BATTERY TECHNOLOGY

I still get some interest in this subject, what with all the digital cameras and remote controls, clocks and even battery driven tools. Battery use is endless and can be expensive too. It pays to know the best way to cope. There has been tremendous progress in both primary & secondary battery technology over the last few years. I once wrote a little treatise for my sons which I will reproduce here. Actually, it came about because of all their battery driven toys. Since then we have seen alkaline, Mercuric-Oxide, Zinc-Air, Silver Oxide, Nickel MetalHydride, Lithium, Li-Ion and today I spotted a Nickel-Zinc type for digital cameras in Boots. Anyway here's how it was a few years ago with one or two updates: -

RE-CHARGABLE BATTERIES
(A collection of information)
Resume
First of all a recap.
The "battery" is made up of a group of "cells".
There are two classes of such cells: -

PRIMARY, those which cannot be re-charged because the chemical action is not reversible.

SECONDARY, those that can be re-charged because it is.
Efficiency is related to the energy that it takes to produce a charged battery, and what energy can then be recovered. It is measured in Amp hours or mAh

ELECTRO-MOTIVE FORCE (EMF). This refers to the UN-LOADED terminal voltage, or the actual potential (Voltage) that the cell delivers before there is any load whatsoever. In practice a very light load as would be drawn by a high resistance volt-meter reads it OK. EMF falls as the current drawn is increased and is in proportion to the internal resistance of the cell. This can change over time or with the state of charge, hence the drop off of voltage as cells "flatten." The internal resistance can, in some chemistries, be used as an indication of the state of charge.

POTENTIAL DIFFERENCE (PD) Refers to the terminal output voltage under load - when a fairly substantial current is being drawn, say at a 1 Hr rate. This means, for example that for a 50Ah battery the load would be 50 Amps; and for a 1600mAH battery, 1600mA.

SURFACE CHARGE There is an apparent increase in EMF when a cell is freshly and fully recharged. It reduces quickly after standing or at first discharge. PD (Potential Difference) is the EMF or Voltage that is present when the cell is being made to work (discharge). This is the parameter that counts in practical use. Fortunately, most cells have a fairly constant and predictable terminal voltage which is maintained over their discharge cycle.

CAPACITY refers to the total energy that a cell contains in Ah (Ampere - hours). This can be too big for some little cells and so we then use mAh (for milli or one thousandth part). i.e. 1000mA = 1A.
A specific discharge rate is implied usually over 10 hours for large capacity cells, and over 1 hour for small cells. This is sometimes referred to as the "C" or "C1" / "1C" rate. For example, a 1.2 Ah cell will supply 1.2A for 1 hour.
The CAPACITY of a cell will vary with the discharge rate, reducing as the process is speeded up. The discharge time at the HOUR RATE, meaning the current that can be drawn over that period that would just render the cell to be FLAT - or discharged. This is sometimes quoted as a PD that is about 15% under the nominal voltage. This gives us 1.05V for Ni-Cad & 1.75V for Lead-Acid.

WATTS PER HOUR
If you prefer to think in the more familiar Watts measurement for power, multiply the terminal voltage by the current in amps. A 12V car battery of say 50 Ah capacity, can deliver 12 x 50 = 600Watt-hours. It's not much really. In practice, at that rate of discharge, it might well be rather less.

RECHARGING
Optimum re - charging is quoted in relation to the ten hour rate at, but with an added EFFICIENCY factor in per cent (%). If the EFFICIENCY is quoted at 40% over the TEN HOUR RATE, then we would proceed with the charging for that extra period of time: 10 hrs + 40% = 14 hrs.
Now if the CAPACITY is say 1Ah at the 10 hour rate (that's 100mA over 10hrs), we charge at that rate over 14 hrs (assume 40% extra for in-efficiency), to achieve full charge. This is the most usual example.
Fast charge / discharge results in reduced efficiency because the chemical action cannot keep up with the demand and therefore energy is wasted, usually as heat or gas. Carried to extremes this will cause damage. This is similar to what happens when you go on charging for too long and is one reason why it is better to start the re - charge from when the cell is flat. However, there are dangers to having some cell types in a flat condition for long. Most cell types must never be reverse charged. This can happen when cells are connected in a serial stack (or BATTERY), as one or more cells become fully discharged before some of the others.

