“Will my computer turn off during a power outage?” – this question is asked every time a system is sold with a warehouse, and the answer lies in one parameter on the data sheet: the time it takes to switch to emergency power. Growatt declares for hybrids SPH UPS function with 10 ms transition, and for island SPF — 10/20 ms transfer depending on the configuration; both numbers sound abstract until we translate them into the behavior of specific receivers. This article explains what really happens in these few milliseconds, how the UPS, EPS and off-grid and what 10 ms does not promise - so that the offer tells the truth and the customer knows what he is buying.
What happens in the milliseconds after a network outage?
Before we get to the numbers, let's see what the transfer time actually measures. The sequence is always three-stage. First, detection: the inverter must recognize that the grid has actually disappeared, not just vibrated—this is handled by voltage-frequency protections, the same ones we described in the grid codes. Then, separation: the unit physically disconnects from the grid (anti-islanding requirement—it's forbidden to power a dead line that could be used by an emergency power supply). Only then does the transfer occur: the emergency output path receives battery voltage. The transfer time declared in the data sheet covers this entire sequence—and therefore is never zero in an architecture where a single inverter serves both paths.
Zero milliseconds is only offered by true online UPSs, which constantly process all energy through their own inverter—at the expense of efficiency, price, and service life. The hybrid inverter consciously compromises: during normal operation, it delivers near-maximum efficiency, but in the event of a fault, it switches quickly enough for the vast majority of home appliances to remain unnoticed.
10 ms and 20 ms in cards Growatt — where do these numbers come from?
Three-phase hybrid catalog card SPH The TL3 BH-UP explicitly lists "UPS function, 10ms transition," with a transfer time of less than 10ms—the current benchmark for home backup architectures. SPF the card specifies a transfer of 10/20 ms - two values, because the time depends on the unit's operating configuration; with a narrower, "UPS" input voltage window, the inverter can react faster than with a wide window that tolerates weak networks and generators (the input voltage modes are described in the article on settings SPF).
How does this apply to receivers? The reference point is one 50 Hz mains cycle, or 20 ms. A 10 ms switchover is half a cycle—switched-mode power supplies for computers, routers, and televisions store energy in capacitors for tens of milliseconds and absorb such a loss without a second thought. At 20 ms, the reserve decreases, but typical electronics still retain it; devices with contactors and sensitive automation—some boilers, older controllers—can be sensitive, however, and can interpret a longer dip as a restart. Hence, the standard practice: critical controllers are tested by an actual power outage upon receipt, not by a card declaration.
UPS, EPS, off-grid — three architectures, three promises
| Architecture | Portfolio example Growatt | How it works in case of decay | Ideal for |
|---|---|---|---|
| Hybrid with UPS function | SPH TL3 BH-UP (10 ms according to card) | a dedicated output takes over the circuits after switching in single milliseconds | a house where the continuity of electronics and boiler operation is important |
| Battery-ready + EPS box/SYN | MIN-XH with SYN 50-XH-10, MID from the EU SYN-100-XH-30, MOD HU with SYN integrated | the box switches the power supply of separate circuits to the battery track | expansion of existing installations to support |
| Off-grid / continuous power supply | SPF ES (10/20 ms transfer between sources) | loads by definition are connected to the inverter; "switching" refers to a change of source (mains↔battery), not a loss of power | objects where the network is the guest, not the host |
The conceptual difference is greater than the numbers—the switching time means something different in each row of this table: in a grid hybrid, the switching time is the moment of switching to the battery; in an off-grid system operating in battery priority, the loads don't even notice the grid outage because they're powered by the inverter anyway—the milliseconds there refer to the return to the grid or its connection as backup. Therefore, the question "what switching time" without asking "in which architecture" has no single answer.
