Tesla Coil Help
skyler, Fri Jan 10 2014, 01:12PMFor a club I started at my high school, everyone agreed on making a tesla coil as a project.
I am starting to struggle realizing how everything has to be tuned, resonant, and I can't just throw a random number of turns on a random size PVC pipe. We are limited in price, so I will say our progress so far of what we have and ask a few questions.
•A piece of 4 inch Diameter 5 foot PVC pipe (actually have 2 of those) and a toilet plounge to hold it up 90 degrees
•A bucket capacitor made out of salt water, beer bottles, oil, I will post the capacitance today when I bring my capacitance meter
• 4 MOTS, we might have to get another for the ballast, correct? We will be hooking two outlets together for the Power Supply
•A stable spark gap (planning on rotary probably in the future, I have a 3400 RPM BIGG motor that may work)
Our Price is very limited, for we have few sponsors, (just my friend and I's parents and our own money)
So what are some next steps, and is the PVC not the right size? (From another question on the forum the pipe seems to be not the right size, my dads gonna get mad that he wasted his money on that and probably wont buy another :'(
I am sort of confused when working with JavaTC so if anyone could help me with that, it would be great!
Safety wise, I Know 4 mots is enough to KILL YOU so we are taking every safety precaution including being at least 10 feet away when any transformer is plugged in.
What should I use for Primary wire?
Thanks for ANY help, Im just a dumb high school student, and need a bit of help from people who know what they are doing
Re: Tesla Coil Help
Fiddy, Fri Jan 10 2014, 02:02PM
the for 5" length 4" diameter makes the coil very skinny, that means it has a height to diameter ratio of: 15:1.
The proper ratio sits between 5:1 and 3:1 for bigger coils, so you might wanna cut the secondary down in size.
In java TC,
first choose measurements cm/inch and centigrade/Fahrenheit
Then choose your tank capacitor size.
then using the units provided, choose the radius of the secondary coil, so for 4 inch diameter put value of 2 in for Radius 1 and 2 in for Radius 2.
Next is the secondary coil height, if at ground level put 0 in Height 1 then if its 5 foot, put in 60 in Height 2.
Choose the amount of turns you suspect roughly and what wire gauge size.
repeat with primary data for the primary radius, height, turns and wire gauge size.
next do the toroid, enter the height of the toroid into the minor diameter field.
then enter the diameter of the toroid in the major diameter field.
then enter the how high the toroid sits on the secondary, so if the secondary coil is 60" tall, put the toroid center height at a tad over 60.
That should get you by, click RUN JAVATC and it should pump out a drawing and all the values, you can fine tune the parameters again and again after.
Fiddy, Fri Jan 10 2014, 02:02PM
the for 5" length 4" diameter makes the coil very skinny, that means it has a height to diameter ratio of: 15:1.
The proper ratio sits between 5:1 and 3:1 for bigger coils, so you might wanna cut the secondary down in size.
In java TC,
first choose measurements cm/inch and centigrade/Fahrenheit
Then choose your tank capacitor size.
then using the units provided, choose the radius of the secondary coil, so for 4 inch diameter put value of 2 in for Radius 1 and 2 in for Radius 2.
Next is the secondary coil height, if at ground level put 0 in Height 1 then if its 5 foot, put in 60 in Height 2.
Choose the amount of turns you suspect roughly and what wire gauge size.
repeat with primary data for the primary radius, height, turns and wire gauge size.
next do the toroid, enter the height of the toroid into the minor diameter field.
then enter the diameter of the toroid in the major diameter field.
then enter the how high the toroid sits on the secondary, so if the secondary coil is 60" tall, put the toroid center height at a tad over 60.
That should get you by, click RUN JAVATC and it should pump out a drawing and all the values, you can fine tune the parameters again and again after.
Re: Tesla Coil Help
skyler, Fri Jan 10 2014, 10:42PM
Thank you, I think I will look for some pipe that is at least 6 inches in diameter
skyler, Fri Jan 10 2014, 10:42PM
Fiddy wrote ...
the for 5" length 4" diameter makes the coil very skinny, that means it has a height to diameter ratio of: 15:1.
The proper ratio sits between 5:1 and 3:1 for bigger coils, so you might wanna cut the secondary down in size.
In java TC,
first choose measurements cm/inch and centigrade/Fahrenheit
Then choose your tank capacitor size.
then using the units provided, choose the radius of the secondary coil, so for 4 inch diameter put value of 2 in for Radius 1 and 2 in for Radius 2.
Next is the secondary coil height, if at ground level put 0 in Height 1 then if its 5 foot, put in 60 in Height 2.
Choose the amount of turns you suspect roughly and what wire gauge size.
repeat with primary data for the primary radius, height, turns and wire gauge size.
next do the toroid, enter the height of the toroid into the minor diameter field.
then enter the diameter of the toroid in the major diameter field.
then enter the how high the toroid sits on the secondary, so if the secondary coil is 60" tall, put the toroid center height at a tad over 60.
That should get you by, click RUN JAVATC and it should pump out a drawing and all the values, you can fine tune the parameters again and again after.
the for 5" length 4" diameter makes the coil very skinny, that means it has a height to diameter ratio of: 15:1.
The proper ratio sits between 5:1 and 3:1 for bigger coils, so you might wanna cut the secondary down in size.
