Clearing confusion with the 230Vac single phase Power Supply Diagram (10 70 230)

[sprayhead]

I'm trying to understand the power the circuit and how each part in it works. A lot of it seems straightforward.

I've got doubts with the 240V E-stop circuitry, ... I did my best to show it through a picture. The circuit includes the Lockable Disconnect Switch, E-stops, a light, the on/off buttons and the contactor. Would someone be patient enough and try to explain how these components interact?

Also, there is a text tag next to the Toroidal transformer that says 1.3amp 300VA. Why is that? At that point Isn't the current a lot higher than that at all times?


thanks
Francis

[Richards]

My eyes aren't good enough to see every detail in the schematic, but let me try to explain how the basics work.

1. Main disconnect switch (usually red handle with a yellow guard). It connects/disconnects all power from the service panel to the controller box. In the drawing, only two poles of three poles are being used, line and neutral. Notice that the Line (hot, power) is routed through a fuse and then through some Normally Closed switches (limit switches and/or E-stop switches). After going through those switches, you get to section 2.

2, 3, 4. This is where my bad eyes just couldn't see clearly enough to describe exactly what the drawing does; however, the Line (hot) connector is routed through a N/C (Normally Closed) Off/E-stop switch and then through a N/O (Normally Open) Start switch. When the Start switch is pressed, the coil of the contactor is energized and the contacts close. In the drawing, immediately above the contactor is drawn the contactor's auxiliary switch. The N/O contacts of that auxiliary switch is used to self-latch the contactor. That means that once the Start switch has been pressed, the contactor's coil energizes and the auxiliary switch closes. Line voltage is routed through the auxiliary switch to keep the contactor's coil energized. The contactor stays energized until the Off/E-stop switch is opened or until the main disconnect is opened. There is also an illuminated indicator in this section that turns on when the contactor is energized to visually warn the operator that the circuits are active.

5. The fuse to the main transformer. Size it to meet your needs. (Remember that the main purpose of a fuse is to stop a fire, not necessarily to protect the electronic parts.) A toroidal transformer is about 90% efficient, so you would divide the output voltage by the input voltage, multiply the result by the current rating of the transformer. Finally you multiply the product by 110% to adjust for the transformer's efficiency and you have a basic idea of the size of fuse that you need. For example, 120VAC line, 25VAC transformer, 12 Amp maximum draw. (25 / 120) X 12 = 2.5A. 2.5A X 110% = 2.75A (slow-blo) fuse. As long as the current passed by the fuse is less than the current allowed by the wire gauge, the wiring should stay within its temperature range. (Trust me when I say that you don't want to scrape melted insulation off every component in the control box just because you tried using 22 gauge wire to feed the transformer. I was a young man, with dark hair when I did that, but some lessons are never forgotten.)

[sprayhead]

Thanks heaps Mike for your contribution and Interest. Too bad a lot of us are so far away, It would be great if we could gather for Barbies, Beers and CNC.

I have zoomed in the circuit that was too small on the other picture.

F.

[Richards]

That's much better. Now that i can see the drawing, I'll try to describe section 2 in a little more detail.

L1 (Line or Hot) becomes available when the main disconnect switch is turned on (Closed). Next, L1 is routed through the 1A fuse, through the Normally Closed E-stops (all E-stops are wired in series, so all MUST be closed to allow electricity to pass), through the Normally Closed Off button to the Momentary On button. When the Momentary On button is pressed, the contactor's coil is activated. As soon as the coil activates, the Momentary On button can be released and the contactor's coil will stay energized because the Auxiliary switch contacts are closed along with the contactor's other switch contacts when the coil's magnetic attraction pulls the contacts closed. Also, when the auxiliary switch is closed, the On Lamp is activated. To turn the contactor Off, electricity to the coil must be interrupted by opening one of the Normally Closed switches (any switch, since they are all connected in series), or the main disconnect must be opened.

Also, note that Neutral is always connected to the coil. If Neutral were not permanently connected to the coil, the coil would never activate.