Small current powered by diesel genset

Want to know the reasons for a small current powered by a diesel genset? In this blog, we explore common causes like load, sizing, and fuel issues.

June 15, 2023
BY BISON

A diesel genset that delivers unexpectedly low current output — or fails to reach its rated amperage — is a common frustration on job sites, farms, and backup power installations. The root cause can range from a simple mismatched load to a failing voltage regulator, poor fuel quality, engine wear, or environmental factors like high altitude and extreme temperatures.

Want to know the reasons for a small current powered by a diesel genset? In this blog, we explore common causes like load, sizing, and fuel issues. Let’s get started.

Common causes of low current output in diesel gensets

Low current output from a diesel genset rarely has a single cause. The factors that affect output fall into three broad categories — issues with the genset itself, problems with fuel or how the unit is operated, and environmental conditions that reduce performance.

1. Genset-side factors

Genset-side factors are problems originating within the generator set itself — from how it is matched to the load, to failures in its electrical or mechanical components. These are the most common culprits and should be checked first.

Load demand

If the connected load is much smaller than the genset’s capacity, the current output will be reduced. Similarly, a genset that is oversized for the connected load will produce lower current — the unit only generates what is demanded of it. These two issues are two sides of the same coin: a mismatch between the genset’s rated output and the actual load it serves.

Solution: Check with a clamp meter against the nameplate rating; if the load is too light, either add equipment to bring it above 30% of rated capacity or switch to a smaller genset.

Voltage regulator (AVR) failure

A faulty voltage regulator (AVR) can prevent the genset from producing the necessary voltage to drive the load. The AVR controls the excitation current fed to the alternator; when it fails, voltage sags and current output drops accordingly.

Solution: Measure output voltage with a multimeter at no load — if consistently below specification, the AVR likely needs replacement.

Alternator & electrical component issues

Several electrical faults inside the alternator and its connections can cause low current output:

Loose or broken cables, diodes, or armature coils
Low regulator voltage
Belt slip
Partial short circuit
Poor contact or increased resistance
Control panel malfunctions

Solution: Visually inspect all accessible wiring and terminals for looseness or corrosion; check diode continuity with a multimeter. Internal armature faults or shorts require a professional technician with a megger tester.

Engine wear & mechanical issues

Engine wear (e.g., worn rings or valves) reduces compression, preventing the engine from producing enough torque to drive the alternator. Loose belts also cause slippage, dropping output speed.

Solution: perform compression tests, check for abnormal exhaust smoke, and regularly inspect or replace drive belts to restore power.

perkins-remote-diesel-alternator-gensets-6

2. Fuel & operational factors

Even a mechanically sound genset will underperform if the fuel supply is compromised or if it is operated well outside its designed load range. These factors are often overlooked but are among the easiest to correct.

Poor fuel quality

Contaminated fuel or fuel with low energy content can prevent the genset from reaching its required power output.

Solution: Inspect a fuel sample for cloudiness or separation; check the fuel filter for sludge. If in doubt, drain and replace the fuel.

Cold-weather fuel gelling

At low temperatures, diesel fuel can gel due to paraffin crystallization, clogging fuel filters and altering the air-fuel ratio.

Solution: This can be prevented by winterizing fuel or using anti-gelling additives.

Improper load operation (wet stacking & the 80% rule)

Gensets are preset for specific output levels and are ideally run at 80% of capacity for continuous use (100% in emergencies). Extended operation below 30% load can cause “wet stacking,” leading to unburned fuel buildup and engine damage.

Solution: If your load is consistently low, periodically run the unit at 70–80% capacity for 30–60 minutes to burn off deposits.

3. Environmental factors

Gensets are designed to produce a specific amount of power under standard temperature and pressure (STP) conditions. Deviations from these conditions can reduce output, especially in extreme environments — for example, altitudes above 5,000 feet or ambient temperatures above 100°F.

High altitude

High altitude reduces air density, which affects ignition and cooling. For every 1,000 feet of altitude increase, diesel gensets should typically be derated by 2–3% of their standard output.

Temperature

High temperatures may also be associated with lower air density and can create similar ignition problems due to insufficient air supply. This burdens the engine that propels itself to deliver the power it was designed for. However, it failed to do so due to inadequate oxygen levels available for combustion. In many of these cases, the engine overheats and sometimes crashes completely.

Humidity

Humidity measures the water content in a given volume of air. High humidity displaces oxygen in the air, affecting ignition since oxygen is needed for combustion.

Derating

Altitude, temperature, and humidity cumulatively reduce power output. Derating combines these environmental factors into a single correction factor to estimate real-world performance versus nameplate ratings. As formulas vary by manufacturer, always refer to your BISON model’s specification sheet.

Solution: Calculate your site’s expected derated output first. If actual performance is significantly lower, check the engine and fuel issues mentioned above. For permanently challenging environments, a turbocharged or higher-capacity unit may be a better long-term fit.

Summary

The causes of small currents powered by diesel gensets can vary widely but typically include load demand, generator size, component failure, poor fuel quality, and engine wear. Proper maintenance and troubleshooting can help identify and resolve these issues to keep your genset running at optimal capacity.

As a leading diesel genset manufacturer committed to engineering excellence, BISON prioritize robust performance and standardized reliability, helping you minimize maintenance needs and power loss. Choose to partner with BISON, to provide your customers with high-efficiency, long-lasting power solutions designed to excel in any environment.

FAQs

How much electricity can a diesel generator generate?

Unit sizes from 8 to 30 kW (also 8 to 30 kVA single phase) for homes, small shops and offices, larger industrial generators from 8 kW (11 kVA) to 2,000 kW (3 phase 2,500 kVA) used in office buildings, factories and other industrial facilities.

What type of current does a diesel generator produce?

Diesel generators use a series of steps to produce alternating current (AC). The process begins when a diesel (internal combustion) engine converts some of the chemical energy in the fuel into rotational mechanical energy.

Why is the output of the generator reduced?

Generators are typically designed to operate most efficiently at or near sea level under standard temperature and pressure (STP) conditions. Any fluctuations in STP conditions can damage the generator and cause output to drop. In extreme cases, the generator may stop running altogether.

What happens if the voltage is too low?

If the voltage is too low, the amperage will increase, which can cause components to melt or cause the device to malfunction. If the voltage is too high, it will cause the appliance to run “too fast and too high”, shortening its lifespan.

What makes a generator more powerful?

To increase the generator’s power, you can replace the magnets with stronger magnets or replace the coils. The new coil must have more windings than the previous coil. The more windings the coil has, the more power the generator can output.

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Winnie

Taizhou BISON Machinery Industry CO.,LTD

6+ years of expertise in generator export. A specialist in BSCI and international standards (EPA, EURO V, CE). Dedicated to providing professional solutions for generators, genest, and generator parts with a global perspective.

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