In java TC,
first choose measurements cm/inch and centigrade/Fahrenheit
Then choose your tank capacitor size.
then using the units provided, choose the radius of the secondary coil, so for 4 inch diameter put value of 2 in for Radius 1 and 2 in for Radius 2.
Next is the secondary coil height, if at ground level put 0 in Height 1 then if its 5 foot, put in 60 in Height 2.
Choose the amount of turns you suspect roughly and what wire gauge size.
repeat with primary data for the primary radius, height, turns and wire gauge size.
next do the toroid, enter the height of the toroid into the minor diameter field.
then enter the diameter of the toroid in the major diameter field.
then enter the how high the toroid sits on the secondary, so if the secondary coil is 60" tall, put the toroid center height at a tad over 60.
That should get you by, click RUN JAVATC and it should pump out a drawing and all the values, you can fine tune the parameters again and again after.
Thank you, I think I will look for some pipe that is at least 6 inches in diameter
Re: Tesla Coil Help
redruM69, Fri Jan 10 2014, 11:11PM
4" PVC is fine. Assuming you get some 22awg magnet wire, make your secondary about 24" long. With a 6" aluminum dryer duct toroid, that puts you around 275khz.
4 MOT's is overkill for a coil this size. 2 will work if you must. If you can get hold of a NST for free at a sign shop, don't use the MOT's. Static spark gaps don't work well with MOT's unless you do a voltage doubler setup which will make things more complicated and expensive. If you can do a rotary gap, then MOT's are awesome. Seriously, if you can get a 12kv 30ma NST, that would be great for a 4" coil!
Use 1/4" or 3/8" copper tubing for your primary coil. It already comes shaped as a spiral, and just needs to be adjusted for your form. You may need a lot of turns. Assuming you decide on a 12kv NST, a 10nf cap, and all the other stuff I mentioned, then it'll be tuned around 10 turns.
Beer bottle / salt water caps will work, but expect them to occasionally pop. Have a bunch of spare beer bottles ready. DO NOT USE brown glass! Get clear Corona bottles.
Did I mention to get an NST? Get an NST!
redruM69, Fri Jan 10 2014, 11:11PM
4" PVC is fine. Assuming you get some 22awg magnet wire, make your secondary about 24" long. With a 6" aluminum dryer duct toroid, that puts you around 275khz.
4 MOT's is overkill for a coil this size. 2 will work if you must. If you can get hold of a NST for free at a sign shop, don't use the MOT's. Static spark gaps don't work well with MOT's unless you do a voltage doubler setup which will make things more complicated and expensive. If you can do a rotary gap, then MOT's are awesome. Seriously, if you can get a 12kv 30ma NST, that would be great for a 4" coil!
Use 1/4" or 3/8" copper tubing for your primary coil. It already comes shaped as a spiral, and just needs to be adjusted for your form. You may need a lot of turns. Assuming you decide on a 12kv NST, a 10nf cap, and all the other stuff I mentioned, then it'll be tuned around 10 turns.
Beer bottle / salt water caps will work, but expect them to occasionally pop. Have a bunch of spare beer bottles ready. DO NOT USE brown glass! Get clear Corona bottles.
Did I mention to get an NST? Get an NST!
Re: Tesla Coil Help
Feathers, Sat Jan 11 2014, 10:27AM
The price of a proper MMC (such as using the cornell dubillier 942C20P15K-F) seems prohibitive, but the investment will pay off in time you would have spent running through beer bottles and power wasted heating a bucket of salt water.
MOT's push a lot of current, which means you will get the most out of them with a very high spark gap breakrate (> 3000 BPS or so). With that amount of average current, you'd be vaporizing a non-tungsten static spark gap.
You'll also be putting much more stress on the capacitors. More reason to go with the 942c20p15k-f.
Remember:
RSG
942c20p15k-f
Use 2x the capacitors you think you'll need based on the datasheet peak current and DC voltage ratings for the capacitor.
These are just time savers, I can't tell you how much effort and money I wasted on lossy, failure-prone DIY capacitors.
Have fun!
Feathers, Sat Jan 11 2014, 10:27AM
The price of a proper MMC (such as using the cornell dubillier 942C20P15K-F) seems prohibitive, but the investment will pay off in time you would have spent running through beer bottles and power wasted heating a bucket of salt water.
MOT's push a lot of current, which means you will get the most out of them with a very high spark gap breakrate (> 3000 BPS or so). With that amount of average current, you'd be vaporizing a non-tungsten static spark gap.
You'll also be putting much more stress on the capacitors. More reason to go with the 942c20p15k-f.
Remember:
RSG
942c20p15k-f
Use 2x the capacitors you think you'll need based on the datasheet peak current and DC voltage ratings for the capacitor.
These are just time savers, I can't tell you how much effort and money I wasted on lossy, failure-prone DIY capacitors.
Have fun!
Re: Tesla Coil Help
skyler, Sat Jan 11 2014, 02:56PM
Well we have a large supply of bottles from a local bar! they just give em away like trash
skyler, Sat Jan 11 2014, 02:56PM
HighVoltageFeathers wrote ...
The price of a proper MMC (such as using the cornell dubillier 942C20P15K-F) seems prohibitive, but the investment will pay off in time you would have spent running through beer bottles and power wasted heating a bucket of salt water.
MOT's push a lot of current, which means you will get the most out of them with a very high spark gap breakrate (> 3000 BPS or so). With that amount of average current, you'd be vaporizing a non-tungsten static spark gap.