IT IS VERY IMPORTANT TO UNDERSTAND THIS LAST POINT!

EXAMPLE
A circuit of cells connected in series (and +ve to -ve to increase the voltage) is to supply a bulb (we call this the LOAD). At first all the cells are in a more or less fully charged condition. As time goes by one, (or more), cells is the first to be discharged to zero Volts at its output terminals. At this point it begins to absorb energy in reverse polarity from the other cells in the circuit that are not yet flat and receives the damaging reverse charge. It is difficult or impossible to rescue cells that are damaged in this way.

The 2Volts / cell LEAD - ACID (as used in car) batteries SULPHATE when areas of their lead plates are no longer in a chemically charged state. {Re-charge every 3 months or keep trickle-charged}.

LEAD-ACID CELLS SHOULD THEREFORE BE STORED IN A CHARGED CONDITION. There are two types of lead involved and it is the negative plate that suffers if they are not fully charged. The white lead-sulphate covers the surface and prevents it being in contact with the electrolyte which is dilute - SULPHURIC ACID - H2SO4. Sulphate is very hard to remove once it has formed although CALCIUM in the acid can help. For this reason it is far better to make sure that LEAD - ACID batteries are always kept in a charged condition or are re - charged at very frequent intervals. Sulphation leads to a loss of CAPACITY, (Ah), as not so much area of material is available for conversion - to absorb the charge. This can lead to inadvertent overcharge-ing which although they are tolerant of a small "trickle" over charge, tends to force material from the plates where it falls to the bottom, is lost for chemical conversion and can cause shorts. Perhaps more serious is that when a fully charged lead - acid cell is still receiving charge current, it produces highly explosive HYDROGEN gas !!
Some heavy duty, slow discharge units produced say, for telephone exchange back - up, can last for 30 years !

Nickel-Cadmium (Ni - Cad) cells have some different problems. In many ways they are superior to other SECONDARY re - charge-able cells, and they are certainly less hazardous if only because they contain no acids. They are however, POISONOUS to all life! Their PD is only 1.2V per cell and for a given Ah capacity will need to be larger in size and heavier than other types.

Some reports say that they are tolerant of persistent overcharging, others say they are not! It may depend upon the construction and re-sealable venting. In actual practice, these batteries do NOT thrive on being continually charged - or over-charged at high current rates. However, they seem happy to be trickle charged. Capacity is adversely affected by high temperatures during charging.

Ni-Cad cells tend to keep their output PD right up to the end of their full discharge, rolling off very suddenly as they go entirely flat. Little warning is given by the terminal voltage and the only real means of knowing the state of charge is to monitor the discharge rate and period. Because these cells should be stored in a discharged state, they are easier to maintain and keep. Their chief draw-back is that they grow DENDRITE hairs of conductive metal when left in a charged state which shorts out the material within and prevents re - charging. One possible solution is to "blow" the hairs away (melt them) with a very high instantaneous current pulse of correct polarity, limited duration and magnitude. For cells up to say, 4Ah use a charged up electrolytic capacitor (say to 12V from a car battery via a series resistor of about 1 to 10 ohms, (to resrict the surge current).
When it is charged, "splash" the capacitor across the cell terminals briefly, then try a few seconds of high charge within normal limits for the cell. As a guide use say 50% of capacity. Once the cell can support its normal 1.2 Volts PD for a light current draw, charge normally, but at 14 hour rate. (One tenth of total capacity for 14 Hrs). Remember that this treatment formula applies to individual cells and NOT battery packs. If individual cells cannot be isolated a higher voltage will be required, say double (24 for V for a 12 Volt battery, with the risk of damage to perfectly good cells in the pack.
NI-CAD cells also suffer from a phenomenon called 'THE MEMORY EFFECT' If a cell is boost charged before it has become exhausted, it behaves as though it has a reduced capacity, subsequently discharging to the level it was at when the boost started and then behaving 'FLAT'. This may be related to the dendrite growth that was mentioned earlier. However, official procedure is to make sure the cell is fully discharged before the re - charge begins. This is reasonably easy with a single CELL as a modern 'intelligent' charger can effect a discharge until the cell voltage first reduces and thereby commence the full charge cycle. Because of the reverse charge dangers that can occur in a BATTERY of several cells, this procedure is not without some problems when say, camcorder batteries are to be re - charged. In any case these 'intelligent' chargers have to be told what the full voltage should be, and the Ah capacity. They are completely duped by a battery with a faulty cell in its stack !
STORE Ni-Cad BATTERIES/CELLS IN FULLY DISCHRGRED STATE!

