Tesla Coil Project - Need Help Please

[marcopolo09190]

Hi

I've built a NST 15kV tesla coil and I hooked it up today and it kinda didn't work. I'm wondering if anyone would like to help me as it's a school project and needs to be finished ASAP so if anyone might have any idea's / advice, that would be amazing!

Pictures of all my parts: https://imgur.com/a/aoHBA
If you want to help I can send more pictures of all my parts and tell you how I wire it all up as it could just be a problem like that but please could someone reply ASAP as I really need help quickly.

Also, I'm always on my email so I'll reply faster if you reply to me here: traveltyler27@gmail.com

Thanks!
Marco

 

[crutschow]

You need to post pictures of the device and the circuit. To do that hit the "Go Advanced" tab and then click the paper clip icon. Do not post JPEG type files for the schematic as they are fuzzy and difficult to read.

 

[marcopolo09190]

There you go sorry bout that, new to here so yeah :3

 

[DerStrom8]

Hello marco.

The thing you should know about Tesla Coils are that they're not something you can finish "ASAP". They require a lot of work, patience, and fine-tuning. It is extremely rare that a Tesla coil will work perfectly the first time. In fact, it's practically impossible.

From the photos, I can see many potential problems. It's a nice, clean setup, but it's unlikely it'll work the way it is now. First of all, what is the value of the capacitor bank? The caps look like microwave oven capacitors, and you will need a lot more of them to get the right capacitance. That is the first thing you need to do when building a Tesla coil--calculate the necessary capacitance for the tank capacitor so that it properly matches the transformer. It must be matched so that the capacitors get fully charged every half cycle, and fully discharged on the other half of each cycle. Otherwise, you'll lose a lot of energy. Second, you have to match the inductance of the primary with the capacitance of the cap bank. You'll have to calculate the frequency of the tank circuit (LC) and make sure it matches the LC circuit of the secondary/topload. Otherwise the coil will not work very well.

We'll need a little more information on what you have so far. The first thing is the value of the tank capacitor. Once you provide that, we'll go from there.

Best wishes,
Matt

 

[marcopolo09190]

Hi Matt.

Yeah sorry bout the asap part, I'm just a bit worried cause I need it working not right now but soonish.

For your questions:
-There are 6 microwave capacitors overall, 5 of which have a value of 2,100V and one of 2,500V which makes the total value 13,000V.
-The value of each transformer output is 7,500V AC to give 15,000V.

Thanks,
Marco

 

[DerStrom8]

Hi Matt.

Yeah sorry bout the asap part, I'm just a bit worried cause I need it working not right now but soonish.

For your questions:
-There are 6 microwave capacitors overall, 5 of which have a value of 2,100V and one of 2,500V which makes the total value 13,000V.
-The value of each transformer output is 7,500V AC to give 15,000V.

Thanks,
Marco

No problem. I don't mind the asap part. I was simply saying that Tesla coils are not projects to be built quickly, in any case. They are very finicky and most likely will not work right away.

As for the capacitors:
I was not talking about the voltage, though that is also very important. The voltage rating on a capacitor is generally the maximum voltage you should ever put into it. Putting 15kv into a 13kv bank is a very bad idea. It's generally a good idea to have a capacitor bank with a voltage rating of TWICE the input voltage. Otherwise, you risk destroying them, and possibly causing explosions, fires, etc.

Anyway, I was talking mainly about the capacitance values on the capacitors, not the voltage. When building a tank circuit for a Tesla coil, you'll need to match the total capacitance with the input voltage, as I mentioned in my previous post. You can calculate the approximate necessary capacitance with the formula,



where C is the capacitance you are trying to find, Z is the transformer's voltage divided by the transformer's current, and FL is the line frequency (50/60 hertz).

Most microwave oven capacitors are around 1μF. Most Tesla coils require a bank with a value in the 1-20 nF range. Also, in your photo it looks like you have the capacitors connected in parallel. When you connect capacitors in parallel, the voltage rating is not changed. If all your caps are connected in parallel, they will only be able to withstand voltages of around 2100v. And if your caps ARE wired in parallel, you have approximately 1μF/6 = 166.7nF, which is way too high.

Another Thing I noticed are microwave oven diodes. Those are generally only rated for around 6-10kv, so they will likely blow, and they'll also cause the tank circuit to not oscillate properly. If I were you, I'd just get rid of the diodes altogether.

