Lighting a bulb from a short circuit? I hope anyone can explain this phenomenon.

J_Nichols · Mar 7, 2011

While learning electronics, I have experimented with different circuits. After trying some different configurations, I built the schematic shown in the picture, and when I joined the wires together (after the capacitors), the lightbulb lits. This phenomenon, as far I know, is not possible. If you join 2 wires, you get a short circuit. But when I connect the wires to the short circuit, the light bulb works.
Anyone can explain why this works?

mbarazeen · Mar 7, 2011

show in your diagram where exactly you make the short circuit. i beleive the IR value gives enough voltage for teh bulb to work. did you try to put the bulb very close to the shorting points & observed?

misterT · Mar 7, 2011

It is possible if the short circuit is a long wire and/or you make the connection just by pressing two stripped wires together. Long wire creates inductance (and resistance) and bad connection resistance.

MrAl · Mar 7, 2011

Hi,

Yeah, i'd have to also ask what the frequency of the voltage source is and also what the amplitude is before the 'short' is applied.

J_Nichols · Mar 7, 2011

mbarazeen said:
show in your diagram where exactly you make the short circuit. i beleive the IR value gives enough voltage for teh bulb to work. did you try to put the bulb very close to the shorting points & observed?

From left to the right after the capacitors, instead of connecting the positive to one wire to the bulb and then the negative to the other wire of the bulb, I connect the positive and negative together (short circuit) and then I connect each wire of the bulb to the short.
You can see what I mean in the attachment.

misterT said:
It is possible if the short circuit is a long wire and/or you make the connection just by pressing two stripped wires together. Long wire creates inductance (and resistance) and bad connection resistance.

You mean to use a long wire instead the light bulb? explain it more please.
The wire I used is stripped and it's only one wire, I mean that I connect one end to the output of one capacitor and the other end to the output of the other capacitor. In that stripped wire I connect the light bulb, but the wires of the light bulb must be separated I(prevent to touch each wire of the light bulb).

MrAl said:
Hi,

Yeah, i'd have to also ask what the frequency of the voltage source is and also what the amplitude is before the 'short' is applied.

The AC main I use is 230 V 50-60 Hz. After the transformer it's 10 Kv 50-60 Hz.

misterT · Mar 7, 2011

Just stop doing that before you kill yourself..

crutschow · Mar 7, 2011

Your short apparently has some resistance (as do all real shorts) which has enough voltage drop from the current going through it to light the bulb.

J_Nichols · Mar 7, 2011

crutschow said:
Your short apparently has some resistance (as do all real shorts) which has enough voltage drop from the current going through it to light the bulb.

But, why I cannot replicate this effect while using a DC battery without the capacitors and the spark? I mean shorting the battery and connect a 12 V bulb.

I have been testing more the circuit. Now I'm able to say that:
You can touch the short circuit and not get shock.
I can lit the bulb underwater.

misterT · Mar 7, 2011

J_Nichols said:
But, why I cannot replicate this effect while using a DC battery without the capacitors and the spark? I mean shorting the battery and connect a 12 V bulb.

The battery probably is not 10kV battery, or is it?

J_Nichols · Mar 7, 2011

misterT said:
The battery probably is not 10kV battery, or is it?

Not, of course. But it's possible that if I try to replicate the same test using a 10kV AC power supply without the caps and the spark, I will get shocked and the light bulb would only lit only a few.

misterT · Mar 7, 2011

You are creating a voltage divider with the wires and the short circuit. With 10kV there is enough voltage to light up the lamp, but with the battery the (allready low) voltage drops too much. The internal resistance of the battery is much higher than the resistance of your short.

DerStrom8 · Mar 7, 2011

At the higher voltage, the wire used to short the circuit has a higher resistance, whereas at a lower voltage, it has a lower resistance. The more resistance there is, the more current will flow through the bulb.
By the way, are you seriously using a light bulb at 10kV?
Der Strom

crutschow · Mar 7, 2011

I suggest you learn more about electricity before you experiment with 10kV circuits. Unless, of course, you are trying for a Darwin Award.

misterT · Mar 7, 2011

J_Nichols said:
I have been testing more the circuit. Now I'm able to say that:
You can touch the short circuit and not get shock.

Touching a circuit is not a good way to test if you can get shocked or not. Same thing with white powders.. tasting is not a good way to find out if it's cocaine or not.

J_Nichols · Mar 7, 2011

DerStrom8 said:
At the higher voltage, the wire used to short the circuit has a higher resistance, whereas at a lower voltage, it has a lower resistance. The more resistance there is, the more current will flow through the bulb.
By the way, are you seriously using a light bulb at 10kV?
Der Strom

yes, I'm using a common light bulb in a circuit at 10kV and it lights normally.

crutschow said:
I suggest you learn more about electricity before you experiment with 10kV circuits. Unless, of course, you are trying for a Darwin Award.

Yes, of course. But if you know about that thing, could you explain me that?

misterT said:
Touching a circuit is not a good way to test if you can get shocked or not. Same thing with white powders.. tasting is not a good way to find out if it's cocaine or not.

I have took a lot of precautions before touching it. But why you cannot get a shock? when I see high voltage installations they always say: danger high voltage!

tcmtech · Mar 7, 2011

I suspect that what you have is two close coupled coils forming a simple air core transformer of sorts and your spark discharge and related one half of the shorted circuit is working like a primary coil and your second half of the shorted circuit is working like the secondary.

By shear luck you just happen to have created two tuned coils that happen to have similar enough resonance frequencies or harmonics of each other to work.

There is a pretty good chance the you could keep the length of wire shorted between the two capacitors and then use the other half of the short circuit on the lamp as an independent loop circuit that would pick up enough induced power to work without being connected to the primary side of the circuit at all.

misterT · Mar 7, 2011

J_Nichols said:
I have took a lot of precautions before touching it. But why you cannot get a shock? when I see high voltage installations they always say: danger high voltage!

You have to be part of a closed circuit to get a shock. If no current can go through you, you won't get shocked.
Watch this wideo about high voltage power line worker
YouTube - High power line workers

mbarazeen · Mar 7, 2011

J_Nichols said:
......... But why you cannot get a shock? when I see high voltage installations they always say: danger high voltage!

luckily the transformer you are using is having good isolation.........also the out put is NOT grounded at some point.

DerStrom8 · Mar 7, 2011

J_Nichols said:
yes, I'm using a common light bulb in a circuit at 10kV and it lights normally.

The fact that the bulb lights normally suggests that significantly less than 10kV is actually passing through the filament of the bulb. I think you would know it if the full current was passing through the bulb. You are just creating a parallel circuit with two resistors in each branch--the wire acts as a low-resistance resistor, and the bulb acts as another resistor. As long as there's some resistance in the "short" wire, you will get current through the bulb. Since the voltage is so high, a significant amount of voltage also goes through the light bulb, causing it to light.
As for not getting shocked when you touch it, I believe that has already been explained.

ronv · Mar 7, 2011

I think TCMtech has it right. Add a short where you are putting it now. Then clip off the lamp right at the short and add a short to the lamp wires. Now see if you can light the lamp by getting it close to the first short. Even bigger magic?

Lighting a bulb from a short circuit? I hope anyone can explain this phenomenon.

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