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POWER8workshop Video Manual

Battery Information

 

 

Li-Ion (Lithium Ion)

Typical cell voltage 3.6V (more voltage in a smaller cell than other batteries)
Cost per KWh ~ £24.00
Very fast charge ~1200 recharge cycles.

ADVANTAGES:

Li-ion batteries are lighter than other equivalent secondary batteries—often much lighter. The energy is stored in these batteries through the movement of lithium ions.
Li-ion batteries do not suffer from the memory effect common with other batteries. They also have a low self-discharge rate of approximately 5% per month, compared with between 10 and 30% per month in other batteries.
Size to voltage ratio.

DISADVANTAGES:

Protection circuits required.
Li-ion batteries are not as durable as nickel metal hydride or nickel-cadmium designs, and can be extremely dangerous if mistreated. They may explode if overheated or if charged to an excessively high voltage. Cells can be irreversibly damaged if discharged below a certain voltage. To reduce these risks, li-ion cells generally contain a small circuit that shuts down the battery when discharged below a certain threshold (typically 3 V) or charged above a certain limit (typically 4.2 V). It is also common to have a Temperature protection circuit which will disable the battery so it can cool down (typically around 70°C).
This circuit adds to the cost of lithium-ion batteries, which is usually higher than that of comparable-capacity NiMH or NiCD batteries.
The circuit can be damaged by impact.

A unique drawback of the Li-ion battery is that its service life is dependent upon aging (shelf life). From time of manufacturing, regardless of whether it was charged or the number of charge/discharge cycles, the battery will decline slowly and predictably in "capacity". This means an older battery will not last as long as a new battery due solely to its age, unlike other batteries. This is due to an increase in internal resistance, which affects its ability to deliver current, thus the problem is more pronounced in high-current applications than low. This drawback is not widely published.

Guidelines for prolonging Li-ion battery life:

Like many rechargeable batteries, lithium-ion batteries should be charged early and often.
Lithium-ion batteries should not be frequently fully discharged and recharged ("deep-cycled"), but this may be necessary after about every 30th recharge to recalibrate any electronic charge monitor (e.g. a battery meter). This allows the monitoring electronics to more accurately estimate battery charge. This has nothing to do with the memory effect.

Good practice would be to place the battery on charge during any break in work and to cycle through several batteries in this way.

Li-ion batteries should be kept cool. Ideally they are stored in a refrigerator. Aging will take its toll much faster at high temperatures. The high temperatures found in cars cause lithium-ion batteries to degrade rapidly.
Li-ion batteries should not be frozen(most lithium-ion battery electrolytes freeze at approximately −40 °C; however, this is much colder than the lowest temperature reached by household freezers).
Li-ion batteries should be bought only when needed, because the aging process begins as soon as the battery is manufactured.

 

Pb (Lead Acid)

Typical cell voltage 2V (in packs of 3-6 cells)
Cost per KWh ~ £8.50
Slow charge ~300 to 500 recharge cycles.

Lead-acid batteries, invented in 1859 by French physicist Gaston Planté, are the oldest type of rechargeable battery. Despite having the second lowest energy-to-weight ratio (next to the nickel-iron battery) and a correspondingly low energy-to-volume ratio, their ability to supply high surge currents means that the cells maintain a relatively large power-to-weight ratio.

Lead acid batteries remain the technology of choice for automotive applications because they are robust, tolerant to abuse, tried and tested and because of their low cost.

Lead-acid batteries are composed of a Lead-dioxide cathode, a sponge metallic Lead anode and a Sulphuric acid solution electrolyte. This heavy metal element makes them toxic and improper disposal can be hazardous to the environment.

Even after 140 years since its invention, improvements are still being made to the lead acid battery and despite its shortcomings and the competition from newer cell chemistries the lead acid battery still retains the lion's share of the high power battery market.

ADVANTAGES:

Reliable. Over 140 years of development, familiar to the majority.
When properly maintained can last for 10 years or more.
Robust. Tolerant to abuse.
Tolerant to overcharging.
Low internal impedance.
Can deliver very high currents.
Indefinite shelf life if stored without electrolyte.
Can be left on trickle or float charge for prolonged periods.
Wide range of sizes and capacities available.
Many suppliers world wide.
The world's most recycled product.

DISADVANTAGES:

Very heavy and bulky.
Danger of overheating during charging
Not suitable for fast charging
Must be stored in a charged state once the electrolyte has been introduced to avoid deterioration of the active chemicals.
Completely discharging the battery may cause irreparable damage.
Toxic chemicals
Very heavy and bulky
Lower temperature limit -15 °C

Guidelines for prolonging Lead Acid battery life:

Do not completely discharge the battery, around 75% is good before recharging.
Cel products will automatically stop the battery from over discharge.
Charge immediately after use., this creates the best balance for the chemicals in the cell.
Always ensure adequate ventilation when charging a lead-acid battery. The charging process can give off hydrogen gas, which if allowed to build up in an enclosed area, is highly explosive.
A cooler charging area will allow more charge to be stored, down to around 15°C.

