Tesla Coil

[Lance]

Using WinTesla' date=' 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?

[/quote']

 

 

If you use a resonant size capacitor bank then it will draw more current from you’re NST (meaning larger sparks). However some people will tell you that this can damage your NST. I think the LTR bank is really for other types of power supplies. NSTS are extremely robust and I have never had a problem with damaging then. My bank is resonant.

 

Do NOT use the capacitor configuration you mentioned. The peak voltage of your transformer is more than 20KV. Not only that but you should probably have a voltage rating of much higher than that. Would it be possible to get any more caps? Do you have to return the caps intact? If those were the only caps I had I would use two strings of 14, which is only 22.4KV; NOT good! My 12-30 NST easily destroys an 18KV bank. You can probably get away with that configuration as long as you don’t run it for an extensive amount of time.Tesla coils are extremely hard on caps because of the high ac frequency and the low resistance of each discharge.

 

Because you’re using an mmc the wire type is not all that important. Individual caps will not have enough power to melt any wire/solder. Just don’t use ultra-thin wire.

 

The spacing is not too important because there should never be more than one thousands volts across each cap. Just don’t have the leads of the bank itself close together.

 

Enjoy your coil!

 

Please don’t take my advice alone though. Everybody builds coils differently. I’m sure somebody else will have other things to add.

[ultimax]

Hi Lance,

 

thanks for your reply!

 

If you use a resonant size capacitor bank then it will draw more[/i'] current from you’re NST (meaning larger sparks). However some people will tell you that this can damage your NST. I think the LTR bank is really for other types of power supplies. NSTS are extremely robust and I have never had a problem with damaging then. My bank is resonant.

 

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.

 

Do NOT use the capacitor configuration you mentioned. The peak voltage of your transformer is more than 20KV. Not only that but you should probably

have a voltage rating of much higher than that. Would it be possible to get

 

Hmm ... how does one calculate the peak voltage of a transformer? How many volts extra should I prepare for?

 

any more caps? Do you have to return the caps intact? If those were the only caps I had I would use two strings of 14, which is only 22.4KV; NOT good! My 12-30 NST easily destroys an 18KV bank. You can probably get away with that configuration as long as you don’t run it for an extensive amount of time.Tesla coils are extremely hard on caps because of the high ac frequency and the low resistance of each discharge.

 

I could get more capacitors. That's not a problem.

 

What configuration would you recommend?

 

 

Because you’re using an mmc the wire type is not all that important. Individual caps will not have enough power to melt any wire/solder. Just don’t use ultra-thin wire.

 

Can I use regular copper wire (exposed)? Will it heat up?

 

thanks a lot!

[Lance]

The voltage rating of the capacitor must be correct for the system or failure is certain. The voltage seen by the tank capacitor will almost always be much higher than the normal output voltage of the supply transformer' date=' and many things such as resonant rise, inductive kick, and missed firings should be considered when specifying the capacitor. It is very difficult to estimate the voltage seen by the capacitor in a particular design, and computer modelling and simulations are by far the best way to get an idea of the stresses that this capacitor will be subject to without risking damaging any real components. Peak voltages of 3 times the RMS rating of the supply transformer are not uncommon across the tank capacitor.

[/quote']

 

 

Although this website says 3 times the RMS can be seen that doesn’t necessarily mean you need a 45Kv cap bank. Capacitors are made with abuse in mind (which is what tesla coil use is). I would go for at least twice the NST voltage.

 

Would it be possible to get different caps? .1 or .15 uf, 2000v caps would be ideal. If I had unlimited 0.047, 1600v caps I would probably use three strings of 22. But that’s 66 caps! Hmm this is a hard one. You may end up just having to cut the voltage rating a bit low and hope for the best. 3 strings of 17 maybe?

 

It’s hard to say whether a LTR bank will give you larger sparks because the output is based on so many things. A smaller bank will give you a higher frequency giving longer streaming sparks. It’s really just a matter of opinion.

 

Copper wire is fine. They should not heat up as long as you don’t use thin wire. You may want to use thicker wire on the bank it self though.

[ultimax]

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?

 

Copper wire is fine. They should not heat up as long as you don’t use thin wire. You may want to use thicker wire on the bank it self though.

 

Ok just to make sure, what's your definition of thin? I've got AWG #22 copper wire. Is this too thin?

