Science Buddies: "Ask an Expert"

hello, im new here, I am currently in grade 10, but I plan to bring something in for grade 11, since there will be a science project next year in one of my classes.

I am currently finishing up my tesla coil, and while I did not build this for a science project, I do plan on one day to maybe bring it in to school as a science project, but one issue arises is safety, because this coil is fairly large, has a varaible supply to provide anywere from a few hundred watts to up to 7KW on full power, so the question here, are there any safety tips to consider, aside from the magnetic field bieng transmited and the danger of high voltage?

on a side note, this is a direct current resonant charging style of tesla coil, and uses high voltage DC with 24KV RMS peaks on the primary circuit. the AC supply is a transformer stack to give around 10KV at 700MA and before bieng rectified and fed through a charging reactor, but is variable due to a variac on the primary side of the transformers, I was thinking of setting up some type of "targets" to prevent the arcs from hitting anything they shouldn't, but any advice is helpfull, thank you for your time.

EnullD - This Tesla coil sounds close to being a weapon of mass destruction. Many years ago I built a small tesla coil (probably in the order of 100 watts) to experiment with. I was fascinated by high voltage and also did a small Van de Graff generator as well. These would easily operate off a standard receptacle that would handle a table lamp. A 7 kW unit would have to operate at minimum off 220 volts, probably single phase, but drawing about 30-35 amps. The variac you plan on using on the mains side might have to be delivered to the classroom by fork-lift (just kidding, I looked at a Staco data sheet and it might only be 150 pounds or so). The high voltage power supply, on the other hand, is going to be a huge, and a potentially very lethal apparatus. Component failures could be calamitous.

You seem to be aware of the logistical challenges that surround this. If I were a school science teacher I would have reservations as to whether this could/should even be demonstrated in a school environment, so before you go too far, have a chat with the science advisor. Beside the sheer safety issue of the 7 kW input power, and all the ramifications it presents, throwing fairly high current 10 foot lightning bolts and accompanying ozone generation (a toxic substance) there is a serious amount of RF energy that will be generated that would have to be grounded/shielded. It's possible that no AM radio would operate within a half mile of the school.

I don't want to discourage you, but there are some big questions that will have to be resolved. You seem to have a pretty good knowledge about what you are doing and safety conscious.

On the positive side, if you have convinced your parents of the desirability of building this at your house, you have a very bright future in technology sales.

Rick Marz

yeah I had a feeling about the possible complications of such a device, I could always bring a solid state tesla coil, that uses power semiconductors (mosfets/igbts) instead, since it outputs a decent lenth, has smaller power requirements and not as loud as its spark gapped counter part.
this particular tesla coil (the large one) has been really build as a backyard/out of town thing, and I was just curious on school possiblities, but now I see the complications, I wasn't really too worried about its power draw, but mostly the fact that it can damage sensetive electronics, if not vital such as pacemakers.
thank you for your advice non-theless, so I will consider bringing a far smaller demo-tool.
also, I was planning on using a fixed ballast in series with the varaic, so such a large 150LB beast wont be needed.
so yeah, I personally think that the small solid state coil will be a better option, or Ill build a dual resonant solid state tesla coil, since I do have some power IGBTS (insulated gate bipolar transistors) and DRSSTC can push decent arcs for fairly low power input.

and now that I am thinking this through, it may be just a bit too large for school, since the secondary's dimentions alone are 36'' by 8''.
so I think I will keep this one at home, and just bring a smaller version of it

also, (yes one more also ) I am going to start redesigning this coil, and rebuild it to be more compact, so the device itself will take up less space, its always nice to have extra clearance for those extra long sparks.