How to Fix Danfoss VLT Alarm 48 or A48 1.8V Supply Low?

Staring at Alarm 48 on your Danfoss VFD? This internal 1.8V supply error affects the control card. Learn how to troubleshoot and fix it in our step-by-step guide.

How to Fix Danfoss VLT Alarm 48 or A48 1.8V Supply Low?


Solving Danfoss Alarm 48: Why the 1.8V Supply is Low

If you are looking at your Danfoss VLT® drive and the display is flashing Alarm 48, the drive is reporting a problem with its internal "nervous system." This code stands for 1.8V Supply Low.

In simple terms, the control card (the "brain" of the drive) uses several different voltages to function. The 1.8V DC rail is specifically used to power the microprocessor and logic chips. If this voltage drops below a safe limit, the brain can no longer think clearly or control the motor safely, so it trips Alarm 48. Let’s walk through the steps to determine if this is a glitch or a hardware failure.

What Causes Alarm 48?

When a Danfoss drive trips on Alarm 48, it is almost always an internal hardware issue, but there are a few external factors to check first:

  • Faulty Control Card: The most common cause. A capacitor or voltage regulator on the control board has failed.
  • Loose Connection: The ribbon cable or the physical connection between the control card and the power card is loose.
  • Option Module Overload: A faulty fieldbus card (Profibus, Profinet) or encoder module is drawing too much power from the control card.
  • Extreme Ambient Temperature: High heat in the cabinet can cause the internal voltage regulators to drift out of spec.
  • Electrical Noise (EMI): Massive electrical interference is "clouding" the internal voltage sensors.

Step-by-Step Troubleshooting for Alarm 48

1. The "Cold Boot" (Full Power Cycle)

Before you replace any parts, try a deep reset.

  • Turn off the main power to the drive.
  • Wait: You must wait for the display to go completely dark and for the internal capacitors to discharge (usually 5–15 minutes).
  • Restore power. In some cases, a minor logic glitch caused by a power surge will clear during a fresh boot-up.

2. Remove Option Modules

If the alarm persists, an external card might be "starving" the control card of its 1.8V supply.

  • Power down the drive and remove any expansion cards (Slot A or Slot B modules).
  • Power the drive back up.
  • If Alarm 48 disappears: One of your option modules is faulty and is shorting out the 1.8V rail.
  • If Alarm 48 stays: The problem is definitely in the control card itself.

3. Reseat the Control Card

Vibration is a common cause of internal "phantom" faults.

  • With the power OFF and Locked Out, carefully unclip the control card from the front of the drive.
  • Inspect the pins where the control card plugs into the power card. Ensure there is no dust, corrosion, or bent pins.
  • Push the card back in firmly until it clicks. A solid connection is required for stable internal voltages.

4. Check the Ambient Temperature

If your drive only trips on Alarm 48 during the hottest part of the day:

  • Ensure the cooling fans on the drive are spinning.
  • Check the cabinet filters. High heat increases the internal resistance of the control card, which can cause the 1.8V rail to sag.

When to Replace the Control Card

If you have cycled the power, removed the options, and reseated the card, but Alarm 48 remains, the internal voltage regulator has physically failed.

The Fix: You will likely need to replace the Control Card.
Tip: Look for the part number on the side of the card (e.g., 130B1107). Swapping the control card is much faster than replacing the entire drive, but remember you will need to reload your parameters!

Summary

The Danfoss Alarm 48 is an internal "health check" failure. It’s the drive's way of saying its brain isn't getting enough fuel. Start with a Full Power Cycle and a Module Check. If the fault persists, it’s time to swap the control card for a new one to get your machine back in production.

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