Really, only UPS that have value are online ones. They take AC and convert it to DC at around 48-96V. Batteries (usually 12V ones connected in chain to get that 48-96V) give out same voltage. Batteries and output of AC-DC converter connected together through diodes. Regardless of what source is giving power, that 48-96V DC then converted to 155 or 315V DC depending on grid voltage, 110V AC or 220V AC. This 155/315V DC then converted to 110/220V AC sine. There are no direct connection between input and output and switching to battery and back occur absolutely seamless. When mains disappear, current continue to flow from batteries like nothing happened. When power is back, you get current from AC-DC converter again. Last stage in that scheme, DC-AC converter, is really not necessary for most tech usually connected via UPS.
You could find parts of online UPS as separate modules, also today you could find modules for building solar power systems based on online UPS principle, when in addition to mains AC-DC converter and battery, to the same 48-96V DC rails also connected solar panels that will be used when they give enough voltage in absense of grid power. Or they will charge batteries if grid is OK. So you could build DIY cheap online UPS using this modules, car batteries and whatever additional source of electricity you have and get a power source that will seamlessly move from one source to another and back by design. If you need it only for modern devices with switching power supply, you don't need to buy final DC-AC converter, which is usually not something cheap, due to expensive high-voltage high-power transistors, you could power your tech from 155/315V DC without any issues.
The thing is, ALL switchers are built to only handle a few milliseconds of stored energy and they MUST be fed sustained power or they simply stop output once the temporarily stored energy is drained from their inductors or capacitors. No switcher will continue to put out power a few milliseconds after input power stops. Thus any switcher needs to have either a UPS input or a very stable AC line, and this means all PCs have to have a UPS or be able to tolerate interrupted power, which is not easy as that glitches CPUs.
So called "smart" UPS produce glitches too. When grid power is OK, they connect it to the output directly. On the power loss they switch to battery powered DC-AC converter or switch additional windings on power transformer. For price saving reasons they do it with relays. All that processes create noticeable glitches in output. Moreover, to avoid need for syncronisation of grid frequency with DC-AC converter ones, "smart" UPSes usually skip at least half of AC period while switching from mains to battery and back.
I don't even mention all that "line conditioners" They perfectly pass half wave gaps that gives noticeable glitch on the output of loaded power supply. They are fine only for cutting high frequency noise from power grid.
So, only online UPS are useful for real protection against glitches, since they always create output from scratch (48-96V DC) using their DC-DC and DC-AC converters, so nothing from input could crawl to the outpur and switching from mains to battery and back is seamless.
I dispute some of that. Line conditioners rely heavily on power stored in the magnetic fields of their inductors. A half wave gap in input power results in an exponential decay in output during that period as the magnetic field collapses. Where did you get the 'perfectly pass half wave gaps' from? That's untrue.
Not all UPSs use relays, some designs use power switching semiconductors with a far faster switching time and they can respond a lot faster than either a mechanical contact or 1/60 of a second half cycle time which is 8 milliseconds. Any input power dropout obviously detectably occurs within that time framework and requires a response time in the range about 1 to 4 ms, perhaps a 1/4 cycle period.
A half wave gap in input power results in an exponential decay in output during that period as the magnetic field collapses.
It already collapsed because input voltage is zero. There is nowere to get power to create full halfwave that is missed.
Not all UPSs use relays, some designs use power switching semiconductors with a far faster switching time and they can respond a lot faster than either a mechanical contact or 1/60 of a second half cycle time which is 8 milliseconds
Most "smart" UPS have dealy while switching from mains to battery and back not because of speed of switching device, but because of unsyncronized mains and internal DC-AC converter. Imagine mains power disappear at the top of sine wave, while DC-AC converter is at the bottom. You will have a problem with twice of grid voltage rapid swing with all consequences. So, UPS have to wait while its DC-AC converter output will reach zero to safely switch to it. Usually things are even simplier - if mains disappear, UPS just switch to DC-AC convertor and start it. This takes time. Also many use the same transformer for mains voltage stabilisation and charging and for DC-AC converter that also limits speed of switching.
UPS manufacturers cheat with speed of reaction to power grid changes, showing time of reaction for grid voltage stabilisation mode, which is done by switching between additional transformer winding parts that does not need any delay or sync, and not for switching from grid to battery and back.
