Full Power on a Mild Day: Why Your HVCH Needs Modulated Output

With the outside temperature at 12 degrees Celsius, the cabin is already comfortable enough, yet the heater is still running at full power—this complaint does not stem from the coldest week of winter, but rather from feedback received from the fleet during spring and autumn. The heater itself is functioning correctly; it simply ‘does not know’ how to reduce its output and can only operate at full power.

The core issue behind this complaint lies in ‘control’, rather than ‘capacity’. If a heater has only two states—’fully on’ and ‘fully off’—it will cycle repeatedly between these two states on mild days; whereas if the heater can adjust its output according to demand, it can precisely match the actual load. This difference is reflected in actual energy consumption, rather than in the rated power figures stated in the product manual.

‘On-off control’ and ‘modulating output’ are two distinct product options.

There are currently two main control architectures, and the choice must be made at the procurement stage, rather than during commissioning. Our B-series products are equipped with a CAN bus and an enable interface: the vehicle controller can send heating commands via the CAN bus and read preset status information. Our E-series products, on the other hand, utilise thermostat control; they do not feature a CAN bus or external control interface, but instead rely on their built-in control logic for on/off switching.

Thermostat control operates on a ‘switch’ principle: heating stops once the setpoint is reached and restarts when the temperature changes. Devices supporting CAN bus control, on the other hand, can receive specific power level commands rather than merely a simple ‘on’ command. This distinction is particularly important on mild days—when vehicles often require only a small fraction of their rated power, and this demand may persist for several hours.

In the EVLINK specification summary, both product series have a power range of 20 to 24 kilowatts (kW) and a voltage range of 400 to 800 volts (V). Looking solely at the ‘Power’ column does not reveal their operational characteristics; however, consulting the ‘Control’ column makes this immediately clear.

Calculating energy consumption in mild weather is very straightforward—it is purely a matter of mathematics.

A 20-kilowatt heater operating at full power for one hour consumes 20 kilowatt-hours (kWh); if it operates at half power on average over the same hour, it consumes 10 kilowatt-hours. Although these figures are not actual measurements for EVLINK heaters, they clearly demonstrate that the key factor determining energy consumption costs in mild weather is ‘output control’, rather than the rated power stated on the nameplate.

Furthermore, PTC elements provide an additional layer of physical regulation: as the coolant temperature rises and approaches the element’s design point, the PTC element’s own resistance increases, thereby automatically reducing its power consumption. This ‘self-regulating’ characteristic is inherent to the PTC material itself, rather than a control strategy; it prevents output power overshoot before the controller intervenes. However, it does not replace the control system; its role is to smooth out the sharp fluctuations caused by ‘on-off’ cycling.

This does not imply that heaters using a thermostat perform poorly, but rather serves as a reminder to buyers to understand the vehicle’s actual operating behaviour. If the vehicle operates at partial load for the majority of the heating period, ‘on-off’ control will result in additional energy loss; whereas for vehicles that typically require full-power heating during cold starts, the impact of this difference is minimal.

Before discussing power (in kilowatts), the control method must first be clarified.

Three key factors must be considered when making a selection: firstly, the vehicle’s voltage range with which the heater must be compatible; secondly, the required control method—for example, whether commands are sent and status feedback received via the CAN bus, or whether on/off control is achieved using a thermostat; and finally, the distribution of the vehicle’s thermal demand during the actual operating season—this must take into account not only demand during the most extreme cold weather but also operating conditions throughout the year.

If any data within the demand distribution is unknown, please state this honestly when requesting a quotation; under no circumstances should you make assumptions. The absence of demand data is a normal part of project input and does not constitute an error in the quotation process. We would much rather perform selection calculations based on ‘clearly defined unknown parameters’ than design based on ‘speculative data’.

Furthermore, one additional check must be carried out during the selection phase: ensure that the control method required by the vehicle matches the control method provided by the heater. If the vehicle controller sends CAN commands to a thermostat-controlled heater, this is not a fault with the equipment but rather a mismatch in selection, and the heater must be replaced with a suitable model. Conversely, if the vehicle never sends control commands, then even if a heater supporting CAN control is fitted, that heater will never be able to regulate its power output.

Issues that cannot be resolved by adjustment functions

Even with output adjustment functions, the following situations cannot be rectified: incorrect heater selection, insufficient flow in the cooling circuit, or the absence of a ‘wake-up’ signal. If the heater never receives a start-up (enable) signal, it will not generate heat regardless of the duty cycle setting; similarly, if there is no flow in the cooling circuit, heat cannot be transferred to its destination. These issues require separate troubleshooting, and each situation has its own specific criteria for diagnosis. For example, there is a dedicated checklist for the ‘wake-up’ process; whilst for power verification, a distinction must be made between the three levels of ‘command output’, ‘electrical input’ and ‘actual heat output’.

Complaints relating to ‘heating range/capacity’ should also follow the same rigorous troubleshooting process. Before attributing the issue to the heater’s output control, please first confirm: has the heater actually received the regulation command? Has the cooling circuit successfully transferred heat? And has the expected heat demand curve been clearly defined? The root cause of most complaints arising in ‘mild weather’ often lies in the aforementioned aspects, rather than in the heater’s own power output.

Information to be provided to EVLINK

When contacting EVLINK regarding High-Voltage Coolant Heaters (HVCH), please provide the following accurate information: the specific heater model, the vehicle’s voltage range, the required control method, and the heat demand curve available to you. Furthermore, please clearly specify the nature of the issue – whether it is abnormal energy consumption in mild weather, a lack of start-up response, or actual heat output that does not match expectations. This will enable us to accurately determine which product documentation or project input data to refer to during our discussion.