Guides · Faisalabad, Lahore, Punjab
Hybrid Inverter Transfer Time: How Fast Backup Takes Over in Load-Shedding
Short answer
When the grid fails, a hybrid inverter with a battery switches your backed-up circuits to battery and solar power in a fraction of a second. Datasheets commonly state about 10 milliseconds in "UPS" mode and about 20 milliseconds in "appliance" mode, and some grid-tied hybrids state 20 ms or less with their backup unit. Fans, lights, fridges and most TVs ride through that gap without you noticing. A desktop computer, router or DVR without its own small UPS may restart, especially at the slower setting.
What "transfer time" means
Transfer time (also called switchover time) is the gap between the grid failing and the inverter supplying your backup circuits on its own. It has three parts:
- Detecting the outage. The inverter must decide the grid has really gone, not just dipped for an instant.
- Switching. A relay disconnects your backup circuits from the grid, for safety.
- Taking over. The inverter supplies the circuits from the battery, and from the panels in daytime.
All of this happens in milliseconds. One cycle of Pakistan's 50 Hz supply lasts 20 milliseconds, so a 10 ms transfer is half a cycle and a 20 ms transfer is one full cycle.
Hybrid inverter transfer time
Grid fails
Inverter detects the loss
Switch
Backup output takes over
UPS mode vs appliance mode
Many low-voltage hybrid inverters common in Pakistan let you choose an AC input setting, usually labelled UPS (sometimes "for computers") and APL or appliance. The setting changes two things at once: how tolerant the inverter is of poor grid voltage, and how quickly it switches.
The example below comes from one off-grid inverter manual. Other models use different numbers.
| Setting | Grid voltage accepted (example) | Transfer time (example) | Behaviour |
|---|---|---|---|
| UPS mode | About 170 to 280 V | About 10 ms | Switches to battery quickly when voltage drops out of a narrow window |
| Appliance mode | About 90 to 280 V | About 20 ms | Keeps using the grid through low voltage; slower switchover |
The trade-off in Punjab conditions
- UPS mode protects sensitive electronics better, because it switches faster and refuses very low voltage. But in areas where the grid voltage often sags in the evening, the inverter will keep switching to battery, using up battery capacity and adding cycles.
- Appliance mode stays on the grid through voltage sags, which saves the battery. But your appliances then see that low voltage, and the switchover is slower. A voltage protector on sensitive loads helps here; see our TOMZN voltage protector guide.
Your installer should set the mode to suit your loads and local grid. This is separate from the SBU and SUB priority settings, which decide which source runs your home and are explained in SBU, SUB and utility-first modes.
Grid-tied hybrids with a backup output
Larger grid-tied hybrid inverters, typical of three-phase homes and businesses, often supply backup through a separate backup port or a backup unit wired between the inverter, the grid and your backup circuits. For example, Huawei's specification page for its SUN2000-MAP0 three-phase hybrid lists an automatic switchover time of 20 ms or less when used with its compatible backup device.
Two points matter with this design:
- Only the circuits wired to the backup output stay on. Everything else goes dark in load-shedding. Agree on the backed-up circuits at the design stage.
- Some models need the backup unit to give backup at all. Without it, they behave like an on-grid inverter and shut down when the grid fails. See can a solar inverter work without a battery?
A pure on-grid inverter has no transfer time to speak of: it simply stops when the grid fails, by design. That safety feature is explained in anti-islanding.
Which loads notice the gap
| Load | How it usually behaves at 10 to 20 ms | Suggestion |
|---|---|---|
| Fans, LED lights, ACs, fridges | Usually ride through; at most a flicker | No action needed |
| TVs and set-top boxes | Usually fine; occasional restart | Fast setting if it bothers you |
| Wi-Fi router, CCTV DVR | May drop the connection or reboot, more likely at 20 ms | A small UPS on these devices |
| Desktop computer without UPS | May restart, especially at 20 ms | UPS mode, or a small UPS at the desk |
| Servers, lab equipment, medical devices | Should not rely on any switchover | A dedicated online UPS on those circuits |
For clinics, labs and IT rooms, an online UPS supplies the load continuously with no transfer at all. The solar and battery system then sits behind it. See solar for hospitals and clinics.