 

Ni-MH (Nickel Metal Hydride)

Typical cell voltage 1.2V
Cost per KWh ~ £18.50
Fast initial charge followed by slow charge to full capacity ~500 recharge cycles.

ADVANTAGES:

NiMH cells are particularly advantageous for high current drain applications, due in large part to their low internal resistance. Digital cameras with LCDs and flashlights can draw over 1000 mA, quickly depleting alkaline batteries. NiMH can handle these current levels and maintain their full capacity.
Now that the technology is reasonably mature, NiMH batteries have begun to find use in high voltage automotive applications. The energy density is more than double that of Lead acid and 40% higher than that of NiCads
They accept both higher charge and discharge rates and micro-cycles thus enabling applications which were previously not practical.
Like NiCd batteries, Nickel-metal Hydride batteries are susceptible to a "memory effect" although to a lesser extent. They are more expensive than Lead-acid and NiCd batteries, but they are considered better for the environment.
Robust - NiMH batteries also tolerate over charge and over discharge conditions and this simplifies the battery management requirements.
Low internal impedance.
Flat discharge characteristic, stable voltage supply (but falls off rapidly at the end of the cycle)
Wide operating temperature range.
Rapid charge possible in 1 hour
Reconditioning is possible.
Environmentally friendly (No cadmium mercury or lead)

DISADVANTAGES:

Very high self discharge rate, nearly ten times worse than lead acid or Lithium batteries.
Can be stored indefinitely either fully charged or fully discharged.
Suffers from memory effect though not as pronounced as with NiCad batteries
Battery deteriorates during long time storage. This problem can be solved by charging and discharging the battery several times before reuse. This reconditioning also serves to overcome the problems of the "memory" effect.
High rate discharge not as good as NiCads
Less tolerant of overcharging than NiCads
As with NiCads the cells must incorporate safety vents to protect the cell in case of gas generation.
Cell voltage is only 1.2 Volts which means that many cells are required to make up high voltage batteries.

Guidelines for prolonging NiMH battery life:

Run down fully once per month to avoid memory effect.
Slow charging method: Constant current followed by trickle charge.
Do not leave battery in charger.
Store at a stable temperature.

 

Ni-Cd (Nickel Cadmium)

Typical cell voltage 1.2V
Cost per KWh ~ £7.50
Fast charge then slow charge to maintain, recharge cycles ~1200

NiCd battery can supply high surge currents, this makes them a favourable choice for remote-controlled vehicles, as well as cordless power tools and camera flash units. Larger flooded cells are used for aircraft starting batteries, electric vehicles, and standby power.

Recently, nickel-metal hydride (Ni-MH) and lithium-ion batteries (Li-ion) have become more commercially available and cheaper, the former type now rivaling NiCds in cost. Where energy density is important, Ni-Cds batteries are now at a distinct disadvantage over Ni-MH and Li-ion batteries. This and environmental considerations have largely relegated the Ni-Cd construction to history. However, the Ni-Cd battery is still very useful in applications requiring very high discharge rates because the Ni-Cd can endure such discharge with no damage or loss of capacity.

ADVANTAGES:

NiCd batteries are more difficult to damage than other batteries, tolerating deep discharge for long periods.  
NiCd batteries typically last longer, in terms of number of charge/discharge cycles, than other rechargeable batteries, and have faster charge and discharge rates than lead-acid batteries, with minimal loss of capacity even at high discharge rates.
NiCd batteries have a much higher energy density than lead-acid batteries. This means that, for a given battery capacity, a NiCd battery is smaller and lighter than a comparable lead-acid battery.
NiMH batteries experience a voltage drop as it nears full discharge, which a NiCd does not.
Similarly-sized NiCd battery has a slightly lower internal resistance, and thus can achieve a higher maximum discharge rate (which can be important for applications such as power tools).

DISADVANTAGES:

The primary trade-off with NiCd batteries is their higher cost and the extreme toxicity. They require extra labour to manufacture, and thus are typically more costly than lead-acid batteries. Typically nickel and cadmium are more costly materials than those used for lead-acid cells. One characteristic of NiCd cells, that should be planned around in usage pattern, is that if a cell (or battery of cells) is repeatedly cycled between a consistent level of discharge and full recharge, it will eventually only discharge to that level. (See Memory and lazy battery effects below for more details on this effect).

Guidelines for prolonging NiCd battery life:

Fully discharge NiCd batteries before recharging to avoid memory effect which reduces capacity.
The safe temperature range for a NiCd battery in use is between −20°C and 45°C. During charging, the battery temperature typically stays low, around 0°C (the charging reaction absorbs heat), but as the battery nears full charge the temperature will rise to 45–50°C. Some battery chargers detect this temperature increase to cut off charging and prevent over-charging.

When not under load or charge, a NiCd battery will self-discharge approximately 10% per month at 20°C, ranging up to 20% per month at higher temperatures.
If the battery is going to be stored unused for a long period of time, it should be discharged down to at most 40% of capacity and stored in a cool, dry environment.