How to read this parameter in cards - comparison traps
Manufacturers call it differently: "transition time", "transfer time", "switswitching time", sometimes "UPS function" with a number next to it - and they don't always measure the same thing. One card will give the typical time, another the maximum; one counts from the loss to the output voltage, another only the contact switching phase. Therefore, switching times are compared only within the same architecture and with the same definition - comparing 10 ms of a hybrid with "0 ms" of an online UPS is like comparing an apple with a generator. In the documents Growatt values are declared per family (SPH: 10 ms; SPF: 10/20 ms depending on configuration) and it is the family, not marketing, that sets the context for the number.
The second pitfall: switching time can be confused with the response time of the entire house. Other factors that stand between outage and comfort include the behavior of the loads (their own energy reserves), the order of start-up after switching, and the power of the emergency circuit. A system with an ideal 10 ms and an overloaded EPS output will produce a worse result than a system with 20 ms and a well-designed circuit list—the parameter is important, but it's the design of the emergency circuit that makes the difference felt by the resident.
What 10 ms doesn't promise - the limits of a fair offer
First, scope: the backup applies to circuits connected to the emergency line, not the entire house. The emergency output power and the bank's capacity limit the list of loads—we described designing this list in the kilowatt-hour selection guide. Second, start-ups: motors (pumps, refrigerators, gates) draw a multiple of their rated current upon startup, and the emergency output has its own overload limits—a cascade of starts immediately after switching can cause a line overload. off-grid (in MOD codes/MID is a 303 warning). Third, device class: a hybrid inverter with a UPS function is not an online medical or server UPS - if a single millisecond of interruption disqualifies the system, the appropriate response is a dedicated UPS behind the critical load, with the storage facility as its power backup.
And fourthly, communication: when the network goes down, the internet often goes down too—a router on a backup circuit is the detail that determines whether monitoring and control systems will survive a failure along with the refrigerator. We automatically include it on the list of critical circuits, yet half of the "applications down during a blackout" are routers outside the EPS path.
From the installer's practice
- From practice: perform the acceptance test using the main switch, in front of the customer, with his computer and boiler on standby - one real outage says more than the card, and the customer knows exactly what he bought.
- From practice: permanently mark emergency circuits in the switchboard ("EPS - do not expand without an installer") - adding loads to the backup circuit after a year is the most common cause of overloads at the first failure.
- From practice: with gas boilers and central heating pumps, check the controller's behavior after a 20-millisecond dip before promising "heating works during a blackout" - boiler manufacturers tend to be more sensitive than inverter manufacturers.
- From practice: in the offer write "support for separate circuits with a switching time of approx. 10 ms", not "UPS for the whole house" - the first version complies with the data sheet and defends itself upon receipt, the second one returns with a complaint.
Frequently asked questions (FAQ)
Will my light go out at 10 ms?
LED bulbs usually flicker or go unnoticed – their power supplies have their own energy reserve. Fluorescent lamps and some fixtures with starters may flicker more noticeably. This is cosmetic; the important thing is that the lighting on the emergency line returns immediately, while outside it, it goes out until the mains power returns.
Will a desktop computer survive the switch?
A typical ATX power supply maintains voltage for a dozen or so milliseconds, so a 10ms transition is within the expected margin. The condition is that the computer must be connected to a maintained circuit. For critical operation (e.g., a cash register, a recorder), we still recommend a small local UPS—the cost is negligible and eliminates any discussion about milliseconds.
What is the difference between switching time and generator start time?
By order of magnitude and role: switching to the battery takes milliseconds, starting the generator takes seconds or minutes. In systems with a generator (we described them in the modes WIT and settings SPF) the battery fills the hole immediately, and the generator comes in later as a long-distance source - these are complementary layers, not replacements.
The fastest way to select the backup architecture is from the inverter side: GROWATT SPH 10000TL3 BH-UP has a UPS function as standard, and the other hybrids can be found in the category 3-phase hybrid inverters; you can verify the pair with the battery in configurator Growatt. Catalog cards with switching times are published download center Growatt.
