Do you understand this electrical scheme?

[tsuwal]

I would like to understand the part of the circuit that is inside the red rectangle in the following picture:

overpic.net/viewer.php?file=xhwae5mil75gq8e7pzpyu.jpg

Thanks for your time.

[Turtle]

Originally Posted by tsuwal

I would like to understand the part of the circuit that is inside the red rectangle in the following picture:

overpic.net/viewer.php?file=xhwae5mil75gq8e7pzpyu.jpg

Thanks for your time.

OVERPIC.net Image Viewer

Just looking it over it's the trigger circuit, but I guess you knew that. What exactly do you need to anser about it?

While they call S1 a "silicon power cube", the diagrammatic symbol is that of a transistor. Looks to me like the circuit in the red is using a switch to apply a voltage to the transistor which then closes (switches on) the high-voltage part of the circuit to energize the coil & fire the projectile. This strikes me as analagous to using a relay in order to switch high-voltage/current circuits with low voltage/current circuits.

Hope that helps.

[C1ay]

Originally Posted by Turtle

While they call S1 a "silicon power cube", the diagrammatic symbol is that of a transistor.

Actually the symbol is of an SCR or thyristor, a device that latches in the "On" or current passing state until the current through the device is interrupted by some other device or the source voltage drains to the point that the current drops low enough for the device to unlatch. See The Silicon-Controlled Rectifier (SCR) : THYRISTORS for more info.

[engineerdude]

To expand a bit on what Turtle said above,

Component S1 is called a solid state relay. It is similar to a transistor, but it is an on-or-off device only. B1 is a 9v battery, SW1 is a push button switch, and R3 is a resistor that will limit the current that flows from the battery B1. If you didn't have the resistor R3 you'd probably get more current than S1 could handle.

If we close switch SW1, a current will flow in the loop, including through the relay S1. These flowing electrons "switches on" the relay, and allows current to flow from 3 to 1 in the relay S1. This current that affects the state of the solid state relay is called a "bias current". When the bias current stops, the relay will shut down.

Why have the relay at all you may ask - doesn't the switch SW1 do the same thing as this circuit in the red box? The answer is that you don't want humans to come close to dangerous voltages - it looks like the main part of the circuit runs at 200VDC, which is way dangerous. With the circuit like this the switch SW1, which a person would push to make things happen, never sees more than 9v, so if there was a short or something nobody would get zapped too harshly.

[Karnuvap]

Originally Posted by engineerdude

Why have the relay at all you may ask - doesn't the switch SW1 do the same thing as this circuit in the red box?

Plus the point of the circuit is to dump all the charge from the Caps into the coil as quickly as possible. A simple switch would be inefficient at this as a lot of the energy would be lost in the arcing of a switch's contacts.

The clue is in the name - this is a coil-gun - the massive pulse into the coil will create a magnetic field which (as it rises very rapidly) will induce an opposing magnetic field in the slug of iron which will cause the iron projectile to be ejected away from the coil at speed.

Let us all know how you get on if you get this coil gun to work.

The Vapinator.