Best Practices for Vehicle Mounted Computer Shutdowns

September 23, 2019 Teguar Corporation

Vehicle mounted computers must be able to connect to the vehicle battery power. If set up incorrectly, the connection between the computer and vehicle battery can have negative consequences for both. For the following discussion, assume that the power being supplied by the vehicle is within the voltage tolerance of the computer, as most vehicle computers have a wide range voltage input (9~36V or wider).

Preventing Power Drains and Protecting Hard Drives in Vehicle Mounted Computers

The main concern for the vehicle is battery drain. This is typically not an issue when the vehicle is running, as the computer is drawing power from the vehicle and not the battery. However, when the vehicle is turned off, a computer can quickly drain the vehicle battery. The computer must be turned off when the vehicle is turned off. You should not rely on human interaction to turn off the computer when the vehicle is turned off, as there will likely be a time when the operator forgets and the vehicle battery is drained.

The computer needs to automatically turn off when the vehicle is shut off, but, shutting off power to the computer while it is running is not good practice. Each time power is suddenly removed from a computer, you run the risk of corrupting the filesystem. When this happens, the computer will fail to boot and the hard drive or SSD will need to be reimaged or replaced. In order to protect the computer's file system, the computer must perform a graceful shutdown.

There are a few different methods to prevent vehicle battery drain and also protect the computer's file system. The two most common methods are explained below.

Ignition Input

There is an ignition signal present in most vehicles. When the vehicle is on, this signal is asserted to the same voltage as the battery, when turned off, it is set to ground. Some specialized computers are available with an ignition input, meaning they have unique hardware that allows the ignition signal to turn the computer on and perform a safe shut down when turning the computer off.  Many computers with ignition input signals have jumper settings or BIOS settings that allow users to program how a computer behaves when the ignition signal is asserted or removed. Users can change how long the computer waits before shutting down after the ignition signal is removed and set the computer to power on automatically when the ignition signal is applied.

Internal UPS Backup Battery

The other method is to select a computer with an integrated battery. Tablets have integrated batteries and many touchscreen computers have optional integrated UPS backup batteries. These batteries can communicate their charge percentage and other information to the operating system. The operating system can then automatically perform a graceful shutdown when the battery is near depletion. This battery support is built into Windows and you may see this on your personal laptop when the battery is almost dead.

Computers with batteries can be safely connected to the vehicle battery, because when the vehicle voltage is disconnected from the computer, the computer's battery takes over. The operating system power settings can be tweaked to change how the computer reacts to changes in the battery status. For example, the computer can be set to perform a safe shutdown as soon as the battery takes over, or it can be set to wait for some period of time before a safe shutdown is initiated. The computer can also be set to power on automatically the next time vehicle power is applied.


Both of these methods work well for protecting vehicle batteries and the computer. The ignition input implementation is most common with box PCs and in extreme conditions such as agriculture machinery and outdoor vehicles. This is largely because box PCs can have wider temperature ranges than computers that include batteries and LCDs. The internal battery implementation is more common with touchscreen computers and tablets for applications such as forklifts, cranes, and in temperature controlled areas. These applications benefit from the simplicity of the power wiring and the flexibility of having a single all-in-one touchscreen computer.

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