The Atlas Copco QAS 125 delivers 100 kW of prime power from a John Deere 4045 HFG04 four-cylinder engine — the first model in the QAS lineup to use a John Deere powerplant instead of Isuzu. The 166-gallon integral tank provides extended runtime, and the unit features DOC and SCR aftertreatment for Tier 4 Final compliance.
The Leroy Somer LSA 44.3 S5 alternator maintains ±0.25% voltage regulation. At 73 dBA, the QAS 125 is louder than the smaller Isuzu-powered models but remains competitive in its class. The unit features 500-hour service intervals and long-run filters for reduced maintenance.
John Deere 4045 platform and extended service intervals#
The transition from Isuzu to John Deere at the 100 kW level brings several advantages. The John Deere 4045 HFG04 is a 4.5-liter four-cylinder diesel used extensively across the generator industry, which means a well-established parts supply chain and broad dealer service network. Oil change intervals extend to 500 hours — double the 250-hour intervals on the smaller Isuzu-powered QAS models — reducing ongoing maintenance costs for high-utilization units.
The Leroy Somer LSA 44.3 S5 alternator steps up from the 42.3 series used in the QAS 25-70, delivering the higher output capacity needed for 100 kW applications while maintaining the same ±0.25% voltage regulation and AREP excitation system that defines the QAS lineup.
The QAS 125 marks the transition point in the Atlas Copco QAS lineup from Isuzu to John Deere power. For service professionals, this is significant — the John Deere 4045 has a broader aftermarket parts ecosystem and a more accessible dealer network than the Isuzu engines in the smaller models. This partially offsets Atlas Copco's well-documented after-sale service shortcomings.
That said, Atlas Copco's own service network remains the brand's biggest weakness. Owners report unreturned service calls, travel charges exceeding $311/hour, and multi-week waits for factory-specific parts (enclosure components, control panels, and Atlas Copco-branded accessories). For QAS 125 owners in Northern California, OnPoint provides local maintenance and repair — we are familiar with both the Isuzu and John Deere powerplants across the full QAS lineup.
Engineering specifications
Acoustic
Sound @ 7m, 75% load
73 dBA
Enclosure
Sound-attenuated
Fuel system & runtime
Integral fuel tank
166 gal
Fuel use @ full load
7.06 GPH
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Get pricing & lead time on the Atlas Copco QAS 125
Tell us about the application — kW, voltage, application, install timeline — and we'll respond within one business day with budgetary pricing, lead time, and any sizing notes.
Adjust load percent and tank size to estimate runtime. Pre-filled with this model's spec where available.
Estimate runtime on this tank
Estimated runtime
30.5 hours(1.3 days)
Fuel consumption ≈ 5.45 GPH at 75% load. Estimate based on industry-typical 1800 RPM standby curves (≈0.07 GPH/kW at full load). Actual consumption varies by engine, ambient temperature, fuel quality, and tuning.
Service intervals
Manufacturer-recommended intervals for the Atlas Copco QAS 125 under standby duty. Field intervals may differ based on load profile, ambient conditions, and fuel quality.
Oil & filter
Every 500 hours or 12 months
Air filter
Every 500 hours
Fuel filter
Every 500 hours
Major overhaul
≈ 20,000 hours
Common failure modes
What we've seen fail on this platform. Use as a service-planning reference, not a diagnostic — actual failure modes depend heavily on duty cycle and maintenance history.
Component
Symptom
Typical hours
Severity
Fuel filter
Restricted fuel flow, hard starting, power loss
500+
minor
Starting battery
Failed start or slow cranking after extended storage
4,380+
minor
Coolant hoses
Weeping at clamp joints, low coolant warning
5,000+
minor
Frequently Asked Questions
What is the prime and standby rating of the Atlas Copco QAS 125?
The QAS 125 delivers 100 kW prime power and 110 kW standby power. It is the first 100 kW model in the QAS lineup and the entry point to the John Deere-powered QAS series.
What engine does the Atlas Copco QAS 125 use?
The QAS 125 is powered by a John Deere 4045 HFG04 4.5-liter inline-4 turbocharged-aftercooled diesel engine running at 1,800 RPM. This is the same engine used in the QAS 95 but paired with a larger alternator to extract 100 kW.
What are the service intervals for the QAS 125?
Oil changes are due every 500 hours or 12 months, whichever comes first. Air filter and fuel filter replacement intervals are 500 hours. Major engine overhaul is specified at 20,000 hours. The John Deere 4045 also requires DEF monitoring for its SCR aftertreatment system.
Is the Atlas Copco QAS 125 EPA Tier 4 Final compliant?
Yes. The QAS 125 is EPA Tier 4 Final and CARB compliant, legal for operation throughout California. It uses DOC and SCR aftertreatment (no DPF) on the John Deere 4045 HFG04 engine.
How does the QAS 125 differ from the QAS 150?
The QAS 150 steps up to the John Deere 6068HFG05 6.8-liter inline-6 engine delivering 120 kW prime vs. the QAS 125's 100 kW. The 6068 is a larger, six-cylinder platform. The QAS 150 also gains a significantly larger 335-gallon fuel tank (vs. 166 gallons) and is paradoxically quieter at 70 dBA vs. 73 dBA.
What fuel does the Atlas Copco QAS 125 use?
The QAS 125 runs on diesel with DEF required for SCR aftertreatment. The 166-gallon integral tank provides approximately 23.5 hours of runtime at full load (7.06 gal/hr) or 30+ hours at 75% load.
Who services Atlas Copco generators in Northern California?
OnPoint Generators provides local service and maintenance for Atlas Copco QAS units across the Bay Area and Northern California. The John Deere 4045 engine in the QAS 125 has broad aftermarket support, and our technicians are familiar with both the Isuzu and John Deere powerplants across the full QAS lineup.
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