Embeded Battery Sensor Technology

Battery monitoring objectives for nearly all battery applications can be divided into two basic categories: state of charge information (SoC), and state of health (SoH) information.  The relative importance of SoC and SoH information can vary greatly and depends upon the application. 

State of Charge information is of primary importance in cycling applications.  If accurate SoC information is available, loads and chargers/generators/alternators can be turned on and off as appropriate to optimize battery utilization and eliminate failures from unintended discharge.

State of Health information is important in reliability sensitive applications.  By measuring SoH, the energy storage capability of the battery can be tracked as it decays over the life of the battery.  Accurate SoH will inform when a battery should be replaced before it fails.  Additionally, accurate SoH information is crucial for accurate SoC calculations as a battery ages.    

Discussed below are the common and traditional methods of battery monitoring, and the Argus LPR method.

Battery Volt Meters
Coulomb Counting
Argus LPR

Battery Volt Meters

Many cars and electric vehicles already include some type of embeded battery volt meter.  While volt meters are normally inexpensive, they do not provide very useful information in a monitoring application.  Volt meters are simply measures of system voltage, and system voltage alone does not correlate well to battery State of Health (SoH) or State of Charge (SoC) or many other useful battery attributes.

The fundamental shortcoming of battery voltage in a monitoring application is that system voltage is a factor of the loads and charging currents applied to the battery, not a function of the battery alone.  In a dynamic environment, the system voltage at any point in time can't be correlated with a particular battery state.   

Generally, system voltage can be corelated with SoC only when the battery is at rest and functionally disconnected from any loads or chargers.  In most applications however, it is most important to track SoC and SoH information while the battery is being used. 

No indication of stored energy level
A voltmeter can't distinguish between a 100Ah battery charged to 12.5V and a 10Ah battery charged to 12.65 volts.  In such an example, while the actual stored energy is different by a factor of 10, the stored energy in the battery is not reflected in the voltage measurement, both batteries simply appear full.  Therefore, even if a battery is at rest, a voltmeter can't be used to understand how much energy is really available.   All that could be learned is the relative state of charge. 

In most battery applications the lack of absolute energy level information is important because a fully charged three year old battery may hold half the energy of the same battery when new, but both appear similarly full to a volt meter.

Poor 'Fuel Gauge' / State of Charge information
A voltage gauge has very limited ability to display relative state of charge (empty to full) of a battery in use.  The reason is battery voltage reflects relative battery charge level only when the battery is completely at rest (not being charged or discharged).  And even at rest, measured voltage can be missleading due to surface charge effects. 

Not surprisingly it is most important to know the battery state of charge while the battery is being used. Ufortunately that is precisely when the information from the voltmeter reflects the charger or load on the battery and not the battery charge level.  The end result is that a voltmeter inevitably delivers inaccurate and premature indications of an empty battery during discharge and inaccurate apparent full indications as soon as the battery begins to rechage.

No Battery Life / State of Health information
There is no ability for a volt meter based monitor to provide any indication of battery health because battery voltage is not related to battery health.  Without battery SoH information there is no ability to understand how much energy is stored or where a battery is in its lifecycle.  A battery may appear to be fully charged, but due to its age and natural capacity decay it may be able to deliver only a fraction of the energy it could when new. 

Coulomb Counting

Current counters or Coulomb-counting systems estimate available energy in a battery by carefully tracking current flow in and out of the battery over time.  Aftermarket coulomb counting battery monitors are relatively expensive, (often more than $300 per sensor) and involve two main components.  A large current sensing shunt or coil is installed at the negative battery terminal, and a separate display indicates current flow and available energy.  Besides being expensive and bulky, coulomb counters have significant shortcomings as charge level meters, and do not provide any battery health information.

Poor 'Fuel Gauge' / State of Charge information
Coulomb-counting avoids some of the deficiencies of the volt meter method as an indicator of battery charge level (state of charge) however, important shortcomings remain. Complex algorithms are required to compensate for un-measurable characteristics of the battery. Furthermore, the compensation is highly specific to the type and size of battery, limiting the flexibility of the system to be adapted to replacement batteries. Shallow discharges (common in most applications) lead to incorrect assumptions about total capacity, and total capacity values are updated only when a full recharge follows a full discharge, a rare situation. Errors often accumulate to the point where a battery may be indicated as empty, but is nearly full.  Frequent 'calibration' is required to 'clear' the system of accumulated errors associated with charge/discharge inefficiencies internal to the battery. 

No Battery Life / State of Health information
Like volt meters, coulomb counters offer no information about battery life or state of health. Without battery life information it is not possible to understand the condition of the battery.  Absent reliable SoH information it is impossible to know if the available capacity can meet the needs of the application or if they have reached end of life and should be replaced.

Even more troublesome is the fact that coulomb counting monitors are not able to adjust the SoC estimate for the lost capacity of a battery over time.  Therefore, even before considering accumulated errors, a battery that has decayed beyond end of life could be indicated as completely fully charged (SoC = 100%) and having 100% of its full new capacity.   If batteries are relied upon for mission critical support over the life of the battery, accurate SoH information is of primary importance.

Argus LPR

The Large Pulse Resistance and Dual Large Pulse Resistance technologies of Argus' embeded battery sensors (and the BB-DCM series) coupled with a powerful microprecessor overcomes the deficiencies of the voltage and coulomb counting methods and delivers state of charge and state of health information with unparalleled accuracy and consistency. 

Accurate State of Charge detection 
By actively measuring DC internal resistance every 60 seconds, Argus embedded sensors continuosly and directly track available energy in the battery calculating SoC%, and providing absolute capacity information (Siemens value) at all times, most importantly, while the battery is in use. 

Automatic State of Health measurements
Because LPR tracks the growth of internal resistance, Argus embedded sensors continuosly and automatically self-calibrate and adjust SoH% for temperature and age, including the effects of sulfation, dehydration, corrosion and other battery decay factors.

Unlike the traditional monitoring techniques of voltage tracking and coulomb counting, Argus embedded sensors using LPR accurately answer the following important questions in real time:

• How full is the battery?
• How much energy is available now?
• How much energy could the battery hold now if fully charged?
• How much storage capability has been lost since the battery was new?
• How much battery life remains?
• When to recharge the battery?
• When to replace the battery?

Learn more about Argus LPR for battery monitoring and DLPR technology