What to Watch for When Buying a Used Generator?
kVA calculation, engine hours, alternator test and load test: the guide to the right choice in a used generator.
Short answer: First define your need with the right kVA (20–25% above total load + motor starting currents), then watch voltage/frequency stability under a load test. On a generator that looks lightly used, the real risk is standstill corrosion: gaskets, hoses and stale fuel.
This guide answers: How many kVA should I buy? · Why is a load test essential? · How is alternator health assessed? · Should I buy a low-hour but old generator?
- Correct kVA = total load + motor starting factor + a 20–25% margin
- On a stored generator the risk is corrosion and gaskets, not hours
- A generator is not bought without a load test — no-load running is misleading
- The switchgear is not deemed sound until the ATS scenario is tried on-site
How many kVA are needed?
Add up device rated powers, account for the starting factor (3–6x) on motor loads, and leave a 20–25% margin. You can use the calculator on the site.
How is a load test done?
Not every generator that runs smoothly at no load is sound; apply load in steps and watch voltage deviation and frequency fluctuation. Black smoke points to fuel/injector, blue smoke to oil burning.
Alternator and switchgear
Ask for a winding insulation (megger) test result; if there is an automatic transfer switch (ATS), try the mains cut/restore scenario on-site.
Frequently asked questions
How important is the hour count? On a generator, the maintenance regime matters more than hours; a 200-hour machine stored for 8 years is risky.
Canopied or open? Canopied for outdoors and noise rules; an open type may suffice in a plant room.
For the current price range: valuation tool · listings for sale · cost calculators
Last updated: 06.07.2026 · This guide is based on field practice and platform data; it does not replace a technical inspection.
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