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From Wikipedia

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 Leclanché 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 (Leclanché) batteries, the electrolyte is potassium hydroxide rather than ammonium chloride or zinc chloride.

The half-reactions are:

Zn (s) + 2OH− (aq) → ZnO (s) + H2O (l) + 2e−
2MnO2 (s) + H2O (l) + 2e−→Mn2O3 (s) + 2OH− (aq)

Capacity

Capacity of an alkaline battery is greater than an equal size Leclanché 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),

Ohmmeter

An ohmmeter is an electricalinstrument that measures electrical resistance, the opposition to an electric current. Micro-ohmmeters (microhmmeter or microohmmeter) make low resistance measurements. Megohmmeters (aka megaohmmeter or in the case of a trademarked device Megger) measure large values of resistance. The unit of measurement for resistance is ohms (Ω).

The original design of an ohmmeter provided a small battery to apply a voltage to a resistance. It uses a galvanometer to measure the electric current through the resistance. The scale of the galvanometer was marked in ohms, because the fixed voltage from the battery assured that as resistance is decreased, the current through the meter would increase.

A more accurate type of ohmmeter has an electronic circuit that passes a constant current (I) through the resistance, and another circuit that measures the voltage (V) across the resistance. According to the following equation, derived from Ohm's Law, the value of the resistance (R) is given by:

R = \frac{V}{I}

For high-precision measurements the above types of meter are inadequate. This is because the meter's reading is the sum of the resistance of the measuring leads, the contact resistances and the resistance being measured. To reduce this effect, a precision ohmmeter has four terminals, called Kelvin contacts. Two terminals carry the current from the meter, while the other two allow the meter to measure the voltage across the resistor. With this type of meter, any voltage drop due to the resistance of the first pair of leads and their contact resistances is ignored by the meter. This four terminal measurement technique is called Kelvin sensing, after William Thomson, Lord Kelvin, who invented the Kelvin bridge in 1861 to measure very low resistances. The Four-terminal sensing method can also be utilized to conduct accurate measurements of low resistances.


Button cell

A watch battery or button cell is a small single cell battery shaped as a squat cylinder typically 5 to 12 mm in diameter and 1 to 6 mm high—like a button on a garment, hence the name. Button cells are used to power small portable electronics devices such as wrist watches, pocket calculators, and hearing aids. Some cells larger than the dimensions above are also called button cells, but are less commonly used. Lithium cells are generally similar but somewhat larger; they tend to be called either lithium cells or batteries or coin cells rather than button cells.

Devices using button cells are usually designed to use a cell giving a long service life, typically well over a year in continuous use in a wristwatch. Most button cells have low self-discharge and hold their charge for a long time if not used. Higher-power devices such as hearing aids, where high capacity is important and low self-discharge less so as the cell will usually be used up before it has time to discharge, may use zinc-air cells which have much higher capacity for a given size, but discharge over a few weeks even if not used.

Button cells are single cells, usually disposable primary cells. Common anode materials are zinc or lithium. Common cathode materials are manganese dioxide, silver oxide, carbon monofluoride, cupric oxide or oxygen from the air. Mercuric oxide button cells were formerly common, but are no longer available due to the toxicity and environmental hazard of mercury.

Cells have a metal can forming the bottom body, with a circular insulated top cap. The can is the positive and the top the negative terminal.

Cells of different chemical composition made in the same size are mechanically interchangeable. The composition affects service life and voltage stability. Using the wrong cell may lead to short life or improper operation (for example, light metering on a camera requires a stable voltage, and silver cells are usually specified). Sometimes different cells of the same type and size and specified capacity in mAh are optimised for different loads by using different electrolytes, so that one may have longer service life than the other if supplying a relatively high current.