Nickel-Metal-Hydride
The Ni-M-H type of cell has become popular & much cheaper over revcent years. These are very similar to the older Ni-Cad having 1.2V cells, but without the terrors of the memory effect, or indeed long term inactivity. Shelf life charge is improved and occasional top up boosting does not cause a problem. Nor does a small continuous trickle charge. It would appear that these types don't grow dendrite hairs. CAN BE STORED IN A CHARGED STATE WITH A MODERATE SHELF LIFE. For long term store discharged.
B.J.Greene. Apr99

LI-ION TYPE CELLS ! {26May2005}
These Lithium-ion batteries are best STORED IN A FULLY CHARGED CONDITION. They are also fussy about the temperature, not liking to be charged in any extremes below freezing or above 40°C. Such operation or even storage will reduce capacity and life.
There is no memory effect and the power to weight ratio is very favourable.

Lithium-ion batteries (sometimes abbreviated Li-ion batteries) are a type of rechargeable battery in which a lithium ion moves between the anode and cathode. The lithium ion moves from the anode to the cathode during discharge and in reverse, from the cathode to the anode, when charging.
Lithium ion batteries are common in consumer electronics. They are one of the most popular types of battery for portable electronics, with one of the best energy-to-weight ratios, no memory effect, and a slow loss of charge when not in use. In addition to uses for consumer electronics, lithium-ion batteries are growing in popularity for defense, automotive, and aerospace applications due to their high energy density. However certain kinds of mistreatment may cause Li-ion batteries to explode.
The three primary functional components of a lithium ion battery are the anode, cathode, and electrolyte, for which a variety of materials may be used. Commercially, the most popular material for the anode is graphite. The cathode is generally one of three materials: a layered oxide, such as lithium cobalt oxide, one based on a polyanion, such as lithium iron phosphate, or a spinel, such as lithium manganese oxide, although materials such as TiS2 (titanium disulfide) were originally used.[3] Depending on the choice of material for the anode, cathode, and electrolyte the voltage, capacity, life, and safety of a lithium ion battery can change dramatically. Lithium ion batteries are not to be confused with lithium batteries, the key difference being that lithium batteries are primary batteries containing metallic lithium while lithium-ion batteries are secondary batteries containing an intercalation anode material.

