Are cheap UPS any good against power dips and brownouts?

Electronics designed to meet that 90 VAC number means it must work even at 85 volts. To work normally even when bulbs dim to less than 40% intensity.

DC voltages also must remain uninterrupted and rock stable even when a full AC power cycle is lost. In reality, many of our designs continue working even during much longer power loss.

A UPS switching to or from batteries will output no power for a short time. Another anomaly made irrelevant by robust electronics and what already exists inside every computer (as even defined in those ATX Standards)

200-270 volt spikes?! If your electronics are 120 volts, or even 120/240 switchable, then it is likely the parts can’t handle much more than 200 volts; for example, 200 volt filter capacitors are common (two in series in a voltage doubler arrangement for switchable supplies). Maybe not so bad if they are universal input (unless you live in a 220-240 volt country, then those spikes would be over 500 volts). Ideally, a square wave (“modified sine wave”) UPS should output a peak voltage near 170 volts, with the width of the pulses set for a RMS voltage of 120 volts, as shown in this image, which would make electronic switch mode power supplies and resistive loads happy (still not good for 50/60 Hz transformers and motors, but not many electronics have line-powered motors or 50/60 Hz transformers these days).

Do analysis at a system level; not just from one part. 120 volt electronics even in the 1970s were required to withstand up to 600 volt spikes without damage. Today’s electronics are more robust.

That does not say a constant 600 volts. But that spike from a UPS must not cause damage to any electronics. Electronics are required to be robust. Which gets ignored when some also claim their UPS is a ‘pure sine wave’.

The same interface semiconductor that alone can be damaged by 50 volts can also withstand 2000 or 15,000 volts when part of a system.

BTW, I forget the exact number. But consumer telephone equipment also withstood voltage spikes somewhere above 300 volts. Electronics have long been required to be that robust.

Concern is a rare transient that can overwhelm robust internal protection. No adjacent UPS claims to protect from that type of transient. A UPS is temporary power so that unsaved data can be saved.

Also noted is why a UPS is not recommended for motorized appliances. Waveforms that are ideal for electronics can be harmful to small electric motors and power strip protectors.

I can see the spikes being harmless, as long as they are short enough so the internal line filter can filter them out, but the broad, flat 200 volt peaks aren’t as benign because they will be passed through (and some things have little or no filtering, and unlike parts like capacitors, a transistor is much more likely to fail on spikes over their rated maximum voltage (a CFL I opened recently used 250 volt transistors); those 15,000 volts spikes you speak of are ESD and contain far less energy than AC mains spikes; I’m sure if I took a 15,000 volt utility line and connected it to that interface the whole device would blow up; heck, I know that even applying 12 volts to a 3.3 volt logic chip with “2 kV ESD” will probably damage it, been there, done that - all about energy in the overvoltage surge). I would rather have a UPS that outputs cleaner/within tolerance voltages even if it cost more since it probably has other problems with it (poor design).

A constant 600 volts or 15,000 volts was irrelevant to the topic. Transient numbers are defined mostly by the nature (waveform) of typical transients.

Meanwhile, a typical UPS connects an appliance directly to AC mains. Many claim their UPS has isolation or ‘cleaning’ because some $600 or $1000 UPS does so. Most UPSes do virtually nothing to protect hardware. Output cleanest power when not powering from its batteries. As manufacturer specs confirm. Superior protection is already inside electronics. A rare transient that puts electronics at risk equally puts the UPS at same risk.

Transients that typically overwhelm existing protection are not defined by voltage. Current spikes mean voltage rises as necessary to blow though anything that might stop or absorb that transient. Ie into a UPS and out into attached electronics. Nothing inside a building stops or absorbs this typically destructive transient.

But that is another topic. This discussion is about what the adjacent UPS does do. It provides temporary power to save unsaved data when incandescent lights dim to less than 40% intensity. Rumored UPS hardware protection (provided without any spec numbers) already exists in electronics.

Battery power will never produce clean power full stop, as it cannot keep the volts/watts flowing constantly, but like I say for the amount of time its in battery mode it dosen’t matter.

It protects it more then if your hardware is directly plugged in to the mains socket during a storm tho?

Also is this correct, are surges suppressed/killed by going in the batts of a ups and thats why the joules are much lower on a ups then a surge protector?

I am confused: ( What else is new? )

If I scope the power from the wall, it is better electricity than power from an inverter that is powered by batteries??

All indications that I can test for say in the long run, I get better ( more consistent or equal ) sine wave for as long as I have sufficient or excess battery power.

The claims of otherwise does not make sense to me? Splain please.

I’m curious what you mean by “superior protection inside electronics” I have opened literally hundreds of electronics (picked up off the curb) and at the most you might find a tiny MOV (a fraction of the size of the ones in surge protectors) and many things don’t even have one; otherwise, the AC line filter used is nothing more than a few capacitors and a filter choke or two, and the main purpose is to suppress EMI from the device itself so it passes FCC regulations (yes, it does also provide some protection from external noise). Never mind that many cheap manufacturers omit or simplify the line filter (see the last picture here for an example; note the two wires used in place of the filter choke). Although it is relatively uncommon to find something with a fried power supply (on the input side); one reason may be that the line impedance is enough to limit the current, and the energy storage of the input filter capacitor limits the voltage increase (although my parents/I had a TV that lasted for about 25 years with no line filter and a half-wave rectifier, which can easily be damaged by spikes in the reverse direction, although using a diode rated at 1000 v offers some protection over a 400 v diode; a bridge rectifier will conduct for spikes of any polarity).

The batteries don’t suppress any surges, unless the UPS is the kind that always runs off the batteries; that is, the inverter is always running with no direct connection to the mains and the charger not only charges the batteries but powers the inverter. These UPSs do in fact provide superior protection against spikes and surges and other power disturbances, as far as the powered equipment is concerned, and can even have an isolated output (as for the UPS, using a 50/60 Hz transformer instead of a SMPS for the charger circuit makes it more resistant to surges; efficiency, size, and weight concerns are the reasons for using SMPSs despite much higher failure rates/need for better surge protection over old-school linear 50/60 Hz supplies).

Note also that your average UPS, which as previously mentioned simply connects the load to the mains when it is inactive, won’t even notice spikes, so any protection will be from its internal line filter/MOVs(which is definitely often much better than what most electronics have), which as I have said don’t have MOVs or one rated for perhaps a few hundred joules, and simpler filters).