Properties of different types

Silver cells may have very stable output voltage until it suddenly drops very rapidly at end of life. This varies for individual types; one manufacturer (Energizer) offers 3 silver oxide cells of the same size, 357-303, 357-303H,and EPX76, with capacities ranging from 150 to 200 mAh, voltage characteristics ranging from gradually reducing to fairly constant, and some stated to be for continuous low drain with high pulse on demand, others for photo use.

Mercury batteries also supply a stable voltage, but are now banned in many countries due to their toxicity and environmental impact.

Alkaline batteries are made in the same button sizes as other types, but typically provide less capacity and less stable voltage (it drops gradually in use) than more costly silver oxide or lithium cells. They are often sold as cheap watch batteries to, and sometimes by, people who do not know the difference.

Zinc-air batteries use air as the depolarizer and have much higher capacity than other types (they use air from the atmosphere which does not need to be supplied in the battery). A seal is removed before use to allow air to enter the cell; the cell will then self-discharge in a few weeks even if not used up.

For comparison, a cell of diameter 11.6 mm and height 5.4 mm from one reputable manufacturer has the following properties. In many cases there are several batteries of the same chemistry and size with different capacities and properties; figures listed are merely indicative.

  • Silver: capacity 200 mAh to an end-point of 0.9 V, internal resistance 5–15 ohms, weight 2.3 g
  • Alkaline (manganese dioxide): 150 mAh (0.9), 3-9 ohms, 2.4 g
  • Mercury 200mAh, 2.6 g
  • Zinc-air 620 mAh, 1.9 g

Examining datasheets for a manufacturer's range may find a high-capacity alkaline cell with a capacity as high as one of the lower-capacity silver types; or a particular silver cell with twice the capacity of some particular alkaline cell. If the powered equipment requiring a relatively high voltage (e.g., 1.3V) to operate correctly, a silver cell with a flat discharge characteristic will give much longer service than an alkaline cell—even if it has the same specified capacity in mAh to an end-point of 0.9V. If some device seems to "eat up" batteries after the original supplied by the manufacturer is replaced, it may be useful to check the device's requirements and the replacement battery's characteristics. For digital callipers, in particular, some are specified to require at least 1.25V to operate, others 1.38V.

Datasheets for some cheaper cells, particularly alkaline, are not available, so it is not possible to say whether capacities are about the same as for documented types. Discussions on web forums suggest that they can be very poor.

In some ways the size is the most important property of a button cell: cells of different chemistry are to a considerable extent interchangeable. In practice only cells of fairly similar voltages are made in any given size; there is no "CR1154" 3V lithium battery mechanically interchangeable with a 1.5V silver or alkaline size 1154 cell. Use of a battery of significantly higher voltage than equipment is designed for can cause permanent damage, but use of a cell of the right voltage but unsuitable characteristics can only lead to


From Yahoo Answers

Question:Two scales on a voltmeter, which is constructed from a galvanometer, measure voltages up to 24 V and 33 V respectively. The resistance connected in series with the galvanometer is 1679 for the 24 scale and 2937 for the 33 scale. Determine the internal resistance of the galvanometer. Answer to 2 s.f.

Answers:The galvanometer resistance is part of two voltage dividers which divide down the 24/33 volts to the full scale voltage of the galvo. There are two unknowns, the FS voltage of the galvo, V, and the resistance, R V = 24R/(R+1679) V = 33R/(R+2937) two equations in two unknowns 24R/(R+1679) = 33R/(R+2937) 24R(R+2937) = 33R(R+1679) 8(R+2937) = 11(R+1679) 8R + 23496 = 11R + 18469 3R = 5027 R = 1675 ohms, or to 2 places 1700 ohms but check the arith. .