You'll also be putting much more stress on the capacitors. More reason to go with the 942c20p15k-f.
Remember:
RSG
942c20p15k-f
Use 2x the capacitors you think you'll need based on the datasheet peak current and DC voltage ratings for the capacitor.
These are just time savers, I can't tell you how much effort and money I wasted on lossy, failure-prone DIY capacitors.
Have fun!
The price of a proper MMC (such as using the cornell dubillier 942C20P15K-F) seems prohibitive, but the investment will pay off in time you would have spent running through beer bottles and power wasted heating a bucket of salt water.
MOT's push a lot of current, which means you will get the most out of them with a very high spark gap breakrate (> 3000 BPS or so). With that amount of average current, you'd be vaporizing a non-tungsten static spark gap.
You'll also be putting much more stress on the capacitors. More reason to go with the 942c20p15k-f.
Remember:
RSG
942c20p15k-f
Use 2x the capacitors you think you'll need based on the datasheet peak current and DC voltage ratings for the capacitor.
These are just time savers, I can't tell you how much effort and money I wasted on lossy, failure-prone DIY capacitors.
Have fun!
Well we have a large supply of bottles from a local bar! they just give em away like trash
Re: Tesla Coil Help
Mads Barnkob, Sat Jan 11 2014, 04:25PM
Just because they are free, doesn't mean they will do you any good, it will just be a waste of your time. Spend the time working, mowing lawns etc instead and pay for some proper capacitors. Have you read through this thread?
Noone says you have to use CDE 942C capacitors, almost all MKP/FKP (metallized / foil film polypropylene) capacitors can be used, just be sure to have a good rating for withstanding the voltages, rms and peak currents. There is a drop down list with capacitors on my MMC calculator, here you can atleast get a feeling of how many capacitors are needed for getting your goal capacitance/voltage rating and compare costs to build such mmc.:
Mads Barnkob, Sat Jan 11 2014, 04:25PM
skyler wrote ...
Well we have a large supply of bottles from a local bar! they just give em away like trash
HighVoltageFeathers wrote ...
The price of a proper MMC (such as using the cornell dubillier 942C20P15K-F) seems prohibitive, but the investment will pay off in time you would have spent running through beer bottles and power wasted heating a bucket of salt water.
MOT's push a lot of current, which means you will get the most out of them with a very high spark gap breakrate (> 3000 BPS or so). With that amount of average current, you'd be vaporizing a non-tungsten static spark gap.
You'll also be putting much more stress on the capacitors. More reason to go with the 942c20p15k-f.
Remember:
RSG
942c20p15k-f
Use 2x the capacitors you think you'll need based on the datasheet peak current and DC voltage ratings for the capacitor.
These are just time savers, I can't tell you how much effort and money I wasted on lossy, failure-prone DIY capacitors.
Have fun!
The price of a proper MMC (such as using the cornell dubillier 942C20P15K-F) seems prohibitive, but the investment will pay off in time you would have spent running through beer bottles and power wasted heating a bucket of salt water.
MOT's push a lot of current, which means you will get the most out of them with a very high spark gap breakrate (> 3000 BPS or so). With that amount of average current, you'd be vaporizing a non-tungsten static spark gap.
You'll also be putting much more stress on the capacitors. More reason to go with the 942c20p15k-f.
Remember:
RSG
942c20p15k-f
Use 2x the capacitors you think you'll need based on the datasheet peak current and DC voltage ratings for the capacitor.
These are just time savers, I can't tell you how much effort and money I wasted on lossy, failure-prone DIY capacitors.
Have fun!
Well we have a large supply of bottles from a local bar! they just give em away like trash
Just because they are free, doesn't mean they will do you any good, it will just be a waste of your time. Spend the time working, mowing lawns etc instead and pay for some proper capacitors. Have you read through this thread?
Noone says you have to use CDE 942C capacitors, almost all MKP/FKP (metallized / foil film polypropylene) capacitors can be used, just be sure to have a good rating for withstanding the voltages, rms and peak currents. There is a drop down list with capacitors on my MMC calculator, here you can atleast get a feeling of how many capacitors are needed for getting your goal capacitance/voltage rating and compare costs to build such mmc.:
Re: Tesla Coil Help
redruM69, Sat Jan 11 2014, 05:48PM
Although these guys are correct that building a real 942c based MMC is obviously going to be superior, I also understand a zero budget build. My first coil was 3", salt water caps, NST, and it threw 20" streamers. I built it with garbage I got for free, and it worked. There is also something to be learned from building your own caps, and building a TC from scrap.
To just keep telling newbs "Its a waste of time" is bullshit. Tesla didn't have 942c's or other polypropylene caps around.
Build the salt water caps. Learn from it, then upgrade to an MMC later when you have the money.
I actually managed to dig up a video of my first coil. Here ya go, salt water caps and all! LOL at the tiny topload.
redruM69, Sat Jan 11 2014, 05:48PM
Although these guys are correct that building a real 942c based MMC is obviously going to be superior, I also understand a zero budget build. My first coil was 3", salt water caps, NST, and it threw 20" streamers. I built it with garbage I got for free, and it worked. There is also something to be learned from building your own caps, and building a TC from scrap.
To just keep telling newbs "Its a waste of time" is bullshit. Tesla didn't have 942c's or other polypropylene caps around.
