US Why a GPU changes the power budget
A small vehicle computer might draw 20 to 40 W, which the vehicle’s electrical system barely notices. Add a discrete GPU and the total can reach several hundred watts, and that changes everything from the cable size to the battery. Current, not power, is what the wiring sees, and at 12 V it rises quickly:
| System power | Current at 12 V | Current at 24 V | Current at 48 V |
|---|---|---|---|
| 100 W | 8.3 A | 4.2 A | 2.1 A |
| 300 W | 25 A | 12.5 A | 6.3 A |
| 600 W | 50 A | 25 A | 12.5 A |
Those are the figures at the nominal voltage. During cranking or with a weak battery the voltage falls and the current rises further, so always size for the lowest voltage the computer will run at. This is one reason heavy GPU systems are easier to fit to 24 V trucks and buses than to 12 V cars, as our guide to 12 V vs 24 V explains.
Step 1: check the vehicle can supply it
Find the alternator’s rated output and subtract what the vehicle already uses for lights, heating, radios and other equipment. The GPU computer’s peak draw has to fit in what is left, with margin, at engine idle as well as at speed, because many alternators deliver much less at idle.
Then decide what happens with the engine off. A 300 W computer drains about 25 A from a 12 V battery, enough to leave a car battery unable to start the engine within an hour or two. For long engine-off running, fit a second battery with a split-charge system or a battery isolator, so the computer can never flatten the starter battery.
Use the computer’s maximum input power from its datasheet, then add any cameras, modems or displays it powers. GPU load is rarely steady: a model that runs in bursts can swing the draw by a hundred watts or more in a fraction of a second. Measuring the real system with a clamp meter or a logging power supply, running the actual software, gives a far better figure than adding up typical values.
Step 2: choose a wide-range DC input
Vehicle supplies are noisy. During cranking a 12 V system can dip well below 9 V for a moment, and lower still in cold weather. When a heavy load is disconnected or a battery terminal comes loose while the alternator is charging, a load dump can drive the voltage far above nominal for hundreds of milliseconds. Standards such as ISO 16750-2 and ISO 7637-2 for road vehicles and MIL-STD-1275 for military vehicles define these events.
A computer built for vehicles handles them with a wide-range DC input and protection on the board. The GPU systems in our in-vehicle computer range accept inputs such as 8 to 48 V or 9 to 60 V DC, so the same system runs on 12 V and 24 V vehicles and keeps running through a cranking dip. For road vehicles, check for E-mark approval too. Avoid powering a GPU system through a car-style inverter or a cigarette-lighter socket: both add losses and neither is built for this load.
Step 3: wire it for the peak current
Run the supply directly from the battery or a distribution point, not from an existing accessory circuit, and fit a fuse as close to the battery as possible, rated for the cable rather than the computer. Size the cable for the peak current and the length of the run: at 25 A, a few meters of thin cable can lose a volt or more, which brings the input closer to its lower limit during cranking. Use a solid ground to the chassis or the battery negative.
Connect the ignition signal as a separate low-current wire, so the computer stays on a permanent feed and uses ignition only to decide when to start and stop. Our white paper on vehicle computer ignition control covers the wiring and timer settings. Locking connectors, such as M12 or screw terminal blocks, keep the supply secure under vibration.
Step 4: plan for power loss
Ignition control handles a normal stop, but not a sudden loss of power from a flat battery, an isolator switch or a crash. If a GPU computer is recording evidence or writing to a database, add a ride-through buffer. A supercapacitor UPS between the vehicle and the computer holds it up long enough to finish writing and shut down, and suits the heat and vibration of vehicles better than a battery. Our industrial UPS range includes modules with ignition control built in, and our comparison of supercapacitor vs battery UPS explains the choice.
Rail vehicles are a separate case. Trains power onboard equipment from battery systems of 24 to 110 V DC, most often 72 or 110 V, so rail computers use inputs designed for those voltages rather than a converter bolted on later. Our range of rugged GPU computers includes vehicle and rail options.
Quick answers on powering vehicle GPU computers
Vehicle power for GPU loads: common questions
Can I use a desktop PC power supply with an inverter?
It works on the bench, not on the road. The inverter wastes power, and neither part is built for cranking dips, vibration or ignition control.
Will a GPU computer drain the battery?
Yes, if it runs with the engine off. Use ignition control with an off delay, a low-voltage cut-off or a second battery.
Do electric vehicles need anything different?
Check the low-voltage system. Most EVs supply 12 V or 48 V from a DC-DC converter, whose spare capacity limits the GPU load.
Should I reduce the GPU’s power limit?
It can help. Capping the GPU’s power lowers peak current and heat, often with only a small loss of inference speed.
Is 48 V better for large GPU systems?
Where the vehicle has it, yes. At 48 V the current is a quarter of the 12 V figure, so cables are thinner and losses lower.
We fit and configure the GPU, storage and operating system as standard, so the system arrives ready to install in the vehicle.