Danfoss FC302 Alarm 48 — What It Means
Alarm 48 (WARNING 48, 1.8 V supply low) on a Danfoss VLT FC 302 indicates that the drive has detected the 1.8 V DC supply on the control card is outside allowable limits. This is an internal electronics problem, not a motor or load issue. Danfoss troubleshooting points directly to the control card as the primary suspect, with option card overvoltage as a secondary contributor if an option card is installed.
The 1.8 V rail powers critical control-card circuitry. When it drops or becomes unstable, the drive cannot safely regulate itself and throws this warning. Field repair focuses on replacing the control card rather than component-level board repair, because the 1.8 V supply circuitry is integrated into the card assembly.
Common Causes
- Defective control card The 1.8 V supply circuit on the control card has failed or degraded, and Danfoss identifies this as the primary cause for Alarm 48.
- Option card overvoltage An installed option card feeding abnormal voltage back to the control card can pull the 1.8 V rail out of spec.
- Loose or corroded control-card connector Poor contact at the control-card connector can interrupt the 1.8 V supply path and trigger the low-voltage alarm.
- Contamination or moisture on the control card Dust, conductive debris, or humidity can create leakage paths that load down the 1.8 V rail below threshold.
- Internal power-supply fault A fault in the drive’s internal DC supply section that feeds the control card can starve the 1.8 V regulator.
Step-by-Step Fix
- Disconnect all power to the VFD and follow lockout/tagout procedures before opening any covers or touching internal components.
- Open the drive enclosure and locate the control card (the main logic board, typically mounted in the upper section of the FC 302).
- Inspect the control card and connectors for obvious damage, burn marks, corrosion, loose ribbon cables, or contamination on the board surface.
- Check for installed option cards and verify connections. If an option card is present, remove it temporarily and attempt to clear the alarm to rule out option-card overvoltage.
- Measure the 1.8 V supply at the control-card test points (if accessible and you have the technical datasheet). If the reading is significantly below 1.8 V, the control card is defective.
- Replace the control card with a genuine Danfoss FC 302 control PCB. Transfer any configuration backup or re-program drive parameters after installation.
- Power up the drive and monitor for Alarm 48. If the fault clears and the 1.8 V supply is stable, the repair is complete. If the alarm persists, inspect the main power-supply section and contact Danfoss technical support for deeper diagnostics.
Parts Often Needed
| Part | Notes |
|---|---|
| Danfoss FC 302 control card (control PCB) | Amazon | Main logic board for the FC 302. Verify your exact drive model and firmware revision before ordering. |
| Option card (if installed) | Amazon | Only if the installed option card is found defective or causing overvoltage during testing. |
When to Call a Pro
Call a qualified VFD technician or contact Danfoss technical support if you are not comfortable working inside energized or recently de-energized industrial drives, if you do not have the tools to measure low-voltage DC supplies safely, or if replacing the control card does not clear Alarm 48. Control-card replacement requires proper ESD handling, parameter backup, and sometimes firmware/configuration tools. If the drive is under warranty or part of a critical process line, professional service ensures you preserve warranty coverage and minimize downtime.