So in short, I'd recommend you scrap your current capacitor bank. The voltage is way too low and the capacitance is way too high. Assuming your transformer has a voltage output of 15kv and current of 30mA, and a line frequency of 60hz (US), it would take approximately 186 microwave oven capacitors wired in series to get the correct capacitance.

I'm not trying to discourage you, and I am sorry if that's how it feels. I am always very excited to see someone trying to build a Tesla coil. It was one of my very first ventures as a kid in the electronics field. It's very difficult because EVERYTHING must be PERFECT for it to run properly--the transformer voltage/current, tank capacitor, primary, secondary, primary-secondary coupling, and toplaod. They all have to be matched just right, and if they're not, the Coil will probably not work at all. I have no doubt that this capacitance issue is what's causing the main problem with your Tesla coil at the moment.

After reading your posts, I get the sense that you are new to Tesla coils. You haven't had much experience making the necessary calculations for the transformer/tank capacitor, etc. Giving me only the voltage ratings of the capacitors when I asked for the capacitance has also made me wonder, so I feel I should stress caution. Tesla coils are very dangerous devices. The tank circuits can pack a lethal punch if you come too close. There is the potential of fire hazard, intense uv light exposure, electrocution, capacitor explosion, etc. So I urge you to have someone who knows what they're doing watch you at all times, just in case. If you get shocked and knocked out, a knowledgeable friend could be the difference between life and death. It happens to the best of us--we come into contact with something by accident and we pay for it. I do know of people who have almost died because they tried building a Tesla coil and didn't know what they were doing. So please, heed my warning. Be extremely cautious when working with such high voltages. Always have a friend nearby who knows what to do if you get hurt. Take every possible precaution against accidental electrocution, fire, medical emergency, etc.
It is the most important thing you could ever do.

Best wishes,
Matt

 

[marcopolo09190]

No problem. I don't mind the asap part. I was simply saying that Tesla coils are not projects to be built quickly, in any case. They are very finicky and most likely will not work right away.

As for the capacitors:
I was not talking about the voltage, though that is also very important. The voltage rating on a capacitor is generally the maximum voltage you should ever put into it. Putting 15kv into a 13kv bank is a very bad idea. It's generally a good idea to have a capacitor bank with a voltage rating of TWICE the input voltage. Otherwise, you risk destroying them, and possibly causing explosions, fires, etc.

Anyway, I was talking mainly about the capacitance values on the capacitors, not the voltage. When building a tank circuit for a Tesla coil, you'll need to match the total capacitance with the input voltage, as I mentioned in my previous post. You can calculate the approximate necessary capacitance with the formula,



where C is the capacitance you are trying to find, Z is the transformer's voltage divided by the transformer's current, and FL is the line frequency (50/60 hertz).

Most microwave oven capacitors are around 1μF. Most Tesla coils require a bank with a value in the 1-20 nF range. Also, in your photo it looks like you have the capacitors connected in parallel. When you connect capacitors in parallel, the voltage rating is not changed. If all your caps are connected in parallel, they will only be able to withstand voltages of around 2100v. And if your caps ARE wired in parallel, you have approximately 1μF/6 = 166.7nF, which is way too high.

Another Thing I noticed are microwave oven diodes. Those are generally only rated for around 6-10kv, so they will likely blow, and they'll also cause the tank circuit to not oscillate properly. If I were you, I'd just get rid of the diodes altogether.

So in short, I'd recommend you scrap your current capacitor bank. The voltage is way too low and the capacitance is way too high. Assuming your transformer has a voltage output of 15kv and current of 30mA, and a line frequency of 60hz (US), it would take approximately 186 microwave oven capacitors wired in series to get the correct capacitance.

I'm not trying to discourage you, and I am sorry if that's how it feels. I am always very excited to see someone trying to build a Tesla coil. It was one of my very first ventures as a kid in the electronics field. It's very difficult because EVERYTHING must be PERFECT for it to run properly--the transformer voltage/current, tank capacitor, primary, secondary, primary-secondary coupling, and toplaod. They all have to be matched just right, and if they're not, the Coil will probably not work at all. I have no doubt that this capacitance issue is what's causing the main problem with your Tesla coil at the moment.

