Voltage – The voltage of a battery while charging.
Discharge Voltage – The voltage of a battery while discharging. Again, this voltage is determined by the charge state and the current flowing in the battery.

Here are a few examples of how the voltage types measurments interact with one another in the same battery:

Number of Cells	Nominal Voltage	Fully-Charged Float Voltage	Fully-Discharged Float Voltage	Discharge Voltage at Ah/20	Charge Voltage at Ah/5
1	2	2.15	1.9	2.0 – 1.7	2.1 – 2.30
6	12	12.9	11.4	12 – 10.2	12.6 – 13.8
12	24	25.8	22.8	24 – 20.4	25.2 – 27.6

Until next time Dan Hagopian www.batteryship.com
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What is A Battery?

A battery is a device that converts chemical energy into electrical energy. Batteries have two electrodes, an anode (the positive end) and a cathode (the negative end). In between the battery’s two electrodes runs an electrical current caused primarily from a voltage differential between the anode and cathode. The voltage runs through a chemical called an electrolyte (which can be either liquid or solid). This battery consisting of two electrodes is called a voltaic cell.

The first inclination that an electrical path-way from an anode to a cathode within a battery or in this first instance “a frog” occurred in 1786, when Count Luigi Galvani (an Italian anatomist, 1737-1798) found that when the muscles of a dead frog were touched by two pieces of different metals, the muscle tissue twitched.

This led to idea by Count Alessandro Giuseppe Antonio Anastasio Volta (Feb. 18, 1745- March 5, 1827), an Italian physicist who realized that the twitching was caused by an electrical current that was created by chemicals. Volta’s discovery led to the invention of the chemical battery (also called the voltaic pile) in 1800. His first voltaic piles were made from zinc and silver plates (separated by a cloth) put in a salt water bath. Volta improved the pile, using zinc and copper in a weak sulfuric acid bath and thus invented the first generator of continuous electrical current.

In 1820, the French physicist André-Marie Ampère discovered many of the laws governing the relationship between electricity and magnetism, along with how a battery works. Ampere found that electrical current move through conductors, and that electrical charges flow from one electrode to the other. Ampere invented the astatic needle, which detected electrical currents.

In an interesting side bar regarding Ampère and Volta:

From Volta’s work we get the Volt – or V – which is an electrical measure of energy potential. For example you can think of energy potential as the pressure being exerted by all the electrons of a PDA Battery’s negative terminal as they try to move to the positive terminal.

From Ampère’s work we get Amps – or A – which is measures the volume of electrons passing through a wire in a one second. One Amp equals 6.25 x 1018 electrons per second.

From both Volts and Amps we get the formula for a battery’s full potential measured in Watts: Volts x Amps = Watts. Watts are important because a watt represents the electrical energy spent by a battery (power generator) and used by an electrical device. Watts in effect is the measure of the amount of work done by certain amperage (amount) of electric current at a certain pressure or voltage.

The batteries we use today are simply variations of the early battery or voltaic pile. Today’s battery’s are made up of plates of reactive chemicals separated by barriers, being polarized so all the electrons gather on one side. The side that all the electrons gather on becomes negatively charged, and the other side becomes positively charged. Connecting a device creates a current and the electrons flow through the device to the positive side. At the same time, an electrochemical reaction takes place inside the batteries to replenish the electrons.

The effect is a chemical process that creates electrical energy with one downside: about 80 percent of the energy put into batteries is lost through this process.

Though the battery maybe inefficient we still need the battery, especially battery replacements that are inexpensive. We are power hungry consumers. We like our power and lot’s of it. Lithium-ion batteries (Li-ions) are generally considered the most powerful, offering the same energy as nickel metal hydride (NiMH) batteries, with 20 to 30 percent less weight. They are expensive compared to older battery technologies, but are valued for high-power portable applications, such as laptops, cell phones, and PDAs.

Until next time – Dan Hagopian, BatteryShip.com

Integrated Power Management Circuits

Integrated Power Management Circuits protects against over-voltage, and under-voltage conditions and they maximize battery life between charges, minimize charging times, and improve overall battery life.

Discussing internal battery design would be incomplete if we did not write on the subject of integrated circuits. Batteries that can be bought at BatteryShip.com for PDAs, MP3s, Digital Cameras, and Laptops have designed within them integrated power management circuits that insure that the deliverance of reliable power is properly managed. Without these power management integrated circuits even fine tuned handhelds will exhibit problems such as over-voltage, and under-voltage conditions. Incidentally, overcharging is potentially a very dangerous problem. Overcharging is the state of charging a battery beyond its electrical capacity, which can lead to a battery explosion, leakage, or irreversible damage to the battery. It may also cause damage to the charger or device in which the overcharged battery is later used.

