WhisperWatt DCA-25 Load Sharing Imbalance: Parallel Operation Fix

Understanding Load Sharing Imbalance

Parallel operation of diesel generators is a reliable way to increase available power and redundancy on job sites and remote installations. When configured correctly, two or more WhisperWatt DCA-25 units should automatically balance the electrical load between them. But when that synchronization fails, you end up with one unit working hard while the other idles—wasting fuel, accelerating wear on the overloaded machine, and potentially triggering overload shutdowns.

Load sharing imbalance doesn’t mean your generators are broken. It means the communication and control systems that keep them in sync have drifted out of specification. The good news is that most causes are adjustable without replacing major components.

At-a-Glance: Most Likely Causes

Diagnostic Walkthrough

Before you start, ensure both generators are running under the same load conditions, synchronized to the same frequency (50 Hz or 60 Hz depending on your region), and that you have a multimeter and basic hand tools available.

1. Check paralleling cable connections. Shut down both units and visually inspect all parallel bus bar connections—the thick cables linking the two generators. Look for corrosion, loose terminals, or burned insulation. Corroded or loose connections add resistance to the circuit, causing voltage drop and triggering unequal load distribution. Use a wire brush to clean any oxidation and tighten all terminal bolts to the torque specification in your manual (typically 25–35 ft-lbs for M8 bolts). This is the cheapest fix and often solves the problem immediately.
2. Measure voltage at both units under load. Start both generators and bring them to full synchronization. Using a multimeter set to AC voltage, measure the output voltage at the terminals of Unit 1, then Unit 2. They should match within 1–2 volts. If one reads significantly higher (e.g., 245V vs. 255V), that unit’s AVR is over-compensating and will attract more load. Note the readings for the next step.
3. Verify droop settings are identical. The droop setting is a potentiometer or digital adjustment on the speed governor that tells each unit how much to reduce speed as load increases. If Unit 1 is set to 2% droop and Unit 2 to 4%, they will never share load equally. Consult your DCA-25 manual for the location of the droop adjustment—it’s usually on the governor control panel. Both units must be set to the same value (typically 2–5%). Adjust slowly and retest after each change.
4. Check governor calibration with a tachometer. At no-load (idle), both units should run at the same frequency. Use a portable tachometer or frequency meter to verify this. If one unit runs 50.5 Hz and the other 49.8 Hz at idle, the governors have drifted. The governor speed adjustment screw (usually on the fuel pump linkage) may need recalibration. This requires care—make small adjustments (quarter-turn increments) and allow 30 seconds for the engine to stabilize before measuring again.
5. Inspect current transformer (CT) connections. Current transformers on the DCA-25 sense load and feed that signal back to the paralleling controller. Loose CT wiring or a disconnected CT will cause the controller to “see” an unequal load even when it’s balanced. Locate the CTs (usually mounted on the output busbar or inside the control enclosure) and verify all wiring is secure and labeled correctly. If a CT is loose, tighten it and retest.
6. Test AVR response time. A sluggish AVR will respond slowly to load changes, allowing one unit to drift ahead of the other. With both units running in parallel, apply a sudden load increase (turn on a large motor or heater) and observe whether both units’ voltage dips equally and recovers at the same rate. If one unit’s voltage sags more or recovers more slowly, that AVR may be fatigued. Note which unit, as you may need to replace its AVR module.
7. Verify CT ratio labeling. Each DCA-25 should have a nameplate showing its CT ratio (e.g., 100/5 or 150/5). If one unit has a 100/5 CT and the other has a 150/5 CT, the paralleling controller will calculate load incorrectly for one of them. Check the nameplates on both units. If ratios don’t match, you’ll need to replace one CT or reprogram the controller (if it’s adjustable) to account for the difference. This is a less common issue but critical if present.
8. Perform a full load balance test. With both units synchronized and running under a steady, known load (e.g., 50% rated capacity), measure the current output from each unit using clamp meters on the output leads. They should be within 5% of each other. If they’re not, and you’ve completed steps 1–7, the issue may be in the paralleling controller itself, which requires professional service.

Parts You May Need

• Paralleling cable (appropriate gauge for your installation)
• Terminal lugs and connectors (copper, tinned)
• AVR module (if replacement is needed)
• Current transformer (CT) module
• Fuel pump governor linkage components
• Multimeter and clamp meter
• Tachometer or frequency meter
• Wire brush and contact cleaner

When to Call a Pro

Stop troubleshooting and contact a qualified diesel generator technician if:

• You’ve cleaned and tightened all connections, matched droop settings, and verified governor calibration, but load imbalance persists.
• One unit’s AVR or governor module shows visible damage, corrosion, or burn marks.
• The paralleling controller displays fault codes or error messages.
• You’re uncomfortable adjusting governor speed or working inside the control enclosure.
• CT ratios don’t match and you don’t have documentation on how to reprogram the controller.
• Load imbalance is severe (one unit carrying 80%+ of the load) and you suspect internal engine damage.

A technician with access to Multiquip factory documentation and calibration tools can diagnose paralleling controller faults, reprogram CT ratios, and replace fatigued AVR or governor modules much faster than trial-and-error troubleshooting.

Frequently Asked Questions

Why does load imbalance happen if both generators are identical?

Even identical units drift over time. Fuel injectors wear slightly differently, governor springs lose tension at different rates, and AVR components age unevenly. Droop and governor settings are field-adjustable precisely because no two units stay in perfect sync without periodic tuning. Paralleling systems are designed to tolerate small differences, but when adjustments haven’t been checked in months or years, drift accumulates.

Can I run the generators in parallel without fixing the imbalance?

Technically, yes—they’ll still produce power. But the overloaded unit will age faster, consume more fuel, and may overheat or trigger automatic shutdown if it exceeds its rated capacity. The underloaded unit will run inefficiently. Over weeks or months, you’ll see higher maintenance costs and reduced reliability. It’s worth spending an hour on diagnostics to avoid those problems.

What’s the difference between droop and governor calibration?

Governor calibration sets the idle speed and full-load speed of the engine. Droop is the intentional speed reduction as load increases—it’s what allows two units to share load proportionally. Both must be correct for parallel operation. Think of calibration as “where the engine runs” and droop as “how the engine responds to load.”

How often should I check parallel load sharing?

If your DCA-25 units run in parallel regularly (daily or weekly), check load balance every 500 operating hours or quarterly, whichever comes first. If they run occasionally, check before each use. A quick visual inspection of connections and a voltage/current measurement takes 15 minutes and prevents costly problems.

Disclaimer

This article provides general troubleshooting guidance for load sharing imbalance on the Multiquip WhisperWatt DCA-25 diesel generator. Always consult your unit’s owner’s manual and shop manual for model-specific procedures, torque specifications, and safety requirements. Diesel generators operate at high temperatures and pressures; improper service can cause injury or equipment damage. If you are unsure about any step, contact a qualified service technician or Multiquip support at https://www.multiquip.com/support/.

Source: Information adapted from official manufacturer documentation (reference). Always consult your generator owner’s manual for model-specific procedures.