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Power Supply for Jacobs Ladder

ElectroPhile

New Member
Dear All,

I recently built a power supply which works well. It uses the classic LM317T with 4 MJ2955 power transistors as pass transistors and will run a 60W halogen car headlight globe at 13 volts. The pass transistors are mounted on a large 3mm sheet of aluminium. I have built smaller power supplies before, but this is the 1st I have built with pass transitors. I am fairly new to it, but with its two panel meters it looks the part. I was quite proud of it, it is useful as a bench power supply, I built it primarily to power a Jacobs Ladder I had built some years before.

The Jacobs Ladder is the old September 1995 "Silicon Chip" design using a modified electric fence circuit built around a 555 timer and MJ10012 transistor running a 12V automotive coil.

Previously I had run the Jacobs Ladder from a car battery but lugging a car battery in and out and having it on the kitchen table was displeasing my wife...

So I built the power supply, it regulates very well, I tried all different types of loads on it, the regulation was excellent.

I connected the Jacobs Ladder, the arc rose, then silence. On checking over the power supply, the regulator LM317 appeared to have died. In went another, I also added a diode to the 12V input of the Jacobs Ladder, thinking voltage spikes are going back into my power supply.


The 2nd test ran a little longer, but the same problem. Another cooked LM317T.

In powering any other device my power supply is fine. I suspect voltage spikes are making their way back from the Jacobs Ladder, or perhaps the very agressive switching provided by the MJ10012 in the Jacobs Ladder is part of the problem. There was a 16 volt Zener in the Jacobs Ladder across the input terminals. There was, until I accidentally burnt it out when I got the porlarity back the front.

Is it likely to be the switching or is the LM317 receiving the emf from the Jacobs Ladder? Would some capacitance across the output of my power supply help?

I'd be most grateful for any ideas.

Electrophile
 

Sceadwian

Banned
I should hope there already is some capacitance across the LM317 output, it's recommend in the datasheet, and your load is obviously very transient. More capacitance will likely help if it's just a transient issue. Schematics of both circuits would really be needed to give a proper response.
 

HarveyH42

Banned
Are you using a heat sink for the LM317? Didn't look it up, but think its 3 Amps max, and you are probably drawing enough with the car coil. You want a good, cheap, supply for a Jacobs Ladder, get a neon sign transformer. Your local, rowdy, and run down bar will likely have a few sitting around collecting dust, since glass is fragile, transformers are tough. Years ago, I picked up three for free, just for noticing them and asking. Beer signs are advertising, and often 'free' to bars, so the owners don't care too much.
 

Boncuk

New Member
Car ignition coils normally have a resistance of 0.7Ω resulting in a short current of 17A.

The LM317 can stand 1.5A of continuous current.

Using an ignition coil for a jacob's ladder you should connect high capacitance smoothingcaps to the output of the regulator.

A better way would be boosting the output current using a power transistor.

Boncuk
 

ElectroPhile

New Member
Dear All,

Thanks to all of you that replied to my thread. I don't think it's the current drawn, the 4 MJ2955 pass transistors take care but I think Sceadwian is correct, the VERY transient nature of the Jacobs Ladder, it runs at around 130 Hz is the problem. I am ashamed to admit, there is NO capacitence in my power supply. I can easily add some, either across the output or the LM317T directly. Possibly a 16 or 20 or such like Zener across the output might save the wretched LM317T.

I very much also like the idea of using a transformer out of an old neon tube as suggested by Harvy H42. I'm off to Jaycar to buy another LM317T, a Zener and a capacitor, I was thinking of 100 to 500 µF electrolytic but if someone suggests poly or tantalum with a different capacitance value, I am all ears.

I'll also be looking for a neon transformer, my toast to Harvey H42, it would certainly be worth the price of a beer...

Thanks again,

Eloectrophile
 

tcmtech

Banned
Most Helpful Member
Fuel oil furnace ignition transformers work very well for Jacobs Ladders too. Check with the local heating and cooling shops and see if they have a old take off unit you can buy or have on the cheap.
 

Sceadwian

Banned
No capacitance at all? No wonder it blew up =O The output caps are optional though recommended, but the input cap is not.
 

chemelec

Well-Known Member
I have Numerous 15 KV Neon Transformers in Both 30 and 60 Ma ratings.
Unfortunately the Shipping Charges make it difficult to send them Anywhere.
 

killivolt

Well-Known Member
I have Numerous 15 KV Neon Transformers in Both 30 and 60 Ma ratings.
Unfortunately the Shipping Charges make it difficult to send them Anywhere.
chemelec, what would the price for them be? Can you check the cost of shipping ?

