Electronics > Beginners
Masuring AC lines Vs power conditioned lines using analog scope SAFELY!
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Brumby:

--- Quote from: rx8pilot on September 16, 2018, 11:54:08 pm ---It still scares me - even 120v outlets. Perhaps the fear is constructive because I am still alive.

--- End quote ---
That is respect.  The second you do not respect electricity - bad things can happen.



--- Quote ---Fortunately, the majority of my daily life now is 30VDC and lower.

--- End quote ---
Funny.  So does mine.
rsjsouza:
A photograph of the innards of a similar model indicate to me it is an actual isolated switching power supply:



(photo obtained from here)

(edit) found a datasheet with the same model and with an inside picture as well - almost identical to the one above.
ArthurDent:
If you look at the photo of the innards of this type of device shown in reply #11, I will explain what I think it does after reading the spec sheet. It has all grounds carried through to the outlet ground prongs and does not isolate the output power lines, which I would consider a waste.

First the power cord is connected at the lower right in the photo then goes through a double pole switch that can disconnect both sides of the line, then through the circuit breaker to the circuit in the upper right corner of the unit. This section has voltage sensing components that control the black cased relay with the number ‘2’ on it. If the average input voltage goes too high (also maybe too low) the relay will disconnect the output to protect your equipment. This circuit does not react to spikes but to a slower average increase or decrease in the line voltage, probably over a second or so.
 
From the relay the power goes through a small silver colored 2-lead device on ceramic spacers that is a thermal fuse that opens if the unit overheats for any reason. To the immediate left of that thermal fuse is a blue surge limiting non-linear resistor to limit inrush current.

Next the line goes through a toroidal inductor that will act as a high impedance to spikes on the line. The output lead from the inductor goes to a full wave bridge rectifier connected across the line with an electrolytic capacitor across the output side of the bridge and there is a brown bleeder resistor on ceramic spacers that is wired across the electrolytic capacitor. While it may not immediately make sense to have this bridge/cap circuit across the power, here is the theory. The inductor, already mentioned, acts as a high impedance to spikes while the capacitor on the output of the bridge acts as an extremely low impedance to spikes thus effectively eliminating any spikes from the output. The brown bleeder resistor discharges the capacitor slowly so its voltage will follow the average value of the line voltage. This inductor is different than the common mode dual inductors you normally see in filters used in switching mode power supplies and is possibly more effective.

You could tell looking at the size of the unit that there was no way there was an isolation transformer inside. If my explanation of what the unit does is correct, it will pretty much do what it claims to do and for the price isn’t that bad. I wouldn’t try to go probing around inside with a scope without the required knowledge and a good reason.
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