The Services > NMEA > DC page displays information received from the boat’s NMEA 2000 network.
This article explains how the general NMEA 2000 processes data shared by battery monitors, BMS devices and alternator regulators.
A Victron Cerbo GX with connected battery equipment can display more fields. For more information, see DataHub: Monitor Battery and Alternator Data.
What the general NMEA 2000 DC page displays
For a general battery or alternator source, the DataHub displays:
Name
Manufacturer
Model
Version
Instance
Voltage
Current
Temperature
State of Charge (SoC %)
State of Health (SoH %)
Battery and alternator values normally update approximately every 10 seconds.
A missing optional value appears as NA.
Why does a Victron Cerbo GX display additional fields?
The DataHub has specific support for the Victron Cerbo GX and connected Victron battery equipment.
When the DataHub identifies and interprets the supported Victron data, the local page can additionally display:
Time Remaining
Ripple Voltage
Amp Hours Used
These fields are not currently included for general NMEA 2000 battery monitors.
Which NMEA 2000 PGNs does the DataHub use?
PGN | Name | How DataHub uses it |
127506 | DC Detailed Status | Identifies the DC source type and instance. The enhanced Victron parser can also use supported extended DC fields |
127508 | Battery Status | Supplies Voltage, Current and Temperature |
127750 | Converter Status | Supplies alternator charge-stage information for internal status handling |
127507 / 127510 | Charger Status / Charger Configuration | Older fallback sources for charge-stage information |
60928 | ISO Address Claim | Supplies device identity information such as manufacturer code and serial number |
126996 | Product Information | Supplies model and firmware-version information |
126998 | Configuration Information | Supplies Manufacturer name text |
PGNs are NMEA 2000 messages. They are not NMEA 0183 sentences.
Why is PGN 127506 required?
For general NMEA 2000 sources, the DataHub must receive PGN 127506 DC Detailed Status before accepting live values from PGN 127508 Battery Status.
PGN 127506 tells DataHub:
Whether the source is a battery or alternator.
Which DC instance belongs to the source.
A chartplotter may display voltage directly from PGN 127508 while the DataHub does not show the source. This can occur when the transmitting device fails to send PGN 127506.
How does Wakespeed WS500 information appear?
The Wakespeed WS500 normally uses:
PGN 127506 to identify the alternator and instance.
PGN 127508 for voltage, current and temperature.
PGN 127750 for charge stage.
The DataHub does not display charge stages such as Off, Bulk, Absorption, Float, Equalise and Fault internally. The current DC Status page does not display the charge stage. Use the Wakespeed interface for detailed charge-stage information.
How do DC instances work?
The transmitting equipment assigns the NMEA 2000 instance.
By assigning different instances, you can see the different sources on your boat, such sources such as:
House battery
Engine-start battery
Generator-start battery
Bow-thruster battery
Alternator
Additional battery banks
Important: Two batteries should not use the same battery instance.
Two alternators should not use the same alternator instance.
A battery instance 0 and an alternator instance 0 can coexist because DataHub tracks the two source types separately.
Why is the entire DC page empty?
An empty page normally means:
No compatible source is transmitting.
DataHub is not receiving data from the NMEA 2000 network.
The NMEA 2000 network is not powered or correctly terminated.
The source is not transmitting PGN 127506.
Confirm that the source equipment is powered and displays valid data on its own interface, if it has one. Then check:
Backbone termination.
Drop cables and connectors.
DataHub’s NMEA 2000 connection.
Why does my chartplotter show the battery but the DataHub does not?
The source may transmit PGN 127508 without PGN 127506.
A chartplotter may use voltage or current directly from 127508. The DataHub requires 127506 to classify the source and associate it with an instance.
Check whether the source device allows individual NMEA 2000 PGNs to be enabled or disabled. If you are unsure, contact your installer for further assistance.
Why do Manufacturer, Model or Version show NA?
Identity information is requested separately after the source is discovered.
Wait one or two minutes after startup or after connecting the source.
If voltage and current continue to update but the identity fields remain NA, the source may not publish or respond to the required product-information messages.
This does not mean there is a problem with your devices.
Why does Temperature show NA?
The source is not providing a usable temperature value. Check:
Whether a temperature sensor is installed.
Temperature-sensor wiring.
Source-device configuration.
Whether the source exposes temperature through NMEA 2000.
For a Victron installation, also check whether the temperature value appears in the Cerbo GX interface.
Why are values frozen or not updating?
Reload the browser page first. If the values remain unchanged:
Check whether the source device is still updating.
Confirm that other NMEA 2000 information continues to reach the DataHub.
Check that the NMEA > GPS or Navigation tab is updating.
NMEA 2000 power, cabling and connectors.
Restart only the affected source using the manufacturer’s approved procedure.
A visible value proves that DataHub received that value at some point. It does not prove that the source is still transmitting.
Why are two battery banks shown with identical information?
The transmitting devices may use the same battery instance.
Configure a unique instance for each battery bank through the manufacturer’s interface or an appropriate NMEA 2000 configuration tool.
The DataHub displays the instance supplied by the source. It does not assign or change it.
Why does information jump between two batteries?
This normally indicates duplicate instances between two sources of the same type.
Assign each battery a unique battery instance, or each alternator a unique alternator instance. Contact your installer if you're unsure how to do this.
Why can I not see Bulk, Absorption or Float?
The DataHub does not currently display charge stage (Bulk, Absorption or Float).
Use the alternator regulator’s own interface for detailed charge-stage information.
Why is the local value present, but GPS Tracking shows as a dash (-)?
A valid local value proves that the DataHub has received device status information from NMEA 2000.
It does not prove that:
Tracking is enabled.
Your NMEA 2000 is powered on.
The DataHub has Internet access.
A tracking report containing the value has been uploaded.
The GPS tracking page is up to date.
Check the timestamp on the GPS Tracking page and confirm each requirement separately.
The enhanced GPS Tracking battery field set is currently documented for the supported Victron Cerbo GX integration.
What should I send PredictWind Support?
In almost all cases, if you are not seeing the expected data, it will be due to one of the issues identified above or to your device not outputting the data in a format the DataHub can interpret.
If you are sure your device should output data that the DataHub can interpret, and the requirements outlined above are met, then, where available, enable Remote Access Type: Support and include:
The DataHub model.
The DataHub firmware version.
Selected NMEA source.
Source equipment manufacturer, model and firmware version.
Whether the source is connected via a Victron Cerbo GX or otherwise, please specify.
Screenshot of the source equipment showing the expected values.
Full screenshot of Services > NMEA > DC.
Battery or alternator instance numbers.
A description of which values are correct, missing, stale or assigned to the wrong source.
Expected result
For a general NMEA 2000 source:
PGN 127506 identifies the source type and instance.
PGN 127508 supplies Voltage, Current and Temperature.
The source appears in the appropriate Battery or Alternator section.
For a supported Victron Cerbo GX source:
The local page can additionally display the enhanced Victron field set.
The DataHub can upload supported Victron battery values to GPS Tracking.