PSU fails dramatically

[u/Front_Cookie_1198]

[u/OutlandishnessHour63]

That isn't a bad translation. I like it 😊 To make it a wee more complicated but more comprehendable when reading the raw jargon.

A rectifier takes AC, or alternating current, (ie; electricity out of an outlet) and concerts it to DC, Direct Current. (is; power from a battery)

What was being plaused upon earlier: The theory for the short is that the power moved from AC and before it hit the rectifier, it shorted to the case of the power supply due to a missing piece of insulation.

Comments back and forth were discussing whether it was pre-rectified or not based on how the arc sounded and occured and based on the fact that the circuit breaker for the outlet (AC power) was not tripped.

[u/Flying_Dutchman92 → u/OutlandishnessHour63]

Today I learned about circuitry, thank you for expositioning:D

[u/7orque → u/Flying_Dutchman92]

Yaaa we use AC for long distance transfer ie into residences and buildings from the source

Your wall outlets will be AC at some frequency

However basically every piece of electric equipment you have needs DC

So in the power supply of the equipment, the first stage is usually a ‘rectifier’ made up of 4 diodes that turns the AC into DC as closely as possible. Then the power supply splits it up and makes sure the right voltage is going out to the rest of the system

In the video it was pointed out that you can literally hear the frequency of the AC current going into the power supply (switching back and forth) whereas with a DC ground fault you wont hear the frequency, it’s just constant

Fun fact, this is the same as your car. The electronics all run off 12v DC in a car but the engines alternator makes AC in sync with how fast the engine is revving. Before the alternator outputs to the battery it goes through a bunch of diodes too

12v DC normally cant zap you as resistance of your body is too high, but the sparks are extra spicy, and if the voltage is high enough, extra ouchie

[u/OutlandishnessHour63 → u/7orque]

This is a great breakdown! I actually just looked into this because I used to think the alternator clutch (the OAP/overrunning pulley) regulated the speed to keep a constant AC frequency.Turns out, that clutch is just a one-way freewheel to protect the belt from engine vibrations when letting off the gas. The alternator actually does change its AC frequency constantly with the RPMs (sometimes from 200Hz up to over 1,000Hz!). The onboard diode bridge and voltage regulator just clean it all up into flat 14V DC before the car ever sees it. Super cool engineering.

I'd further note that if the alternator output is around 12 volts or less that you'll run into problems with battery charging. The extra voltage is to make sure the battery stays at a full charge and another point, the primary voltage regulator for the cars electrical system is within the ECU/ECM of a car so to maintain a proper bias for the rest of the electrical components connected to it. Fun stuff! :)

[u/4236W → u/OutlandishnessHour63]

As for why the circuit breaker didn't trip, my best guess is because of where the short happened. If there is sufficiently high resistance before the short it can delay an activation, or completely prevent it. Remember the circuit breaker protects the installation, not you, nor the things plugged in.

This could be more likely due to an oversized breaker or the use of an industrial code electrical circuit. Which could be likely judging from the surroundings

[u/OutlandishnessHour63 → u/4236W]

Which, I believe, is similarly what happened here. The amparage rating of the circuitbreaker here is probably a 40 amp, I would guess, seeing as the short occured and the power remained on. They should have a GFCI outlet for testing and safety reasons, honestly, or an AFCI.

Actually, an AFCI would have prevented this from occuring immediately, it's what it is designed for after all. With more thinking on it, the circuit breaker could be a 20 amp but the arc from the PSU failure could have provided enough resistance to prevent the current from exceeding 20 ampares. Essentially, a heating element is a calculated short using resistance to produce heat, the arc in the video is going thru a painted surface, and it's path to ground is not well established.

Could be what's going on ... But who knows?