How to Buy a Diesel Generator Set from China: Sizing and the RFQ

Size from the load list, never from a guess

Write down every load the set must carry, with its running power and — for motors — its starting demand. Sum the running loads that operate simultaneously, then check the largest single starting event against the set's capability. That total, with the duty margin your practice requires, is your required rating. It is not the building's floor area, not the previous set's badge, and not the size a salesperson suggests. The listed data on this site shows why precision matters: within one catalogue, complete diesel generator sets are listed from a Ricardo series set at 30–50 kW upward, and genset-drive engines span from the 4BTA3.9-G2 at 58 kW to QSB6.7 G4 rows at 168/185 kW. Somewhere in that span is exactly one right size for your load list, and several expensive wrong ones.

Then fix the duty honestly. A standby set that runs during outages lives a different life from a prime-power set that runs daily, and the same engine carries different ratings for the two duties. The listed tables show why the question cannot be skipped: the QSB6.7-G3 is listed at 151/166 kW at 1,500 rpm — paired figures for the same variant at the same speed — and the listing does not state what either figure stands on. State the duty in the enquiry and require the rating basis of the figure you are buying to be confirmed in the quote.

Frequency is a specification, not a detail

Fifty-hertz service runs at 1,500 rpm and sixty-hertz at 1,800 rpm in the listed tables, and ratings move with speed: the 6BT5.9-G2 is listed at 80 kW at 1,500 rpm and 115 kW at 1,800 rpm. A quote that mixes the rows — a 60 Hz rating priced into a 50 Hz project — produces a set that cannot make its nameplate at your frequency. Put the frequency and voltage in the first lines of the enquiry, and check the quoted rating against the row for that speed. The 6BT family page shows the two rows side by side; the 4BT vs 6BT comparison works through a complete small-genset choice using them.

Complete set or genset-drive engine?

Decide which product you are buying. A complete set arrives as a packaged unit — engine, alternator, controls, baseframe, and canopy where the model includes one; the listed Ricardo set at US$22,000 with a minimum of 1 set is the catalogue's published example. A genset-drive engine (the G-variant rows) is for buyers building or repowering their own sets. The two are priced, scoped and warranted as the units they are, and an enquiry that does not say which one it means will be answered with questions, not a price. If noise matters — a hotel, a hospital, a residential standby site — specify a silent set from the start rather than planning to enclose a standard set later; the enclosure is part of the product, and its cost belongs in the comparison from day one.

The five-line RFQ

• Required rating and duty: for example, 120 kW, continuous prime, with the load list attached.
• Voltage and frequency: for example, 400 V, 50 Hz.
• Product form: complete set, or genset-drive engine (name the variant if known).
• Site conditions that affect rating: altitude and ambient temperature, if unusual; noise limit, if any.
• Destination port, so the quote can be built on the delivery terms on record (FOB, EXW, CFR, CIF, DAP or FCA via Tianjin, Qingdao or Dalian).

Close on the written quote

The listed commercial terms for complete units are delivery of 15–30 days and a warranty of 1 year or 1,200 hours, whichever comes first. Treat those as the starting frame, and have the quote restate, for your specific set: the model, the rating and its basis, the scope of supply, the price, the delivery window and the warranty. Read that document the way you would read a contract — because commercially, it is one. A set bought on a chat message and a round number is a dispute scheduled for commissioning day; a set bought on a five-line RFQ and a restated quote is machinery.

Standby versus prime: the decision inside the decision

Buyers often treat duty as a formality. It is not — it changes the number you are allowed to use. A standby rating assumes the set runs during outages, for limited hours, at variable load. A prime or continuous rating assumes it is the site's power supply. The same physical set carries both numbers, and the gap between them is the margin that keeps a prime installation alive. When you read any listed table, ask which basis each figure stands on, and buy the figure that matches your duty. A project that needs continuous-duty output and buys a figure that stands on a standby basis has purchased a problem that will introduce itself during the first long outage.

What the delivered price must contain

An export genset quote is only comparable when its delivery basis is stated. The terms on record for this supplier span FOB, EXW, CFR, CIF, DAP and FCA through Tianjin, Qingdao and Dalian — six different splits of freight, insurance and risk. Two quotes at the same headline price on different bases are different prices. Fix the basis in your RFQ (most buyers ask for CIF or DAP to their port or site), insist that the quote states it, and compare like with like. While you are there, confirm what the set price includes on the machine itself: control panel, baseframe, canopy or silent enclosure where specified, and the documentation set your import process needs. Certificates, as this site states wherever it matters, are available upon request — request them as part of the order, not after the vessel sails.

A note on methanol and other fuels

Everything in this guide is fuel-agnostic except the product itself. If your project's fuel decision points at the methanol line, run the identical sequence — load list, duty, frequency, RFQ, written quote — and add the fuel specification to the confirmations, because the methanol line's per-model data is not published — it has to be produced in the quote. The method does not change when the fuel does; only the confirmations grow by one line.