I saw "smart" UPS that constantly run separate DC-AC converter in sync with grid, to make the switching process fast and safe, but they are not a cheap ones you usually see on the market and cost a little less than normal online UPS that just have no any switching process at all.
Really, only UPS that have value are online ones. They take AC and convert it to DC at around 48-96V. Batteries (usually 12V ones connected in chain to get that 48-96V) give out same voltage. Batteries and output of AC-DC converter connected together through diodes. Regardless of what source is giving power, that 48-96V DC then converted to 155 or 315V DC depending on grid voltage, 110V AC or 220V AC. This 155/315V DC then converted to 110/220V AC sine. There are no direct connection between input and output and switching to battery and back occur absolutely seamless. When mains disappear, current continue to flow from batteries like nothing happened. When power is back, you get current from AC-DC converter again. Last stage in that scheme, DC-AC converter, is really not necessary for most tech usually connected via UPS.
You could find parts of online UPS as separate modules, also today you could find modules for building solar power systems based on online UPS principle, when in addition to mains AC-DC converter and battery, to the same 48-96V DC rails also connected solar panels that will be used when they give enough voltage in absense of grid power. Or they will charge batteries if grid is OK. So you could build DIY cheap online UPS using this modules, car batteries and whatever additional source of electricity you have and get a power source that will seamlessly move from one source to another and back by design. If you need it only for modern devices with switching power supply, you don't need to buy final DC-AC converter, which is usually not something cheap, due to expensive high-voltage high-power transistors, you could power your tech from 155/315V DC without any issues.
The thing is, ALL switchers are built to only handle a few milliseconds of stored energy and they MUST be fed sustained power or they simply stop output once the temporarily stored energy is drained from their inductors or capacitors. No switcher will continue to put out power a few milliseconds after input power stops. Thus any switcher needs to have either a UPS input or a very stable AC line, and this means all PCs have to have a UPS or be able to tolerate interrupted power, which is not easy as that glitches CPUs.
So called "smart" UPS produce glitches too. When grid power is OK, they connect it to the output directly. On the power loss they switch to battery powered DC-AC converter or switch additional windings on power transformer. For price saving reasons they do it with relays. All that processes create noticeable glitches in output. Moreover, to avoid need for syncronisation of grid frequency with DC-AC converter ones, "smart" UPSes usually skip at least half of AC period while switching from mains to battery and back.
I don't even mention all that "line conditioners" They perfectly pass half wave gaps that gives noticeable glitch on the output of loaded power supply. They are fine only for cutting high frequency noise from power grid.
So, only online UPS are useful for real protection against glitches, since they always create output from scratch (48-96V DC) using their DC-DC and DC-AC converters, so nothing from input could crawl to the outpur and switching from mains to battery and back is seamless.
I dispute some of that. Line conditioners rely heavily on power stored in the magnetic fields of their inductors. A half wave gap in input power results in an exponential decay in output during that period as the magnetic field collapses. Where did you get the 'perfectly pass half wave gaps' from? That's untrue.
Not all UPSs use relays, some designs use power switching semiconductors with a far faster switching time and they can respond a lot faster than either a mechanical contact or 1/60 of a second half cycle time which is 8 milliseconds. Any input power dropout obviously detectably occurs within that time framework and requires a response time in the range about 1 to 4 ms, perhaps a 1/4 cycle period.
It already collapsed because input voltage is zero. There is nowere to get power to create full halfwave that is missed.
Most "smart" UPS have dealy while switching from mains to battery and back not because of speed of switching device, but because of unsyncronized mains and internal DC-AC converter. Imagine mains power disappear at the top of sine wave, while DC-AC converter is at the bottom. You will have a problem with twice of grid voltage rapid swing with all consequences. So, UPS have to wait while its DC-AC converter output will reach zero to safely switch to it. Usually things are even simplier - if mains disappear, UPS just switch to DC-AC convertor and start it. This takes time. Also many use the same transformer for mains voltage stabilisation and charging and for DC-AC converter that also limits speed of switching.
UPS manufacturers cheat with speed of reaction to power grid changes, showing time of reaction for grid voltage stabilisation mode, which is done by switching between additional transformer winding parts that does not need any delay or sync, and not for switching from grid to battery and back.
I saw "smart" UPS that constantly run separate DC-AC converter in sync with grid, to make the switching process fast and safe, but they are not a cheap ones you usually see on the market and cost a little less than normal online UPS that just have no any switching process at all.