DIGITAL & ANALOGUE

At first the complex sound-wave contours were represented by the shape & extent of the record groove. It just needed to be amplified and applied to an air pump transducer (Speaker). Then the talking films used light patches at the side of the film. This was followed by magnetic tape where the magnetisation depth still represents the sound-wave. These schemes are "ANALOGOUS" to the original wave shape.
Digitization is very different and quite hard to get a handle on. The same sound-wave is repeatedly measured for its instant strength and the value is recorded as a binary number or code. This has to be done very quickly and a favourite standard rate is 44.1 KHz. This is to ensure that nothing of importance is missed.
The range of levels that the coding system can represent depends on the total number of digits in the number. If it was a decimal system we know that two digits can represent 99 levels, three 999, and so on. {Actually 100 & 1000 since zero is a level too}.
In the binary system each "bit" (for binary digit) can represent either a "0" or a "1" and it turns out that the numbers can get unreasonably long. 1000 levels needs 10 bits. (1024 levels actually). This doesn't fit well with the architecture of most computers and long numbers take lots of time to handle. It is common to place a limit on the maximum number of "quantities" that can be represented.
This "quantization" process can be "shifted" to represent more levels without the need of more bits. That process is not that unlike the "SHIFT" keys used on a typewriter to switch from upper to lower case letters - WITHOUT the need of more & more keys.
Advantages of the digital method:
Analogue signals can never be faithfully copied. There is always some degradation from the original. Digitized quantities can be copied exactly, and much more quickly too.
It is useful to be able to manipulate sound tracks. In a computer the binary coded signal can be pitched changed or speed changed independantly.
Cutting & patching are possible in the software.
Effects (echo, reverb, harmonoy, tremelo, vibrato) can all be added to the signal without destroying the original sound track.
The necessary physical storage space is less than with other media.
The cost of the optical media (CD/DVD) is very low.
DISADVANTAGES: -
The argument that digital sound sources are "better" is not usually true. This is because practicalities dictate that space-saving devices are used. (mp3 files). The sound quality can seem almost too clean as it is possible to remove all "noise" signals completely. It can be argued that the complex compression techniques that are used actually change the sound in subtle
ways that is not always to the listeners liking.
The jury is still out on digital longevity. The old bakelite & celluloid records will take some beating in that respect with some still playing after 100 years. It isn't thought that CD/DVD life will be anything like that long. The compact nature of the track data militates against a long term life. Flash memories have only a 10 yr life. The magentic stores might fare a little better in this respect.
Comapatibility has always ben an issue. Phonographs, gramophones, record players, reel to reel and cassette tape machines have all had a turn. With digital both the media and the software format might be overtaken. While common software formats may be maintained & even regenerated fairly easily, it is the hardware that poses the biggest problem. Where would you now go, for example, to get played one of the original 7" floppy disks from the 1980's? The 5.25" format is also gone. Even a 3.5" FDD is getting hard to find now. What will the future bring?

Thermionic Valves

Millions of thermionic valves were made and used long before the pheonomen of the "Cat's Whisker" gave rise to the transistor and integrated industry that followed on.

A link (below) will take you to a short video that graphically shows how much work is involved in the making of a simple triode valve. Most of the process is very traditional, although the use of some modern technology is also evident. This is a most delightful "silent" French film with absorbing background music.

The glassblowing tradition was what brought the Dutch company Philips to electronics.

http://dailymotion.virgilio.it/video/x3wrzo_fabrication-dune-lampe-triode_tech

MICROPHONE TECHNOLOGY

PHANTOM POWER

First of all we need to consider & understand the operation of a capacitor microphone. A thin plastic diaphragm coated with gold or aluminium is stretched over a shallow hollow cavity which has a flat metal back-plate. These two plates form a capacitor of some 5 to 75pF {Nominally 20 to 30 pF}. A polarising charging voltage is provided by a DC source. Electrostatic attraction keeps the diaphragm taut, but sound waves that impinge upon it will cause a small variation in the capacitive value which varies in sympathy with the air pressure waves. The output impedance is very high at around 100Mohms. To avoid the losses of HF, a long cable cannot be used and a very adjacent pre-amplifier is required. The low mass and inertia of the diaphragm gives a very flat and wide response, while the output is high because of the pre-amp.
The need of power is a drawback and ways and means have been sought to provide the small but necessary power from within the amplifier with which the microphone is used. This is known as "Phantom Powering" The generally adopted standard is for a 48V DC supply. This is sometimes obtained within the actual microphone from a small battery. Otherwise it must come from the amplifier itself which might mean having extra wires. This is often overcome by the following circuitry.
The positive is taken to a centre tap in the input transformer or to the junction of a pair of resistors across the winding. Another similar method avoids the disadvantage of having to have the screen connected at both ends, a practice known to induce hum & noise pick-up. In this circuit both the signal wires are used to carry the dc power and the screen does not form a part of any circuit.