After reading your posts, I get the sense that you are new to Tesla coils. You haven't had much experience making the necessary calculations for the transformer/tank capacitor, etc. Giving me only the voltage ratings of the capacitors when I asked for the capacitance has also made me wonder, so I feel I should stress caution. Tesla coils are very dangerous devices. The tank circuits can pack a lethal punch if you come too close. There is the potential of fire hazard, intense uv light exposure, electrocution, capacitor explosion, etc. So I urge you to have someone who knows what they're doing watch you at all times, just in case. If you get shocked and knocked out, a knowledgeable friend could be the difference between life and death. It happens to the best of us--we come into contact with something by accident and we pay for it. I do know of people who have almost died because they tried building a Tesla coil and didn't know what they were doing. So please, heed my warning. Be extremely cautious when working with such high voltages. Always have a friend nearby who knows what to do if you get hurt. Take every possible precaution against accidental electrocution, fire, medical emergency, etc.
It is the most important thing you could ever do.

Best wishes,
Matt

Hiya Matt, sorry I didn't reply quickly, been a bit busy with exams

I did the calculation and the capacitance is 6.361μF
Transformers Voltage = 15,000V
Transformers Current = 25 / 30mA
Line Frequency = 50Hz

And yes I am quite new to Tesla Coils, but I do know excactly the kind of danger these devices can cause, and I do have people who know the basics around me when I test it out. My teacher used to be in the air force and has had a few dangerous experiences with high voltages by diving right in and he has drilled that into me.

Also, I don't know about my primary coil and if you think that could also be a problem, I can build a new one as I have heaps of copper tubing the same size.

So your saying to completely scrap the capacitors and wire them up in a series circuit with new ones? Would you be able to help me a bit here as:

A. I don't know excactly what the best capacitors to get and where bouts for some cheap ones and you seem to have a very good knowledge on it.

B. If the capacitor isn't the only problem, would you be able to help me out with anything else?

Thanks so much Matt if you can and can I ask where you've gotten all this knowledge?

I have about 5 weeks before it kinda needs to be working a bit so thats a deadline

Thanks,
Marco

 

[DerStrom8]

Hiya Matt, sorry I didn't reply quickly, been a bit busy with exams

I did the calculation and the capacitance is 6.361μF
Transformers Voltage = 15,000V
Transformers Current = 25 / 30mA
Line Frequency = 50Hz

And yes I am quite new to Tesla Coils, but I do know excactly the kind of danger these devices can cause, and I do have people who know the basics around me when I test it out. My teacher used to be in the air force and has had a few dangerous experiences with high voltages by diving right in and he has drilled that into me.

Also, I don't know about my primary coil and if you think that could also be a problem, I can build a new one as I have heaps of copper tubing the same size.

So your saying to completely scrap the capacitors and wire them up in a series circuit with new ones? Would you be able to help me a bit here as:

A. I don't know excactly what the best capacitors to get and where bouts for some cheap ones and you seem to have a very good knowledge on it.

B. If the capacitor isn't the only problem, would you be able to help me out with anything else?

Thanks so much Matt if you can and can I ask where you've gotten all this knowledge?

I have about 5 weeks before it kinda needs to be working a bit so thats a deadline

Thanks,
Marco

Hey Marco, no worries. I've been pretty busy myself

The capacitance won't be in the μF range. It makes much more sense to be in the nF. 6.361nF sounds much more realistic, considering your transformer values. Another question I've had: How are your transformers connected? Parallel or series? That will make a huge difference. I'd recommend just using one of them--the 15k/30mA--and leave it at that. That'll give you just 6.3nF.

The primary coil looks good for now. After the capacitor bank is fixed, and it still doesn't work, we'll go from there.

As for the capacitors, just wiring the ones you have in series will get nowhere near the right value. Something to remember is that when connecting capacitors, two identical ones in parallel doubles the capacitance but keeps the same voltage rating, and wiring them in series doubles the voltage rating but cuts the capacitance in half. You'd be better off not using microwave oven capacitors. I'd look on ebay for some high voltage, low capacitance ones, or you can build your own beer bottle capacitor bank. They're cheap, but they work fairly well, especially for school projects.

