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The NiMH batteries are recommended for use in the Central Office ( CO ), Outside Plant ( OSP ), and at locations such as Controlled Environmental Vaults ( CEVs ), Electronic Equipment Enclosures ( EEEs ), huts, and in uncontrolled structures such as cabinets.
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NiMH and batteries
NiMH batteries have replaced NiCd for many roles, notably small rechargeable batteries.
NiMH batteries are very common for AA ( penlight-size ) batteries, which have nominal charge capacities ( C ) ranging from 1100 mA · h to 2800 mA · h at 1. 2 V, measured at the rate that discharges the cell in five hours.
NiMH batteries normally operate at 1. 2 V per cell, somewhat lower than conventional 1. 5 V cells, but will operate most devices designed for that voltage.
About 22 % of portable rechargeable batteries sold in Japan in 2010 were NiMH.
This percentage has fallen over time due to the increase in manufacture of lithium-ion batteries: in 2000, almost half of all portable rechargeable batteries sold in Japan were NiMH.
The significant disadvantage of NiMH batteries is the high rate of self-discharge ; NiMH batteries lose up to 20 % of their charge on the first day and up to 4 % per week of storage after that.
LSD NiMH batteries significantly lower self-discharge, but at the cost of lowering capacity by about 20 %.
The earliest pioneering work on NiMH batteries — essentially based on sintered Ti < sub > 2 </ sub > Ni + TiNi + x alloys for the negative electrode and NiOOH-electrodes for the positives — was performed at the Battelle-Geneva Research Center starting after its invention in 1967.
Ovonic Battery Co. in Michigan altered and improved the Ti-Ni alloy structure and composition according to their patent and licensed NiMH batteries to over 50 companies worldwide.
Unfortunately, linked to their composition, the calendar and cycle life of such alloys always remains very low, and all NiMH batteries manufactured at the present time consist of AB < sub > 5 </ sub >- type rare earth metal alloys.
Currently, more than 2 million hybrid cars worldwide are running with NiMH batteries, Many of these batteries are manufactured by PEVE ( Panasonic ) and Sanyo.
Panasonic's handbook, however, recommends that NiMH batteries on standby are kept charged by a lower duty cycle approach, where a pulse of a higher current is used whenever the battery's voltage drops below This can extend battery life and use less energy.
Eneloop low self-discharge NiMH batteries
Standard NiMH batteries may lose half their charge in the same time period.
Besides the longer shelf life, they are otherwise similar to normal NiMH batteries of equivalent capacity and can be charged in typical NiMH chargers.
After only a few weeks of storage, the retained capacity of low-self-discharge batteries often exceeds that of traditional NiMH batteries of higher capacity.
NiMH and are
More economically viable alloys using mischmetal instead of lanthanum were soon developed and modern NiMH cells are based on this design.
This is because the capacity of NiMH cells significantly declines as the cells are cooled.
C types are typically higher than their usual NiMH cousins, with 4000 mA · h and the D type being 8000 mA · h.
When compared to regular NiMH batteries, LSD ( low self discharge ) NiMH are most useful when more than three weeks elapse between charge and discharge to empty, on average, or to ensure that stored devices are usable several weeks after charging of batteries.
Specifications for the self discharge rate are not always clear or widely published, and virtually any LSD NiMH may claim to maintain some level of charge after 12 months.
There are many brand names for LSD NiMH batteries.
NiMH cells and chargers are readily available in retail stores in the common sizes AAA and AA.
Real NiMH C and D batteries are expensive ( and the chargers are uncommon ); they should be rated at least 5000 mA · h for C and 10, 000 mA · h for D sizes.
PP3 ( nine volt ) NiMH batteries are available ; these usually have an output voltage of 8. 4 V ( 1. 2 × 7 ) and a capacity of roughly 200 mA · h.
NiMH cells are not expensive, and the voltage and performance is similar to primary alkaline cells in those sizes ; they can be substituted for most purposes.
Although alkaline cells are rated at 1. 5 volts and NiMH cells at 1. 2 volts, during discharge the alkaline voltage eventually drops below that of NiMH.
NiMH cells are often used in digital cameras and other high drain devices, where over the duration of single charge use they outperform primary ( such as alkaline ) batteries.
With the development of low self-discharge NiMHs ( see section above ), many occasional-use and very low-power applications are now candidates for NiMH cells.
NiMH cells are particularly advantageous for high current drain applications, due in large part to their low internal resistance.
NiMH and recommended
The claimed top speed varies from 25 + mph on 14. 4 volts from twin 6 cell NiMH battery packs ( 7. 2 volts each, not recommended by Castle Creations ) and the stock gear ratio to 65 + MPH on 22. 2 volts from twin 3S LiPo batteries ( 11. 1 volts each ) and an optional taller gear ratio.
NiMH and for
The typical specific energy for small NiMH cells is about 100 W · h / kg, and for larger NiMH cells about 75 W · h / kg ( 270 kJ / kg ).
The first consumer grade NiMH cells for smaller applications appeared on the market in 1989, the culmination of over two decades of research and development.
The association of this high-energy electrode with high-energy hybrid alloys for the negative electrode led to the new environmentally friendly high-energy NiMH cell.
A NiCd charger should not be used as an automatic substitute for a NiMH charger.
The Panasonic NiMH charging manual warns that overcharging for long enough can damage a battery and suggests limiting the total charging time to 10 to 20 hours.
This method is often used with Nickel-Cadmium cells which have a large drop in voltage at full charge but the voltage drop is much less pronounced for NiMH and can be non-existent at low charge rates, which can make the approach unreliable.
A non-LSD battery typically self discharges at a rate of about 20 % within the first 24 hours, then at 4 % per day for NiMH ( compared to 1 % per day for NiCd ) thereafter.
The equivalent daily self-discharge rate for LSD NiMH is just 0. 04 % to 0. 1 % ( based on the annual 70-85 % figures above ).
In devices not accurately calibrated to closely predict battery level, run-times for LSD NiMH batteries can be as good or even better than normal cells with higher rated capacity, because the slightly higher operating voltage doesn't trip a device's under-voltage shut off circuit.
This is particularly true for high drain applications, where the voltage of even a fresh alkaline battery can be lower than a NiMH battery while under a load.
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