Solar Inverter Overload Issue: The Hidden Cause

At MSPD Africa, one of the most common questions we get from solar installers and technicians is:

“Why does my inverter appear to be overloading when starting certain appliances, yet I can’t see this reflected on the monitoring or inverter screen?”

The answer lies in a lesser-known concept related to inrush current in solar inverters — also known as startup current.

What Is Inrush or Startup Current?

Inrush current is the brief surge of electricity that occurs when you start a motor or an inductive load like a water pump, fan, or compressor. This surge is significantly higher than the appliance’s running current and typically lasts for only a fraction of a second.

What Causes Startup Current Spikes in Hybrid Inverters?

To demonstrate this, we set up a real-world test at our MSPD Africa premises. At the time, our building was running around 10 to 12 kW of load on a single 30 kW inverter. A second inverter was disconnected for this test to isolate the results.

We then started two motors concurrently:

• A three-phase generator
• A single-phase water pump

While these started up, our team monitored both the inverter screen and the online monitoring portal.

What Did We See?

Interestingly, you could barely detect the startup loads on either the monitoring software or the inverter’s display screen. That’s because these inrush events last for about 0.07 seconds (7/100ths of a second) — far too short for most monitoring systems to register.

This short burst is still real and powerful, but unless you’re using the right tools, it’s easy to miss.

Measuring Initial Surge in Energy Storage Inverters

The only reliable way to capture inrush current is by using an inrush current meter. For our test, we used a clamp meter placed directly on the positive wire of each load from the distribution board.

These meters are specifically designed to detect and record short-duration current spikes, giving accurate readings that other systems can’t.

How to Handle Peak Load at Startup in Battery Inverters

If you’re troubleshooting why your inverter seems to trip or overload during motor starts — but see no data to support it — chances are you’re dealing with inrush current.

Understanding and measuring inrush helps you:

• Size your inverter correctly
• Prevent overloads
• Accurately assess performance

Stay tuned for more practical solar insights from the MSPD Africa team.

Watch the video here.