Simulation

Most battery models fail not because the equations are wrong — but because the assumptions smuggled in with them are wrong. Fifteen years working with battery models across the stack: from ECM spreadsheets that needed to survive a BMS real-time loop, to full electrochemical models trying to capture what actually happens inside the cell during a fast charge. The gap between “runs on paper” and “works in a vehicle” is where most of the interesting problems live. ...

GitHub Repository CFD-based battery simulation is powerful and routinely impractical. OpenFOAM can model the coupled thermal-flow behavior of a battery pack in detail that lumped models can’t touch. It can resolve cell-to-cell temperature gradients, coolant channel flow distribution, and transient heat propagation through complex pack geometries. It can also take an experienced CFD engineer a day to set up a single case, another day to run it, and significant effort to extract anything useful from the output. ...

Most battery simulation work happens inside large OEM simulation frameworks — tools with hundreds of subsystems, long setup times, and infrastructure built for full-vehicle analysis. Useful when you need the full vehicle. Counterproductive when you need to iterate quickly on battery-specific questions. At Volvo Trucks, the problem was clear: the battery and BMS teams needed a simulation environment they could actually use — fast iteration, battery-focused, not dragging a full vehicle model along for every run. ...

The DC junction box doesn’t get much attention in EV thermal discussions. People focus on the battery pack, the inverter, the motor. The junction box is a metal enclosure with some contactors, fuses, and busbars — it switches current and protects the circuit. How hot can it get? Hotter than you expect, under the conditions that matter most. Why the Junction Box Gets Hot The DC box carries the full HV current whenever the vehicle is driving or charging. The heating is straightforward: I²R losses in the busbars and contactors. At peak power — high speed driving or DC fast charge — this current is large. ...

In battery development, the cell you’re simulating is rarely the cell you have test data for. A customer RFI comes in specifying a 60 Ah prismatic. Your characterisation data is for a 40 Ah cylindrical from the same chemistry family. The programme timeline doesn’t allow for a full test campaign on the new cell before the simulation deliverable is due. This is the normal situation — not the edge case. ...

An EV thermal management system is not one problem. It’s eight problems that happen to share coolant. The battery wants to stay between 15 and 35°C. The power electronics want active cooling at high load. The cabin wants heat in winter and cooling in summer, and it’s competing for the same refrigerant circuit the battery uses. The motor generates heat during aggressive driving. The DC-DC converter has its own overtemperature failure mode. All of these are connected — through coolant loops, refrigerant circuits, and control logic — and all of them interact dynamically. ...