Problem diagnosis · Victron Energy

Victron Generator Auto-Start Fault — SoC Trigger, Relay Wiring & Frequency Rejection

Your Victron system should start the generator automatically when the battery runs low — but it isn't. Either the generator never starts, starts but the MultiPlus rejects the power, or runs for the wrong duration. This is one of the most common faults in UK off-grid systems that rely on a backup generator.

Start diagnosis

SoC trigger & relay wiring
Frequency & voltage rejection
Run-time & cool-down logic

Generator not starting when your battery runs low?

We review VRM generator run logs, check Cerbo GX auto-start conditions and relay assignment, verify MultiPlus AC input acceptance settings, and identify why the generator isn't responding to low battery.

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13 Trustpilot reviews

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I have a GivEnergy system consisting of two batteries, two inverters and a controlling EMS (Energy Management System) which has not worked since Nov 2025. After six months I discovered Solar Tech Support, reached out to them and Ron phoned me back – how often do you get that service? Could not be more helpful – worked directly with me over the phone, outside what I would call normal working hours. Lucid explanations and we were able to discuss the issues and history using camera and email history. As this was a very rare setup, Ron was able to access an EMS expert in the field to confirm the solution. One sunny day in, I am now only paying for standing charge and a few pence for spikes in grid consumption while battery catches up with house demand.

Ian · May 2026 Trustpilot

When my GivEnergy system had an issue, I was completely left without support and had honestly lost all hope. Thankfully, I searched online and found Ron, which completely turned things around. After sending him a message, he responded incredibly fast and called me to assure me that he would get the problem fixed. I really admire his dedicated, supportive nature and his determination to find a solution. With this kind of outstanding attitude and customer service, he has absolutely secured a future customer in me.

Sree · May 2026 Trustpilot

Ron want out of is way to help, nothing was to much. He was very thorough in what he did Very knowledgeable I would highly recommend Ron and his company He did a fantastic job for me. if you have any problems, he'll do his best to help you out and resolve your problem. I wouldn't hesitate to recommend them

Dennis Brown · May 2026 Trustpilot

Ron took me through a diagnostic to confirm my GivEnergy Inverter had a fault. A common one as it turns out with the AC Inverter. As GivEnergy is defunct there is no immediate fix, aside from sourcing 2nd hand replacement. It may be that a fix becomes available over the summer which would make a lot of GivEnergy customers happy (Again)

Tony Deacon · May 2026 Trustpilot

Contacted Ron with a problem and he sorted it out quickly with no problems at all. Very knowledgeable on anything solar/ batteries. I would recommend him to anyone

Phill · May 2026 Trustpilot

I've spoken to Ron a couple of times with issues with my Givenergy installation. Such a friendly knowledge guy very highly recommended. Thank you very much for resolving my issues

michael fairhurst · May 2026 Trustpilot

Contacted Solar Tech Support in desperation. After explaining the issues I had with my system a diagnosis was made and a solution proposed. Fantastic service, even contacted a manufacturer to arrange replacement parts for me. Great communications, explained all they were doing and what I had to do, clearly and precisly. Followed up to confirm all was ok. Excellent service.

Mr Machin · May 2026 Trustpilot

After GivEnergy went into liquidation, just my luck, my battery started playing up (internal board crashed). Contacted my installer - not interested! Found Solar tech support on a Google search. Sooo glad I found this company! Ron is extremely helpful and has plenty of experience. He soon confirmed what the fault was, and helped me to get my system up and running again. Now moved my GivEnergy account to Solar tech support, and will definitely use again if I have more issues. Unusual to find such a helpful company in these times, no morons reading scripts, just direct contact with the engineer.

Keith Ballard · Apr 2026 Trustpilot

Contacted Solar Tech Support when trying to understand what my Givenergy inverter problem might be and what might be my options. Received good/honest advise which backed up my thoughts.

Hugh Speirs · Apr 2026 Trustpilot

Ron is a super star. Two months ago my GivEnergy battery failed a firmware upgrade leaving it a brick. My installer couldn't/wouldn't fix it. GivEnergy couldn't/wouldn't fix it. Then they went into administration and all hope was lost. A flurry of emails later and Ron had diagnosed the fault (failed USB flash drive, something I'd suspected) and talked me through resolving it. Two months of nothing resolved in about 3 hours. It's great to work with someone who pays attention to the details, knows that they're doing (not just following a script) and gets stuff sorted without a fuss or up-charging.

