David Woodroffe, Teslathon
Ben - This week also saw the annual Teslathon, held at the Cambridge Museum of Technology. The Teslasthon sees enthusiastic amateurs get together to show off their home made tesla coils Ė high voltage devices based on the same principal as an electric transformer.
A transformer works because a current in one circuit Ė called the primary, induces a current of a different size in the secondary circuit. This is how mains electricity is scaled down from the high voltage in power lines into the safer voltage that gets to your house. I met up with Derek Woodroffe to find out more about what the Teslathon isÖ
Derek - Teslathon is a group of people who are interested in high voltage electronics, Tesla coils and pretty much anything to do with high voltage, current, static electricity: all sorts of technology-related stuff like that.
Ben - So really anything that can make a nice big spark.
Derek - Thatís very much part of it. Some of us try and make the biggest spark possible. Some of us try and do it in more interesting ways. Of course we try and push the modern technology to do something that couldnít be done 18th century-wise by Tesla himself.
Ben - How do Tesla coils work? They seem a very simple principle.
Derek - They are a very simple principle. Effectively itís a standard transformer with a primary and a secondary. What Tesla did was he also introduced resonance so the primary has an associated capacitance. The secondary has an associated capacitance. The two synchronise with each other and form a resonant coupling, very much like a young child pushing somebody on a swing. You can get a very small movement that can be made into a very large movement just by the process of resonant rise or multiplication.
Ben - And this enables you to have huge voltages and this is what gives you these lightning-like forks that seem to be flying across the room behind us.
Derek - Thatís right. Some of the coils start at about 240 volts. They quite often cheat and go up to 10,000 volts or so into the primary of the coil. Then, due to resonant rise in the way the Tesla coil is constructed weíll get 100,000 volts or 200,000 volts from the top. But because it is high frequency AC that means we can then push quite a lot of power into a spark or an arc which will then grow much longer than the 100,000 volts sounds.
Ben - And thatís why they do seem to be reaching out and fingering their way across the room. There are some really huge forks of lightning across here. Is it actually safe?
Derek - No. Is the simple answer. Like most things that are interesting or fun it isnít safe. You have to be very careful. Most of the people in this room have been doing it for very many years. They know their equipment because theyíve had to build it from scratch. Itís not something you can just go out and buy. There is inherent safety: we all abide by a set of rules for the safe running of these sorts of events. People have to stand back from the equipment. The equipment has to be able to be made safe but obviously there is that inherent danger. Any high voltages, high currents, unpredictable equipment youíve got to view with a degree of distrust.
Ben - Iíd imagine that the element of distrust you have means you have to be fairly reserved in public. The people who come along to the Teslathon this weekend wonít really see the full power of what your devices can do.
Derek - They will see a limited amount. There are some things certainly that we wouldnít do in a public environment that we would do in private. Obviously thereís the safety of the public and the people who are watching the Tesla coils here today is absolutely paramount. We donít want to hurt anybody. It would really ruin the enjoyment of the whole event for everybody.
Ben - Cambridge Industrial Museum, where we are today, seems like a very appropriate setting for this. I understand you come back each year to do another Teslathon here. Does it feel like home?
Derek - Certainly for me. Iíve been doing this for about seven years now and the actual Teslathon has been here to my knowledge for 9 or 10. Itís usually on the same weekend every year, which for some reason happens to be Halloween. I donít know whether thatís by planning or by accident! Weíve always been very welcome here and obviously with the connection to 18th century technology we seem to fit in very well with the other machines and equipment at the pumping station. Of course, we all like to go and have a look round that sort of technology too.