Automotive circuits are expected to handle several transient over-voltage/under-voltage conditions. Most of these conditions are short-lived and can be handled with surge suppression components such as TVSs and MOVs.
There are two particular over-voltage conditions, however, that are longer lived. The 24V jump start condition and the failed regulator condition.
The 24V jump start condition is described in
this document as follows:
Jump Start
The jump start transient results from the temporary application of an overvoltage in excess of the rated battery voltage. The circuit power supply may be subjected to a temporary overvoltage condition due to the voltage regulator failing or it may be deliberately generated when it becomes necessary to boost start the car. Unfortunately, under such an application, the majority of repair vehicles use 24V battery jump to start the car. Automotive specifications call out an extreme condition of jump start overvoltage application of up to 5 minutes.
The failed regulator condition is a steady state condition (that is, it will potentially be very long-lived) and the voltage can reach +18V.
A circuit that I am designing controls two 12V solenoid-operated valves. These valves each require about 1.5A at 12V. Naturally, the manufacturer says nothing about what happens when the solenoid is driven at 24V. It's probably fairly safe to assume this shouldn't be done, if it can be avoided.
My question is, what is typically done in these cases? Ideally, I want to keep the solenoids energized during these conditions. What is the best, most cost effective way to protect the solenoids but keep them energized? Or is it even a problem? Would the solenoid coils survive these conditions?