Come and Meet Extreme Electronics and the Twin PI tesla coils (and some other stuff 🙂 at Derby Mini Maker faire. We will be by the jet engine just off the main hall.
Ok so it started as one of those phone calls that asks if I can make safe sparks. Quite a regular ask for me and I always start with no. High voltage isn’t safe.
Anyway after a number of discussions. I was asked to make a “relatively” safe way of allowing a BBC presenter to create lichtenburg figures.
The method I came up with was to use a 15KV OBIT (Oil Burner Ignition Transformer). I prefer this type of transformer to a MOT (Microwave Oven Transformer) for purely safety reasons. One touch from an MOT and you are either Burnt, Dead or Burnt and Dead, Not good odds. This is due to them giving up to 100mA at 2KV, plenty to get 1-2mA across the heart of the unwary. The other issue with MOT’s is they are low enough voltage not to cause corona, which means they are silent, a dangerous mix. OBITS on the other hand give out 10-15Kv at 5-10mA. Not safe, but you are much more likely to survive an accidental contact. Also due to the OBITs high voltage, you can hear when they are on.
The boxes were split in to two, the Transformer and high voltage at the “HOT” end and the lower voltage (mains) at the other.
The control box had a key lockout which needed to be in place for the HV to be turned on. This key was attached to me with a short lead so I could ensure the HV area was safe before I allowed any power to the box. The Go button was momentary, so that if any danger was spotted the power could be quickly removed.
The HV end was in a roped off area (out of shot)
The mains was supplied via an earth leakage trip for added safety.
The HV end was supplied via 30KV insulated cable to two crock clips that attached to the screws on the board.
The board was dampened with water and washing up liquid, (required to properly soak more than just the surface of the board)
This really is a don’t try it at home experiment, when the power is on, you can’t touch ANYTHING, damp wood, water and high voltage not a good mix.
Luckily the presenter was Marty Jopson a HV fan so the explanation and safety briefing was fairly easy as he understood the risks. (He has his own collection of HV equipment including a one Tesla.)
This was all done in the most glamorous of locations 🙂
The result. No one died… and I think they got a good film of the Lichtenburg figures being produced. I will find out 19:00 BBC1 4th July 2016.
Other Making Lichtenburg links
Im bound to lose this card, so a link to it so I know here it is
The PIZero Simple setup without network or monitor. (Requires some prior knowledge of RS232 adapters and serial port setup)
First start by getting a PI SD image I used Raspian Jesse Light https://www.raspberrypi.org/downloads/raspbian/
Install into a sd card and make sure it runs (green light at least)
With a 3.3v RS232 adapter connect earth and RX/TX to your PI. Be careful some adapters are only 5V and will damage your PI’s UART pins.
Setup your PC (I use Tera Term) serial adapter for 115200, 7 bits, even parity, 1 stop bit.
Boot your PI
If you get a screen of gobbledegook then good, otherwise swap your TX and RX around. When the gobbledegook has finished, press return a couple of times, and you should get a login prompt.
For some reason the console and boot up output at different baud rates (Caused by auto baud rate detect, settings above amended so this shouldn’t happen now)
Configure your PI the usual way. You will need some network to get your updates, but apart from that you have a working PI.
If you are brave (or idle) you can connect the +5v line from your serial adapter to power your PI too so you don’t need another usb power lead. Just be very careful that you attach it to the correct pins, otherwise your PI will be damaged.
(although I found the baud rate setting wrong everywhere I looked. Either auto baud rate detect at work, or it changes from distro to distro)
The baud rate is auto detected, the native speed is 115200 (amended above) The auto detection only happens at the login prompt. The auto detection won’t pick up changes in bits/stop bits/ or parity. You can change the console getty port/speed/parity settings look at RPi serial connection above.
