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Moltech Smart Battery Paper.pdf

Smart Battery <-> Host Device

The ability for the Smart Battery to communicate with a host device opens up a wide range of power management options which are not available when using dumb batteries. Both fixed and dynamic data is available to the host device, the latter being supplied after internal measurements and calculations have been performed by the battery’s on-board microprocessor.

Data Functions

Device Name, Manufacturer Name, Manufacture Date and Serial Number:
This information is useful when a manufacturer is supplied with
batteries from multiple suppliers. It can also be used to log usage patterns or validate customer warranty claims.

Design Voltage and Design Capacity:
The nominal voltage and capacity of the battery at it’s time of manufacture.

Device Chemistry:
Identifies the chemistry of the cells in the battery (NiCd, NiMH, LiIon etc)

At Rate Time To Full/Empty:
When being charged, the host device can request the expected charge time based on a charge current set by the host. Similarly, when being discharged the expected remaining time will be given based on a discharge current set by the host. An additional feature is the ability for the battery to signify whether it is possible to supply an additional discharge current for 10 seconds operation – useful if the host device wants to perform a high current operation close to end of discharge.

Charging Current and Charging Voltage:
Based on the chemistry, state of charge and environmental condition, the battery will request appropriate voltage and current from a smart charger.

Max Error:
Based on recent calibration data, the battery will predict it’s current fuel gauge accuracy as a percentage.

Full Charge Capacity:
Returns the predicted pack capacity in mAh or mWh. When compared with the original Design Capacity, it is a useful indication of battery life deterioration.

Cycle Count:
The battery stores a cycle count based on usage (one cycle is a level of discharge activity equal to the Design Capacity). This feature is very useful for OEM’s wishing to monitor battery usage or for validating warranty claims from customers.

Absolute State Of Charge and Relative State Of Charge:
The battery returns it’s ASOC (expressed as a percentage of the Design Capacity) or it’s RSOC (expressed as a percentage of the Full Charge Capacity).

Remaining Capacity:
The battery returns it’s current state of charge in mAh or mWh.

Temperature:
Internal battery temperature expressed in °K.

Current:
The instantaneous current flowing in or out of the battery expressed in mA.

Average Current:
The battery returns a one-minute rolling average current expressed in mA.

Voltage:
Battery terminal voltage in mV.

Alarm Functions

The smart battery is capable of broadcasting a number of alarms when it is critical that the host device or charger should take some form of action.

Over Temperature Alarm:
If the battery is getting too warm inside the device it is able to broadcast an over-temperature alarm which the host device should respond to by reducing discharge current or suspending operation.

Remaining Capacity Alarm:
When the remaining capacity falls below the low capacity value, the battery will broadcast a Remaining Capacity Alarm. The host system can signal the user that battery capacity is running low and that they should consider shutting the system down or putting the battery onto charge. The low capacity value is programmable.

Remaining Time Alarm:
When the Average Time To Empty falls below the remaining time value, the battery will broadcast a Remaining Time Alarm. The host system can signal the user that battery capacity is running low and that they should consider shutting the system down or putting the battery onto charge. The remaining time value is programmable.

Terminate Discharge Alarm:
If the battery continues to discharge past the
Remaining Capacity Alarm, the battery will eventually signal a critically low capacity by broadcasting a Terminate Discharge Alarm. This alarm is used by the host device to take control of the system and initiate a controlled shutdown before battery power completely fails.

Terminate Charge Alarm:
When connected to a Smart Battery Charger, the battery will broadcast a Terminate Charge Alarm once it has reached top of charge. The charger should respond by setting it’s output to zero.

Conclusions

The supporting argument for implementing a smart battery system is very strong given the information above. Without such a system, power management is limited to a high level of guesswork on the part of the host device and the charger, with the user of the host device being unable to rely on the information being presented to him/her. The non linear characteristics of battery performance, and the tactic of sourcing from more than one battery vendor, requires the intelligence to be embedded in the battery. Only with this level of integration will users fully benefit from the light weight and high capacity of today’s rechargeable batteries.