Overview#
The Atlas Copco QAS 45 delivers 36 kW of prime power (45 kVA) from an Isuzu 4LE2X turbocharged intercooled engine at 1,800 RPM. It shares the QAS 25's compact platform but steps up power output while maintaining the same 67 dBA sound level and 75-gallon fuel tank.
The Leroy Somer LSA 42.3 S5 alternator provides ±0.25% voltage regulation with AREP excitation. At 2,565 lbs with trailer, the QAS 45 is one of the most compact units in the 35-40 kW portable class, with a footprint up to 20% smaller than previous-generation competitors.
Fuel efficiency and compact design#
The QAS 45 extracts 36 kW from the same 2.2-liter Isuzu block used in the QAS 25, achieving higher specific output through turbocharging and aftercooling. This shared platform strategy keeps the unit compact and parts-common with the smaller model. The Leroy Somer LSA 42.3 S5 alternator with AREP excitation delivers ±0.25% voltage regulation — twice as tight as the ±0.5% standard in most portable generators — making the QAS 45 suitable for sensitive electronics and precision equipment.
The 75-gallon fuel tank, while shared with the QAS 25, provides somewhat shorter runtime at the QAS 45's higher fuel consumption rate. Operators running extended shifts should plan refueling accordingly.
Our service experience#
Atlas Copco's QAS series represents some of the best portable generator engineering available — the sound attenuation, fuel efficiency, and voltage regulation are genuinely best-in-class. However, the QAS 45 specifically has a documented history of coolant system issues that owners should be aware of. We have seen coolant leaks and overheating under sustained high-load operation on this model more frequently than on other QAS units.
Beyond model-specific concerns, Atlas Copco's after-sale service network is a well-known weak point across the brand. Owners frequently report unreturned service calls, travel charges exceeding $311/hour, and multi-week waits for parts. For QAS 45 owners in Northern California, OnPoint provides local maintenance and repair with faster response times and direct experience managing the coolant issues specific to this model.
