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# how to find the terminal voltage of a battery

From Wikipedia

Lead-acid batteries, invented in 1859 by FrenchphysicistGaston PlantÃ©, are the oldest type of rechargeable battery. Despite having a very low energy-to-weight ratio and a low energy-to-volume ratio, their ability to supply high surge currents means that the cells maintain a relatively large power-to-weight ratio. These features, along with their low cost, make them attractive for use in motor vehicles to provide the high current required by automobile starter motors.

## Electrochemistry

In the charged state, each cell contains electrodes of elemental lead (Pb) and lead(IV) oxide (PbO|2) in an electrolyte of approximately 33.5% v/v (4.2 Molar) sulfuric acid (H|2|SO|4).

In the discharged state both electrodes turn into lead(II) sulfate (PbSO|4) and the electrolyte loses its dissolved sulfuric acid and becomes primarily water. Due to the freezing-point depression of water, as the battery discharges and the concentration of sulfuric acid decreases, the electrolyte is more likely to freeze during winter weather.

The chemical reactions are (discharged to charged):

\mbox{PbSO}_{4} (s) +5\mbox{H}_2\mbox{O} (l) \leftrightarrow \mbox{PbO}_{2} (s) +3\mbox{H}_3\mbox{O}^+ (aq)+\mbox{HSO}_{4}^{-} (aq) +2e^- \quad\epsilon^o = 1.685 \ \mathrm{V}
\mbox{PbSO}_{4} (s) +\mbox{H}_3\mbox{O}^+ (aq)+2e^- \leftrightarrow \mbox{Pb} (s) +\mbox{HSO}_{4}^{-} (aq) +\mbox{H}_2\mbox{O} (l) \quad\epsilon^o = -0.356 \ \mathrm{V}

Because of the open cells with liquid electrolyte in most lead-acid batteries, overcharging with high charging voltages generates oxygen and hydrogen gas by electrolysis of water, forming an explosive mix. The acid electrolyte is also corrosive.

Practical cells are usually not made with pure lead but have small amounts of antimony, tin, calcium or seleniumalloyed in the plate material to add strength and simplify manufacture.

## Voltages for common usages

These are general voltage ranges for six-cell lead-acid batteries:

• Open-circuit (quiescent) at full charge: 12.6 V to 12.8 V (2.10-2.13V per cell)
• Open-circuit at full discharge: 11.8 V to 12.0 V
• Loaded at full discharge: 10.5 V.
• Continuous-preservation (float) charging: 13.4 V for gelled electrolyte; 13.5 V for AGM (absorbed glass mat) and 13.8 V for flooded cells
1. All voltages are at 20|C|F, and must be adjusted -0.022V/Â°C for temperature changes.
2. Float voltage recommendations vary, according to the manufacturer's recommendation.
3. Precise float voltage (Â±0.05 V) is critical to longevity; insufficient voltage (causes sulfation) which is almost as detrimental as excessive voltage (causing corrosion and electrolyte loss)
• Typical (daily) charging: 14.2 V to 14.5 V (depending on manufacturer's recommendation)
• Equalization charging (for flooded lead acids): 15 V for no more than 2 hours. Battery temperature must be monitored.
• Gassing threshold: 14.4 V
• After full charge, terminal voltage drops quickly to 13.2 V and then slowly to 12.6 V.

Portable batteries, such as for miners' cap lamps (headlamps) typically have two cells, and use one third of these voltages.

## Measuring the charge level

Because the electrolyte takes part in the charge-discharge reaction, this battery has one major advantage over other chemistries. It is relatively simple to determine the state of charge by merely measuring the specific gravity (S.G.) of the electrolyte, the S.G. falling as the battery discharges. Some battery designs include a simple hydrometer using colored floating balls of differing density. When used in diesel-electric submarines, the S.G. was regularly measured and written on a blackboard in the control room to indicate how much longer the boat could remain submerged.

## Construction

### Plates

The lead acid cell can be demonstrated using sheet lead plates for the two electrodes. However such a construction produces only around one ampere for roughly postcard sized plates, and for only a few minutes.

Gaston PlantÃ© found a way to provide a much larger effective surface area. In PlantÃ©'s design, the positive and negative plates were formed of two spirals of lead foil, separated with a sheet of cloth and coiled up. The cells initially had low capacity, so a slow process of "forming" was required to corrode the lead foils, creating lead dioxide on the plates and roughen them to increase surface area. Initially this process used electricity from primary batteries; when generators became available after 1870, the cost of production of batteries greatly declined. PlantÃ© plates are still used in som

Alkaline battery

Alkaline batteries are a type of primary battery or rechargeable battery dependent upon the reaction between zinc and manganese dioxide (Zn/MnO2).

