UK How ignition control works
Ignition control is a power management feature on vehicle computers that watches the vehicle’s ignition signal and switches the computer on and off with it. When the driver turns the key or presses the start button, the computer powers up after a short delay. When the ignition goes off, the computer keeps running for a set time, then tells the operating system to shut down, and finally cuts its own power.
A vehicle computer cannot simply lose power when the engine stops: an abrupt cut can corrupt the operating system, a database or a video recording. Wiring it to a switched supply would do exactly that. Ignition control solves the problem by keeping the computer on a permanent battery feed and using the ignition line only as a signal.
It is handled by a small power controller on the computer’s board or in its power supply, separate from the main processor, so it works even if the operating system has hung.
The settings that matter
Ignition control is configured with a handful of timers and thresholds, set by DIP switches, in the BIOS or through a utility. Ranges vary by model; the table shows typical values.
| Setting | What it does | Typical range |
|---|---|---|
| Power-on delay | Waits after ignition on before booting, so the supply settles after cranking | A few seconds to a minute |
| Power-off delay | Keeps running after ignition off to finish uploads or recording | Seconds to several hours |
| Shutdown signal | Sends a soft power-button event so the OS closes cleanly | Immediately after the off delay |
| Hard-off timer | Cuts power if the OS has not shut down in time | Around 1 to 30 minutes |
| Low-voltage cut-off | Shuts down before the battery is too flat to start the engine | Around 11 V on 12 V, 22 V on 24 V systems |
The right off delay depends on the job. A taxi terminal may need only a minute; a bus CCTV recorder may stay on for an hour to upload footage over depot Wi-Fi.
Test the settings on the vehicle, not just on the bench. Time a full shutdown with the real software running, add a margin, and set the hard-off timer above that figure, so a slow update never gets cut off halfway. Check too that a quick stop and restart, such as a stall or a refuelling stop, is handled: most controllers cancel the shutdown if the ignition comes back during the off delay, so the system carries on without a reboot.
Why ignition control matters
Ignition control protects three things at once.
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Data. A clean shutdown every time prevents file system corruption and lost recordings.
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The operating system. Windows and Linux both need an orderly shutdown; repeated hard power cuts eventually stop a system booting.
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The battery. The computer never stays on long enough to leave the vehicle unable to start, even if a driver leaves the ignition in accessory mode.
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The driver’s time. The computer is ready when the vehicle is, with no button to press, which matters on fleets where drivers change shifts.
Wiring and starting voltage
A computer with ignition control usually takes three connections: a fused permanent battery feed, ground and the ignition (or ACC) signal. The power input is wide range, commonly 9 to 36 V or more, so the same computer runs on 12 and 24 V vehicles.
Engine starting is the hard part. During cranking, a 12 V supply can dip well below 9 V for a moment, and load dumps and spikes follow. Vehicle electrical standards such as ISO 16750-2 and ISO 7637-2 define these events, and military vehicles use MIL-STD-1275. A supercapacitor UPS between the vehicle and the computer rides through dips and keeps the computer alive long enough to shut down if power is lost completely; our industrial UPS modules include versions with ignition control built in. For road vehicles, check E-mark approval too; our guide to E-mark certification explains what it covers.
Where ignition control is used
Ignition control is standard on computers built for vehicles: buses and trains, police and ambulance fleets, delivery and refuse trucks, forklifts, mining and agricultural machines. Almost all of our in-vehicle computers include it, as do rugged Jetson systems for autonomous machines. Our ignition control guide goes into the wiring and timing for specific models.
It also turns up outside vehicles, wherever a computer should follow an external on and off signal, such as a machine’s main switch or a generator start.
Quick answers on ignition control
Ignition control: common questions
What is ignition sensing?
The same thing. Ignition sensing describes the input that detects the ignition signal; ignition control describes the whole start and shutdown sequence. Suppliers use the terms interchangeably.
Can I add ignition control to any PC?
With an external controller, yes. Add-on ignition controllers and vehicle power supplies can switch a standard PC, but a computer with it built in is simpler and more reliable.
How long should the shutdown delay be?
Long enough to finish the job. Set it to cover uploads, recording or brief stops, such as refuelling, without draining the battery. One to fifteen minutes is common.
Will the computer drain the battery when parked?
Not with low-voltage protection. The low-voltage cut-off shuts the computer down before the battery drops too far to start the engine.
Is ignition control the same as an ignition control module?
No. An ignition control module fires the spark plugs in a petrol engine. Ignition control on a computer only uses the ignition signal to manage the computer’s own power.
We set the ignition timers, low-voltage threshold and shutdown behaviour to suit each vehicle as standard, and test the power sequence before the computer ships. Tell us the vehicle supply and how long the system must stay on after the engine stops.