I'll be happy to help you with any other problems you have with your coil. Hopefully we can have this thing running by the time it's due

As for where I've gotten my knowledge, it's accumulated over quite a long time. I built my first Tesla coil when I was about 14, and I've been building them ever since, constantly improving on the last. I've done a lot of research, math, and experimentation in order to get to where I am now. However, I still feel I have a lot to learn on the subject, and there is no way I'll ever understand it as well as Tesla did

Keep me posted on the progress!

Best wishes,
Matt

 

[marcopolo09190]

Hey Marco, no worries. I've been pretty busy myself

The capacitance won't be in the μF range. It makes much more sense to be in the nF. 6.361nF sounds much more realistic, considering your transformer values. Another question I've had: How are your transformers connected? Parallel or series? That will make a huge difference. I'd recommend just using one of them--the 15k/30mA--and leave it at that. That'll give you just 6.3nF.

The primary coil looks good for now. After the capacitor bank is fixed, and it still doesn't work, we'll go from there.

As for the capacitors, just wiring the ones you have in series will get nowhere near the right value. Something to remember is that when connecting capacitors, two identical ones in parallel doubles the capacitance but keeps the same voltage rating, and wiring them in series doubles the voltage rating but cuts the capacitance in half. You'd be better off not using microwave oven capacitors. I'd look on ebay for some high voltage, low capacitance ones, or you can build your own beer bottle capacitor bank. They're cheap, but they work fairly well, especially for school projects.

I'll be happy to help you with any other problems you have with your coil. Hopefully we can have this thing running by the time it's due

As for where I've gotten my knowledge, it's accumulated over quite a long time. I built my first Tesla coil when I was about 14, and I've been building them ever since, constantly improving on the last. I've done a lot of research, math, and experimentation in order to get to where I am now. However, I still feel I have a lot to learn on the subject, and there is no way I'll ever understand it as well as Tesla did

Keep me posted on the progress!

Best wishes,
Matt

Hey Matt, thanks for that

Yeah 6.3nF sounds better than the other, silly me

Ok cool thanks for checking the primary coil.

And I did try making 4 beer bottle capacitors and I could show you some pictures if you want but they didn't seem to work properly.

Also what circuit should I use because you seemed to write that like a riddle

And oh cool that sounds awesome how you learnt about Tesla Coils How many have you made? Could I see them? Sorry bout asking all these questions you just seem awesome.

THanks Matt
Marco

 

[DerStrom8]

Hey Matt, thanks for that

Yeah 6.3nF sounds better than the other, silly me

Ok cool thanks for checking the primary coil.

And I did try making 4 beer bottle capacitors and I could show you some pictures if you want but they didn't seem to work properly.

Also what circuit should I use because you seemed to write that like a riddle

And oh cool that sounds awesome how you learnt about Tesla Coils How many have you made? Could I see them? Sorry bout asking all these questions you just seem awesome.

THanks Matt
Marco

Hi again, Marco!

I think photos of the bottle capacitors would be very helpful. From experience, in order to get 6nF, you'll need (on average) 10-12 bottles. I doubt 4 bottles will be enough. A video of it running would also be helpful, if possible.

When I started building my own capacitors for Tesla coils, the first thing I did was to buy a multimeter that could measure capacitance. It's a worthy investment, and you'll never stop using it. It's a great tool to own, and I recommend getting one if you haven't already. It will let you know if your homemade capacitor bank is around the correct value.

Also, what circuit are you referring to? The capacitor bank?

No need to apologize. I enjoy reading and answering questions--that is the reason I'm here on this forum. I'm very happy to help in any way I can

My first Tesla coil can be found on YouTube, here. It's a small one, but it puts out about 100kv.

Best wishes,
Matt

 

[marcopolo09190]

Hi again, Marco!

I think photos of the bottle capacitors would be very helpful. From experience, in order to get 6nF, you'll need (on average) 10-12 bottles. I doubt 4 bottles will be enough. A video of it running would also be helpful, if possible.

When I started building my own capacitors for Tesla coils, the first thing I did was to buy a multimeter that could measure capacitance. It's a worthy investment, and you'll never stop using it. It's a great tool to own, and I recommend getting one if you haven't already. It will let you know if your homemade capacitor bank is around the correct value.

Also, what circuit are you referring to? The capacitor bank?

