Advantages of Ni-MH batteries

Write down the advantages of the Ni-MH batteries.

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a) Number of cycles: The Ni-MH is rated for only 500 charge/discharge cycles. Shallow in place of the deep discharge cycles are preferred. The battery's longevity is directly related to depth of discharge.

b) Fast charge: The Ni-MH produces considerably more heat during charge and need a more complex algorithm for the full-charge detection in comparison to the NICAD if temperature sensing is not available. Additionally, the Ni-MH cannot accept as fast a charge as the NICAD; its charge time is typically double that of the NICAD. The trickle charge should be controlled more carefully than on the NICAD.

c) Discharge current: The recommended discharge current of the Ni-MH is considerably less than that of NICAD. For best results, manufacturers recommend the load current of 0.2C to 0.5C (one-fifth to one-half of the rated capacity, see 3.1 C-Rate). This shortcoming may not be critical if the needed load current is low. For applications requiring high power or the pulsed load, like on GSM digital cellular phones, portable transceivers and power tools, the more rugged NICAD is the recommended choice.

d) Self-discharge: Both Ni-MH and NICAD are affected by sensibly high self-discharge. NICAD loses around 10% of its capacity within the first 24-hours, after that self-discharge settles to around 10% per month. Self-discharge of Ni-MH is one-and-a-half to two times higher in comparison to that of the NICAD. Hydride materials are selected that increases the hydrogen bonding in order to decrease the self-discharge typically also reduce the battery capacity.

e) Capacity: Ni-MH delivers around 30% more capacity in comparison to the NICAD of same size. The comparison is formed with the standard, rather than new ultra-high capacity NICAD. Some ultra-high capacity NICAD cells offer a capacity level approaching that of Ni-MH.

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