Question:I know the general set-up of the experiment and the equation v= E-Ir. Now I need to think of modifications to improve accuracy, etc so I think I need to find a way to control the temperature in the circuit? I think using a thermistor in some way will help. But how? And any other ideas? Thanks a lot x

Answers:What sort of experiment is it? Do you want to chart IR against temperature? Or just get a single value? Or a series of values at the same temperature after increasing amounts of discharge? If a single value, just measure the open-circuit voltage, and then connect the load resistor and voltmeter to the battery, take a quick reading and disconnect. If you're charting IR vs temp, bring the battery to each temp of interest and take readings as described above. The idea of course is to minimize self-heating of the battery. If you're trying to get a time-series at constant temperature, I'd suggest a zero-C mixture (easily done with ice & water) in which you immerse the battery. If the water and ice are reasonably pure there shouldn't be any significant parasitic current drain. Again, keep the loaded reading times short.

Question:I have a rocket plane in one of my flight simulators. I am currently about 1,000,000 feet above sea level with a vertical speed of 1,000,000 feet per minute. I want to calculate how long it will take for the plane to fall back to earth if I cut the throttle. I calculated it with the standard formula that we learned all the way back in Algebra I; a=-16t^2+vt+h, where a=current altitude, t=time, v=initial vertical speed, and h=initial height. Now, that worked out fine and dandy until I realized that 1,000,000 feet per minute is WAYYYY above escape velocity and that air resistance is a major factor at 1,000,000 feet per minute. So my question is, is there an all-encompassing formula for this thing that includes air resistance and the inverse square law of gravity? Thanks everybody. ;)

Answers:No. The problem domain is far too complex for that. 1. If your speed up is faster than escape velocity, you won't be falling down at all. 2. The formula a=-16t^2+vt+h is fine for Algebra I but not for physics. The formula for constant acceleration, the formula for distance is: D = Vi T + (1/2) A T^2 where Vi is the initial velocity and A is the acceleration. At the surface of the earth, the acceleration due to gravity is approximately 32 ft/sec^2 (9.8 m/s^2). But the force gravity falls off as 1/R^2 so once you are a significant distance from the surface of the Earth, the gravitational force is lower. The radius of the Earth is about 6300 km: http://en.wikipedia.org/wiki/Earth or about 20,000,000 feet. So your altitude is a significant enough fraction of the Earth's radius that using g = 32 ft/s^2 is not going to be very accurate. Even if you ignore air resistance, etc. you have to use: V(t) = integral of A(t) dt + Vi D(t) = integral of V(t) dt + Di A(t) = G Me / (D(t) + Re)^2 3. Not only is 1,000,000 feet per minute faster than escape velocity, it is also much faster than the speed of sound, even in very thin air. That means you are not dealing with ordinary air drag but hypersonic drag. http://en.wikipedia.org/wiki/Hypersonic 4. 1,000,000 feet above the surface of the Earth is well above most of the atmosphere, in the thermosphere, where the International Space Station and many other satellites orbit: http://en.wikipedia.org/wiki/Earth's_atmosphere You are not going to get any significant air drag here because there is no air. But since you are above the aurora, you are going to have all sorts of interesting electrical effects if you aren't careful. And as you fall, the air density will be changing and hence that element of the drag equation as well.

Question:12 volt battery. Internal resistance of 1-ohm resistor. Don't I use equation voltage = current x resistance So 12 = current x 1 current = 12 Thats the answer I get...I have an answer key that shows the answer is 3 amperes, so I'm checking to see if there is something I missed. Thanks.

Answers:12 amps is correct, you are missing some information. possibly 6 amps if your question is to read as a battery with a 1 ohm internal resistance and with a 1 ohm external resistor.

From Youtube

How to test the internal resistance of a battery :The internal resistance of a battery can be tested in 4 steps: 1) measure the voltage [V_bat] of the battery 2) measure the resistance of an external load [R_ext] 3) measure the current [I] when the battery is attached to the load: 4) Calculate the internal resistance with: R_int = V_bat/I - R_ext examples: R_int_Alkaline = 8.4/1.0 - 5.6*1.0 = 2.8 Ohm R_int_ZincCarbon = 8.1/0.55- 5.6 = 9.1 Ohm

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