ELF-A Experimentation Notes

Documenting my experiments in developing a portable Lorentz Force Accelerator.

Bench Top POC

The first step to getting ELF-A built is getting a bench top proof of concept going. I need to build a mini-rail gun. The pieces do not have to be pretty, well-crafted, or mobile or even ready to go onto a mobile platform. I just have to prove the electronics and functional process work.

My current challenges include figuring out how to craft the rails and getting a high voltage source (HVS) operational.

My current plan is to craft the rails out of erector set pieces that have been stacked to the appropriate thickness (~6 mm, remember we're using aluminum airsoft BBs as projectiles) and then sanded to provide a smooth edge. I'll probably mount them a little close together. Closer to 5mm than 6 so I can then use a bristle drill bit to give the rails a bit of a rounded profile to better fit with the spherical projectile.

As far as the HVS, I've been experimenting with the electronics out of a CFL. By design these things take 120 volts input, rectify it, use two transistors (or MOSFETs / power FETs with heat sinks on the larger-wattage models) to oscillate at around 40 kHz, then kick out a 1000 Vac output. 1000 Vac is the “ignition” voltage for a CFL. Operationally they normally run at around 300 Vac, but a greater voltage is required to start the bulb.

I've experimentally determined that 8.5 volts (ala a 9 V rechargeable battery) is not enough to get the oscillator going. Using a nice little LM2596 based booster converter to take that same battery up to 40 volts proved the CFL circuit just needs more volts to work. At 40 V I could hear the circuit clicking at around 120 hz (guessing by ear). I cranked down the booster converter's output until it the CFL stopped clicking. That was around 30 volts. So we'll say minimum operational voltage is 30 volts.

At 30 volts (and 40 volts) I measured the CFL circuit's output. It started around 350 V and crept slowly upward to 1000 volts. Bingo. At 1000 volts, my multimeter started beeping its safety limit warning and the booster converter cut out.

I'm annoyed the oscillator doesn't work at a lower voltage. My ultimate plan is to use an 18V battery to power the complete ELF-A. I do not want to have to throw in a booster converter between the two. I could just fall back to my original plan of making my own oscillator and step up circuitry but that does not sound like fun or a good use of time and resources. I may drop a few dollars buying up various CFLs from a thrift shop and see if any of them can operate at a lower voltage.

I still, despite many books and online videos, do not fully understand the operation and interaction of basic electronics components well enough to design the exact circuit I need. I'd rather not have to (poorly) reinvent the wheel. Much better to plug well-designed components into one another. But at the same time I want to minimize the amount of components I have.