No need to apologize. I enjoy reading and answering questions--that is the reason I'm here on this forum. I'm very happy to help in any way I can

My first Tesla coil can be found on YouTube, here. It's a small one, but it puts out about 100kv.

Best wishes,
Matt

Well I guess great minds think alike seeing as I did exactly the same thing and bought a multimeter as well Yes I was referring to the capacitor bank circuit and I can try and take pictures of it but like I said, the bottle capacitors I made didn't work so I can't really take a video.

Thanks,
Marco

 

[marcopolo09190]

Oh and wow that video or your mini tesla coil looks amazing!

 

[marcopolo09190]

Here are the pictures of my beer bottle capacitors that don't seem to work: https://imgur.com/a/8OB0q

Enjoy Matt

 

[unclejed613]

one good reason not to use microwave oven capacitors, especially in series with voltages much higher than 5kV...... the metal cans and the terminal insulators. the terminal insulators tend to fail often in microwave ovens, and arc over to the metal can. another failure mode is these caps failing by breaking down internally to the metal can. although the metal cans should be isolated from ground and each other in a Tesla coil, the high crest values of the RF will make them more prone to breaking down. remember this is a "damped oscillation" device, and the initial crest values of the RF waveform can be extremely high, especially at resonance. most microwave caps are also fitted internally with a 1 to 10Meg resistor in parallel with the cap, which will seriously effect the Q of the primary circuit.

 

[DerStrom8]

Well I guess great minds think alike seeing as I did exactly the same thing and bought a multimeter as well Yes I was referring to the capacitor bank circuit and I can try and take pictures of it but like I said, the bottle capacitors I made didn't work so I can't really take a video.

Thanks,
Marco

Good to hear! Have you measured the capacitance of your beer bottle capacitor yet then?

I wasn't actually telling you the circuit you needed for the capacitor bank. It depends entirely on what capacitors you are using. I was saying that in general, parallel capacitors double the capacitance shown on each one, but the voltage rating stays the same, and series capacitors double the voltage rating shown, but cut the shown capacitance in half. In my experience, one beer bottle capacitor has a rating of about 0.5nF, which means you'll need 12 of them to get 6nF if connected in parallel. I have a feeling that your 4-capacitor bank is only about 2nF, according to this generalization I've found in my experience.

Here are the pictures of my beer bottle capacitors that don't seem to work: https://imgur.com/a/8OB0q

Enjoy Matt

Hmm, they seem to be fairly well built, except I'd try smoothing out the foil a bit more. Crinkled foil will cause unwanted arcing within the capacitor and it'll keep them from charging to where they should.
Looking at the wires connected to the top of the caps, it appears you have them connected in parallel (which increases the capacitance, and that's what you want). But have you made sure that the foil parts are all touching each other? If they're not connected properly, you might get arcing and you won't get the full capacitance.

one good reason not to use microwave oven capacitors, especially in series with voltages much higher than 5kV...... the metal cans and the terminal insulators. the terminal insulators tend to fail often in microwave ovens, and arc over to the metal can. another failure mode is these caps failing by breaking down internally to the metal can. although the metal cans should be isolated from ground and each other in a Tesla coil, the high crest values of the RF will make them more prone to breaking down. remember this is a "damped oscillation" device, and the initial crest values of the RF waveform can be extremely high, especially at resonance. most microwave caps are also fitted internally with a 1 to 10Meg resistor in parallel with the cap, which will seriously effect the Q of the primary circuit.

That's true, I didn't even think of that. I was only thinking about matching capacitance. I wasn't thinking of their construction....

Honestly Marco, I think at this point the beer bottle capacitors are the best way to go. You'll probably just have to build 8 more of them

Regards,
Matt

 

[marcopolo09190]

Good to hear! Have you measured the capacitance of your beer bottle capacitor yet then?

I wasn't actually telling you the circuit you needed for the capacitor bank. It depends entirely on what capacitors you are using. I was saying that in general, parallel capacitors double the capacitance shown on each one, but the voltage rating stays the same, and series capacitors double the voltage rating shown, but cut the shown capacitance in half. In my experience, one beer bottle capacitor has a rating of about 0.5nF, which means you'll need 12 of them to get 6nF if connected in parallel. I have a feeling that your 4-capacitor bank is only about 2nF, according to this generalization I've found in my experience.

