Parallel Inverter Error: Why Parallel Inverters Stop Syncing

What a parallel inverter error means

When inverters run in parallel, they share one AC output (or form three phases together). To do that safely, every unit must produce exactly the same voltage, frequency and phase at the same instant. One unit acts as the master and the others follow it, exchanging data many times a second over a dedicated communication link, usually a CAN cable between the parallel ports.

If that data stops, arrives late, or shows that one unit is different from the others, the units cannot safely share load. They raise a fault and either drop out of parallel mode or switch off. Our guide to running two inverters in parallel explains how these systems are designed; this page is about what to do when one shows an error.

Typical parallel fault codes

Codes are different for every brand, so always check your own manual. As an example, the parallel manual for one widely sold low-voltage hybrid platform lists these:

Our brand guides to Solis inverter error codes, Inverex inverter error codes and Knox inverter fault codes cover those brands.

Quick-check table: parallel inverters not syncing

Safety first

Safety box. Parallel systems carry large battery currents and live AC from more than one source. Never unplug or swap parallel or battery cables while any unit is on, never open inverter covers, and do not change DIP switches or parallel settings. If you smell burning or see heat marks on cables, switch off in the manufacturer's sequence only if you can do so safely, keep away and call a qualified engineer.

Safe owner checks, step by step

1. Photograph every inverter screen with the fault showing. Note which unit shows which code and the time.
2. Note what happened just before: load-shedding, a generator start, a storm, a firmware update, someone working on the wiring, or a heavy load starting.
3. Read the battery voltage and SOC on each unit. In a shared-battery system they should read almost the same. Write the values down.
4. Read the load and output on each unit. In a healthy parallel system the load is shared fairly evenly.
5. Read the firmware version on each unit if the menu shows it (view only).
6. Look, do not touch: is the parallel cable between units visibly unplugged, crushed or chewed? Are there heat marks on battery cables?
7. Reduce the load if the fault came with overload or current unbalance. See inverter overload.
8. Restart only in the manufacturer's sequence, once. Parallel systems usually need every unit switched off and started in a set order. See how to restart a solar system safely. If the error returns, stop and call.

Parallel cable error and other causes an engineer will check

A parallel cable error is the most common single cause, but an engineer will look at the whole chain:

• Communication cabling: the right cable type, plugged into the correct ports in the correct chain order, good connectors, not run alongside power cables. Solis, for example, links units in a daisy chain from Parallel-A to Parallel-B ports and sets DIP switches ON only on the first and last unit.
• Unit IDs and master/slave roles: each unit needs a unique ID, and only one master. Solis sets the master as ID 1 and slaves from 2 upward.
• Firmware: all units on exactly the same version. Solis requires matching firmware before connecting, and the low-voltage hybrid manual above lists a separate fault for a mismatch.
• Same model and rating: mixing models, ratings or hardware generations is generally not supported. Solis allows up to six hybrid units in one parallel system, all the identical model.
• Battery arrangement: many low-voltage hybrids require all units to share one battery bank, with battery cables of equal length, or they go into fault. Others give each unit its own battery. See battery and inverter communication.
• AC wiring: equal cable lengths from each unit to the common busbar, neutrals connected together where the manual requires, and grid breakers closed together. The manual above notes that if grid breakers are not closed at the same time, later units can show a sync fault.
• Phase settings in three-phase parallel systems: each unit set to the correct phase, and the incoming phases matching those settings. See inverter phase loss error.
• Generator input: an unstable generator can make units see different input frequency and lose sync.

How to prevent parallel inverter errors

• Design parallel systems properly from the start: identical models, the battery layout the manual specifies, equal cable lengths and correct protection. Our parallel inverters guide lists the rules.
• Update firmware on all units together, never on one alone.
• Leave settings to your installer, changed through the master as the manual instructs.
• Protect the communication cable from rodents and heat.
• When replacing one inverter, match the model and firmware exactly, or plan to replace the set. See replacing a faulty solar inverter.
• Consider one larger three-phase inverter for bigger homes and businesses instead of several small units. Our guides to three-phase vs single-phase inverters and 12 to 20 kW three-phase hybrids compare the options. Current models are on our solar inverter price page.

If the inverters restart over and over rather than showing a single fault, see inverter keeps restarting. For other alarms, start with our solar inverter faults guide or the solar troubleshooting guide.

How Solar Works Pakistan helps

We design parallel and three-phase hybrid systems in-house, and our own engineering team handles after-sales complaints on systems we install. WhatsApp 0336 666 4321 with photos of every inverter screen, the inverter models and the fault codes. We target sending service personnel within 48 hours of a registered complaint to begin diagnosis; fix time depends on the fault, firmware and parts, and may involve the manufacturer. Our 1-year service warranty applies under the applicable project terms. See how after-sales service works.

We can also diagnose parallel faults on systems installed by other companies, as a chargeable service, across Punjab.

Frequently asked questions

What does parallel inverter error mean?

It means inverters working together have lost communication or synchronisation, or have found a difference in settings, firmware, battery voltage or grid input. They stop sharing load or shut down to stay safe.

Why are my parallel inverters not syncing?

Common reasons are a loose or damaged parallel cable, different firmware or settings on one unit, unequal battery or AC wiring, or the grid or generator being seen differently by each unit. An engineer checks each of these in turn.

What is a parallel communication fault?

It means the data link between the inverters, usually a CAN cable between the parallel ports, has failed or is giving errors. The cable, its ports, the chain order or the end-of-line settings can be the cause.

How do I fix a parallel cable error?

Do not unplug or swap the cable yourself while the system is on. Take photos of the screens and the cable and call your installer, who will power down in the correct order and check the cable, ports and settings.

Can I run two different inverters in parallel?

Generally no. Parallel operation needs identical models, ratings and firmware. Mixing brands or generations usually causes faults even if it seems to work at first.

Why do my parallel inverters fault after load-shedding?

When the grid returns, units can see it at slightly different moments, or one grid breaker closes before another. Some manuals note this as a cause of sync faults. If it happens after every outage, ask for the wiring and settings to be reviewed.

Does a firmware update cause parallel errors?

It can, if only one unit is updated. All units in a parallel system must run the same firmware version.

Sources

1. MUST Power, EP1800 manual for parallel connection (parallel fault codes 80-90, shared battery, equal cable lengths, firmware, grid breaker closing)
2. Solis, "Hybrid Inverters Parallel Communication Setup Params" (identical models, up to six units, daisy-chain cabling, DIP switches, master ID, matching firmware)