[dylan604]

If you get dips in voltage below the range that the PSU can handle, it will kill the PSU. If you get spikes higher than the range that the PSU can handle, it can kill not only the PSU but things attached to the PSU as well. Most people are familiar with spikes with things like surge protectors, but most are unaware of how damaging voltage dips can be as well.

[Dylan16807]

> If you get dips in voltage below the range that the PSU can handle, it will kill the PSU.

How does that happen? Let's say it's running and I drop the input to 80 volts. Why do I get any behavior that isn't "runs at reduced capacity" or "shuts off"? And what part of the circuit is failing?

Are we assuming a combination of missing current limiting and a heavy load? If I'm just watching youtube then it shouldn't overload any components even if it keeps running at a really low voltage.

[dylan604]

My experience is from older analog equipment. Specifically, I worked in a video/film post house that also had a VHS duplication department. Analog tape machines run at a certain rate. For those old enough, VHS had SP, LP, and SLP modes. Those were defined speeds that the tape was fed through the system. If the voltage dipped, the speeds would slow down. When played back at a constant rate, the signal could not be read as the signal wasn't recorded at that speed. So our meter would sound an alarm when the voltage dipped too low that would introduce that problem which would tell the operators to stop the recordings and rewind/restart. That's more of an annoyance than damaging, however, some of the records of a certain model would fail which was usually a power supply issue.

Same facility was fed 3-phase power, but due to some construction mishap nearby, one leg was cut. That lost us a lot of expensive power supplies that day for some of the more expensive equipment.

Those are examples, but not really an answer to the how question. I'm not an electrical engineer, so :shrug-emoji: I asked the engineers that question at the time, and they told me it was something along the lines of the equipment tried really hard trying to function instead of just shutting off. The dip was low, but not that low. Described like a ceased electrical motor where it keeps pulling more power where normally a breaker/fuse would trip, but something different. It wasn't a satisfactory answer then any more than it is now.

[Dylan16807]

Well, I can think of a lot more ways for losing a phase to break things than a voltage drop.

For a voltage drop, the main idea that comes to mind is something trying to keep up a constant wattage and drawing increasing current to make that happen. But you have to do quite a bad job to design that circuit and not have a current limit.

And a PC power supply is inherently flexible on the input voltage, so it would never have the problems you get with a fixed ratio transformer on that old equipment.

[dylan604]

Unfortunately, there are a lot more things in the world that need a power supply than a PC. Sorry if my use of PSU unintentionally narrowed the focus, just faster to type. The power supply for these high end video machines were not small, nor come with a cheap price tag. I would not have expected them to be made poorly as they are specialty units designed to run precision analog electronics. That would be comparable to expecting nylon seats in a Ferrari.

From all of that, I have learned the lessons of how dips can ruin electronic equipment (even if not the exact why back then), so for me and my house all electronics are hooked up to a UPS or power conditioner. Appliances are on their own though as that's the landlords problem! Multiple times a week, I get noticeable dips where the lights visibly dim and I can hear all of the UPS units kick in and back to mains a few seconds later.

[cwillu]

Low voltage requires higher current to maintain a given output power.

[Dylan16807]

Yeah but that's what the shutoffs are for.

[exmadscientist]

This really should not happen, at least for units that are qualified to the relevant IEC standard.

But, certainly, garbage devices are all over the place.