ultimax

Hi YT, I was in the garden the other day and noticed the lightning rod's ground strap terminating at what appears to be a solidly constructed stake pounded into the ground. Was wondering if I could make use of that instead of pounding another stake into the ground. That would save me some time and money. It's just a thought. If it doesn't work well I can always go back to the ol' fashion way.

Hi Lance' date=' well I fiddled arnd with the spark gap length and blew a capacitor haha. Thank god I had spares, and that the rest of the bank was unaffected I've tuned it somewhat and have gotten another inch or two. I think I'll leave it at that. Next, I'll try it with a proper ground connection. What do you think of hooking hte coil up to the lightning rod's ground strap? Good idea? Or bad idea? Here's another photo: [img']http://web.singnet.com.sg/~shuhuang/tesla_maltese_cross.jpg[/img]

so how should it go? More turns = wider gap? What's the relationship between gap length and increasing the length of the primary? hey you've already been a great help. thanks a lot!

Hi YT, thanks for the compliment! I'm probably gonna go ahead with the traditional toroid. Just to make sure it's not the toroid which is the obstacle to having longer sparks. I'm prob gonna redo the spark gap...again. My Prof pointed out that the rubber tubes I used to strap the aluminium rails down may lose their elasticity with time. I'm prob gonna cut my casing horizontally into 2, and sandwich the rails between them. the 2 halves will be joined by a plastic hinge on one side, and maybe leather or a piece of vinyl on the other. I'll also shift the fans to the top of the housing so that they're blowing down onto the fans, thru the gap. Right now most of the air is blowing across the bottom of the rail. Only a bit makes it thru the gaps between them. So who knows ... maybe quencing will be better and we'll see bigger sparks? I'm also gonna take the coil home and borrow a variac from the lab. I'm suspicous of the ground connection we used in the lab. I'm not sure where it's from, or what it leads to, but I wanna try running the coil with a good ol' copper stake in the ground! Shu P.S. How good is an average coat of polyurethane? I'm trying to get my gap to spark in the middle, rather than the ends, so I'm thinking of dipping both ends in polyurethane? As it is, the sparks are sort of shielded from the air flow by the plastic supports they rest on.

Hi everyone, tested my coil out in school today and it worked right away, much to my relief. Here are some of the specs of my coil : Transformer : NST, 15kV, 30mA Diameter of secondary coil: 90mm Diameter of magnet wire: 24 AWG, 0.51mm Number of turns: ~883 Toroid: 2 aluminium wok covers joined together with aluminium tape. Estimated dimensions: 310mm in diamter, 210mm in height. (I'm probably gonna construct a traditional toroid as I can't calculate the capacitance of this toroid, and I'm not sure if it's any good in the first place) Inner diameter of primary coil: 140mm Diameter of copper tubing: 1/4" Spacing between coils: 1/4" Number of turns: 13-14 Spark gap: Number of electrodes: 7 Material used: Aluminium curtain rails Spark gap: ~1.5mm between each rail, ~9mm in total. Cooling mechanism: 80mm computer fans, blowing into the spark gap housing, rather than sucking air out. Total construction time: ~7 days from start to finish. Photos: My coil in the lab. Note the atypical toroid. The spark gap. I removed the last rail as I needed a wider spark gap. The fans limited how far I could go with 8 rails. So I now have 7. Performance: The good news is, everything worked from the start. There was some arcing on the capacitor bank because of a poorly soldered connection, but that was soon fixed. Other than that, the coil generated a good amount of noise, ozone and streamers. The transformer was connected to a variac, and we never went above 150V (the transformer's rated at 240V). After the initial satisfaction of having everything work, discontent took over. My prof was very happy with the streamers, but seeing how other coils using similar NSTs have generated sparks 2-3 times the length of what I saw today, I was somewhat disappointed haha. It's funny that we didn't run the coil "as is" ie. without an electrode at the top of the toroid. So I don't know if breakouts are possible from the toroid. But anyway, max streamer length of the day was abt 200-250mm. Maybe 180mm's a more conservative estimate. Here are some pics! My 1.3 megapixel camera is really bad with shots in the dark, so pls excuse the quality. It barely captured the streamers! QUESTIONS and improvements. Yes, more from me! The general question is (as if it isn't already obvious haha), how do I improve spark length? Where do I start? Is there a methodical approach? More specific questions: 1. How do I calculate the capacitance of this atypical toroid? 2. WOuld a traditional doughnut shaped toroid work better? 2. DOes it matter if the fans blow into the spark gap housing, or suck air out (the traditional way). I find there's more air flow with the former than with the latter. 3. How impt is using a stake in the ground as the RF ground? Does the length of the stake really matter? Like 3m VS 5m? We were in a lab (on the 5th storey of a building) so we hooked the coil up to a ground wire. I have no idea where it's connected to, but it definitely wasn't from a socket. Anyway, if you don't have access to a patch of dirt/grass, what's the best ground to use? thanks! Shu

