1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Tesla Coil Primary

Discussion in 'High Voltage' started by Yergaderga, Mar 17, 2014.

  1. Yergaderga

    Yergaderga Member

    Joined:
    Feb 18, 2014
    Messages:
    32
    Likes:
    1
    I didn't have any copper tubing for my tesla coil, so I used steel wire , about 12 gauge. Will that work? It made some small arcs from from a tabletop coil driver (no the driver did not burn out) when I quickly tested it. The arcs were only around an inch, but would it work if I had a power supply that would actually be used to power something this size, and not a small coil? For example, flyback or NST? I wasn't sure if steel would work.
     
  2. Yergaderga

    Yergaderga Member

    Joined:
    Feb 18, 2014
    Messages:
    32
    Likes:
    1
    Photo by the way. It's about three feet tall. Without the topload. image.jpg
     
  3. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

    Joined:
    Aug 9, 2010
    Messages:
    5,484
    Likes:
    503
    Location:
    Vermont (GMT-5:00)
    Hi Yergaderga. Looks great so far!

    Steel wire should be ok, though if you can get your hands on copper tubing/wire that would be even better. Using steel wire may hinder the flux fields around the coil from transferring the energy into the secondary. But you should be fine for now.

    As for getting small arcs there are several reasons. First of all, for a Tesla coil that size I would recommend a 450W+ power supply (I'm assuming this is a SGTC). For example, a 15kv 30mA neon sign transformer would be good. Obviously higher current would be desirable. I wouldn't go beyond 20KV though, of course 20KV neon sign transformers are pretty tough to come by ;)

    Another possible cause for small arcs is that the coil is out of tune. If you're using a tank capacitor that is designed for a smaller TC, the resonant frequency of the primary and secondary circuits will probably not match up. Out-of-tune primary and secondary circuits are the most common cause of poor Tesla coil output.

    Keep us posted on the progress!
    Regards,
    Matt
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. Yergaderga

    Yergaderga Member

    Joined:
    Feb 18, 2014
    Messages:
    32
    Likes:
    1

    Yeah, I'll need to work on that, of course. Is there any power supply other than an NST I could use? Also, how safe is an NST relative to other ways of powering it ? (MOTs are definitely not happening!). I'll have to look in junkyards and whatnot. There aren't any neon shops around. I don't know where else to look for them that they would be cheap.
     
  6. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

    Joined:
    Aug 9, 2010
    Messages:
    5,484
    Likes:
    503
    Location:
    Vermont (GMT-5:00)
    Besides NSTs, OBITs are another good choice. That is, Oil Burner Ignition Transformers (for oil-fired furnaces). I suppose you could drive your coil with a very powerful ZVS flyback driver/transformer, though that would not be ideal.

    As for MOTs, they are usually not a good idea, as you seem to know already. Yes, they can be wired up in series/parallel with chokes to get a higher voltage, but the insulation will likely break down once you get a useable voltage from it. Most people who use MOTs to drive their TCs immerse the whole transformer setup in oil, which gets very sloppy.

    Keep in mind, if you do end up getting your hands on a neon sign transformer or oil burner ignition transformer (from a junkyard, perhaps), make sure it's one of the older, heavy iron core type, not the solid-state ones. Solid state ones run at a frequency much too high for use with Tesla coils.

    Good luck!
    Matt
     
  7. Yergaderga

    Yergaderga Member

    Joined:
    Feb 18, 2014
    Messages:
    32
    Likes:
    1
    Yeah, I have been looking into Oil burner transformers. I might go with that. Also, I didn't know there was a frequency too high for a tesla coil, why is that? Of course, don't larger coils usually output a lower frequency than smaller ones? Thanks for the help. I'll look into these.
     
  8. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

    Joined:
    Aug 9, 2010
    Messages:
    5,484
    Likes:
    503
    Location:
    Vermont (GMT-5:00)
    In an ordinary AC SGTC the capacitor should charge every half cycle, and discharge the second half through the spark gap. This is why matching your transformer to your tank capacitor is very important. If your transformer runs at too high a frequency, your capacitor will not have a chance to charge during the first half-cycle, so you will have very inefficient energy transfer from the transformer to the capacitor to the primary.