Build the salt water caps. Learn from it, then upgrade to an MMC later when you have the money.
I actually managed to dig up a video of my first coil. Here ya go, salt water caps and all! LOL at the tiny topload.
Re: Tesla Coil Help
skyler, Thu Mar 27 2014, 10:46PM
Hopefully we are getting down there on getting the tesla coil working.
We have finally assembled the secondary out of a 12 inch by 48 inch sona tube, with enough 24 gauge wire with fishing line to wind to the top (we estimated 900-1200 turns based on how much wire we had, 3500 feet, using almost all of it)
We have a bunch of MOTS, at least Five good ones, and 5 more that we don't know are good or bad and hope to get that power supply working (maybe voltage doublers or something if they keep arcing internally- we have almost 10 microwave diodes and capacitors)
3500 RPM spark gap is almost complete with the tungsten rods ordered
And we still have not got MMC capacitors, but will hopefully get the funds for that after we get it to work with the beer bottle caps.
For the primary, we currently have 5 turns of copper tubing, 20 feet, and probably will need more copper tubing to get more turns, but that stuff is pretty expensive so we will try it with this first.
For the toroid, we just got some heater duct at the local home depot, hope that works
Any problems popping up to anybody? We are out out of major money, so hopefully we don't have to redo the whole thing!
And I will try to get some pictures when I get to school tomarow
skyler, Thu Mar 27 2014, 10:46PM
Hopefully we are getting down there on getting the tesla coil working.
We have finally assembled the secondary out of a 12 inch by 48 inch sona tube, with enough 24 gauge wire with fishing line to wind to the top (we estimated 900-1200 turns based on how much wire we had, 3500 feet, using almost all of it)
We have a bunch of MOTS, at least Five good ones, and 5 more that we don't know are good or bad and hope to get that power supply working (maybe voltage doublers or something if they keep arcing internally- we have almost 10 microwave diodes and capacitors)
3500 RPM spark gap is almost complete with the tungsten rods ordered
And we still have not got MMC capacitors, but will hopefully get the funds for that after we get it to work with the beer bottle caps.
For the primary, we currently have 5 turns of copper tubing, 20 feet, and probably will need more copper tubing to get more turns, but that stuff is pretty expensive so we will try it with this first.
For the toroid, we just got some heater duct at the local home depot, hope that works
Any problems popping up to anybody? We are out out of major money, so hopefully we don't have to redo the whole thing!
And I will try to get some pictures when I get to school tomarow
Re: Tesla Coil Help
skyler, Tue May 27 2014, 01:27AM
Pictures so far are located here amsatnet.info/#coil
skyler, Tue May 27 2014, 01:27AM
Pictures so far are located here amsatnet.info/#coil
Re: Tesla Coil Help
Graham Armitage, Tue May 27 2014, 12:33PM
I think many of us started with ultra low budgets on our first coils. My first caps used thin glass sheets and aluminum foil. Not great but we got them to work. What I later found to be a good homemade cap is using polyethylene sheet (painter's drop cloth). It has a very high dielectric constant and good breakdown strength. Calculate how many sheets you need to sustain the primary voltage and double that. Then place alternating layers of aluminum foil and poly and roll it up with a terminal on each end. If you can, place the whole capacitor roll in a plastic pipe or tube and seal the ends after filling it with cheap vegetable oil from the supermarket. This will prevent corona discharge that will destroy your poly sheet very quickly. I have used these for years with minimal failures.
This should be a cheap and very efficient capacitor. Good luck.
Here is a large coil running off the caps I just described -
You can see the white pvc tubes in the bottom right.
Graham Armitage, Tue May 27 2014, 12:33PM
I think many of us started with ultra low budgets on our first coils. My first caps used thin glass sheets and aluminum foil. Not great but we got them to work. What I later found to be a good homemade cap is using polyethylene sheet (painter's drop cloth). It has a very high dielectric constant and good breakdown strength. Calculate how many sheets you need to sustain the primary voltage and double that. Then place alternating layers of aluminum foil and poly and roll it up with a terminal on each end. If you can, place the whole capacitor roll in a plastic pipe or tube and seal the ends after filling it with cheap vegetable oil from the supermarket. This will prevent corona discharge that will destroy your poly sheet very quickly. I have used these for years with minimal failures.
This should be a cheap and very efficient capacitor. Good luck.
Here is a large coil running off the caps I just described -
You can see the white pvc tubes in the bottom right.
Re: Tesla Coil Help
skyler, Thu Aug 07 2014, 10:55PM
How would 6 or 8 of these in series hold up?
skyler, Thu Aug 07 2014, 10:55PM
How would 6 or 8 of these in series hold up?
Re: Tesla Coil Help
Mads Barnkob, Fri Aug 08 2014, 05:53AM
Big snubber capacitors work great in DRSSTC, just be sure to check its numbers to your coil and current setting, there is a MMC calculator on my site for this:http://kaizerpowerelectronics.dk/calculators/ mmc-calculator/
Mads Barnkob, Fri Aug 08 2014, 05:53AM
skyler wrote ...
How would 6 or 8 of these in series hold up?
How would 6 or 8 of these in series hold up?