Hi YT, what exactly is an earth strap? The RF ground connection from the secondary coil? thanks!

Lance, YT, I've finished building my coil! It took me ~5 full days from start to finish but it's done! I'm testing it in school tomorrow. Hopefully it'll work. Will post pics soon. Maybe a video too! THanks for all your help guys. You guys have been wonderful and were really forthcoming with answers and suggestions! Can't say the same for some coilers I emailed for help ...

hey sorry I've got (yet) another question. There are a couple of metal screws directly under the primary coil. The deck that's supporting the primary coil is in turn supported by 4 PVC pipes. I'm guessing the screws won't affect anything because the deck's insulated from the ground by the PVC pipes). Am I correct? thanks!

Hi Lance, thanks for your help as always....I really appreciate it. 1. I applied the polyurethane in haste (because it was late at night) so I'm afraid I didn't cover all the wood, or the coat was too thin. I've got my copper pipes resting on the chipboard. There's a layer of epoxy holding everything together so hopefully that'll absorb the heat and spare the wood. I've also got 2, 8mm fans an inch away from the copper pipes. That should keep things cool. 2. Can't find any sort of flex-tubing greater than an inch and half in diameter. I know I'm not searching hard enough, but I haven't the time haha. I think i'll go with the bowls. The fact that everyone's using aluminium this and aluminium that got me concerned so I wanted to double-check with you guys first. 3. I'll prob leave an inch and a half. If the coupling's poor, I'll raise it...somehow. Have to figure that out

Hi lance, so how do coilers estimate the capacitance of salt water caps? Is there a method? How many bottles do you start with? Or is it completely trial and error? I've got a couple quick questions abt the coil i'm building now. 1. WOOD. I rebuilt my spark gap and at 2 in the morning, I wasn't thinking straight. I cut the board used to hold the copper pipes out of chipboard. It was dry, and it had 2 coats of polyurethane. In the morning, I realised that wood can actually be a conductor of electricity at high voltages! Do I have to be concerned abt this? Everything sort of fits together perfectly so I really don't want to be dismantling anything. Besides, I epoxied everything together.... 2. Toroid. Ok...the toroid I built looks like crap. It's uneven, and pretty creased up. It's almost embarrassing to look at (considering the amt of time spent on it!). I want to build another one, but I haven't had any luck finding 4" drain hose (my neighbourhood hardware shop says they're no longer popular so they're no longer stocked) or 4" aluminium duct (DIY isn't big here, so you can only get such items from a contractor). I did, however, see 2 metal dishes the other day. Put together, they form a perfect toroid with a lip. I was thinking of joining the 2, and grinding the lip away. However, all toroids I've seen seem to be made from aluminium. The dishes are made from stainless steel probably. What's your opinion on this. 3. Primary coil. I made a flat primary coil then realised something - when winding the secondary coil, I had every intention of making my primary an inverted cone. So I started winding my secondary coil abt 3-4" from the bottom of the form. With my flat primary, the secondary coil only starts 2" above the primary. Again, should I be concerned? How does this affect "coupling"? I can easily saw off a few inches but I don't want to do more work than necessary. OK that's all for now guys. I'm pretty excited. My first coil's looking good. I hope it works though - a lack of proper tools has resulted in parts which don't fit together accurately. But I've been working on it non-stop for 4 days now so let's hope everything works out ...

hey i used zinc plated wire to extend the leads of my caps. Is that OK?

