# A Portable Jacob´s Ladder

A Jacob´s ladder is a favorite project of high voltage enthusiasts. It makes a visually attractive and fun display of a high voltage electrical arc climbing a pair of electrodes. [Keystone Science] shows us how to make a Jacob´s ladder that runs on 9 V batteries.

The ladder itself is pretty easy to make. It is nothing more than a pair of stiff wires in a V shape, connected to a high voltage power supply. The more difficult part is the HV power supply. [Keystone Science] explains how to build one using a flyback transformer from an old CRT tv and a few other components. It is a pretty simple circuit and can be powered by a 9 V battery. The ladder works because, when HV is applied to the electrodes, an arc is established at the bottom, where they are nearest each other. The arc is at high temperature so the air rises, and the arc starts to climb the ladder. Since the electrodes are further away from each other as the arc rises, at a certain point the distance is too large to sustain the arc and the process repeats.

This is a nice weekend project if you want to try it. In case you don´t want to make your own HV power supply, you can try another ladder project that uses a commercial one.

## 16 thoughts on “A Portable Jacob´s Ladder”

1. Als says:

I kind of know what I am doing and these flyback transformers projects make me nervous. I wonder what chance they have to kill newbies trying to get them out old tvs and connecting them to real voltages.

1. RÖB says:

The High Voltage (HT) output isn’t too bad as the input drive voltage is low but not mentioned is how to discharge the TV tube so that you can remove or cut the High Voltage wire.

A Flyback Transformer (LOPT) normally runs at 90v to 160v. This project runs at 6v – 24v.

It’s still dangerous if mishandled but it’s not at the worst end of the scale.

Just learn how to discharge a tube before you start.

1. Martin says:

You can disconnect the HV “suction” cup by pinching it in the right way without touching the connection point on the tube.

1. The last thing you want is an imploding tube. I had one go off in my shed in my early teens. Luckily it was the fact I closed the door and a something fell on it. Scared the shit out of my through. Opened the door to see horizontal shards of glass in every surface.
Respect is required. Also the plasma tends to burn fingers if you hold it for too long. :D

2. RÖB says:

Flyback transformers have an inbuilt voltage tripler and the capacitor in that will sore energy to, so you really do need to discharge first.

In any case I would never suggest to go anywhere near the anode cap until the tube is discharged. Not even to lift the cap a little to assist with inserting the discharge tool.

2. Jeff says:

Watching the included video of his guy building this…. made me feel a bid anxious with how little time between each time he moved from one step to the next.
Pacing man!

3. matseng says:

“The base, emitter and collector of my mosfet transistor”… :-) :-)

1. RÖB says:

It was a bipolar (2SDxxxx) and probably had an internal diode from emitter to collector so perhaps the diode made him think it was a MOSFET.

1. hubert says:

He has more Videos online. In all of them he uses bipolar transistors and calls them Mosfet. But for me thats ok.

2. ComeOnNow says:

And in his schematic, he uses the symbol for a BJT. I don’t think he knows the difference.

1. Als says:

Maybe he is confusing it with BobaFET

3. RÖB says:

It’s a 2SD1878 with internal diode to shunt any back EMF from the flyback transformer (LOPT) and has a base shunt resistor to bleed off any base voltage from the parasitic capacitor Cbe so that it shuts off faster and acts more like a switch and reduces heat dissipation from keeping away from the linear range (partially on)

4. Chris says:

Let’s see… seventh grade would have been more than 35 years ago for me, As the son of an electrician I had a fair amount of exposure to electrical knowledge as a youngster, built one of these with a 10,000v electric fence transformer as a science project for class. Mine wasn’t particullarly portable as it had to be plugged into a normal US 110v wall outlet.Fun to play with, when you exercise appropriate caution.

5. ejonesss says:

mosfets have drain gate and source not base emitter and collector.

so it probably a normal power transistor.

6. Sgt Sandbox says:

These can be built with the transformer from a household oil burner, the kind many people heat their homes with. They can be bought at your average plumbing/HVAC supply store.

Just sayin’.

7. dbear says:

I can’t watch the video but they work much better if enclosed in a glass or plastic tube. Any ambient breeze will blow out the spark otherwise.