Big snubber capacitors work great in DRSSTC, just be sure to check its numbers to your coil and current setting, there is a MMC calculator on my site for this:http://kaizerpowerelectronics.dk/calculators/ mmc-calculator/
Re: Tesla Coil Help
loneoceans, Fri Aug 08 2014, 06:41PM
Hey Skyler,
It looks like your coil is really big. Did you start off with a 4" pipe and are now using a 12" pipe? A 4 x 1 foot secondary is pretty big! For reference, today's electronic DRSSTC coils at that size take in about 5 to 10kW input power to make ~10+ to 13ft of spark. Are you also now using a NST or your 4-MOT stack? As a reference, I built a 4" secondary rotary spark gap coil about ten years ago and it's still going strong. It used a 4 MOT stack in series for 8600VAC, which was I think what you originally planned to do? Would be good to know the current status of the project in more detail.
Above's my coil running at about 4kW input power. Not too overkill if you ask me
. Check out my build page here which you might find useful:
As for the caps you linked, I'm sure they'll work fine, but you need to size them correctly. What sort of power supply are you using now? 8 in series would give a 14.4kV 225nF bank which looks like a bit too much capacitance for a RSG coil. But despite the 1.8kVDC capacitor rating, they're probably closer to 500VAC. If I was building one for my 4-MOT power supply, I'd use more like 14-20 in series, and then it gets pretty expensive. If you're using a NST, I'll go for the smaller individual polypropylene film capacitors and have more of them in series.
loneoceans, Fri Aug 08 2014, 06:41PM
Hey Skyler,
It looks like your coil is really big. Did you start off with a 4" pipe and are now using a 12" pipe? A 4 x 1 foot secondary is pretty big! For reference, today's electronic DRSSTC coils at that size take in about 5 to 10kW input power to make ~10+ to 13ft of spark. Are you also now using a NST or your 4-MOT stack? As a reference, I built a 4" secondary rotary spark gap coil about ten years ago and it's still going strong. It used a 4 MOT stack in series for 8600VAC, which was I think what you originally planned to do? Would be good to know the current status of the project in more detail.
Above's my coil running at about 4kW input power. Not too overkill if you ask me
. Check out my build page here which you might find useful: As for the caps you linked, I'm sure they'll work fine, but you need to size them correctly. What sort of power supply are you using now? 8 in series would give a 14.4kV 225nF bank which looks like a bit too much capacitance for a RSG coil. But despite the 1.8kVDC capacitor rating, they're probably closer to 500VAC. If I was building one for my 4-MOT power supply, I'd use more like 14-20 in series, and then it gets pretty expensive. If you're using a NST, I'll go for the smaller individual polypropylene film capacitors and have more of them in series.
Re: Tesla Coil Help
skyler, Sun Aug 10 2014, 12:43PM
I realize that the size of our coil may be way overkill.
Theres not much we are going to do about it though, because we spent a long time winding that secondary.
We do know the resonant frequency, which is about 83 Khz, and I now have 100 feet of copper tubing for the primary instead of the 20 feet before.
Reason we are going back from NST to MOT:
The rotary spark gap keeps failing when we try it because the NST keeps GFI interrupting, and they promised that the NST was non GFI but sure enough the tripper in it breaks. We opened the top off and there was all of this solid insulator stuff covering it, so we did not want to mess with that. The NST is the old type, not the new semiconductor. So we are going back to MOTS.
I can't spend lots of money on primary caps. Only about $100, so if anybody has suggestions, please say.
The bucket cap seems like it won't work because when I tested it with the NST, a beer bottle just broke.
Thanks for the help
skyler, Sun Aug 10 2014, 12:43PM
I realize that the size of our coil may be way overkill.
Theres not much we are going to do about it though, because we spent a long time winding that secondary.
We do know the resonant frequency, which is about 83 Khz, and I now have 100 feet of copper tubing for the primary instead of the 20 feet before.
Reason we are going back from NST to MOT:
The rotary spark gap keeps failing when we try it because the NST keeps GFI interrupting, and they promised that the NST was non GFI but sure enough the tripper in it breaks. We opened the top off and there was all of this solid insulator stuff covering it, so we did not want to mess with that. The NST is the old type, not the new semiconductor. So we are going back to MOTS.
I can't spend lots of money on primary caps. Only about $100, so if anybody has suggestions, please say.
The bucket cap seems like it won't work because when I tested it with the NST, a beer bottle just broke.
Thanks for the help
Re: Tesla Coil Help
skyler, Thu Sept 11 2014, 10:16PM
•I finally got the MOTS (microwave oven transformers) to work, by correctly wiring the secondary coils (using the core of two mots as the center, and removing the connection to the core on the outer MOTS, as well as submersing the entire power supply in oil) and have a HIGH current 8KV power supply.
•I have experimented with several ballasts, including a MOT with the secondary shorted, a big hunk of aluminum etc, and am close to finding a good setup with the amount of current I have available (20amps-30amps)
•I used a 3450 RPM pool pump motor for the rotary spark gap. (Yes, I know it isn't Synchronous, and blah blah but this youtube video has an awesome Quad mot coil using 3450.
The motor is very similar to this setup, using tungsten rods. -->
•I have a primary coil of 100 feet copper wire wound, but it might be a bit uneven (like goes up and down a bit).
•I still have my 12-15nf home-brew bucket capacitor as well as the large secondary with 12ft diameter and 4 feet height.
THE PROBLEM
I got the spark gap to fire Perfectly, so next step, I hook up the Series string of primary coil and bucket cap in parallel with the spark gap, which was firing perfectly
But.... Nothing, the primary coil fails to fire until I disconnect the capacitor primary string, and then it fires again.