If you have a wifi adapter and micro USB to USB lead, you can connect to WIFI. After connecting via RS232 edit the file [code]]czozOTpcIi9ldGMvd3BhX3N1cHBsaWNhbnQvd3BhX3N1cHBsaWNhbnQuY29uZlwiO3tbJiomXX0=[[/code] using sudo nano
add in the lines
[[code]]czoyNDg6XCJuZXR3b3JrPXsNCiAgICBzc2lkPVwiWW91cl9XSUZJX1NTSURcIg0KICAgIHBzaz1cIllvdXJfd2lmaV9wYXNzd29yZFwiDQp9e1smKiZdfQ0KDQphbmQgcmVib290IHRoZSBwaSBzdWRvIHNodXRkb3duIC1yDQoNCnJlIGxvZyBpbiB0byB0aGUgcGkgYW5kIHR5cGUgaWZjb257WyYqJl19ZmlnIHRvIGZpbnMgdGhlIHdpZmkgSVAgYWRkcmVzcy4gDQpUaGVuIHlvdSBjYW4gc3NoIHRvIHlvdXIgUEkgYW5kIGV2ZW4gYmV0dHtbJiomXX1lciB1cGRhdGUgdGhlIHNvZnR3YXJlLg0KDQpcIjt7WyYqJl19[[/code]]Note : for Pi 3. You may need some changes to get the headless conf working, especially at non default baudrates, take a look at http://www.briandorey.com/post/Raspberry-Pi-3-UART-Boot-Overlay-Part-Two
Yes, I know, its was taught to you at school. Me too. I even have a book that has separate chapters of static electricity and conventional current electricity. So what is the problem, well it took me years to work out that there is no such distinction. Its all electricity. Static electricity on the terminal of a VDG sphere doesn’t suddenly transform in to current electricity when it is discharged and current electricity doesn’t transform into static when its stored in a capacitor.. The same rules must apply to both.
To use the water analogy, water is the same if its in a lake or in a stream.
I’m my mind I can’t think of any situation where static electricity exists. Capacitors, Van de graph terminals (also capacitors) all store charge. But non are static, there is always leakage current. To charge these devices there must be current.
So is its not static electricity, its stored electricity (charge) or conventional electricity(current) , both or just electricity.
Reading Physics books there appears to be a whole set of laws that govern each “type” of electricity, but in reality the effects are always there. One of the problems is that ‘static’ electricity is generally taught with high DC voltages, current electricity is taught with low DC voltages. The effects you see are dominated by the voltage, for example.
Electrical attraction occurs in all capacitors. But at high voltage the effects are much larger and so easier to see.
Resistive heating has a larger effect at low voltages, but is harder to see at high voltages (which is why transmission lines are high voltages)
The more you work on high voltage, or with high frequency electricity the more these effects become apparent.
So banish ‘static’ as a description and replace with high or low voltage, charge or current this is really what is going on.
Bill Beaty’s Thoughts on this What’s the Difference Between ‘Static’ Electricity and ‘Current’ Electricity?
After a lot of work, I just managed to get everything to Notts Gaussfest. This was really the first time all of the pieces had run together for any length of time.
I found a number of issues. The belt stuck together at high charges, usually stopping the belt completely and the motor control would crash when there was a really good discharge.
The motor problem was a partially solved by coating the controller in aluminium foil, which at least let me run the VDG for the day at Notts Gaussfest.
First light tonight 6″ sparks, not bad for the first time I’ve powered it up.
At the moment the limiting factors to the spark length/voltage is the unfinished top load and a problem with the belt. The top load has a very uneven surface, I believe I’m losing charge this way.
When the VDG starts charging the two sides of the belt are attracted to each other and they rub together, reducing the charging. I tried tightening the belt with no effect, so I have ordered 0.4mm (was 0.25mm) latex to make another thicker belt.
Work continues to complete the top load.
After changing the charging belt to 1mm pure rubber I finally achieved the full 1MV
At full out the motor is really working hard and gets very hot, so I suspect I can get more out of the VDG with another motor.