Electronics > Projects, Designs, and Technical Stuff
Lots of recalls of solar panel DC disconnect switches
floobydust:
--- Quote from: soldar on June 02, 2019, 08:20:45 pm ---Oh, please! Nets to protect pedestrians from the falling bodies of suicides? Really? You believe this? Can we have some corroboration?
--- End quote ---
OT It was Foxconn that installed suicide nets. They are also at various chinese factories.
Vell:
Somewhat off-topic, but I want to thank a member who suggested that this topic should be iirc in General matters. However, it's now into multiple pages, and I'm too new to this Forum to try to move the whole thread. I surely wouldn't mind a tall if some experienced and responsible person did, though. I have yet to read most of the posts.
Someone asked how DC has been switched; that has probably been answered, but I'll say what I know about it. A DC arc has a magnetic field, and one stratagem is to have a blowout magnet that forces the arc to lengthen. Long before Alnico, permanent magnets were weak, and demagnetized easily. An electromagnet, the "blowout coil", supplied the field. Pole pieces were on both sides of the arc, as I recall.
As well, there were arc suppression chambers, with multiple insulating baffles to split up the arc. This is as I remember, but only from illustrations.
The Boston T light-rail Green Line depot at Riverside, its western terminal, had a siding where 3400 series "hangar queens" were stored. Covers had sometimes been removed, and it was quite interesting sometimes to see the goodies, especially electricals. I distinctly recall that what must have been control-circuit relays had huge insulating chambers for their contacts.
Off-topic, but also of interest was an air-core power inductor which occupied maybe an 8-inch/20 cm cube, maybe even 12-inch/30 cm. It might have been wound with litz wire, have forgotten.
DC for the traction motors must have been modulated by pulse modulation, but quite likely pulse frequency, audio range, instead of width. I recall riding in 3400-series cars, and you could easily hear the "pulser".
soldar:
--- Quote from: floobydust on June 02, 2019, 08:44:18 pm ---
--- Quote from: soldar on June 02, 2019, 08:20:45 pm ---Oh, please! Nets to protect pedestrians from the falling bodies of suicides? Really? You believe this? Can we have some corroboration?
--- End quote ---
OT It was Foxconn that installed suicide nets. They are also at various chinese factories.
--- End quote ---
quote Wikipedia:
--- Quote ---although the number of workplace suicides at Foxconn is large in absolute terms, the suicide rate is actually lower when compared to the overall suicide rate of China[33] or the United States.[34]
--- End quote ---
Reading the article it seems to me like a copycat phenomenon where people copy the method they see being used.
I don't understand it very well but it seems one guy or guys burn a car or a mailbox and next thing you know other people are doing it.
In this case it seems someone jumped out the window and others, who might have committed suicide in other ways, decided to follow suit. But Wikipedia says the overall rate is no worse than in other places.
It seems like management thought it prudent to install the nets than have to explain themselves which, in cases like this, is never successful. And the nets would be to save the "suiciders" not pedestrians. I guess once the nets are there you would go commit suicide off company property.
At any rate, I have visited some pretty big factories in China and the conditions of the line workers would kill my soul, probably like any assembly line anywhere, but let us not forget that they go there willingly because the alternative is grueling work in the fields; much worse than the factory.
Edit: Vell, I want to acknowledge your post had a good factual basis.
Vell:
--- Quote from: ogden on May 31, 2019, 11:59:12 am ---
--- Quote from: mikerj on May 31, 2019, 11:29:27 am ---Because Dave's solar installation has failed due to a bad isolation switch. I agree the topic is very random and assumes everyone has watched Dave's video.
--- End quote ---
Topic is educational. Many may not know dangers of mechanical DC switching. Demonstration of DC switch arcing which does not happen in case of AC: https://youtu.be/mQpzwR7wLeo?t=359
--- End quote ---
There were lots of messages there; some groups of replies took too long to load, so I ignored them.
One reply near the end pointed out that the arc continues because the air is ionized. (Comment didn't mention ionized metal vapor. : )
This reminded me of vacuum switches; the contacts are in a vacuum. Afaik, they were (and maybe still are) used to switch high-power RF. Contact gaps are quite small.
schmitt trigger:
Vell;
I once saw the inside of a control panel for a large DC motor driving a steel mill.
I distinctly remember the "blowout coils" in the main contactor.
What I don't remember is how these coils were excited, they might have been in series with the current being interrupted.
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