This is achieved by the circuit configuration known as A-B powering thus: See how cleverly the routes for the ac signal and the DC power is preserved over the same wires whilst the dc is blocked from the ac signal with scarcely any loading.

There is much more to know about microphones which all have their pros & cons. We have to weigh up their performance in several important ways: - Cost, performance, ruggedness, weight, size and pick-up qualities are the main considerations.
Since the latter may be the most obscure we will start with that. We may simply need a microphone that will pick up in an even way all around its site. Or we may need a performance that is more DIRECTIONAL. Here is a diagram that shows the most popular choices.

"Directivity" also Rejection ratio" - "Discrimination" - "Cancellation" and "Front to back ratio" are common terms used. Typical values are 15 to 20 dB which is about a twelvefold difference.

A is Omni-directional
B has a cardioid pick up
C is a super cardioid
D is a figure of eight velocity
E is a gun/interference tube type.
The latter is a very directional specialised type mainly used in noisy crowded rooms. You point it at what you want to hear. An open ended tube with a series of slots along one side is attached to a cardioid microphone. It operates by phase displacement cancelling down to a frequency that is a half wavelength of the tube length.

NOISE CANCELLATION
It often happens that unwanted background noise is picked up. There have been, and still are, novel ways to deal with it. Two microphones can be connected in antiphase to produce almost absolute cancelling. Announcements are made through one or the other from close proximity and this balance is overcome. Some capacitor units have two diaphragms facing front & rear. They each have a cardioid pick-up area. Polarising voltages can be variously switched off or reversed to form pick-up lobes.

EAR - 'ERE

HUMAN EAR - 'ERE
The final link in the sound reproduction chain is the human ear. How can you ignore the basic knowledge of it if you like or make music? It is a vital element to all those involved in audio engineering too. A read of this will cast doubt on Darwinian ideas of "natural selection".

DIRECTIVITY
Sounds from a source situated to one side of the listener arrive at the furthest ear fractionally later than the nearest. Thus there is a delay in phase which the brain interprets in terms of direction. Long wavelengths, (lower frequencies/notes), have less phase shift than the higher frequencies which fact is why it is much more difficult to locate the source of a low frequency note. The rattle of a box of matches is a bone-fide test used to demonstrate this.

Refer now to the drawing of the human ear below. The convolutions of the Pinner or outer ear produce reflections and phase delays which differ according to the angle of incidence with which the sound wave arrives. {A wave in this context is a variation in air pressure of a cyclic nature}. This also aids in direction location, especially, it is believed, in the vertical registration of the source. Again only the higher frequencies are effectively so identified. At mid frequencies the masking effect of the head plays a part by introducing small difference in amplitude.

IMPEDANCE MATCHING
The ear drum or tympanum vibrates in sympathy with the received sound and transmits the vibrations through three small bones called the ossicles in the middle ear. These are the hammer, anvil and stirrup {or stapes as some say}. The first two form a pair of pivoted levers that produces a nominal leverage ratio of 3:1, and the third communicates vibrations to the window of the inner ear. The ratio matches the mechanical impedance of the ear drum to that of the window, so obtaining optimum power transfer.
The tiny bones are held in place by small muscles which permit the pivotal positions, and hence the sensitivity, to alter. Thus the sensitivity is not linear, following a logarithmic law, being at a maximum for quiet sounds reducing to a minimum for loud ones.
This automatic volume control allows the ear to process an enormous range of sound levels being in the order of 10 to the power of 12 which is 1 million X 1 million = 1 trillion levels.
The Eustachion tube equalises the atmospheric pressure on both sides of the eardrum by venting the middle ear to the throat.

