It occurred to me that it should be possible to charge the quarter shrinker using a battery and a couple of transformers in series. Let’s try it and find out!
After digging through my old box of transformers, I found a couple that didn’t arc too badly when powered up. I connected the outputs in series, using two independent ZVS circuits to drive them. The final output is approximately 20kV at 30mA with a charged battery.
I also added a little fan to help cool the IGBTs on the driver boards.
It began charging as expected, quickly climbing to a couple of kilovolts. At around 7kV, the rate slowed a bit. The fan gradually slowed down, and various components (the battery, main switch, and IGBTs) all started to heat up.
By 8kV (about two minutes charge time) it was clear that the battery was about to give up the ghost. I switched it off at 8280 volts and pulled the trigger.
The results were excellent! The coin in the middle was shrunk on battery power. The one on the right was from an earlier run with the usual NST supply, fired at 10kV. The standard quarter on the left is for scale.
I think it was a very successful experiment. If I swap the cheap IGBTs on the driver board for beefier switches, I think I can put together a reasonable power supply that lets us shrink on battery power all the way up to 10kV.
That will be handy next time there’s a tiny coin emergency during a power outage.
Back in 2009, I was one of several folks that built the coin shrinker at Hackerbot Labs. After several hundred firings and sitting in a closet for months, it badly needed some love. We moved it to my shop and I got to work.
As with most projects on this site, the hazards here are many and subtle and include high voltage, extreme UV production, supersonic shrapnel, a several Tesla EMP, charging and discharging hazards, toxic smoke… In short, DON’T TRY THIS AT HOME. Come to my shop instead and we’ll shrink some coins. ^_^
Here’s a breakdown of how the Quarter Shrinker does its magic.
Energy is stored in three 10kV/100uF Aerovox capacitors wired in parallel with thick copper bus bar. The capacitor bank is quite heavy, weighing in at about 200 kg (450 pounds). When fully charged, the capacitor holds 15,000 joules. Is this dangerous? To quote Wikipedia,
Any capacitor containing over 10 joules of energy is generally considered hazardous, while 50 joules or higher is potentially lethal.
Caution is clearly advised.
(Aside: we do in fact see dielectric absorption hysteresis after every firing. This toy can be lethal even after you think you’ve turned it off!)
The capacitor is connected to a high voltage DC power supply for charging. It includes a neon sign transformer, variac, and high voltage rectifier. The state of charge of the capacitor is monitored using a cheap semi-disposable volt meter and a 1000:1 voltage divider. Every volt on the meter represents 1000V on the bank.
The red and black twisted leads are connected to a hinged plate that is raised during use, but can be brought down at any time by pulling a long rope. Doing that immediately puts a large resistor across the capacitor, quickly and safely discharging it.
The main switch is a mechanical trigger with tungsten carbide contacts and an HDPE and delrin housing. It too can be gravity-closed by pulling a long rope. This is assisted by a rubber band made of surgical tubing, closing the switch as quickly as possible.
The trigger is shaped so that the contacts come very close together, but don’t actually touch. This keeps them from welding to each other or getting damaged from physical impact.
Current starts to flow well before the contacts come together, creating a fantastically bright flash of light (including ridiculous amounts of UV). Do not look at trigger with remaining eye.
The big plastic box on top is the blast chamber. It’s designed to absorb the force of the exploding coil without breaking. A baffle system allows the rapidly expanding air and copper vapor to escape while trapping the copper shrapnel inside.
The copper coil consists of twelve windings of 12 gauge solid copper wire. Vice grips clamp the wire to the copper bus bar. As with nearly everything on this machine, the vice grips, sacrificial chunks of HDPE, and bus bar ends are all semi-disposable.
Physics Girl has a fantastic description of the physical forces at play, including how the quarter shrinks and why the coil explodes.
After pulling the trigger, the capacitor discharges in to the coil, shrinking the coin in less than 40 microseconds. The explosion is extremely loud. Ear protection, distance from the machine, and yelling “fire in the hole” are all mandatory.
The resulting shrunken coin glows white-hot during the process, and is quite hot for several minutes afterwards. Some of the copper coil is vaporized by the electric arc, creating a green copper plasma. The coin is typically covered in an atomically thin layer of copper, discoloring it. (Note to self: try to get an SEM photo of the copper plating on a coin when Millie is back online.)
My shop-mate Sirus made a nice 4k video of the setup process and first post-rebuild firing. (The charge time is probably greater than your attention span. To skip directly to the trigger pull, CLICK HERE.)
I finally got around to making a couple of much needed upgrades to the Tesla gun. First: a trigger! I had previously been using a switch with a molly guard as the on/off mechanism. Now the switch “arms” the gun and turns on the turbine fan (both as an audible warning and to keep the HV switch cool). When it’s armed, just pull the trigger for lightning-at-your-fingertips convenience.
The second upgrade was a better, cooler hockey puck of doom. This one uses silicone compound impregnated with hexagonal boron nitride. It conducts heat much better than straight silicone, and should theoretically extend the life of the hockey puck driver.
I couldn’t find a heat sink of appropriate size, so I cut one out of an old discarded 12″ Mac Powerbook. It was covered in stickers, which I think greatly add to the aesthetic appeal of the resulting heat sink.
Finally, I added a new grounding ring with better strain relief to the back of the gun. This makes a much stronger mechanical connection to the gun. The wire is soldered on for the best possible electrical connection. The wire doesn’t carry much current, and needs to flex well, so I used some stranded 18 AWG.
With these upgrades, I think the Tesla gun is ready for the busy summer zapping season!
Staci Elaan is an electrical engineer who has been making Tesla guns since 2006. Her sixth generation MK6-18V is a battery powered, solid state piece of badass kit:
In the course of building my Tesla gun I had trolled YouTube and had found a few odd videos, like RMCybernetic’s infamous plasma gun:
…and this sketchy fellow:
But I wanted to build something different. Yet somehow I had missed Staci’s incredible designs. Back in May she published a history of Tesla gun designs in an effort to set the record straight. I had no idea that hand-held Tesla gun designs have been around since at least 2004!
My project got a surprising amount of attention for an idea that has been around for the better part of a decade. The Tesla gun I built this year is by no means the first (or even the first battery powered device). My simple static spark gap design is a kid’s toy compared to some of the solid state designs that came before mine.
My hat goes off to Staci and all the pioneers of hand-held lightning devices!
Do you know of other Tesla gun builds that haven’t gotten the attention they deserve? Post them below!