But let us take a step back a moment to build a platform with which to discuss power management integrated circuits. At its most basic level an integrated circuit in general is a miniaturized electronic circuit. An electrical circuit is a network that has a closed loop, giving a return path for current. The goals of integrated circuits are multifaceted, for example when designing for signal processing integrated circuits apply a predefined operation on potential differences (measured in volts) or currents (measured in amperes). Typical functions for such electrical networks are amplification, oscillation and analog linear algorithmic operations such as addition, subtraction, multiplication, division, differentiation and integration.

For batteries the use of integrated circuits with the goal of power management is integrated battery management which include voltage regulation and charging functions. Power management integrated circuits offer other key benefits as well including maximizing battery life between charges, minimize charging times, and improve battery life.

The other critical aspect of power management integrated circuits is their functioning design to detect and monitor voltage levels in batteries. When certain parameter thresholds are exceeded or dangerous conditions exist, these “supervisory circuits” react through a programmable logic design to protect the monitored system and correct problems as programmed. Supervisory circuits are known by a variety of names, including battery monitors, power supply monitors, supply supervisory circuits and reset circuits. They perform critical functions including power-on-reset (POR) protection to ensure that processors always start at the same address during power-up. Without POR, even well-functioning systems can exhibit problems during power-up, power-down, overvoltage, and undervoltage conditions.

A real example of a battery pack protector circuit is a Texas Instrument two-cell lithium-ion (Li-Ion) and lithium-polymer (Li-Pol) battery pack protector device. The device’s primary function is to protect both Li-Ion and Li-Pol cells in a two-cell battery pack from being either over-charged (over-voltage) or over-discharged (under-voltage). It employs a precision band-gap voltage reference that is used to detect when either cell is approaching an over-voltage or under-voltage state. When on-board logic detects either condition, the series FET (field effect transistor) switch opens to protect the cells. (Side bar: a FET is a transistor that uses an electric field to control the conductivity of a particlular 'channel' in a semiconductor material. FETs at times are used as voltage-controlled resistors).

I won’t be getting anymore technical as this topic is better left to engineers. But suffice to say power management integrated circuits are a critical design aspect of your handheld battery. Without these integrated circuits your handheld device would have stopped working a long while back.

Until next time – Dan Hagopian, BatteryShip.com
Copyright © BatteryEducation.com. All rights reserved.

Amps, Volts, and mAh

Batteries have electrical specifications that include its volt and milliAmp hour rating. These terms are abbreviated as we see in the following example: 3.7 V, 1600 mAh.

What do these terms mean, and why should you care about the specifications of pda batteries?

Volts – or V – are an electrical measure of energy potential. You can think of it as the pressure being exerted by all the electrons of a PDA Batteries negative terminal as they try to move to the positive terminal.

Amps – or A – is an abbreviation of Ampere, a 19th century French scientist who was a pioneer in electricity research. Amps measure the volume of electrons passing through a wire in a one second. One Amp equals 6.25 x 10¹⁸ electrons per second.

Amp hours – or Ah – measures capacity. That is what we want to know about PDA Batteries – how long can it deliver a certain amount of charge before it runs out. As with all metric measurements, Amps can be divided into smaller (or larger) units by adding a prefix.

In the case of batteries for PDAs, digital cameras, and laptops, a milliAmp hour (mAh) is most commonly used. Note that 1000 mAh is the same a 1 Ah. (Just as 1000mm equals 1 meter.) Note that Amp hours do not dictate the flow of electrons at any given moment. Batteries with a 1 Amp hour rating could deliver ½ Amp of current for 2 hours, or they could provide 2 Amps of current for ½ hour.

Typically, PDA Batteries will use 1 to 3 Amps per hour, depending on the model's processor speed, screen size, screen brightness adjustment, usage, and other factors.

Keep in mind that slight variations in voltage generally do not impact the performance of your device. We see this all the time with universal and external batteries. The original battery might be specified at 10.8 Volts, but customers using a universal part can operate their laptop, for example, safely at either the 10 or 11 Volt setting.

Until next time – Dan Hagopian, BatteryShip.com
Copyright © BatteryEducation.com. All rights reserved.

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