Christopher · Apr 2026 Trustpilot

I can add to the list of customers who had already 'given up' on GivEnergy due to their appalling customer service, and that was before they went into administration (their Trustpilot reviews don't lie!). So you can imagine my desperation when, having changed my ISP and my Inverter, predictably, proving to be the only device that didn't connect automatically to my new network, I found zero prospect of any customer support with GivEnergy having called in the administrators just five days earlier! The salvation came from Solar Tech Support. My IT advisor stumbled across their web site and some very helpful tips for beleaguered GivEnergy customers, as well as an offer to provide direct assistance. Nothing ventured, I decided to drop them an E-Mail, with very low expectations based on my experience of GivEnergy customer support. Within an hour Ron had responded with some pin point advice, and after a few exchanges of E-Mails he had nailed the problem, enabling the combined efforts of my IT advisor and solar installer to resolve it and reconnect my Inverter. Thank you Solar Tech Support, and Ron in particular, for coming to the aid of a deserted and despondent GivEnergy customer. Expert, razor sharp advice and first class customer service, even though I wasn't officially a customer.

customer · Apr 2026 Trustpilot

This company are a rare gem, I had a very unusual problem following a failed firmware upgrade on my GivEnergy kit. I then found out GivEnergy were in administration and had dismissed all their support staff! None of the usual fixes to try and restore my inverter comms would work, and I looked everywhere, forums, GivEnergy youtube support videos - even AI couldn't figure it out. My installer was talking about huge sums for system replacements, and being vague / evasive about if they'd even install replacement GivEnergy inverter. Enter Solar Tech Support, reassuring and knowledgeable from the very start, I've learnt loads about my solar system though the friendly chat while my engineer worked as he diagnosed the problem and figured out a fix procedure that I've not found anywhere else - amazing . If you need solar system repairs - especially if you like me have been left high and dry by GivEnergy, I cannot recommend this company enough. Give them a call.

Andy Thomas · Apr 2026 Trustpilot

I sent a message on their website regarding a problem I have on my Givenergy system. Although not supplied by Ronald, I thought it was worth an email. Within the hour on a Saturday, he phoned and we discussed the problem. He logged in remotely and gave excellent advice. I'm too far away for his on-site help but he did diagnose the problem and was happy also to chat through my thoughts about an upcoming solar/battery install I'm planning. Great bloke.... if only he was nearer!

Philip · Apr 2026 Trustpilot

Ian · May 2026 Trustpilot

Sree · May 2026 Trustpilot

Dennis Brown · May 2026 Trustpilot

Tony Deacon · May 2026 Trustpilot

Contacted Ron with a problem and he sorted it out quickly with no problems at all. Very knowledgeable on anything solar/ batteries. I would recommend him to anyone

Phill · May 2026 Trustpilot

I've spoken to Ron a couple of times with issues with my Givenergy installation. Such a friendly knowledge guy very highly recommended. Thank you very much for resolving my issues

michael fairhurst · May 2026 Trustpilot

Mr Machin · May 2026 Trustpilot

Keith Ballard · Apr 2026 Trustpilot

Contacted Solar Tech Support when trying to understand what my Givenergy inverter problem might be and what might be my options. Received good/honest advise which backed up my thoughts.

Hugh Speirs · Apr 2026 Trustpilot

Christopher · Apr 2026 Trustpilot

customer · Apr 2026 Trustpilot

Andy Thomas · Apr 2026 Trustpilot

Philip · Apr 2026 Trustpilot

⚡ Safety Warning

Do not open your inverter or interfere with DC cabling. Solar panels produce live DC voltage whenever exposed to light. Always use your DC isolator switch and contact a qualified solar engineer for hands-on fault diagnosis.