Compared with zinc-carbon batteries of the LeclanchÃ© or zinc chloride types, alkaline batteries have a higher energy density and longer shelf-life, with the same voltage. Button cellsilver-oxide batteries have higher energy density and capacity but also higher cost than similar-size alkaline cells.

The alkaline battery gets its name because it has an alkaline electrolyte of potassium hydroxide, instead of the acidic ammonium chloride or zinc chloride electrolyte of the zinc-carbon batteries. Other battery systems also use alkaline electrolytes, but they use different active materials for the electrodes.

## History

The alkaline dry battery was invented by Canadian engineer Lewis Urry in the 1950s while working for the Eveready Battery company. On October 9, 1957, Lewis Urry, Karl Kordesch, and P.A. Marsal filed US patent (2,960,558) for the alkaline battery. It was granted in 1960 and was assigned to Union Carbide Corporation.

## Chemistry

In an alkaline battery, the anode (negative terminal) is made of zinc powder, which gives more surface area for increased current, and the cathode (positive terminal) is composed of manganese dioxide. Unlike zinc-carbon (LeclanchÃ©) batteries, the electrolyte is potassium hydroxide rather than ammonium chloride or zinc chloride.

The half-reactions are:

Zn (s) + 2OHâˆ’ (aq) â†’ ZnO (s) + H2O (l) + 2eâˆ’
2MnO2 (s) + H2O (l) + 2eâˆ’â†’Mn2O3 (s) + 2OHâˆ’ (aq)

## Capacity

Capacity of an alkaline battery is greater than an equal size LeclanchÃ© or zinc-chloride cell because the manganese dioxide anode material is purer and denser, and space taken up by internal components such as electrodes is less. An alkaline cell can provide between three and five times capacity.

The capacity of an alkaline battery is strongly dependent on the load. An AA-sized alkaline battery might have an effective capacity of 3000 mAh at low drain, but at a load of 1 ampere, which is common for digital cameras, the capacity could be as little as 700 mAh. The voltage of the battery declines steadily during use, so the total usable capacity depends on the cut-off voltage of the application. Unlike Leclanche cells the alkaline cell delivers about as much capacity on intermittent or continuous light loads. On a heavy load, capacity is reduced on continuous discharge compared with intermittent discharge, but the reduction is less than for Leclanche cells.

## Voltage

The nominal voltage of a fresh alkaline cell is 1.5 V. Multiple voltages may be achieved with series of cells. The effective zero-load voltage of a non discharged alkaline battery varies from 1.50 to 1.65 V, depending on the chosen manganese dioxide and the contents of zinc oxide in the electrolyte. The average voltage under load depends on discharge and varies from 1.1 to 1.3 V. The fully discharged cell has a remaining voltage in the range of 0.8 to 1.0 V.

## Current

The amount of current an alkaline battery can deliver is roughly proportional to its physical size. This is a result of decreasing internal resistance as the internal surface area of the cell increases. A general rule of thumb is that an AA alkaline battery can deliver 700 mA without any significant heating. Larger cells, such as C and D cells, can deliver more current. Applications requiring high currents of several amperes, such as high powered flashlights and portable stereos, will require D-sized cells to handle the increased load.

## Construction

Alkaline batteries are manufactured in standardized cylindrical forms interchangeable with zinc-carbon batteries, and in button forms. Several individual cells may be interconnected to form a true "battery", such as those sold for use with flashlights and the 9 volt transistor-radio battery.

A cylindrical cell is contained in a drawn steel can, which is the cathode connection. The cathode mixture is a compressed paste of manganese dioxide with carbon powder added for increased conductivity. The paste may be pressed into the can or deposited as pre-molded rings. The hollow center of the cathode is lined with a separator, which prevents mixing of the anode and cathode materials and short-circuiting of the cell. The separator is made of a non-woven layer of cellulose or a synthetic polymer. The separator must conduct ions and remain stable in the highly alkaline electrolyte solution.

The anode is composed of a dispersion of zinc powder in a gel containing the potassium hydroxide electrolyte. To prevent gassing of the cell at the end of its life, more manganese dioxide is used than required to react with all the zinc.

When describing standard AAA, AA, C, sub-C and D size cells, the anode is connected to the flat end while the cathode is connected to the end with the raised button.

## Recharging of alkaline batteries

Some alkaline batteries are designed to be recharged (see rechargeable alkaline battery),

Question:I know that, in a parallel circuit, the voltage is the same across each branch as it is in the battery. Say, for example, a battery is 15 V and a parallel circuit has 2 resistors. If you're asked to determine the total voltage, is it simply 15 V? Is that the total voltage? If it is, then if you have two circuits with the same battery, one parallel and one series, would the total voltage be the same for both circuits?