What is going on? Does it have to do with it not resonating and the cap having a wayy off value (which i know is true, I thought I could compensate by buying 100 feet of copper tubing)
Thanks for any help, we are out of ideas and would love any input!!! HD Pictures of setup will come as soon I can get to my friends house again (as he has the coil)
skyler, Thu Sept 11 2014, 10:16PM
•I finally got the MOTS (microwave oven transformers) to work, by correctly wiring the secondary coils (using the core of two mots as the center, and removing the connection to the core on the outer MOTS, as well as submersing the entire power supply in oil) and have a HIGH current 8KV power supply.
•I have experimented with several ballasts, including a MOT with the secondary shorted, a big hunk of aluminum etc, and am close to finding a good setup with the amount of current I have available (20amps-30amps)
•I used a 3450 RPM pool pump motor for the rotary spark gap. (Yes, I know it isn't Synchronous, and blah blah but this youtube video has an awesome Quad mot coil using 3450.
The motor is very similar to this setup, using tungsten rods. -->
•I have a primary coil of 100 feet copper wire wound, but it might be a bit uneven (like goes up and down a bit).
•I still have my 12-15nf home-brew bucket capacitor as well as the large secondary with 12ft diameter and 4 feet height.
THE PROBLEM
I got the spark gap to fire Perfectly, so next step, I hook up the Series string of primary coil and bucket cap in parallel with the spark gap, which was firing perfectly
But.... Nothing, the primary coil fails to fire until I disconnect the capacitor primary string, and then it fires again.
What is going on? Does it have to do with it not resonating and the cap having a wayy off value (which i know is true, I thought I could compensate by buying 100 feet of copper tubing)
Thanks for any help, we are out of ideas and would love any input!!! HD Pictures of setup will come as soon I can get to my friends house again (as he has the coil)
Re: Tesla Coil Help
loneoceans, Thu Sept 11 2014, 10:40PM
Photos and more specific details of the setup will help.
Do you mean that your spark gap isn't firing, but you have made it close enough such that without the capacitor/primary in series (parallel with the gap), the spark gap no longer fires? As for your ballast, I found that using a secondary-shorted MOT as a ballast does help in current limiting, but at least for my transformer, I was getting more like 1 to 1.5kVA maximum. This will limit the output to about 2-3 feet or so. I now simply run my quad MOT coil on a 30A circuit with no ballast and it draws about 17A at 240V with great performance.
Since your gap is not firing, do you have a short somewhere in your capacitor bank? Is your MOT stack drawing lots of current without the spark? If it is, there might be some arcing-over or a short somewhere in which case the gap would not fire when the caps are attached.
Once you get the gap to fire, you'll need to work on your tuning, which isn't going to be solved by adding a 100ft primary without matching the frequencies. The primary circuit should be slightly lower frequency (5 to 10% is a good place to begin) than the secondary. Fine tune for maximum performance - no shortcuts here.
loneoceans, Thu Sept 11 2014, 10:40PM
Photos and more specific details of the setup will help.
Do you mean that your spark gap isn't firing, but you have made it close enough such that without the capacitor/primary in series (parallel with the gap), the spark gap no longer fires? As for your ballast, I found that using a secondary-shorted MOT as a ballast does help in current limiting, but at least for my transformer, I was getting more like 1 to 1.5kVA maximum. This will limit the output to about 2-3 feet or so. I now simply run my quad MOT coil on a 30A circuit with no ballast and it draws about 17A at 240V with great performance.
Since your gap is not firing, do you have a short somewhere in your capacitor bank? Is your MOT stack drawing lots of current without the spark? If it is, there might be some arcing-over or a short somewhere in which case the gap would not fire when the caps are attached.
Once you get the gap to fire, you'll need to work on your tuning, which isn't going to be solved by adding a 100ft primary without matching the frequencies. The primary circuit should be slightly lower frequency (5 to 10% is a good place to begin) than the secondary. Fine tune for maximum performance - no shortcuts here.
Re: Tesla Coil Help
skyler, Fri Sept 12 2014, 10:06PM
My MOTS are definitely not shorted, high currents are not drawn when the mots aren't connected to anything, and we built a fully functional Jacobs ladder out of it to test it.
To get this straight forward,
A. the spark gap fires when nothing is connected (exept the mots of course)
B. the spark gap fails to fire when the primary capacitor and 100ft primary coil is connected
Capacitor have a short?
Last time I measured (a few months ago), it did not have a short cirucit but I don't know now, something could have happened. I emailed my friend to test for shorts and will get back as soon as possible.
skyler, Fri Sept 12 2014, 10:06PM
My MOTS are definitely not shorted, high currents are not drawn when the mots aren't connected to anything, and we built a fully functional Jacobs ladder out of it to test it.
To get this straight forward,
A. the spark gap fires when nothing is connected (exept the mots of course)
B. the spark gap fails to fire when the primary capacitor
and 100ft primary coil is connectedCapacitor have a short?
Last time I measured (a few months ago), it did not have a short cirucit but I don't know now, something could have happened. I emailed my friend to test for shorts and will get back as soon as possible.
Re: Tesla Coil Help
skyler, Mon Sept 15 2014, 09:42PM
Yup the capacitor had a short!!! Dead short.
skyler, Mon Sept 15 2014, 09:42PM
Yup the capacitor had a short!!! Dead short.