I'm prob gonna fire it up in the lab with my prof present. I want to make sure I've got all the connections right, and I do not overlook a problem which could blow something up, or be a hazard. Anyway, he liks trouble-shooting things so even if it doesn't work I'm sure he won't penalise me. Besides, he knows that I'm not an electrical engineering/science student in the first place (i'm actually a history major haha). I may make a saltwater cap for the professor during the hols, just to demonstrate the point that everyday materials can hold a huge amount of charge. I came across a tesla coil (I think the owner's name is Greg) on a website and he used 52 beer bottles for his tank cap and it worked really well. Seeing those pics was pretty inspirational. THe prof is also big on using everyday materials for science experiments, esp for this class. He gave me proper caps this time round because he wanted something neat and robust. BTW, to answer your question, no the tesla coil doesn't have to be compact. As long as I can transport it to sch by car, and it's sturdy, it can be of any size. Abt saltwater tank caps, is there a formula used to calculate its capacitance?

Hi Lance! Just want you to know I really appreciate all your advice. It's great being able to talk to someone abt specific questions/concerns I have. Websites are great, but talking to someone with experience is always much much better!

Oh yeah 2 more questions! 1. Should I be very particular abt how smooth my secondary coil form is? I'm using PVC pipe which I've varnished with polyurethane. Unfortunately, it's sort of bumpy. Not very bumpy, but if you run your fingers around the pipe it's certainly not smooth. I suppose that is to be expected with paintjobs done with a brush, but is that a big deal? I'm gonna sand the surface a bit before I start winding as most coilers recommend but I doubt it'll be as smooth as the unvarnished PVC. Also, I'll be varnishing the coil once I'm done with it. Should I sand each layer down too. Or leave it be? Should I be concerned abt the smoothness? 2. What sort of wire should I use for the general wiring of my tesla coil. It's hard to get specialist wire around these parts, and HV wire tends to be very expensive. I read that regular AWG 12-14 wire is good enough. Is this true? thanks!

Hi Lance, thanks for your suggestions. I'll talk to my prof about this. Can I mix capacitors of different ratings together? Or do they all have to be identical? Ok just to make sure, what's your definition of thin? I've got AWG #22 copper wire. Is this too thin?

Hi Lance, thanks for your reply! Ah ok .. that makes sense. But will a LTR value result in better performance? Most coilers say that's the second benefit of using a LTR value. Hmm ... how does one calculate the peak voltage of a transformer? How many volts extra should I prepare for? I could get more capacitors. That's not a problem. What configuration would you recommend? Can I use regular copper wire (exposed)? Will it heat up? thanks a lot!

I'm building my first coil and I need some advice. It's for sch so they're providing most of the components. I'm getting a 15kV 30mA 50hz NST from them (suggested by my prof) and they've given me 30, 1600V 0.047uF capacitors for my MMC. Using WinTesla, the resonant capacitance for this transformer is 0.0064uF. I've read stuff abt how coilers should use a Larger Than Resonant Cap value, 1.5 times that of the resonant. That means the LTR value is 0.0096uF. How should I configure my capacitors? Having 2 parrellel strings of 10 caps in series will give me a capacitance of 0.0094uF. Is this ideal? Also, the leads which came with the capacitors are really short. I need to extend them so that I can solder the caps together. What type of wire should I use? Or will anything be OK? Should I also space the capacitorss a certain distance from each other? Will the leads arc? Thanks! Shu