161 lines
6.3 KiB
ReStructuredText
161 lines
6.3 KiB
ReStructuredText
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===============
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Battery Monitor
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===============
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.. image:: bms-cell-monitor.png
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:width: 90%
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:align: center
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The BMS cell monitor is a **live view** of the battery pack and cell status.
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It shows all individual cell voltages and module temperatures recorded
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by the BMS, their average values and standard deviations.
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The battery monitoring availability and detail depends on the vehicle
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adaptor to provide cell voltage and temperature measurements. The BMS
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framework takes care of doing the statistics.
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The OVMS BMS normally records over a typical usage period, i.e. a full
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driving or charging period. You can also issue a reset manually any time
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using the button (or command ``bms reset``).
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All statistics (min/max values and deviations) relate to the recording
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period, so a reset clears these, as well as the warning and alert status
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of all cells.
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Of course all data shown is also available as metrics, namely the
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``v.b.p.`` (vehicle battery pack) and ``v.b.c.`` (vehicle battery cell)
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range of metrics.
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-----------
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Chart Usage
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-----------
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Voltage and temperature sensors normally differ in number, as voltages
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are measured for each cell bundle (cells connected in parallel), while
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temperatures only are measured for a cell module (multiple cell bundles
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connected in series). Accordingly the monitor is divided into a voltage
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and a temperature chart.
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Click on the chart series names below the charts to show/hide the
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respective series or group of metrics in that chart.
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The charts can be zoomed and pinched using the mouse or dual touch finger
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gestures as usual. When zoomed, a zoom reset button is shown in the upper
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right corner. To move the zoom window, hold the ``Ctrl`` key while clicking,
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or tap and move two fingers. Note: horizontal zoom needs an up to date
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firmware.
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Hovering or clicking on a cell/module chart column will show the actual
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values (numbers) in a small overlay window.
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Values may change while viewing the chart, that's normal: the chart is
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a live view of the actual current measurements. That allows to see how
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the cells respond to sudden high loads.
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-----------------------
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Cell/Module Info Detail
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-----------------------
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.. image:: bms-cell-info.png
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:width: 90%
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:align: center
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-----------------
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Overall Pack Info
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-----------------
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The table at the bottom shows the overall pack statistics in numbers.
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This includes the overall cell/module averages, the maximum and minimum
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voltage/temperature readings recorded, and the current and recorded maximum
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standard deviation.
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**On the cell gradient & max stddev deviation**: voltages are very volatile,
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as current battery cells immediately react to load changes. A high discharge
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pulse will lead to an instantaneous substantial drop of the cell voltages.
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So, depending on how the vehicle's BMS does the measurements, a full series of
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voltages may include such a change in between some cells. That would lead to
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wrong standard deviations and possibly false alerts, so the BMS framework
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analyses the full voltage series for a gradient, and ignores the series
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if the configured threshold is exceeded.
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The series is also ignored if the standard deviation exceeds the configured
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"max stddev deviation" value. Combine both thresholds to filter unusable
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series. The vehicle adaptor provides sensible default thresholds, but you
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may need to adjust them depending on the age and health of your battery.
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------------------------
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Cell Alert Configuration
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------------------------
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Cell voltage and temperature warnings and alerts are triggered by cell
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deviation from the current average. Warnings and alerts are detected by
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the BMS framework in the background, so you don't need to keep the monitor
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open to get them.
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Deviations exceeding configured threshold are shown color coded, yellow
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for warnings and red for alerts. Alerts will also trigger text notifications
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of type ``alert`` subtype ``batt.bms.alert`` unless disabled.
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Click "Alert config" to change the thresholds or control text alert
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notifications. Adjust the warning & alert thresholds as needed.
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The vehicle adaptor provides reasonable defaults for the warning and alert
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thresholds matching the specific type of battery normally built into the
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vehicle, but you may need to change the thresholds to adapt to the quality
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and age of your battery.
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The BMS configuration can also be changed directly via the ``config``
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command. The parameters are located under ``vehicle``, issue
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``config list vehicle`` and look for parameter names including ``bms``.
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In case you don't see any, save some custom values in the UI to create
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them.
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---------------------
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Health Interpretation
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---------------------
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You generally want your cells to be as close together as possible in terms
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of voltages and temperatures. When aging, deviations will rise, as internal
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resistances rise.
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The weakest cell normally defines the overall discharge and charge limits
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of the pack, as the vehicle BMS normally cannot shift load around individual
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cells -- current flows through all cells equally (more or less). A weak cell
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will reach the safety cutoff limits first, causing the BMS to terminate
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discharging or charging or to limit the power levels available.
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The higher the pack standard deviation the worse the overall battery
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performance. A high standard deviation is a sign for an old battery, or
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for a new battery with a very poor cell matching (read: poor build
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quality).
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A high individual cell voltage deviation is a sign for a defective cell
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that should be checked and possibly replaced as soon as possible to avoid
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further damage.
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A high voltage drop under load implies a high internal resistance and/or
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some chemical defect.
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A high positive temperature deviation of a cell or module can be a sign for
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a chemical defect (e.g. dendrites causing short circuits) or for a bad
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connector (e.g. a lose screw). Both not only degrade the overall pack
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performance but can lead to battery fires in the worst case, so must be
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addressed as soon as possible.
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Some temperature & voltage deviation may be normal, caused by the layout
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of the cells in your vehicle: cells placed closer to the outside will
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have a higher temperature variance than those deep within the pack, and
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a cell with higher temperature will have a higher voltage stability.
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Also keep in mind, not all deviations may be caused by actual battery
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issues. Voltage and temperature sensors can lose their calibration or
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become defective as well.
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