 Profile Ni-MH
BatteryCharging
Methods |
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CHARGING
METHODS |
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 Ni-MH
BATTERY |
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 Specification
tables |
The
charge method for nickel-metal hydride batteries is almost same
as Ni-Cd batteries.But
there is slight different between them. For this reason, a special
charger
is necessary. In order for a battery to be usable for a long period
of time, it must
be charged via the proper charge method. Various methods are used
to charge rechargeable
cells, but We recommends the charge methods
described below tocharge
its nickel-metal hydride batteries. |
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| Overview |
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| Features |
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| Comparison
of Ni-MH and Ni-Cd Cells |
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| Major
applications |
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| Structural
designs |
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| Electrochemical
processes |
1.
Rapid charge current: 1CmA (rapid charge temperature range: 10 Celsius
to 40 Celsius). |
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| Discharge
characteristics |
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| Charge
characteristics |
In
order to exercise proper control to stop rapid charge, it is recommended
that batteries
be charged at over 0.5CmA but less than 1CmA. Charging batteries
at a current
in excess of 1CmA may cause the safety vent to be activated by a
rise in the internal
pressure of the batteries, thereby resulting in electrolyte leakage.
When the temperature
of the batteries is detected by a thermistor or other type of sensor,
and their
temperature is under 10 Celsius or over 40 Celsius at the commencement
of the charge,
then trickle charge, rather than rapid charge, must be performed.
Rapid charge
is stopped when any one of the values among the types of control
described in
(4),(5),(6) and (11) reaches the prescribed level. |
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| Charging
methods |
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| Cycle
life characteristics |
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| Storage
characteristics |
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| Safety
characteristics |
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| Designing
for Ni-MH cells |
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| Battey
pack designs |
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| Battery
pack configurations designation system |
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| Precautions
for using Ni-MH batteries |
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| Battery
selection |
2.
Allowing a high current to flow to over discharged or deep-discharged
batteries during charge may make it impossible to sufficiently restore
the capacity of the batteries. |
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To
charge over discharged or deep-discharged batteries, first allow
a trickle current to flow,
and then proceed with the rapid charge current once the battery
voltage has risen. |
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3.
Rapid charge start voltage:Approx.0.8V/cell.Rapid charge transition
voltage restoration current: 0.2-0.3 CmA |
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| 4. Peak voltage control: Approx.1.8V/cell. | |||||||||||||||||||||||||||
The
charge method is switched to trickle if the battery voltage reaches
approximately 1.8V/cell
due to trouble or malfunctioning of some kind. |
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| 5. DV(delta V)value: 5 to 10mV/cell. | |||||||||||||||||||||||||||
When
the battery voltage drops from its peak by 5 to 10mV/cell during
rapid charge, rapid
charge is stopped, and the charge method is switched to trickle
charge. |
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| 6. dT/dt value: Approx.1 to 2 Celsius/min. | |||||||||||||||||||||||||||
When
a rise in the battery temperature per unit time is detected by a
thermistor or other
type of temperature sensor during rapid charge, and the prescribed
temperature rise
is sensed, rapid charge is stopped and the charge method is switched
over to trickle
charge. |
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| 7. TCO: 55 Celsius | |||||||||||||||||||||||||||
The
cycle life and other characteristics of batteries are impaired if
the batteries are allowed
to become too hot during charge. In order to safeguard against this,
rapid charge
is stopped and the charge method is switched over to trickle charge
when the battery
temperature has reached the prescribed level. |
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| 8. Initial delay timer: to 10 min. | |||||||||||||||||||||||||||
This
prevents the -delta V detection circuit from being activated for
a specific period of
time after rapid charge has started. However, the dT/dt detection
circuit is allowed to
be activated during this time. As with Ni-Cd batteries, the charge
voltage of nickel-metal
hydride batteries may show signs of swinging (pseudo -DV) when they
have been
kept stand by for a long time or when they have discharged excessively,
etc. The
initial delay timer is needed to prevent charge from stopping (to
prevent malfunctioning)
due to this pseudo - delta V. |
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| 9. Trickle current: 1/30 to 1/20 CmA. | |||||||||||||||||||||||||||
When
the trickle current is set higher, the temperature rise of the batteries
is increased,
causing the battery characteristics to deteriorate. |
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| 10. Rapid charge transfer timer: 60 min. | |||||||||||||||||||||||||||
| 11. Rapid charge time: 72 min. (at 1C charge) | |||||||||||||||||||||||||||
| 12. Total time: 22to 32hours. | |||||||||||||||||||||||||||
The
overcharging of nickel-metal hydride batteries, even by trickle
charging, causes a deterioration
in the characteristics of the batteries. To prevent overcharging
by tricklecharging
or any other charging method, the provision of a timer to regulate
the total charging
time is recommended. |
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| Recommended nickel metal hydride battery charge system* | |||||||||||||||||||||||||||
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*:The
temperature and voltage of nickel-metal hydride batteries varies
depending on the
shape of the battery pack, the number of cells, the arrangement
of the cells and other
factors. Therefore we should be consulted for more detailed information
on the referenced
charge control values. The charge methods described previously can
be applied
also when both nickel-metal hydride batteries and Ni-Cd batteries
are employed
in a product, but we should be consulted for the control figures
and other details. |
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