Monitoring an electric vehicle battery over OBD

The device. FMx003 is a range of compact Teltonika trackers that draw both power and data straight from the OBD-II socket, the vehicle's built-in self-diagnostic system. There are 2G and 4G LTE versions; this case study looks at the FMC003 with LTE. No wiring has to be run: the tracker plugs into the socket under the steering wheel and the vehicle goes out on a run the same day.

What data is transmitted. From the electric vehicle's BMS the tracker reads the state of charge of the high-voltage battery (SOC), the charge level, the state of health (SOH) and the battery temperature. To that are added the usual telematics: position, mileage, speed, operating time.

Charge and vehicle readiness. At any moment the dispatcher can see which vehicles have enough charge for a shift and which need putting on charge. The morning dispatch is planned from actual data rather than from what the drivers report.

The charging schedule. Knowing the charge of each vehicle, you can spread charging out over time: first those leaving earlier or going further, then the rest, in the night hours where possible. That reduces the peak load and helps avoid holding the whole fleet at 100% when there is no need.

Battery ageing. SOH shows how much capacity the battery has left relative to a new one. If SOH on one vehicle is falling noticeably faster than on its neighbours of the same model, that is a reason to have it checked at a workshop before the problem turns into a failure. Comparison within the fleet is especially useful: identical vehicles with identical mileage should age at roughly the same rate, and one that stands out from the row is spotted at once. In the long run this data helps in planning battery replacement and in assessing the residual value of vehicles at sale.

Temperature. The tracker reports battery temperature in real time. If the battery often runs hotter than normal — during fast charging in hot weather, for instance — that shows up on the graph, and the regime can be changed: charge more slowly, park the vehicles in the shade, avoid fast charging in the hottest hours.

Reacting to deviations. Notifications are set up for the parameters that matter: low charge on a vehicle out on the road, battery overheating, a sharp drop in SOH. The dispatcher learns about the problem straight away rather than after a call from a driver on the verge.

An example from fleet life. In the evening the dispatcher opens the vehicle list and sees that three electric vehicles are below 20% charge and are on long routes tomorrow. He puts those on charge first, while for the ones at 60-70% with a short day in town he moves charging to the night. In the morning all of them go out with the reserve they need, and not one stops in the middle of a shift.

Analysis of mileage and energy consumption. Set the charge against the mileage and you can see how much energy each vehicle uses per 100 km. A sharp rise in consumption on one vehicle on the same routes is a reason to check the tyres, the brakes or the driver's style. Hard acceleration in an electric vehicle eats into the range just as noticeably as it eats fuel in a conventional one.

Checking the readings. Before the figures are trusted, they are checked. On a pilot vehicle the charge shown in the platform is compared with the dashboard or the manufacturer's app, and you confirm whether SOH and temperature arrive at all and how often the values update. If SOH on some vehicle has started falling noticeably faster than on its neighbours, that is a reason for service diagnostics at the dealer: the tracker's data shows a trend, and the workshop makes the diagnosis.

Planning replacement. Once the fleet has a year or two of SOH history, you can work out roughly when the batteries in particular vehicles will reach the threshold beyond which the range no longer covers a working day. That makes it possible to put battery replacement or fleet renewal into the budget in advance rather than learning about it from driver complaints.