"Spanfeller is a twat" (theaspiringengineer)
06/27/2019 at 23:30 • Filed to: None
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"Spanfeller is a twat" (theaspiringengineer)
06/27/2019 at 23:30 • Filed to: None | 1
| 6 |
I was trying to test a transformer with a bro-physics(tm) technique.
Basically, we connected a 120V to 24V transformer to the mains. with one cable we tested the voltage of the mains (which is typically 127Vrms in Mexico), with the other we would be testing the output of the transformer.
We supposed that by connecting the oscilloscope leads
directly to both ends of the transformer we would get a good idea of how well it was actually doing it’s job. Since the transformers we get tend to be pretty bad; some were going from 120 to 40 or 50
, and we wanted to be sure it was doing it’s job properly.
Instead, it exploded almost immediately
after we turned on the mains
. While I have no clue what happened, I suspect we tried to throw too much current at the oscilloscope
and it murdered the cable in self defense. It was quite spectacular actually; though it exploding directly in front of my lab partner’s face is not ideal.
MrDakka
> Spanfeller is a twat
06/28/2019 at 00:17 |
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T hat’s not how you test a transformer; an oscilloscope is far too precious a machine for such trivial task. You use a metal fork and a grad student, plenty of those around.
Distraxi's idea of perfection is a Jagroen
> Spanfeller is a twat
06/28/2019 at 00:30 |
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“ which is typically 127Vrms in Mexico”
Boy, what part of Mexico are you in? The company I work for has a couple of hundred thousand voltage monitoring devices scattered round Mexico - admittedly mostly in the less photogenic parts of the country - and the most precise I’d get is to say that it’s “typically between 60V and 250V”
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Spanfeller is a twat
> Distraxi's idea of perfection is a Jagroen
06/28/2019 at 00:53 |
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Mexico City used to have it’s own electricity company until 2010. It was “Luz y fuerza” if you know anything about electricity history you might trace L&F to the Canadian Light and Power company but hey maybe it has an effect, since the rest of the country has always used the Federal Electrical Comission.
W
eird voltages are common, and supposedly the reason why Tesla refrained from entering the Mexican market until late 2017.
It’s a running gag that you can’t be a FEC
tech without having a transformer blowing up near or in your face. The residential ones blow up very often.
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Spanfeller is a twat
> MrDakka
06/28/2019 at 00:54 |
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Well, we ran out of grad students, and they don’t actually give very precise measurements...
(what dumb me didn’t do was test it with a goddamn multimeter
like a regular person)
diplodicus forgot his password
> Spanfeller is a twat
06/28/2019 at 06:27 |
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I was going to say why didn't you just test the output with a multimeter. Or use a fluke scopemeter
tpw_rules
> Spanfeller is a twat
06/28/2019 at 08:25 |
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Ah, you forgot that oscilloscopes aren’t isolated. At least you’ve learned effectively and won’t ever forget.
All the metal on the oscilloscope, including the case, the shell around the connectors, and the
black clips of all the probes
, are all connected
directly to ground
. Presumably, you hooked the black clip to the hot side of the input, created a direct short to ground through the oscilloscope, and the probe acted as a fuse and vaporized. Another possibility is that your two probes had the black clip connected to different voltages, and you shorted those together.
If you want to safely perform such a measurement, you need to isolate the scope. You can do this by plugging it into an isolation transformer, which separates the ground on its input from the ground on its output. Or you can use a battery powered scope or multimeter or some such thing. Of course, you can still short two things together through the black clips.
Note that other things can be grounded too, like metal parts of PCs, including USB cable shells!