What kind of transformer/power supply is needed to make Lichtenberg Figures?

[drummerdimitri]

I've been wanting to make Lichtenberg Figures in wood but I have some doubts regarding what kind of voltage and current levels are needed to make such figures.

It would make sense that the larger the piece of wood the more voltage is required to create the pattern since the resistance increases between the two points of contact.

I've seen people using microwave oven transformers however, I'd rather not fool around with the wiring of those as any mistakes can be lethal so instead was looking for an all in one solution.

I've found a 10 KV Neon transformer that can output 30 mA of current however I am not sure if this is enough current to create the patterns.

How can one do this safely?

[cdev]

Be careful!

They are very pretty but we would hate to lose you, or anybody here, ya know!

[DaJMasta]

I think most of the safety options actually just come from your environment and handling of the equipment.
a cutoff switch that isn't just connecting up the transformer and is not right next to what's powered
make sure nothing will fall on it, that it's mounted sturdily so it won't fall
make sure other people/animals can't mess with it
wear eye protection, make sure there's adequate ventilation, keep an extinguisher (one that works on electrical fires) nearby
an enclosure of some sort may be good for your power supply, in case it doesn't protect itself from overcurrent/heat, especially


You know, the sort of stuff that's easy to forget but is also easy to set up to dramatically improve the safety of your experiments.  It's worth reading up or watching videos for it as well, especially if they detail their setups, safety precautions, or operating parameters.  I've heard of people applying stuff to the surface to encourage the pattern forming with lower voltages (maybe water to moisten the surface?) and using nails driven in as mounting points - you could get a board with several at different distances and see how a given voltage fares in terms of distance and speed.

[floobydust]

Big Clive uses around 4kV 25mA neon sign transformer and covers some safety points.
He is against MOT because there the HV output winding has one leg tied to earth ground, which is why people get electrocuted touching the artwork in progress.

[james_s]

Neon sign transformers have the center tap tied to ground, so they are little safer in that respect. They are current limited to a much lower value which is unlikely to be lethal, but it can still certainly be dangerous.

[drummerdimitri]

Thanks for the replies and I figured the neon sign transformer would be the correct option as it is current limited and that's what kills!

Should i get a 10 KV model or a 4KV model? Will I be able to use a variac to somehow have some degree of control over the output voltage for different wood grains/sizes?

[SeanB]

Depends on the transformer if the variac will control it. Electronic ones ( the most common ones) do not work well off a variac, while the heavy magnetically ballasted ones do work quite well off the variac, though as they have magnetic shunts in them the voltage output is not linear with input current.  10kV will work better, and make bigger figures possible, but whatever one you get will work for the style shown by Big Clive.

[floobydust]

... I figured the neon sign transformer would be the correct option as it is current limited and that's what kills!

No, you're a little off-  electrocution danger is still there even if your transformer has much less output current. Going from 500mA MOT to 30mA neon sign transformer - it's still way more than enough current available to kill, especially if left-handed.
The reduced voltage is less danger as your shoes, gloves would not arc-through as easily, but this is still trusting your life to luck.
For the safety aspect, you need discipline to not move electrodes or spray water when power is on!
Using HV safety boots, an insulated floor, a fence so kids/pets don't come running in, HV gloves and a stick to poke things etc. are some ideas.

A neon sign transformer has a constant-current characteristic so it may do better than an MOT which is fierce at burning things. I thought the 10kV ones have shunts and a tertiary winding and resonant capacitor and don't simply throttle down. The voltage for making the arcs is also about the size of the piece.

[james_s]

A MOT has magnetic shunts just like a neon transformer so it is also limited, but the limit is far higher.

You should look for one of the old style iron transformer types, the modern electronic neon transformers are much more prone to blowing up if you use them for things other than their original design purpose. You might call some sign shops in your area and see if any have a pile of old transformers and offer to buy a few. Newer outdoor neon transformers have a GFCI built in which seems to be rather failure prone, fortunately you can usually remove it fairly easily, I fixed one that had the GFCI inside the casing but on top of the potting and it was easy to find the wires leading to the center taps and wire them together with the GFCI removed.

[Teledog]

A little late on the comments here..
I use a 12kV 30mA old school (not switching) neon sign transformer, attached to a Variac with a voltage readout (usually start around 80VAC & work up until something happens)
Also, big important things here..I use a (fused) deadman's pedal to switch the line AC,  and a long insulated probe, one hand behind the back and insulated CSA or rubber boots.
Huge fan running in the garage with the door open (it is smokier than h*ll!)...not a terribly healthy project, by any means.
Wetting /misting solution is baking soda and water.. don't ask the proportions..~ 1/2 tsp in 500ml water maybe-ish??
Wood penetration varies like you wouldn't believe..depends on the wood, moisture, etc.
Leave it on a thin laminated wood too long (ie: dollar store wood boxes) & the baking soda discolors & warps the wood.
Lots of (smoggy) experimentation for sure!
Good luck & above all, be safe!!!

**edit** Also..use at least 20kV wires..please!!