    Size of coils has little to no effect on the frequency. If you drive a coil with 60Hz, you will get 60Hz on the output. If you drive it at 400Hz, you will get 400Hz out. However, the solid-state transformers often use a type of switching supply, which is why the frequency is greater. It has nothing to do with the physical size. The older style are only bulky because they have to contain a heavy iron core and thousands of turns of wire.
     
  9. Yergaderga

    Yergaderga Member

    Joined:
    Feb 18, 2014
    Messages:
    32
    Likes:
    1
    Okay. Sorry, I was thinking in terms of solid state and the high frequency oscillations that the LC circuit makes with each discharge. Should I attempt to make a rotary gap, or can I use a stationary one still?
     
  10. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

    Joined:
    Aug 9, 2010
    Messages:
    5,484
    Likes:
    503
    Location:
    Vermont (GMT-5:00)
    You can still use a stationary one. Just keep in mind that the air will become more conductive as it heats up, so you will get unstable arcing if you don't quench it. Rotary gaps are a bit tricky. While they automatically quench it, it's generally best to synchronize it with the 60Hz output from the transformer (to ensure it arcs every half cycle). However, this involves determining the exact speed of your motor and spacing the contacts just right. You could always hook the motor up to a variac and adjust it by hand for the best output (indicating you are synchronized). You can also use an asynchronous rotary spark gap, but they are generally less efficient.

    If you have a small AC motor, a variac, and a perfectly round disc that you can mount contacts to, then by all means, go for a rotary spark gap. Otherwise, just use a static spark gap with air blowing across it to quench the ark and keep it cool.
     
  11. Yergaderga

    Yergaderga Member

    Joined:
    Feb 18, 2014
    Messages:
    32
    Likes:
    1
    Are Oil Burner Transformers current limited?
     
  12. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

    Joined:
    Aug 9, 2010
    Messages:
    5,484
    Likes:
    503
    Location:
    Vermont (GMT-5:00)
    Most, if not all, yes. You should be able to just plug it right in and have a stable output. I have one that is 17.5kv, 45mA. The most common you'll find is around 10kv, 20mA, so do your best to find a higher powered one. It'll work better for a coil the size that you have made yours.
     
    • Like Like x 1
  13. Yergaderga

    Yergaderga Member

    Joined:
    Feb 18, 2014
    Messages:
    32
    Likes:
    1
    Thank you very much for the help! I cannot wait to get this working. I might use an MMC or more likely bucket caps, due to my low budget. :grumpy:
     
  14. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

    Joined:
    Aug 9, 2010
    Messages:
    5,484
    Likes:
    503
    Location:
    Vermont (GMT-5:00)
    Always glad to help someone out with Tesla coils! :)

    I know what you mean regarding the bucket caps and low budget. The trick with bucket capacitors is that they're quite messy, it's very important to have smooth "plate" surfaces to prevent corona, and that they have to be quite large and filled with salt water (I believe 26.9 grams of salt per 300 milliliters of water is the ideal ratio). Another option that would be easier to handle and move around are beer bottle capacitors. Salt to water ratio should be about the same. You'll still need smooth contacts, though if you put the beer bottles in a bin of water and use that water as the outer contact, it will eliminate major problems with corona leakage. In my personal experience I found that a single beer bottle generally offers between 0.5 and 1.5 nF of capacitance when properly constructed. This means you'll probably need between 10 and 15 beer bottle capacitors. The actual capacitance you'll need based on your transformer is determined by the following formula:

    I%29*f%29

    where C is the capacitance (to be determined), E is the transformer voltage, I is the transformer current, and f is the line frequency (60Hz in the US). Obviously you'll need to find a transformer first before figuring out what you'll need for a capacitor.

