Jacob's ladder design - Page 1
Forum section: electronics / general

author: Rachie5272
author_rank: Regular Contributor
timestamp: February 17, 2014, 06:09:38 pm
content: I'm building a Jacob's ladder as a science fair demonstration, and could use a bit of help designing the circuit. Yes, I know most ladders are simply a big transformer and a pair of metal rods, but I want to do things a bit differently.I'm using a microwave oven transformer as the high voltage source, in conjunction with a Cockcroft–Walton voltage multiplier. The transformer is about 1950 VRMS, and I have a big HV 10 k? resistor in series with the secondary winding. I know many people think MOTs are unsuitable for ladders because of the lower voltage, but I think they're great. They can supply much higher current than neon sign transformers, and thus can create much bigger sparks.What's a good way to use the voltage multiplier as a starter for the ladder? Initial tests show it's capable of arcing across the gap, but the multiplier circuit doesn't have the current to draw out the arc. Can I simply place a third electrode at the bottom of the ladder V, allowing it to use the raw high current secondary to arc after initiation?Also, what's a good source of high voltage diodes? I kind of fried mine.

author: Rachie5272
author_rank: Regular Contributor
timestamp: February 18, 2014, 06:25:18 am
content: I tried a different tactic, using a marx generator instead. Not much luck though. It didn't burn out, but it only rarely gave large sparks. I'm still not sure why.

author: Rachie5272
author_rank: Regular Contributor
timestamp: February 24, 2014, 03:18:35 am
content: So, no one knows how to help? It seems so simple.

author: GK
author_rank: Super Contributor
timestamp: February 24, 2014, 03:24:51 am
content: Quote from: Rachie5272 on February 17, 2014, 06:09:38 pmSure, if it's a design requirement that accidental contact with the ladder electrodes on display should result in a 90% probability of death.

author: N2IXK
author_rank: Frequent Contributor
timestamp: February 24, 2014, 03:34:06 am
content: A Marx generator is good for generating HV pulses. You need a continuous voltage for a Jacobs ladder. Usually AC is used, as it gives a hotter "sizzling" arc, rather than the "snapping" of DC (as you will get from a voltage multiplier). The arc rises up the wires because it heats the air, so an arc that is intermittent will just sit there snapping across the base, and not climb the rods.What you really want is a neon tube transformer, or an old fashioned ignition transformer from an oil burner. These transformers are designed to be current limited, and will not burn up even if short circuited. A microwave oven transformer is VERY dangerous for this kind of application, as it can source LOTS of current, and it needs to be rectified to DC in a multiplier in order to get enough voltage to break down the gap.

author: Rachie5272
author_rank: Regular Contributor
timestamp: February 24, 2014, 03:52:17 am
content: But Jacob's ladders need high current in order to create large arcs. I know it's dangerous, but I have a current limiting resistor, and the whole thing will be enclosed in glass and a metal screen. I've used neon sign transformers before, and they don't work very well.I only want to use the voltage multiplier/marx generator as a starter to jump the gap initially. Once a low impedance path is established, the lower voltage can take over.

author: 6E5
author_rank: Regular Contributor
timestamp: February 24, 2014, 03:53:22 am
content: Quote from: GK on February 24, 2014, 03:24:51 amI strongly recommend you don't use a MOT.Many years ago I wasn't paying attention and I got shocked my a MOT. It was a wonder that I didn't die, but I was in the hospital for a week. I haven't touched another one since.I'm sorry to be such a downer, but these things are literal deathtraps and will kill you in a moments notice. 2kv @ 1/2 isn't cool, it's scary.

author: andtfoot
author_rank: Unknown
timestamp: February 24, 2014, 04:02:39 am
content: From memory, the Jacobs Ladder kit from Jaycar uses a 555 timer in astable mode into a power transistor/mosfet/something to drive an automotive coil.Doesn't seem to work too badly for coat hanger rod sized ladders.

author: Joshuamcd22
author_rank: Contributor
timestamp: February 24, 2014, 04:56:51 am
content: Quote from: 6E5 on February 24, 2014, 03:53:22 amWhile I do agree that mot's are incredibly dangerous and can kill you. I still think that you can use one,as long as you know and follow proper safety procedures, as with any high voltage at lethal levels. I have personally used a mot for a jacobs ladder project, and I never even think about plugging it in without a second person standing by on a kill switch. I also use a 6ft chicken stick if I need to adjust anything while its running, or bridge the gap to create an ark. Also, NO other person is allowed to come within 10-15ft of anything while running at high voltage, or I press my kill switch.Finally I physically disconnect the mot from my kill switch and the mot from the ladder, before anyone, including me, approaches the ladder without using a safety stick.All that being said, mot's are still very dangerous, and I, like 6E5, would advise that you don't use one, unless you have the needed knowledge to not kill yourself.If you don't have the needed knowledge, or even haveany doubts at allabout your ability to remain safe, you can curb your high voltage cravings by watching a bit of photonicinduction

author: Strada916
author_rank: Frequent Contributor
timestamp: February 24, 2014, 05:36:41 am
content: siliconchip magazine did a Jacobs lader mk11. 555 oscillator with an automotive spec transistor. which then fired a gmc v6 dual coil pack. ( aka as holden commodore v6 coil pack. ) not sure what issue have a look atwww.siliconchip.com.au.

author: Psi
author_rank: Super Contributor
timestamp: February 24, 2014, 06:18:17 am
content: The main safety concern using a MOT in something isn't just you own safety, it's the safety of others who are ignorant of the danger or drunk around the device.If you use a MOT in a Jacob's ladder make absolutely sure no one can touch anything live or get within arcing distance.

author: krux
author_rank: Unknown
timestamp: February 24, 2014, 07:09:25 am
content: Quote from: Rachie5272 on February 24, 2014, 03:52:17 amThey mostly need high voltage to bridge the gap, not high current. I have used a high voltage capacitor (or MMC) in parallel with the gap to increase the size of the spark without having to change out the neon sign transformer. Making a "beer bottle" capacitor is a good method of this. Alternatively you can run NSTs in parallel (never in series) to give you more power. But unless you are damn certain it is being operated safely 100% of the time don't use a MOT, as they WILL kill you the instant you don't respect them.

author: Rachie5272
author_rank: Regular Contributor
timestamp: February 24, 2014, 07:43:14 pm
content: As I said, everything will be behind glass and a grounded mesh screen. I'll have several kill switches, as well as a physical lock. I've worked with high voltage before, and always use a long plastic pole to manipulate things, keep one hand in a pocket, discharge any capacitors before touching, and staying well out of the radius for things tipping over.This is going to be a fairly large ladder, at 1.5 m tall. Neon sign transformers aren't likely to work here. I already have the mechanical supports figure out, but I'm still not sure how to make a high voltage starting circuit. Would it make more sense to wind a small transformer in series with one electrode, and connect it to an automotive ignition coil? The thought is the ignition coil can provide a small high voltage pulse to make an initial spark at the bottom, while allowing the main transformer to continue providing higher current, allowing the arc to be drawn out.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 24, 2014, 11:24:40 pm
content: Try adding some intermediate electrodes with current limiting resistors.http://bigclive.com/jacobs.htm

author: 6E5
author_rank: Regular Contributor
timestamp: February 25, 2014, 04:49:29 am
content: In the end, it's your choice. I didn't listen to the warnings about MOTs either.