Re: Tesla Coil Help
skyler, Mon Jan 26 2015, 07:58PM
I am getting frustrated, my coil project has been going on for over a year, and it still barely works, 4-6 inch sparks with help with a grounded material stuck right next to it is all that I get.
I have gotten the primary and secondary to resonate at the same frequency, first the primary was a bit high in frequency, but we added some extra coil, and they are both somewhere around 100khz.
Any suggestions on what I can try next? I will upload all of the videos and pictures on YouTube when I get home today and maybe the visual will help.
Primary capacitance: 24 nF (two beer bottle bucket capacitors like above)
Primary inductance .23 millihenries (and varied by position on coil)
Rotary Spark gap 3450 RPM, yes I know it should be 3600, but I have seen plenty of videos where 3450 works great with arcs order of magnitudes bigger than mine.
Power supply, 4 MOTs
Ballast , 1 MOT
What am I doing wrong, can anyone give me steps that I can troubleshoot? The coil is built to everything it should be, and I have no idea why it is not behaving even close to the power input.
skyler, Mon Jan 26 2015, 07:58PM
I am getting frustrated, my coil project has been going on for over a year, and it still barely works, 4-6 inch sparks with help with a grounded material stuck right next to it is all that I get.
I have gotten the primary and secondary to resonate at the same frequency, first the primary was a bit high in frequency, but we added some extra coil, and they are both somewhere around 100khz.
Any suggestions on what I can try next? I will upload all of the videos and pictures on YouTube when I get home today and maybe the visual will help.
Primary capacitance: 24 nF (two beer bottle bucket capacitors like above)
Primary inductance .23 millihenries (and varied by position on coil)
Rotary Spark gap 3450 RPM, yes I know it should be 3600, but I have seen plenty of videos where 3450 works great with arcs order of magnitudes bigger than mine.
Power supply, 4 MOTs
Ballast , 1 MOT
What am I doing wrong, can anyone give me steps that I can troubleshoot? The coil is built to everything it should be, and I have no idea why it is not behaving even close to the power input.
Re: Tesla Coil Help
redruM69, Tue Jan 27 2015, 05:28AM
4" coil, 4' high, 10" topload, 24awg ~154khz
With a 24nf cap, you'll need about 9-12 turns on your primary.
2 beer bottles is not 24nf. Each bottle will give about .5-1nf. So you're not even close. You'll need to build about 24 of em if your goal is 24nf
How many electrodes are on your RSG rotor?
Again with 4 MOT's?? We keep saying that is TOTAL overkill for a 4" coil but you keep ignoring us. 2 is MORE than plenty for that coil
redruM69, Tue Jan 27 2015, 05:28AM
skyler wrote ...
I have gotten the primary and secondary to resonate at the same frequency, first the primary was a bit high in frequency, but we added some extra coil, and they are both somewhere around 100khz.
I have gotten the primary and secondary to resonate at the same frequency, first the primary was a bit high in frequency, but we added some extra coil, and they are both somewhere around 100khz.
4" coil, 4' high, 10" topload, 24awg ~154khz
With a 24nf cap, you'll need about 9-12 turns on your primary.
2 beer bottles is not 24nf. Each bottle will give about .5-1nf. So you're not even close. You'll need to build about 24 of em if your goal is 24nf
How many electrodes are on your RSG rotor?
Again with 4 MOT's?? We keep saying that is TOTAL overkill for a 4" coil but you keep ignoring us. 2 is MORE than plenty for that coil
Re: Tesla Coil Help
Sigurthr, Tue Jan 27 2015, 12:11PM
Without seeing clear, focused, shots of the build in question all I can offer is general causes of issues.
1) Losses.
You need to minimize wire lengths between all points. Having heavy gauge wire isn't enough by itself. Reducing an extra ten inches of wire can have a tremendous impact in efficiency.
2) Ground effectiveness.
Lots online about good RF grounding, it isn't hard to find either since Hams (amateur radio) are well versed in it.
3) Environmental factors.
I recently had a student build a SGTC only to have disappointing results. It turns out his run environment was way too small and conductive for his coil. As a result it artificially detuned the secondary resonator and robbed it of most of the incoming power. Upon relocating to the driveway with a proper RF ground he found he was ~90KHz too high on the secondary. Fixed it and doubled the output.
Sigurthr, Tue Jan 27 2015, 12:11PM
Without seeing clear, focused, shots of the build in question all I can offer is general causes of issues.
1) Losses.
You need to minimize wire lengths between all points. Having heavy gauge wire isn't enough by itself. Reducing an extra ten inches of wire can have a tremendous impact in efficiency.
2) Ground effectiveness.
Lots online about good RF grounding, it isn't hard to find either since Hams (amateur radio) are well versed in it.
3) Environmental factors.
I recently had a student build a SGTC only to have disappointing results. It turns out his run environment was way too small and conductive for his coil. As a result it artificially detuned the secondary resonator and robbed it of most of the incoming power. Upon relocating to the driveway with a proper RF ground he found he was ~90KHz too high on the secondary. Fixed it and doubled the output.
