Delta ASDA-B2 Servo Fault AL003 Under Voltage

Getting the AL003 error on your Delta ASDA-B2 servo drive? This guide explains how to troubleshoot under-voltage issues, check main circuit power, and verify wiring to get your machine running again.

 

If your Delta ASDA-B2 servo drive has stopped and the display is flashing AL003, the system has detected an Under Voltage condition in the main circuit. This is a protective state that prevents the drive from operating when there isn't enough electrical "pressure" to move the motor safely or maintain torque.

While this might sound like a major failure, it is often caused by external power issues or simple wiring mistakes. Here is a human-made guide to help you find the root cause and restore your servo system to full operation.

What Exactly is an AL003 Fault?

The ASDA-B2 monitors the DC bus voltage—the internal reservoir of power that drives the motor. If this voltage drops below the factory-defined safety threshold (usually due to low incoming AC power), the drive trips the AL003 alarm. If it didn't do this, the motor could stall, overheat, or move erratically under load.

Common Causes of AL003

• Low Input Voltage: The incoming AC power is sagging or is lower than the drive’s rated requirement.
• Missing Main Power: You might have power to the control circuit (L1c, L2c), but the main power (L1, L2, L3) is missing.
• Tripped Breaker or Fuse: An upstream circuit breaker has tripped or a fuse has blown.
• Faulty Power Contactor: If your system uses a magnetic contactor to feed the drive, the contacts may not be closing properly.
• Incorrect Power System: Attempting to run a 220V rated drive on a 110V supply, or using an incompatible phase configuration.

Step-by-Step Troubleshooting Guide

1. Check the "Dual" Power Terminals

The Delta ASDA-B2 drive uses two sets of power inputs. A common mistake is only powering one set.

• L1c and L2c: These power the Control Circuit (the screen and logic). If these have power, the screen will be ON.
• R, S, and T (or L1, L2, L3): These power the Main Circuit (the motor). If these terminals are empty or the power to them is cut, the drive will display AL003 even if the screen is lit up.
• The Fix: Ensure both the control power and the main power terminals are properly wired and energized.

2. Measure Incoming AC Voltage

Use a multimeter set to AC Volts to measure the voltage at the drive's input terminals.

• Measure between L1-L2, L2-L3, and L1-L3.
• Result: If the voltage is significantly lower than the rating on the drive's nameplate (e.g., measuring 160V on a 220V system), the issue is your facility's power supply or a transformer.

3. Inspect Upstream Hardware

If there is 0V at the drive terminals, follow the wire backward:

• Check the Magnetic Contactor (MC). Does it click when you try to enable the machine? If not, the coil might be dead or the PLC signal is missing.
• Check for a blown fuse or a tripped circuit breaker in the control cabinet.
• Ensure the emergency stop (E-Stop) isn't cutting the main power to the drive while leaving the control power active.

4. Parameter Check (Advanced)

While AL003 is usually a physical wiring issue, ensure the drive isn't being "fooled" by noise or settings. In some cases, a high-resistance connection at the terminal can cause the voltage to "dip" only when the motor tries to move. Tighten all screw terminals to ensure a solid connection.

Summary Checklist

Checkpoint	Desired State
L1c / L2c Terminals	Should have stable control voltage (Logic ON).
R, S, T Terminals	Should match the drive’s rated input voltage.
Main Breaker / MC	Must be CLOSED (ON) during operation.
Voltage Range	Must be within +10% / -15% of the nameplate rating.

How to Reset the Fault

1. Identify and fix the power interruption (e.g., reset the breaker or fix the wiring).
2. Power the drive OFF completely and wait for the screen to go blank.
3. Power the drive back ON.
4. If the main power is restored correctly, the AL003 alarm will disappear, and the drive will show "bb" (Baseblock) or "Ready."