S
ScottM
For an art project, I need to generate a bright, noisy arc about 1/2" long.In the past I've successfully done this with with this: https://www.sparkfun.com/products/11218 but that isn't working in the new installation; the devices get hot and fail after a few minutes of use. I'm looking for someonewith expertise in this area to suggest a design I can build.
The requirements are:
Able to be run off a small 12v lead acid battery. Extra points if it can run off 5v and 3A, which is what the sparkfun device uses.
Portable - I'll be carrying the circuit in a backpack. Large Marx generators need not apply. Neither do designs that require twenty pounds of copper tubing.
Stable and Safe - I'll be carrying the circuit in a backpack and long term stability is a concern. It will be heavily insulated but I am still very uninterested in sudden failures, magic smoke, fires, internal arcing, and other surprise effects. I need long-term reliability.
A bright, fat, noisy, snarling, visually continuous arcing spark - which probably means I need an output frequency somewhere between 40Hz and 200Hz. Idon't have specs on the sparkfun device, but it does "loud" and "bright" very well.
Capable of more or less any duty cycle; the design calls for about 10 seconds on and a few seconds off, repeating, but I want it to be able to run continuously.
Able to survive any sort of spark gap from "too big to actually arc" to "brief short circuit", but the typical gap is 3/8ths inch to 3/4ths inch.
Repeatability - I need to be able to build several and I want repeatability, so "scavenge a flyback from a CRT" is much less interesting than a mouseror digikey part number.
And - crucially - able to handle a capacitive load. The high voltage travels through two longish (several feet) parallel wires, though a small brass tube and into a chunk of aluminum that showcases the spark, but it all adds to the capacitance, and I think that's why the sparkfun devices are dying.
I'll say it now - yes, I know a spark that can bridge 3/4" and be "fat", bright and noisy requires tens of thousands of volts and several mA. I know that misuse of that kind of power leads to pain and possible death. Since I'll be carrying the device and the high voltage wires will be running down my arm I will be paying a lot of attention to insulation and safety concerns.. Extra points if the voltage and current can be minimized to limit risk, but no matter what I will consider any design as potentially fatal and treatit accordingly. I know about the one hand rule, and "heavily insulated" ismy favorite phrase.
I just built a Mazilli ZVS circuit (http://wiki.4hv.org/index.php/Flyback_transformer#High_Power_Drivers), and it works as advertised but it's not suitable here. Running the output through a twisted pair of insulated bell wire caused a very pretty purple corona glow along the length of the wires, and no spark at the end. When it does spark. it's much too high frequency - it hisses instead of snarls, and glows instead of being a fat bright spark. And it's too powerful - the voltage cracks the glass tubing I use as insulation. If it's possible to lower the frequency (greatly) without destroying the MOSFETs, it could be a candidate, but I don't know how to do this safely.
I'll accept any help, but I'm less interested in "well, you could try this"than "here is what is known to work." I've been researching things I couldtry for days, but mostly I've fried components and lost time. If you have expertise and don't mind drawing a schematic I will be very grateful. TIA!
The requirements are:
Able to be run off a small 12v lead acid battery. Extra points if it can run off 5v and 3A, which is what the sparkfun device uses.
Portable - I'll be carrying the circuit in a backpack. Large Marx generators need not apply. Neither do designs that require twenty pounds of copper tubing.
Stable and Safe - I'll be carrying the circuit in a backpack and long term stability is a concern. It will be heavily insulated but I am still very uninterested in sudden failures, magic smoke, fires, internal arcing, and other surprise effects. I need long-term reliability.
A bright, fat, noisy, snarling, visually continuous arcing spark - which probably means I need an output frequency somewhere between 40Hz and 200Hz. Idon't have specs on the sparkfun device, but it does "loud" and "bright" very well.
Capable of more or less any duty cycle; the design calls for about 10 seconds on and a few seconds off, repeating, but I want it to be able to run continuously.
Able to survive any sort of spark gap from "too big to actually arc" to "brief short circuit", but the typical gap is 3/8ths inch to 3/4ths inch.
Repeatability - I need to be able to build several and I want repeatability, so "scavenge a flyback from a CRT" is much less interesting than a mouseror digikey part number.
And - crucially - able to handle a capacitive load. The high voltage travels through two longish (several feet) parallel wires, though a small brass tube and into a chunk of aluminum that showcases the spark, but it all adds to the capacitance, and I think that's why the sparkfun devices are dying.
I'll say it now - yes, I know a spark that can bridge 3/4" and be "fat", bright and noisy requires tens of thousands of volts and several mA. I know that misuse of that kind of power leads to pain and possible death. Since I'll be carrying the device and the high voltage wires will be running down my arm I will be paying a lot of attention to insulation and safety concerns.. Extra points if the voltage and current can be minimized to limit risk, but no matter what I will consider any design as potentially fatal and treatit accordingly. I know about the one hand rule, and "heavily insulated" ismy favorite phrase.
I just built a Mazilli ZVS circuit (http://wiki.4hv.org/index.php/Flyback_transformer#High_Power_Drivers), and it works as advertised but it's not suitable here. Running the output through a twisted pair of insulated bell wire caused a very pretty purple corona glow along the length of the wires, and no spark at the end. When it does spark. it's much too high frequency - it hisses instead of snarls, and glows instead of being a fat bright spark. And it's too powerful - the voltage cracks the glass tubing I use as insulation. If it's possible to lower the frequency (greatly) without destroying the MOSFETs, it could be a candidate, but I don't know how to do this safely.
I'll accept any help, but I'm less interested in "well, you could try this"than "here is what is known to work." I've been researching things I couldtry for days, but mostly I've fried components and lost time. If you have expertise and don't mind drawing a schematic I will be very grateful. TIA!