[YT2095]

Lance, I got 6 36x67mm alu plates, perfectly flat, and have 3 sheets of 2mm polycarb perspex sheets thus far, I need more and orders for such out there

 

I recon that`ll make a mighty fine HT plate cap

 

what you recon?

[ultimax]

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!

[YT2095]

the "bumpy" is fine

 

there will be no corrona discharge unless the coil coating is broken or at a shrp bend, you`re suposed to re coat it a few times after anyway, so it`ll not be an issue (unless the PVC is a carbon doped type).

 

 

DO NOT SAND YOUR COIL!!!!! EVEN AFTER COATING!!!!

 

you Can use 12 ->14 guage wire if it`s a monster coil, try taking the wire from the secondary off a large 6volt transformer, that`s worked for me (a few times) in the past

[Lance]

Lance' date=' I got 6 36x67mm alu plates, perfectly flat, and have 3 sheets of 2mm polycarb perspex sheets thus far, I need more and orders for such out there

 

I recon that`ll make a mighty fine HT plate cap

 

what you recon?[/quote']

 

Yea, Be sure at let me know how it works out. A while ago I atempted to make a plate cap out of aluminum tape and acylic. It was pathetic and I tore it apart after I measured the capatence. I think it was like .9 nf.

 

Ok just to make sure, what's your definition of thin? I've got AWG #22 copper wire. Is this too thin?

 

That's fine.

 

I think you can mix caps together as long as the voltage is the same but I would avoid doing that.

 

Also I just realized that if your bank is underrated you should keep your spark gap distance low so the caps are not over-volted.

 

Smoothness of the secondary from is not a problem. It doesn’t even need to be sealed unless you live in an extremely humid environment and even then I don’t think the performance difference is that much. It is mostly hard-core coilers that do this. There is no need to sand down the finishing coats. The finish is only to keep it from falling apart and to make it look pretty.

 

The general wire you use is only critical if you plan on making the coil compact. The insulation is what’s important, not the thickness. As long as there is half an inch between wires then there’s no problem. If there is less than then I would look for some high voltage wire. It doesn’t not have to be labeled as 'high voltage' wire though. You can experiment with different wire types and your NST before making your coil.

 

Also I didn’t even think about this till YT mention it but you could also try making your own caps. I have had a lot of success with salt-water caps.

[ultimax]

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!

 

The general wire you use is only critical if you plan on making the coil compact. The insulation is what’s important' date=' not the thickness. As long as there is half an inch between wires then there’s no problem. If there is less than then I would look for some high voltage wire. It doesn’t not have to be labeled as 'high voltage' wire though. You can experiment with different wire types and your NST before making your coil.

 

Also I didn’t even think about this till YT mention it but you could also try making your own caps. I have had a lot of success with salt-water caps.[/quote']

 

Ok I've got some 1.5mm core wire lying arnd. I'll probably use that then. So you're saying at this voltage, I don't have to worry abt factors like resistance etc. impeding my coil's performance? And heavy duty HV cable is only useful for its insulation, rather than it's conductivity?

 

Abt salt-water caps, I may try this one day. For the time being, my prof wants something that's neat and durable, something that he can keep for future demonstrations

[YT2095]

Yea' date=' Be sure at let me know how it works out. A while ago I atempted to make a plate cap out of aluminum tape and acylic. It was pathetic and I tore it apart after I measured the capatence. I think it was like .9 nf.

 

[/quote']

it`s a pain when that happens

I rem making a cap several years ago using Turkey baking foil (the thick stuff) and dozen glass sheets from an old greenhouse.

for some reason it couldn`t hold a charge and actualy showed a resistance somehow, and was nearly as good as a dead short on AC. I didn`t have a capacitance meter back then to measure it, but it was the leakiest cap ever!

I spent all day cleaning the glass too, I figure I probably hadn`t dried it enough.

pity `coz the thing looked really Mean!

[Lance]

So you're saying at this voltage' date=' I don't have to worry abt factors like resistance etc. impeding my coil's performance? And heavy duty HV cable is only useful for its insulation, rather than it's conductivity?

[/quote']

 

Exactly.

 

Abt salt-water caps, I may try this one day. For the time being, my prof wants something that's neat and durable, something that he can keep for future demonstrations

 

 

Just be sure to do extensive testing before you present your coil. Wouldn’t want it to fail at the last minute.

 

Does the coil have to be compact? Saltwater caps take up quite a bit of space.