PM me.

kv
 

Oznog

Active Member
You should be able to fit it into a USPS flat-rate box. They're not all that large, just heavy.

Be sure to pad them well, you don't want to break off the insulated terminals.
 

chemelec

Well-Known Member
You should be able to fit it into a USPS flat-rate box. They're not all that large, just heavy.

Be sure to pad them well, you don't want to break off the insulated terminals.
If you hadn't noticed, I'm In Canada. NO USPS HERE!
 

Boncuk

New Member
Hi,

how about using an Elektor project? I don't know the English title. The German title is "Lichtbögen auf der Jakobsleiter".

The article was published in March 2006.

The circuit works with standard parts except for some diodes and capacitors. HV is generated by using HV-cascades consisting of a diode-cap network from 1,000 to 10,000V.

Here are the main circuits.

I also attached the full article (German).

Boncuk
 

Attachments

chemelec

Well-Known Member
Hi,

how about using an Elektor project? I don't know the English title. The German title is "Lichtbögen auf der Jakobsleiter".

The article was published in March 2006.

The circuit works with standard parts except for some diodes and capacitors. HV is generated by using HV-cascades consisting of a diode-cap network from 1,000 to 10,000V.

Here are the main circuits.

I also attached the full article (German).

Boncuk
Not very useful for a Jacobs ladder.
 

HarveyH42

Banned
Looks similar to a Marx Generator, but seems like I remember a spark gap at each stage. There was a website dedicated to the Marx generator, might do a search. But if all you are looking to do is a Jacobs Ladder, the neon sign transformer can't be beat. Simple, cheap, and tough to destroy. I've never ran one for more than a few minutes at a time (noise/ozone), but have read plenty on the car coil designs, which seem to run hot, fail frequently, and a few minutes run time is about as good as it gets.
I'm sure the neon transformer would run a very long time, don't see it being abused. I gave my Jacobs Ladder to my brother years ago, not sure what ever came of it. Got one good transformer left, and another with a broken output insulator (dog had an interest in electronics for a while, mostly remotes, extension cords, mix components...).
 

chemelec

Well-Known Member
This circuit will run a Car Coil from Direct 110VAC Line and will run a Jacobs Ladder, QUITE WELL.
But you need to be Aware that ALL PARTS are LIVE VOLTAGE.
SO KEEP EVERYONE AWAY from Touchiong Any part of it.

110 VAC, Car Ignition Coil Driver

I use a Neon Transformer on my Jacobs ladder and put it out on the Porch Every Halloween for the kids to see.
It Runs Continuous for about 5 Hours and they love it.
 

Sceadwian

Banned
I personally think that circuit is just asking for death or serious problems in the case of a component failure, an isolation/currentlimiting transformer on the primary would simplify things.
 

chemelec

Well-Known Member
It basically is Current Limited by Capacitive Reactance. So unless the Caps Fails, No Problem.
And If you use a FUSE as Shown, It will blow if the caps fail.

I have ran this circuit for many HOURS with no Problems.

However, If you don't want your Car Coil to Fail on ANY types of these Coil Driver Circuits, You MUST always have a LOAD, Either Resistive or a Reasonable Arc Length.
Failue to do so, WILL result in Internal Arcing on the coils Secondary, and probable failure.
 

Sceadwian

Banned
chemelec said:
It basically is Current Limited by Capacitive Reactance. So unless the Caps Fails, No Problem.
And If you use a FUSE as Shown, It will blow if the caps fail.
And if the fuse trips there's still a finite amount of energy available during the moment of failure which may be catastrophically high (read as meaning fatal to nearby humans or equipment) You running a circuit regardless of how long without failure does not mean it's safe. The circuit takes care of all best case scenarios, not worse case, and being a public circuit on the Internet recommending that is probably NOT a good idea to thousands of idiots that will try to make it and hopefully do nothing more than trip a fuse.
 

chemelec

Well-Known Member
I Agree there are Idiots out there. And if a Person doesn't have the Skills to make it SAFE, They shouldn't make it!

But there are Many Direct line Projects and Commerical Products on the market. And if you don't take proper care, they can also be dangerous. (Like using a Hair Dryer while in the Bath Tub.)

Even using Current Limiting and an Isolation Transformer, as you suggested, Does Not solve anything, If the Idiot Doesn't know how to Properly Wire them up.
 

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