WiremanWireman · Standby generator fails its exercise: troubleshooting for electricians · 2023 NEC ·
Standby generator fails its exercise
Battery, charger power, controller settings and fuel. Engine work goes to the dealer.
Before you start
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How it works
A standby generator runs a short exercise on a schedule set in its controller, so problems show up before an outage. The controller needs its battery to crank the engine, and the battery is kept charged by a charger that runs from utility power through a small circuit to the generator. Most failed exercises come down to a weak battery, a charger that has lost its power, a controller that is off or has the wrong clock, or fuel. Engine and fuel repair belong to the manufacturer’s dealer.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- What does the controller show?
- Blank display or deadTest: Measure the batteryExpect: A 12 V lead-acid battery at rest reads about 12.6 V when fully charged. With the charger working, it should read higher than that, roughly 13 to 14 V; check the manual for the charger’s float voltage.
- Low, and doesn’t rise with utility onTest: Check utility power to the chargerExpect: About 120 V at the charger supply.
- No voltage at the chargerThe battery charger has no power
- 120 V present, charger not chargingFailed battery charger
- Low, rises with utility onWeak or worn-out battery
- GoodController or starter problem
- Low, and doesn’t rise with utility onTest: Check utility power to the chargerExpect: About 120 V at the charger supply.
- Low battery or cranking alarmTest: Measure the batteryExpect: A 12 V lead-acid battery at rest reads about 12.6 V when fully charged. With the charger working, it should read higher than that, roughly 13 to 14 V; check the manual for the charger’s float voltage.
- Low, and doesn’t rise with utility onTest: Check utility power to the chargerExpect: About 120 V at the charger supply.
- No voltage at the chargerThe battery charger has no power
- 120 V present, charger not chargingFailed battery charger
- Low, rises with utility onWeak or worn-out battery
- GoodController or starter problem
- Low, and doesn’t rise with utility onTest: Check utility power to the chargerExpect: About 120 V at the charger supply.
- Running, but at the wrong time or neverController off, or schedule and clock wrong
- Cranks but won’t start, or a fuel or engine alarmFuel or engine problem
- Blank display or deadTest: Measure the batteryExpect: A 12 V lead-acid battery at rest reads about 12.6 V when fully charged. With the charger working, it should read higher than that, roughly 13 to 14 V; check the manual for the charger’s float voltage.