Hmm, they seem to be fairly well built, except I'd try smoothing out the foil a bit more. Crinkled foil will cause unwanted arcing within the capacitor and it'll keep them from charging to where they should.
Looking at the wires connected to the top of the caps, it appears you have them connected in parallel (which increases the capacitance, and that's what you want). But have you made sure that the foil parts are all touching each other? If they're not connected properly, you might get arcing and you won't get the full capacitance.

That's true, I didn't even think of that. I was only thinking about matching capacitance. I wasn't thinking of their construction....

Honestly Marco, I think at this point the beer bottle capacitors are the best way to go. You'll probably just have to build 8 more of them

Regards,
Matt

Hey Matt

Like I told you before, I did test and measure them but they didn't seem to work at all, so I'm going to build some from scratch using that site that you sent me.

I've reformatted the link a bit just to make it look nicer which you can find here:
https://docs.google.com/document/d/11A3TIiamG-YubDqfz0urnLnUf6bBm6b-vMiNtU7H5Gk/edit

So your saying build 12 now? I thought you said 6 would be enough before

Thanks and can't wait to see your reply
Marco

 

[DerStrom8]

Hey Matt

Like I told you before, I did test and measure them but they didn't seem to work at all, so I'm going to build some from scratch using that site that you sent me.
So your saying build 12 now? I thought you said 6 would be enough before

Thanks and can't wait to see your reply
Marco

Hi Marco.

I said 6 nF would be enough, and since each bottle gives you about .5nF (from my experience), it will require 12 total.

When you built yours and measured them, what capacitance did the meter read? Having just the right value is crucial in getting the Tesla coil to work properly.

I think where you can start is measuring the capacitance of one beer bottle capacitor, and letting me know. From there we'll figure out exactly how many you'll need and where we should go from there

For the time being, though, I should go to bed. It's nearing midnight here and I have work tomorrow morning, so I should probably get some rest. I'll chat with you tomorrow.

Best wishes,
Matt

 

[marcopolo09190]

Hi Marco.

I said 6 nF would be enough, and since each bottle gives you about .5nF (from my experience), it will require 12 total.

When you built yours and measured them, what capacitance did the meter read? Having just the right value is crucial in getting the Tesla coil to work properly.

I think where you can start is measuring the capacitance of one beer bottle capacitor, and letting me know. From there we'll figure out exactly how many you'll need and where we should go from there

For the time being, though, I should go to bed. It's nearing midnight here and I have work tomorrow morning, so I should probably get some rest. I'll chat with you tomorrow.

Best wishes,
Matt

Hey Matt.

Ohhhh haha ok, now I understand

I'm not going to measure / worry about the 4 bottle capacitors cause I want to just to make all of them exactly the same. I'll get all the stuff I need after my exams and then I'll begin building them and then we can find out how many I'll need

Have a nice sleep and have fun at work haha

Thanks
Marco

 

[DerStrom8]

Hey Matt.

Ohhhh haha ok, now I understand

I'm not going to measure / worry about the 4 bottle capacitors cause I want to just to make all of them exactly the same. I'll get all the stuff I need after my exams and then I'll begin building them and then we can find out how many I'll need

Have a nice sleep and have fun at work haha

Thanks
Marco

Good evening Marco.

Your priority is to have the correct capacitance. That is absolutely critical. I would build 12 capacitors and measure the total capacitance first. It's always better to have too much capacitance than too little, because you can always take one away if it's too high.

Or, you could build one and measure it, just to get the overall idea of its values, and then decide how many you need to build. Either way, you absolutely MUST measure it.

Hope all is going well

Regards,
Matt

 

[marcopolo09190]

Good evening Marco.

Your priority is to have the correct capacitance. That is absolutely critical. I would build 12 capacitors and measure the total capacitance first. It's always better to have too much capacitance than too little, because you can always take one away if it's too high.

Or, you could build one and measure it, just to get the overall idea of its values, and then decide how many you need to build. Either way, you absolutely MUST measure it.

Hope all is going well

Regards,
Matt

So its late over there? Only lunchtime here

I think I may make them all at the same time and then decide if I have too many / not enough. I've taken a picture of my multimeter. After I build them, how shall I measure them all? I haven't really done this before so just needing to know haha.

https://imgur.com/a/BO8LZ

Thanks,
Marco