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Joined: Mar 2005
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You have to be careful with ratings. NEC and most of the products electricians frequently use all use RMS voltages- 600V insulation rating, for instance, is 600V RMS.

You can easily get into trouble with rectifier circuits and other things that are rated for peak voltage, though (like when the marketing department takes the product and misleadingly advertizes insulation rating), if you fail to consider than 480V RMS is 680V peak, 11.5kV RMS is 16.2kV peak, etc. More of an engineering issue than an electrician issue, but still worth having in the back of your head if you're trying to do anything fancy.

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Joined: Aug 2001
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Originally Posted by SteveFehr
You can easily get into trouble with rectifier circuits and other things that are rated for peak voltage


You can even find some cheap commercial designs of power supply where the PIV (Peak Inverse Voltage) rating of the rectifier diodes is not high enough -- Whether through somebody not understanding the principles involved or through a cost-cutting exercise on the basis that "Most of them will last out the warranty anyway," I don't know.

But if you were building just a very simple half-wave rectifier circuit with reservoir capacitor, to allow for the worst case where there is no load the PIV of the rectifier needs to be equal to the peak-to-peak voltage of the transformer secondary, e.g. with a no-load secondary voltage of, say 24 volts, the rectifier needs to be rated for at least 68 volts PIV.

Joined: Mar 2005
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I was thinking industrial appliations, but good point with the DIY rectifier. If you want 12V DC and try to rectify 12V AC... even if the diodes can handle it, you're going to end up with 17V DC and risk blowing up whatever you plug into it.

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For the time being, you should stick to trying to understand toasters and other resistive loads only.
They have what is known as a "unity power factor".

Once you get comfortable, you can start in trying to understand the wonderful 'real world' of Power Factor, where the product of Volts x Amps is always larger than Watts.

Happy studying!


Ghost307
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Although this post is beyond late blink, the Attached Animated Gif Kind'Of demonstrates some key functions, applicable to a Polyphase System.
(applicable if Two or more of these Transformers are connected together and supplied with a Polyphase AC Input)

[Linked Image]

Link to Full-Size Version:
https://www.electrical-contractor.net/theory/1PH3W_FLOW_ANIM01.gif

The Animation describes a Single Phase Transformer's flow characteristics, as observed on the Two Wire Primary, and the Three Wire Center-Tapped Secondary.

Simplest way to observe Polyphase "Phases":
Connect (2) Transformers in an Open Delta configuration on both the Primary and Secondary sides.
Per the Secondary connections, only connect the "ENDS" of each Winding - leaving the Center-Taps unused.

Drive the Primary side with an Alternating Current comprised of at least Two separate - yet interconnected - Voltage (E) & Current (I) "Lines", derived from the Generating Source.
Each of these interconnected "Lines" is an individual _PHASE_

If only Two E&I "Lines" are established by the AC Generating Source, the Polyphase System is "Two Phase".

If Three E&I "Lines" are established by the AC Generating Source, the Polyphase System is "Three Phase".

Since the Animation example above can only be connected across _TWO WIRES_ of an AC Generating Source, there is only _ONE_ E&I "Line" available for use - resulting in a "Single Phase System".

-- Scott


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Oct 2000
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how'd he do that....?

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It is an animated GIF file, like those little cartoon avatars you see on web sites


Greg Fretwell
Joined: Apr 2002
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Never saw that before?

Interesting!!

Thanks Scott!!


John
Joined: Jul 2002
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Scott,
That is the best, mate!
Thanks very much for the effort you've put into diagrams such as this, on this site.
I've sent a few apprentices here saying "Check out Scott's diagrams", they come back the next day and said something like, "Man that guy is pretty good, I learned exactly what I wanted to know".


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