Battery Charging Voltage Above Upper Limit

Common Symptoms

• COMMANDER display shows fault code 5 and the unit shuts down or holds in standby
• Battery feels warm or hot to the touch shortly after startup
• Electrolyte bubbling or white crust visible around battery terminals
• Lights flicker or run brighter than normal before shutdown
• STOP or alarm indicator illuminates on the operator panel
• Unit cranks and runs briefly then trips offline within minutes of starting
• External battery charger was left plugged in while the engine is also running

Probable Causes (Ranked by Likelihood)

• Alternator voltage regulator stuck in full-field mode, pushing DC charging voltage above 15.5V on a 12V system Very Likely
• External battery charger left connected and active while the engine is running, stacking voltage on top of the alternator output Very Likely
• Failed or shorted zener diode in the alternator rectifier bridge causing unregulated output Likely
• COMMANDER controller battery voltage sense wire shorted to a higher voltage source, giving a false high reading Possible
• Corroded or loose battery ground strap creating a voltage offset that the controller reads as overvoltage Possible
• Wrong battery installed (24V battery in a 12V system) after a recent service Less Likely
• COMMANDER controller internal voltage monitoring circuit fault requiring controller replacement Less Likely

Step-by-Step Diagnostic Procedure

1. Set the tower to OFF on the operator panel and disconnect any external battery charger before you do anything else. A charger left on the battery while the engine runs is the single most common cause of code 5.

2. Measure DC voltage directly at the battery terminals with a multimeter before starting. A fully charged 12V battery should read 12.4V to 12.8V at rest. Anything above 13.2V at rest means a charger or another source is still active.

3. Start the engine and let it reach operating RPM (typically 1800 RPM at full load). Measure DC voltage at the battery terminals again. Normal charging range is 13.8V to 14.8V. A reading above 15.0V confirms the alternator or regulator is overcharging.

4. Inspect the alternator charge wire and the COMMANDER battery sense wire (usually a small-gauge wire separate from the main charge cable). Look for chafing, bare copper touching a 24V accessory circuit, or a splice that should not be there.

5. Check the battery terminals and ground strap. Clean any green or white corrosion with a wire brush. A bad ground can cause phantom voltage readings at the controller. Torque the ground strap bolt snug and re-measure.

6. If voltage at the battery is confirmed above 15.0V with the engine running and no external charger connected, the alternator regulator is the prime suspect. Swap the alternator with a known-good unit or bench-test the regulator. This step requires basic electrical knowledge and a second alternator to confirm.

7. If battery voltage is actually normal (13.8V to 14.8V) but code 5 still fires, backprobe the COMMANDER sense wire at the controller connector with the engine running. Compare that reading to the battery terminal voltage. A difference greater than 0.5V means you have a wiring fault between the battery and the controller, not an actual overvoltage condition.

8. If all wiring checks out and the fault persists, the COMMANDER controller itself may have a failed internal reference. Document your voltage readings and contact your Allmand dealer or distributor. Controller-level diagnosis and replacement is an advanced repair.

Frequently Asked Questions