"My backup is slow": other common causes
If your equipment goes off for much longer than a blink, the transfer time is probably not the problem. Common causes are:
- The battery is not available. Depending on the priority setting, the battery may already be at its cut-off level when load-shedding starts, so the inverter has nothing to switch to. See SBU and SUB modes.
- Overload at the moment of transfer. If several ACs, a water motor and an iron are running when the grid fails, the inverter may trip on overload. See inverter overload and beeping.
- The circuit is not on the backup side. Common after renovations or added sockets.
- Grid-fault messages and reconnection delays. After the grid returns, inverters often wait for it to stabilise before reconnecting. See inverter shows grid fault during load-shedding.
Do not open the distribution board or inverter wiring yourself. Note the time, the message on the screen and what was running, and call your installer.
A generator with an automatic transfer switch is far slower, taking seconds rather than milliseconds; in a hybrid system the inverter and battery cover that gap. See changeover switches and using a home generator with a hybrid inverter.
How to check transfer time before you buy
- Find the "transfer time" or "switchover time" line on the exact model's datasheet (how to read one), and whether it depends on a mode setting or backup unit.
- List the devices that must not restart, and plan a small UPS or online UPS for them if needed.
- At handover, ask for a switchover test under normal load.
If you are deciding between a home UPS and a hybrid solar system, read UPS vs solar for load-shedding.
How Solar Works Pakistan sets up backup
Our in-house engineers choose the hybrid inverter, backup wiring and mode settings from your load list and how your local grid behaves. All necessary tests and checks for safe commissioning are completed before handover, and we show you how the inverter behaves when the grid goes off. We supply hybrid inverters from Huawei, Sungrow, Solis, GoodWe, Knox, Luminey, Inverex and Primax; see our brands page and the solar inverter price in Pakistan list. If something is not right after installation, our target is to send service personnel within 48 hours of a registered complaint.
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Tell us which loads must stay on in load-shedding, and we will design the backup around them.
- WhatsApp or call: 0336 666 4321
- Email: info@solarworks.pk
- Head office: Main Boulevard, Sargodha Rd, Block F FDA City, Faisalabad
- Lahore branch: 2nd Floor, Jeff Heights, Gulberg, Lahore
- Hours: 9:00 AM to 6:00 PM daily
We serve customers throughout Punjab, with site surveys normally free. See our Faisalabad and Lahore pages, or contact us.
Frequently asked questions
How fast does a hybrid inverter switch to battery?
Datasheets commonly state about 10 ms in UPS mode and about 20 ms in appliance mode, and some grid-tied hybrids state 20 ms or less with their backup unit. Check the exact model's datasheet, as figures vary.
Will my computer turn off during load-shedding with a hybrid inverter?
It may, especially at a 20 ms setting. Many desktop computers and routers ride through 10 ms but not always 20 ms. A small UPS at the desk removes the risk.
Should I use UPS mode or appliance mode?
UPS mode switches faster and refuses low voltage, which suits electronics but uses the battery more when the grid sags. Appliance mode saves the battery but passes low voltage to your appliances. Let your installer set it for your loads and grid.
Is a hybrid inverter the same as an online UPS?
No. A hybrid inverter switches over when the grid fails, with a short gap. An online UPS supplies the load continuously, so there is no gap. Critical equipment should have an online UPS.
Why does my whole house go dark although I have a hybrid inverter?
Only circuits wired to the inverter's backup output stay on. Some models also need a backup unit to provide backup at all. Ask your installer which circuits are on backup.
Sources
- RCT Axpert MKS inverter manual (example input voltage ranges and 10 ms / 20 ms transfer times for computer and appliance settings)
- Huawei, SUN2000-5-12K-MAP0 specifications (automatic switchover time with compatible backup device)
- EPEVER, hybrid inverter EPS transfer time (typical switchover ranges and device tolerance)
- Power Forum, UPS and APL modes in solar inverters (user-reported manual figures)