The Ni-MH batteries produced by ARTS Energy have clearly demonstrated their high level of performance since more than 20 years. The VHT technology offers an exceptional robustness inside a very large range of temperature.
Many technologies are available with their own features and benefits.
ARTS Energy Ni-MH cells have to be used according ARTS Energy technical recommendations.
Charging of Ni-MH cells shows many analogies and similarities as with that of Ni-Cd cells, however the main difference is that the temperature change is exothermic from the beginning of the charge, with a strong temperature increase when the battery reach overcharge (see the curve below).
Therefore, the most efficient way to detect end of charge is to measure the battery temperature change and to follow DT/dt.
Fast charge will be stopped when DT/dt level will reach the value allowing to detect the end of the main charge before the peak voltage. The value of this dT/dt, depends upon the battery pack configuration and charge rate, for single cells, 0.5°C/min is generally adapted.
Use of –dV charge termination is not recommended as main charge method because when the detection of –dV occurs, the temperature is too high to ensure good cycling, especially in NI-MH battery packs.
C/10 charging rate can be used, but with a timer (16h) and starting from a fully discharged cell (to avoid too strong overcharge).
Below 0°C, charge voltage must be limited to 1.55V/ cell.
Permanent charge is not permitted for Ni-MH as it is detrimental to life duration. Intermittent charge is mandatory.
To limit temperature increase during charge (detrimental to life duration) and to compensate the battery self discharge, it is mandatory to use intermittent charge after full charge.
Starting with a main charge of 24h at C/20, the intermittent charge frequency has to be adjusted according to operating temperature. Consult ARTS Energy.
For a usage at temperatures lower than 0°C it is mandatory to limit the charge voltage at 1.55V per cell.
Repeated overcharging out of the specification could cause leakage and deteriorates cell performances.
A deep discharge or “over discharge “damages the cell performance so it is recommended to manage the discharge with an appropriate low voltage disconnect system (consult ARTS Energy for advice) and to avoid to leave the cell/battery connected to the equipment for a long period (>6 months) when the equipment is disconnected from the main.
ARTS Energy recommends to store the cell/battery within the temperature range +5°C to +25°C in a 65 ± 5% relative humidity atmosphere and to avoid storing a cell discharged.
After 4 months storage at RT or 1 month at +40°C, Ni-MH shall recover 100% of its minimum capacity (after a complete cycle).
An extended storage between –40°C and 5°C and between+25°C and +70°C at 65% relative humidity, is permitted no more than one month.
Long term storage leads to battery self discharge and deactivation of chemical components. ARTS Energy recommends storing for a long period between 5°C and 25°C.
In such case, it is recommended to partially recharge the cells/battery each 6 months. In addition, when using the cells/batteries for the first time after 6 months storage, in order to restore the initial cell performances, it is recommended to full cycle the cell/battery (maximum 5 cycles).
In these conditions, Ni-MH cell shall recover 90% of its initial capacity.
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