What Is MIL-STD-1275?

MIL-STD-1275 specifies the 28 V DC power environment inside a military ground vehicle. Vehicle power is far from clean: engine cranking, alternator behaviour, battery state and switching loads such as turrets, winches and radios produce surges, spikes and ripple well beyond a steady 28 V. The standard defines those disturbances so equipment can be designed to ride through them.

It applies to tanks, armoured vehicles, trucks and other tactical vehicles, and to the equipment connected to their 28 V DC bus. MIL-STD-1275E, issued in 2013, is still the revision most datasheets quote, and MIL-STD-1275F has since replaced it. As with other military standards, the contract names the revision.

The standard describes three operating modes, and the limits differ for each: normal operation with batteries and generator connected, generator-only operation with the batteries disconnected or failed, and battery-only operation with the engine off. Generator-only mode is the harshest, because there is no battery to absorb surges.

The table gives the commonly quoted MIL-STD-1275E figures for each disturbance. Exact limits depend on the revision and mode, so always design to the document your contract cites.

Spikes are short but carry real energy, so they are tested with a defined source impedance. Surges last longer and stress the input stage with heat as much as voltage. Starting disturbances matter most in practice: a computer that browns out during cranking may restart repeatedly or corrupt its storage, even if no part is damaged. Battery-only operation, with the engine off and loads such as radios running, also drags the voltage down slowly over time.

Compliance is shown by testing the equipment’s power input against each disturbance in each operating mode, usually at an independent lab or with a 1275 test generator in the maker’s own lab. The report should state the revision, the modes tested and whether the equipment kept working or only survived each test.

An in-vehicle computer specified for a military platform needs a power input that meets, or is protected to, MIL-STD-1275. Otherwise transients on the vehicle supply can reset it during engine start, corrupt its storage or damage its power stage. The usual design measures are:

MIL-STD-1275 is the ground-vehicle counterpart to MIL-STD-704 for aircraft. Our guide to MIL-STD-704 covers the aircraft standard, which includes AC power as well as 28 V DC. Civil vehicles use ISO 7637-2 for transients and ISO 16750-2 for supply conditions, and computers sold for road vehicles in Europe also need E-mark approval. Our guide to E-mark certification covers the civil route.

The civil limits are generally lower than 1275, so a computer that meets MIL-STD-1275 usually has margin on a commercial truck, but it still needs the civil tests and approvals for road use. The reverse is not true: a computer designed only for civil 24 V vehicles may not survive the 100 V generator-only surge or the 250 V spikes of a military vehicle.

Many systems in our rugged mission computers range list MIL-STD-1275 compliance for their DC input, typically alongside MIL-STD-461 and MIL-STD-810. Our wider in-vehicle computers range covers commercial and emergency-service vehicles, where wide DC input and ignition control do a similar job against civil standards. Our overview of US military standards shows how the power standards fit with the others.

We supply rugged and mission computers with MIL-STD-1275 power inputs and ignition control, and integrate and test each system before it ships. Tell us the vehicle, its power system and the standards your programme calls up, and we will shortlist systems to suit.