Generator auto-start MultiPlus not charging Inverter overload VE.Bus error codes Battery BMS disconnect VRM portal offline Victron hub →

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How Victron generator auto-start works. The Cerbo GX monitors battery SoC (via BMV, SmartShunt, or BMS) and activates its built-in relay when the SoC drops below a configurable threshold. That relay provides a dry contact signal to the generator's remote start circuit. When the battery charges back above the stop threshold, the relay opens and the generator shuts down. The MultiPlus then accepts the generator's AC output as its input source — but only if the frequency and voltage are within tolerance.

Diagnostics

5-step generator auto-start diagnosis

Generator auto-start faults fall into three categories: the generator never starts (trigger or wiring issue), the generator starts but the MultiPlus rejects the power (frequency or voltage), or the generator runs for the wrong duration (condition logic). These steps cover all three.

Verify the auto-start conditions on the Cerbo GX

The Cerbo GX controls the generator start/stop logic. Navigate to Settings → Generator start/stop and check every condition:

Key settings to verify

Auto-start enabled: Must be ON. If disabled, the generator only responds to manual commands.

SoC start threshold: Typically 20–30% for off-grid. If set too low (e.g. 10%), the battery BMS may cut power before the generator triggers.

SoC stop threshold: Typically 80–90%. Must be significantly higher than start to avoid short-cycling. A gap of at least 40–50% is recommended.

Battery voltage condition: If enabled alongside SoC, both must be met simultaneously — this can prevent starting if only one condition is true.

If multiple start conditions are enabled (SoC AND voltage AND load), the generator only starts when ALL conditions are met. Use OR logic if you want any single condition to trigger the start.

Check the relay wiring between the Cerbo GX and the generator

The Cerbo GX built-in relay provides the physical signal to the generator. Two things must be correct — the relay assignment and the physical wiring:

• Relay assignment: On the Cerbo GX, go to Settings → Relay. The relay function must be set to "Generator". It can be accidentally reassigned to temperature alarm, tank pump, or other functions.

• Relay type: The Cerbo GX relay is a normally-open dry contact rated at 6A / 30VDC. It does not supply power — it just closes a circuit. Your generator's start input must be wired across the relay terminals.

• Start signal type: Some generators need a sustained contact closure (relay held closed while running). Others need a momentary pulse (brief closure to start, separate signal to stop). Check the generator manual. Wrong mode = starts then immediately stops, or never starts.

• Wire run: Long wire runs between the Cerbo GX and the generator can suffer from voltage drop if the generator start circuit draws significant current through the relay. Use adequate gauge wire and check for corroded terminals.

If your generator needs more than 6A start current or runs on voltages above 30VDC, use the Cerbo GX relay to drive an interposing contactor rather than wiring it directly.

Diagnose why the MultiPlus rejects generator power after startup

The generator starts but the MultiPlus won't accept the AC input. This is almost always a frequency or voltage issue:

MultiPlus AC input acceptance settings

Frequency window: Default 45–65 Hz. For generators, widen to 40–65 Hz. Cheap portable generators often dip below 45 Hz under sudden load.

Voltage window: Default 180–270V. For generators, widen to 170–280V. Generator voltage sags under load and spikes when load drops suddenly.

UPS function: Enable this for generator use. It improves the MultiPlus response to frequency fluctuations during load changes.

Dynamic current limiter: Enable this to prevent the MultiPlus from drawing its full charge current immediately on generator connection — the inrush can cause the generator to stall or trip.

Check VRM for "AC input not accepted" alarms. VRM logs the frequency and voltage at the moment of rejection, which tells you exactly which parameter was out of range.

Check run-time limits and cool-down conditions

The Cerbo GX generator logic includes timing conditions that can cause unexpected behaviour:

• Minimum run time: The generator won't stop until this period has elapsed, even if the battery reaches the stop threshold. Prevents short-cycling. Typical setting: 15–30 minutes.

• Maximum run time: If enabled, the generator stops after this period regardless of battery SoC. Useful for fuel management but can cause the battery to remain low if the charge time is insufficient. Disable during initial testing.

• Cool-down period: After stopping, the generator cannot restart for this duration. Typical: 3–5 minutes. If the battery drains quickly (high load, small battery), the system may shut down during cool-down. Reduce the cool-down or increase the stop SoC threshold.

• Quiet hours: If configured, the generator will not start during these hours regardless of battery state. Check whether quiet hours are accidentally blocking starts during critical periods.

