72V Range Extender

72 V is where a range extender stops being a trickle charger and starts carrying a working vehicle. The same power moves at two-thirds of the 48 V current, so the cable, the connectors and the contactors all come down a size — on a machine that has to carry its own wiring for fifteen years, that is weight you never get back once the architecture is set.

Innotec Power builds the 72 V units as permanent magnet alternators driven by a small combustion engine, feeding the pack directly through a passive rectifier. No inverter stage, no synchronous speed, no mechanical connection to the driveline. The engine is there to make charge and nothing else. The line has been in third-party testing since Innotec first proved DC gensets on its own PMAs in 2014.

Three frames are built at 72 V, all at 3,000 rpm and all air cooled. The 25 kW frame has no 48 V equivalent — it is the reason a lot of machines move up to this bus.

Note the shaft change at 25 kW. The 5 and 15 kW frames use a spline into a driveline; the 360-EZ is foot mounted with a key-locked shaft, which suits a machine bed rather than a vehicle transmission. It is the point where the product stops being a driveline component and becomes a power module.

As finished packages rather than alternators to integrate, the 14 kW and 25 kW sets ship complete at 72 V as DCGO-14-72-KSD1403TC-000 and DCGO-25-72-KDI1903TC-000, charging across a 72–84 VDC window.

The arithmetic is the argument. Take the 15 kW unit, which is the volume seller across both buses:

A third less current for identical output. That flows straight through to conductor cross-section, connector rating, fuse and contactor size, and the heat all of them have to shed. On an off-road machine or a boat, where the run from the extender to the pack is rarely short, it is usually the deciding factor rather than a refinement.

The trade is component availability. Off-the-shelf 48 V controllers and DC-DC converters are easier to source than 72 V ones, so the auxiliary side of the system wants deciding at design stage rather than at commissioning.

The same machine can be programmed to work as a starter motor for its own engine and then switch to generating. On a 72 V machine that removes both the separate starter motor and the dedicated starter battery — parts that exist only to crank an engine which, in a range extender, may run for an hour a day.

It also opens the door to regenerative capability in a series-hybrid driveline, where the same frame recovers energy rather than only producing it. Specify it at the outset: the winding and the controller are chosen differently for dual-direction duty. See starter generators.

• Overload protection by design. Output current is capped per power and voltage rating, so a deeply discharged pack cannot drag the alternator or the engine past their design point.
• Charging curve, not a fixed voltage. The controller follows the profile the pack chemistry specifies across the 72–84 V window.
• Nothing to service in the alternator. NdFeB magnets, Class H windings, no brushes, no slip rings, no AVR, and a bearing-less or direct-mounted rotor on most builds.
• Power to weight. Substantially smaller than a conventional machine of the same rating — the reason a 25 kW unit is a practical thing to carry.
• Fuel flexible. Petrol, diesel or LPG micro-engines, with engine speed following charge demand rather than holding a synchronous speed.

• Electric and hybrid construction machinery, where the duty cycle is long and the charge window is short
• Agricultural and off-road equipment, including ATVs and utility vehicles
• Material handling and larger warehouse fleets on extended shifts
• Electric boats and marine series-hybrid propulsion, where cable runs are long
• Ground support equipment and airside vehicles
• Autonomous and remote-operated platforms that cannot return to a charger on schedule

Related: DC generators for hybrid vehicles, DC generators for battery charging, and the 72 V motor range for the traction side of the same driveline.