Answers:Yes, the same 15 V for each one. That results because the voltage potential between the anode and cathode of the battery remains 15 V no matter what's attached or how it's arranged. What changes are the currents through the circuits. In the parallel circuits, with two resistors R and r, the current across R is i = V/R and across r is I = V/r. So there are two currents i and I. The total current then is i + I between the battery terminals. In the series, we have i = V/(R + r); so there is but one current i. And i is the only current between the battery terminals.

Question:I have some Nickel Cadmium Batteries, each one has 2 cells . They are aproximately 15" x 6" x 8", I guess they weigh about 10 kg each. It says the brand name is NIFE. I'm on a 12v solar power system for my home and need to know how many of these Nickel Cadmium batteries I need to replace my dying leadacid battery bank. At the moment a multimeter puts them between 2.4v and 2.8v per cell, but I don't know their present state of charge

Answers:I hope you mean 2.4 volts per battery, which is 2 cells. This puts the cell voltage at 1.2 volts, about right for Ni-Cd. 2,4 volts per cell doesn't make sense.

Question:We think of Voltage only in terms of a difference of potential, but does it have to be that way. For example, if there existed a body with zero net charge isolated from anything that might put it in an electric field, could we say it had an absolute voltage of zero? If so, could we use this definition of zero absolute voltage to find the absolute voltage of anything else? For example, could we measure the absolute voltage of planet Earth by finding the potential difference between Earth and this isolated chargeless body?

Answers:Some insight could be had into the secretive states of matter acquired during attempts to reach an absolute zero on the Kevin scale of temperature. It is amazing to see how weird or wonderful things could be when depletion of energy goes beyond certain limits. Helium, the gas normally used for the experiment, obviously turns into liquid first, but hen then that liquid starts to act like no other normal liquid. It, for instance, defies gravity and rises up along the walls of its container, or starts to seep through glass. But perhaps the most astounding and useful a phenomenon observed in of super-cool materials is that of superconductivity, a state of superfluity for resistless electronic passage through a conductor cooled down to very low temperature. The electrical properties of any material are directly related to its temperature. And it is the common law in solid-state physics that the conductively of any conductor is inversely proportional to its temperature. If then a material is kept within a magnetic field of uniform intensity and heated up gradually, we could observe its electrical behavior against the controlled variation in temperature. Heat and magnetism, in the case of our question, seem to be the only variables. The absolutes are the holy grails of any scientific search. They are impossible to reach, but they are indispensably in the mind along every avenue of thought, and in every path of research. We can philosophize here that we could not count from one to two if the number line would not be infinite. This is how fundamental their conception in the mind is, however unrealistic that might be. Voltage, unlike other inherent properties of matter, like degree of heat energy, is only relatively observed. An object can be colder than another object, but it can also be the coldest out of countless others in the surrounding. In case of voltage however, which is merely a measure of potential difference, the range is limited only to two objects. All things can be electrically polarized in parts. But when any two oppositely charged materials are brought together they form one system and act like one object, as in d.c. batteries, where cathode and anode form one cell. I therefore do not think that the concept of absolute voltage is a valid concept. Besides, there are all sorts of materials that are naturally in their state of electrical inertness. This they demonstrate in their chemical properties, the way they react to other things. Water and air, for instance, are two substances that in their pure form do not react with metals. It is only when they ionized they cause metals to corrode, that is when air is moisturized, or when water is aerated. Then both air and water cause metals to rust forming deposits of sulfate, oxide and carbonate depositions of metallic surfaces, for instance.

Question:Are the Prius batteries made with conventional lead plates and sulfuric acid with multiple cells rated at about 2 volts per cell?

Answers:Which model Prius? NHW10, NHW11, or NHW20? Which battery? The 12v accessory battery is a standard conventional lead-acid battery, but it is an AGM about the size of a motorcycle battery. It is only used to power the computers and run the accessories (radio, clock, fans, etc.). Once the computers are on, they flip a relay which connects up the hybrid traction battery. The hybrid traction battery is what starts the gasoline engine through one of the electric motor-generators, and also provides power for electric propulsion. The hybrid traction battery is NiMH (nickel-metal hydride), NOT lead-acid. They are built by Panasonic EV Energy Corp. in Japan: http://www.peve.jp/e/shouhin.html The differences in the battery pack designs and voltages are highlighted on this page: http://john1701a.com/prius/prius-history.htm#Generations The author calls the NHW10 model the "Original," the NHW11 model the Classic, and the current NHW20 model the "Iconic." You may want to read more through the Toyota training document "Hybrid03 High-Voltage battery.pdf" found at http://www.autoshop101.com/autoshop15.html#Hybrid For the NHW11 and NHW20 Prius (the models sold internationally), the hybrid battery pack is comprised of many prismatic modules (28 or more). Each prismatic module is made up of six 1.2V individual NiMH cells, so each module is 7.2V. Toyota is experimenting with lithium-ion LiO packs for future Prius releases, but none are commercially on the market yet...