FREQUENCY DIVISION
The inner ear consists of a long liquid filled tube that is rolled up like a shell called the cochlea. A horizontal basilar membrane divides the tube along its length into upper & lower compartments except at the sealed far end where there is a connecting gap called the helicotrema. The compartments are termed the scala vestibule and scala tympani respectively.
Sound vibrations are applied to the Oval window at the entrance to the upper chamber by the Stirrup bone. From there they travel through the fluid to the gap at the end, then down into and along the lower compartment and back to its round window where they are absorbed. En route they pass through thousands of sensitive hair cells located on the upper surface of the membrane, which are linked to nerve fibres. These cells respond to different frequencies and are divided into 24 bands with one third octave spacings, starting with the highest band near to the entrance and the lowest at the far end. Individual bands occupy about 1.3mm of space, each being termed a bark.
The centre frequencies of the bands start at 50Hz for the No.1 and go up to 13.4KHz for band 24. Cut off outside of each band is sharp at the lower side but more gradual as the bands rise in frequency. The lowest band is 100Hz while the highest is 3.5KHz. The overall response in a healthy person under 30yrs is 16Hz to 16KHz with the girls generally having better HF hearing than the boys.

FREQUENCY RESPONSE
The frequency response of the ear is not flat, being at a maximum from 2 to 4KHz. The rest of the curve varies according to the sound level. At lower volumes the response to both treble & bass is less which is why some audio units boost these at low listening levels. Speech frequencies come well within the overall range but music encompasses greater range in both frequency & loudness. These contours show the sound pressures required to produce sensations of equal volume at various frequencies. They are known as "Equal Loudness Contours" and are the inverse of frequency response curves.
The contours are an averaged sample taken from an age group of 18 to 25 yrs.

HEARING DAMAGE
Temporary damage to hearing sensitivity results from exposure to loud sounds. It can become permanent if the exposure is prolonged. Damage is greater if the sound contains percussive energy bursts. Impairment is in the 4 kHz range (bark 18 in the cochlea) irrespective of the nature of the sound that caused the damage. As exposure extends the damage tends to reach down to 1 kHz.
Industry regs. give the following maximum exposures shown in the chart. It should be noted that disco music and headphone listening levels in excess of 100dBA can easily be realised. The dangers are obvious.

PRESBYCUSIS
This is an almost inevitable condition where hearing deteriorates with age. It starts slowly from 20 - 30 yrs and worsens over time. Exposure to loud noise plays its part. This chart shows the expected deterioration.

DE-Gaussing

Johann Carl Friedrich Gauss was a German mathematician & scientist 1777-1856 whose name was adopted for the CGS unit of magnetic flux density. {Magnetisation}. Sometimes bits of metal (iron/chrome) become magnetised when we don't want them to. It happens in tape recorders. If you bring those parts under the influence of a powerful "saturating" and alternating magnetic field, that is made to decay away relatively slowly , their magnetism will be removed. "De-Gaussed"
Magnetite is a naturally occuring ferrite commonly called Lodestone. It exhibits "ferrimagnetism" as opposed to "ferromagnetism". "Ferroxcube" is a tradename for similar man-made magnetic ceramic materials. A china that contains ferrous particles, mixed with other metals. It is very useful in conjunction with inductors at higher frequencies.

The Theremin

The theremin was invented in 1919 by a Russian physicist named Lev Termen. It is not like any other instrument, since it is played without being touched. Two antennas protrude from the theremin - one controlling pitch, and the other controlling volume. The electronic oscillators are tuned by hand capacity affects. As a hand approaches the vertical antenna, the pitch gets higher. Approaching the horizontal antenna makes the volume softer. They were originally built in the 1930's by RCA, GE & Westinghouse and found immediate use in the film industry because of their weird ethereal sounds. Robert Moog was building these in the 60's before the synthesizer.