VRM logs every generator start, stop, and the reason for each event. Review the generator run history to see whether the timing conditions are causing premature stops or blocked starts.

Test the generator start circuit with a manual override

Use the Cerbo GX manual start to isolate trigger logic faults from physical wiring faults:

• Manual start test: Navigate to Settings → Generator start/stop and select Manual start. If the generator starts, the relay and wiring are working — the fault is in the auto-start conditions or the SoC reading.

• Generator doesn't start on manual: Check the relay with a multimeter across the Cerbo GX relay terminals. With manual start active, you should see continuity (closed circuit). If the relay closes but the generator doesn't start, the fault is between the relay and the generator.

• SoC accuracy: If the auto-start conditions look correct but the generator never triggers, the SoC reading may be inaccurate. A BMV or SmartShunt that has not been calibrated (or has drifted) can show 40% when the battery is actually at 15%. Perform a full charge cycle and verify the SoC resets to 100% at the end.

• VE.Bus interaction: A VE.Bus error can prevent the MultiPlus from requesting generator power even when the relay circuit is working. Check for active VE.Bus alarms.

After resolving the fault, run a full test cycle: drain the battery below the start threshold, confirm the generator starts, charges the battery, and stops at the correct SoC. Monitor the first few cycles via VRM.

Why generator integration is uniquely complex on Victron

Most all-in-one hybrid inverters from other brands either don't support generator auto-start at all, or handle it with a simple built-in relay and fixed logic. Victron's approach is fundamentally different — the generator logic lives on the Cerbo GX, not the inverter, which gives far more flexibility but also far more places for configuration errors. You can set up multiple start conditions (SoC, voltage, load, time), combine them with AND/OR logic, add quiet hours, minimum run times, cool-down periods, and even schedule regular test runs. That power comes at the cost of complexity.

The second layer of complexity is AC input acceptance. Single-box hybrid inverters that come with a "generator mode" typically have relaxed frequency and voltage tolerances built in. The MultiPlus treats all AC inputs the same by default — it applies grid-quality standards to generator power, which most generators cannot meet consistently. Adjusting the acceptance windows in VEConfigure is an essential but frequently missed step. In our experience, about 40% of generator auto-start faults are actually frequency rejection issues rather than start-circuit problems.

Generator auto-start — common questions

Why does my Victron system not start the generator when the battery is low?

The most common cause is an incorrect SoC start threshold on the Cerbo GX. If set too low (e.g. 10%), the battery BMS may cut power before the generator triggers. Check Settings → Generator start/stop and verify the threshold — typically 20–30% for off-grid. Also confirm the relay is assigned to the generator function and the wiring between the Cerbo GX and the generator start circuit is intact.

What causes a MultiPlus to reject generator power?

The MultiPlus checks AC frequency and voltage before accepting an input. Portable and older diesel generators often produce unstable frequency, especially under sudden load changes. If frequency drifts outside the acceptance window (default 45–65 Hz) even momentarily, the MultiPlus disconnects. Widen to 40–65 Hz for generator use in VEConfigure. Also check the voltage window — generators may sag below 180V under load.

How do I wire a generator to a Victron Cerbo GX for auto-start?

The Cerbo GX has a built-in normally-open dry contact relay rated at 6A / 30VDC. Wire the relay output to the generator's remote start input. In Cerbo GX settings, assign the relay to the Generator function and configure start/stop conditions. Check your generator manual for the correct start signal type — sustained closure or momentary pulse. Test with manual start on the Cerbo GX before relying on auto triggers.

Can I use a BMV or SmartShunt to trigger generator auto-start?

Yes — the BMV-712 and SmartShunt have a built-in relay configurable for SoC threshold. However, if you have a Cerbo GX, use its generator start/stop function instead — it offers more sophisticated logic including SoC, voltage, load, time schedules, and manual override. The BMV/SmartShunt relay is a simpler fallback for systems without a GX device.

How much does it cost to diagnose a generator auto-start fault?

Our free remote diagnostic and covers VRM generator run history, Cerbo GX auto-start condition audit, relay assignment verification, MultiPlus AC input acceptance settings, and SoC trigger analysis. Most faults are caused by incorrect thresholds, relay misconfiguration, or frequency rejection — all identifiable remotely.

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