In many cases, especially for centralized CPMs, there are multiple loads (motors, lighting, and so forth) potentially needing power from the backup energy source. The energy required for each motor can be calculated as described in Section 3.4.1.1. The total energy is then the sum of all the motors to be driven after a collision. There can also be requirements for multiple attempts to activate the motors, in case the initial activation is unsuccessful.

In addition to the total energy needed, another consideration is the maximum current required; this is an important parameter is designing the power conversion circuits. As discussed above, the maximum current for each motor occurs during the first phase of activation and when the motor stalls at the end of travel; in both cases the motor rotation is effectively zero.

If multiple motors are to be activated, there are two options in terms of timing: either simultaneous activation or sequential activation. With simultaneous activation, all motors are activated at the same time, and the maximum current needed is the sum of all the maximum motor currents. This method has the advantage in being the quickest to activate the motors, and is simple to implement.

With sequential activation, the motors are activated in sequence, so that the maximum current is that needed by only one motor at a time. This has the advantage of reducing the peak current requirement for any boost circuit supplying the motors from the supercapacitors. However, the time to activate all the motors is longer, and this method is more complex to control the sequence of activation.

Figure 3-8 Simultaneous (Left) and Sequential (Right) Current Profiles