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by pseudohadamard 90 days ago
It's not just cheap UPSes, it's cheap surge protectors as well. They exist because the vendor can throw in a MOV costing a few cents and increase the price of the power strip by 50%, not because they're any good. MOVs are sacrificial components which have either degraded to uselessness by the time they're actually needed or, if they're still working, can explode or catch fire from the energy dissipated. Even if they don't, all they're doing is converting an x-kV spike on active into an around-x-kV spike on neutral or ground. If you want to do it properly, use a series tracking filter, not a "surge protector".
1 comments
tharkun__ 90 days ago
No offense, but can you tell me how my 4.5 kW generator is gonna generate that kind of power surge?
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tlb 89 days ago
One scenario: there's a short circuit somewhere, say rats chewing through insulation. This can cause a very high current through the short. A non-inverter 4500 watt 120 volt generator might have 0.2 ohms coil resistance, so the short circuit current can hit 170 volts / 0.2 ohm = 850 amps. When the shorted branch's circuit breaker trips, the inductance in the generating windings wants to keep that 850 amps flowing for at least a few microseconds, and it gets distributed across everything else that's still connected. Depending on what else is connected (hopefully including some surge protectors) the peak voltage can get into many kilovolts.

The circuit is something like this:

  voltage source -- parasitic inductor --+- circuit breaker -- short
                                         |
                                         +- circuit breaker -- your PC
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pseudohadamard 89 days ago
More generally, for the previous poster, look at what happens when a magnetic field collapses suddenly, you can get kilovolt spikes. There's probably a ton of YouTube videos demonstrating this in various ways, it sounds like the sort of thing that Electroboom would do. Normally this is handled via snubber circuits which dissipate the energy before it can do anything, but in exceptional cases it could end up going where it shouldn't.
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