I recently encountered a frustrating issue with my Victron-based solar system using lead-acid batteries. Everything seemed fine — until suddenly, nothing worked:
- No charging from any source.
- Inconsistent voltage readings.
- Communication glitches.
- Erratic behavior from inverters and charge controllers.
After hours of troubleshooting, double-checking settings, connections, and even suspecting firmware bugs, I found the unexpected culprit:
A fuse that tested “OK” with a multimeter… but was actually the problem.
The Root Cause
The fuse had partially melted internally. It still showed continuity with a voltmeter (low resistance), but under load it caused a significant voltage drop — enough to confuse the entire system.
In DC systems (especially low-voltage, high-current setups), this type of issue is dangerous:
- The fuse doesn’t blow completely.
- It limits current silently.
- It causes voltage drop that leads to false logic and cascading faults in connected devices.
Key Symptoms
- Everything appears normal when idle.
- Voltage drops drastically under load.
- Devices stop charging batteries or shut down unexpectedly.
- Logs and readings don’t make sense anymore.
Lessons Learned
- Don’t trust continuity tests alone — especially in DC systems.
- Always check voltage drop across fuses under real load.
- If something doesn’t add up and the fuse is old or suspect: just replace it.
- A “passing” fuse might still be a silent killer.
Quick Tip for Victron Users
If your MultiPlus, BMV, or MPPTs are acting weird all at once and nothing charges…
Check your fuses. Even the “good” ones.