    Hope this helps!
    Regards,
    Matt
     
  15. Yergaderga

    Yergaderga Member

    Joined:
    Feb 18, 2014
    Messages:
    32
    Likes:
    1
    Thanks for the help with the equation! Depending on how many bottles I can get, I'll see what I can do. I might even use plexiglas as a plate and layer metal sheets between them, because it is less messy and I have some plexiglas. Will it thermal shock? I might submerge it in oil, I want this to be portable, and messy oil and all that will be difficult to carry. If I can come across some money, I might actually look into MMCs .
     
  16. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

    Joined:
    Aug 9, 2010
    Messages:
    5,484
    Likes:
    503
    Location:
    Vermont (GMT-5:00)
    Plexiglas capacitors are quite difficult for a few reasons. First is that the dielectric must be very thin in order to have a high capacitance, but thick enough to be able to withstand the high voltages. Second you most likely will need to submerge it in oil for temperature and leakage reasons. They tend to be very inefficient and again, very sloppy. If you do opt for this method you can roughly calculate the capacitance by the following:

    gif.latex?C%3D%5Cfrac%7BA*k*8.85*10%5E%7B-12%7D%7D%7Bd%7D*%28n-1%29

    where A is the area (length * width) of the individual plates, k is the dielectric constant of the material (plexiglas is ~3.4), d is the distance between the plates (i.e. the thickness of your dielectric), and n is the number of plates.

    A MMC bank is definitely a great option, but you'll have to ensure you use capacitors that can handle the high voltage and frequency. Many of them break down at high frequencies, so you'll need to find some that can handle hundreds of kilohertz.

    If you decide to use a capacitor bank, just keep in mind that capacitors in series have an equivalent voltage of the labeled V * the number of caps, and the capacitance is divided by the number of caps. Capacitors in parallel multiply the capacitance, but the voltage stays the same. For example, 5 1nF, 6KV capacitors in parallel have an equivalent value of 5nF, 6KV, whereas the same capacitors in series would have an equivalent value of 0.2nF, 30KV. Also ensure that your capacitors are rated for at least twice the voltage that your transformer puts out.

    Hope this is useful for you. Feel free to ask if you have any more questions :)
    Regards
     
  17. tvtech

    tvtech Well-Known Member Most Helpful Member

    Joined:
    Mar 27, 2010
    Messages:
    3,166
    Likes:
    348
    Location:
    South Africa
    My friend Matt :)

    What else can I say. :cool:

    Got my own thing going here with Transformerless Power Supplies.....

    Stay well Champ :)

    All the best,
    tvtech
     
    • Thanks Thanks x 1
  18. Yergaderga

    Yergaderga Member

    Joined:
    Feb 18, 2014
    Messages:
    32
    Likes:
    1
    Ugh! What should I look for to find this kind of stuff!? The nearest neon sign shop according to Apple maps is over an hour away! Should I look for pawn shops, flea markets, maybe junk yards? There Æ some cheap NSTs on eBay, but at the highest in my budget are rated for about 200 watts.
     
  19. Yergaderga

    Yergaderga Member

    Joined:
    Feb 18, 2014
    Messages:
    32
    Likes:
    1
    Also, the Secret of Nikola Tesla is on Netflix! It's actually a very good movie, and Petar Bozovic is a good Tesla.
     
  20. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

    Joined:
    Aug 9, 2010
    Messages:
    5,484
    Likes:
    503
    Location:
    Vermont (GMT-5:00)
    All of those are good options. Junk yards are a great idea, as are pawn shops. Look up "neon sign repair" in your yellow pages, that's how I was able to get my hands on two (360W and 540W). Keep your eyes open and make sure you never pass up a good opportunity. Also, if you have some plumbers/furnace repairer friends, ask them to see if they can get their hands on an OBIT for you. A lot of the time they're just thrown out (I think they have to be replaced after a certain period of time whether they work or not, and the old ones often just get chucked). Keep an eye open on Ebay too, set up a watch list for NSTs. Every now and then one sneaks by for fairly cheap. What is your budget for a transformer?
     
  21. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

    Joined:
    Aug 9, 2010
    Messages:
    5,484
    Likes:
    503
    Location:
    Vermont (GMT-5:00)
    I think I saw that one recently on Youtube. I enjoyed it. Accuracy wasn't excellent but it was well put-together.
     

Share This Page