 

 

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!

 

I'm happy to help. I completely agree.

[ultimax]

Exactly.

Just be sure to do extensive testing before you present your coil. Wouldn’t want it to fail at the last minute.

 

Does the coil have to be compact? Saltwater caps take up quite a bit of space.

 

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?

[ultimax]

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

[Lance]

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

 

That should be fine.

 

I’m not sure about the calculator for saltwater caps. I think there are some for normal plate caps but I have never come across any for saltwater. I think it would be pretty hard to make a calculator for saltwater because of all the different types of bottles

[YT2095]

Copper is the prefered material as it`s conductance is greater at a cross section.

 

 

zinc being 0.167 as opposed to copper being 0.593 taken as: 10^-8 k?Sm^-1.

 

"k" being the conductance and siemens: S = Ohms ^-1

 

 

as you can plainly see, copper is about 4 x as conductive

[Lance]

as you can plainly see' date=' copper is about 4 x as conductive [/quote']

 

He said zinc plated though. I would be more worried about pure zinc wire melting anyway.

[YT2095]

sorry, maybe it`s me, but I missed the part where he said it was Copper?

[Lance]

sorry, maybe it`s me, but I missed the part where he said it was Copper?

Sorry... that was a typo. Fixed.

[YT2095]

I`ve never known Copper to be zinc plated, that`s what made me wonder, I`ve only even seen Iron/steel zinc plated (Galvanised), and iron`s only 0.10 ((

 

even less conductive than Zinc

[RICHARDBATTY]

Will the spark gap produce bad uv probs for your eyes and whats the potential for x ray production. Has anyone ever tried to build a silencer exhaust around the spark gap and what about using a rotating gap to keep it cool. Has anyone tried to make a motor control for the spark gap instead of controling the supply volts. sorry for all the questions in one go.

[Lance]

"Will the spark gap produce bad uv probs for your eyes?"

 

Yes, but its bright enough that you won’t want to look at it anyway. Its too bright to be able to make out any shapes.

 

"and what’s the potential for x ray production"

 

I don’t think there is much of any.

 

"Has anyone ever tried to build a silencer exhaust around the spark gap"

 

I have not heard of one. I think it would make the gap too hot.

 

"and what about using a rotating gap to keep it cool."

 

Yes that works too. It just takes a bit more work than two nails.

 

YT can probably answer some of these better.

[ultimax]

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 ...

 

 

 

 

That should be fine.

 

I’m not sure about the calculator for saltwater caps. I think there are some for normal plate caps but I have never come across any for saltwater. I think it would be pretty hard to make a calculator for saltwater because of all the different types of bottles

[Lance]

I think most people use a multimeter for measuring saltwater caps.

 

1. Will the spark be raised above the board? Normally the only reason wood becomes conductive is when it starts to burn and caramelizes. So as long as the gap is above the wood and there’s no chance of it heating you should be alright. Also, if you coated with polyurethane first I don’t see why it would be a problem. My first primary was on a piece of round particle board and I never had any problem with it.

 

2. What’s wrong with the normal 6" ducting? I don’t think steal will be a problem. YT uses a toroid that’s just two steel bowls wielded together. (Correct me if I’m wrong)

 

3. This is really hard to predict. The problem is that if you cut the bottom off and get smaller sparks you can’t to go back to the other coupling. 2" seems a bit high though. You may want to cut a very small bit off at a time after you finish everything else and see how it affects performance.

 

 

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 ..

 

Good luck!

[ultimax]

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

 

I think most people use a multimeter for measuring saltwater caps.

 

1. Will the spark be raised above the board? Normally the only reason wood becomes conductive is when it starts to burn and caramelizes. So as long as the gap is above the wood and there’s no chance of it heating you should be alright. Also' date=' if you coated with polyurethane first I don’t see why it would be a problem. My first primary was on a piece of round particle board and I never had any problem with it.

 

2. What’s wrong with the normal 6" ducting? I don’t think steal will be a problem. YT uses a toroid that’s just two steel bowls wielded together. (Correct me if I’m wrong)

 

3. This is really hard to predict. The problem is that if you cut the bottom off and get smaller sparks you can’t to go back to the other coupling. 2" seems a bit high though. You may want to cut a very small bit off at a time after you finish everything else and see how it affects performance.

 

 

 

 

Good luck![/quote']

[ultimax]

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!