Re: Tesla Coil Help
skyler, Wed Jan 28 2015, 12:07AM
Thanks. First, here is a shot of the coil in operation:
skyler, Wed Jan 28 2015, 12:07AM
Thanks. First, here is a shot of the coil in operation:
Re: Tesla Coil Help
Kolas, Wed Jan 28 2015, 12:50AM
Don't loose hope! My first coil was ugly but it did work. And as long as you don't have carbon racing through your secondary, your losses wont add up to your power input.
Your biggest issue is probably within your resonant charging technique.
8900 or whatever volts is plenty to fire through a spark gap. Especially a rotary style gap. Also short output is probably indicative of tuning to a
Fo that is too high in the primary. once spark outbreak occurs, the capacitance of the streamer becomes quite sizable. Be sure to tune (theoretically) about 5-10% below the resonant frequency of the secondary and topload to cause the secondary to be most effective under load.
Bottle caps are definitely terrible. Fact
The dissipation of glass at your frequency is high. any yet it will still work!
Take pictures of what you have currently and I'm sure that ppl will be able to offer specific advice.
Kolas, Wed Jan 28 2015, 12:50AM
Don't loose hope! My first coil was ugly but it did work. And as long as you don't have carbon racing through your secondary, your losses wont add up to your power input.
Your biggest issue is probably within your resonant charging technique.
8900 or whatever volts is plenty to fire through a spark gap. Especially a rotary style gap. Also short output is probably indicative of tuning to a
Fo that is too high in the primary. once spark outbreak occurs, the capacitance of the streamer becomes quite sizable. Be sure to tune (theoretically) about 5-10% below the resonant frequency of the secondary and topload to cause the secondary to be most effective under load.
Bottle caps are definitely terrible. Fact
The dissipation of glass at your frequency is high. any yet it will still work!
Take pictures of what you have currently and I'm sure that ppl will be able to offer specific advice.
Re: Tesla Coil Help
skyler, Wed Jan 28 2015, 02:36AM
Here is a video of how we found the resonant frequency of the primary. We used an oscilloscope and a square wave generator and found that the resonant frequency with the extra wire we just added to the primary was at 80-90khz ish.
Here is a video of the general setup we had going on. Notice how much chicken wire we put for ground. For the power supply, we are using a 5th MOT as a ballast.
In this video, I am testing the resonant frequency of the secondary using a sine wave input on the bottom and using a probe at a distance to watch the voltage climb on resonant frequency.
Here is a picture of the rotary spark gap with the tungsten rods
skyler, Wed Jan 28 2015, 02:36AM
Here is a video of how we found the resonant frequency of the primary. We used an oscilloscope and a square wave generator and found that the resonant frequency with the extra wire we just added to the primary was at 80-90khz ish.
Here is a video of the general setup we had going on. Notice how much chicken wire we put for ground. For the power supply, we are using a 5th MOT as a ballast.
In this video, I am testing the resonant frequency of the secondary using a sine wave input on the bottom and using a probe at a distance to watch the voltage climb on resonant frequency.
Here is a picture of the rotary spark gap with the tungsten rods
Re: Tesla Coil Help
Hazmatt_(The Underdog), Wed Jan 28 2015, 04:46AM
You guys are doing a great job! I bet you're learning a lot too!
For the Primary, 10 turns should be fine, I realize that's going to throw everything off, but 10 turns spaced equally will work out for you better then 40 turns closely spaced.
That will raise the frequency of course, but you can some capacitence to the top of the coil and primary and get back in tune, or close enough to tap it.
Also, good solid connections with heavy wire really is key here. any loose connection = loss. Thin wires = loss, and long wires = loss.
Remember that every inch if wire in your primary circuit, IS inductance, that means it literally is the tank circuit, not just your primary coil. That also means that every inch of wire that is not part of the primary is radiating energy that is being lost to space, and not your primary tank circuit, so it's not feeding the coil.
Also, if you're close to the coil, your proximity to it will de-tune the coil, so when making precision measurements, try to be at least 4 feet away.
If you get it tuned sharply enough, you can actually see the effect of proximity on the scope. Tune it for resonance and get your hand near, and you will see the amplitude diminish, it's pretty neat.
Keep up the good work!
Hazmatt_(The Underdog), Wed Jan 28 2015, 04:46AM
You guys are doing a great job! I bet you're learning a lot too!
For the Primary, 10 turns should be fine, I realize that's going to throw everything off, but 10 turns spaced equally will work out for you better then 40 turns closely spaced.
That will raise the frequency of course, but you can some capacitence to the top of the coil and primary and get back in tune, or close enough to tap it.
Also, good solid connections with heavy wire really is key here. any loose connection = loss. Thin wires = loss, and long wires = loss.
Remember that every inch if wire in your primary circuit, IS inductance, that means it literally is the tank circuit, not just your primary coil. That also means that every inch of wire that is not part of the primary is radiating energy that is being lost to space, and not your primary tank circuit, so it's not feeding the coil.
Also, if you're close to the coil, your proximity to it will de-tune the coil, so when making precision measurements, try to be at least 4 feet away.
If you get it tuned sharply enough, you can actually see the effect of proximity on the scope. Tune it for resonance and get your hand near, and you will see the amplitude diminish, it's pretty neat.
Keep up the good work!
Re: Tesla Coil Help
Kolas, Wed Jan 28 2015, 07:09AM
indeed, to get a lower primary resonant frequency, you will need a larger tank capacitor. you've got too many turns.
Kolas, Wed Jan 28 2015, 07:09AM
indeed, to get a lower primary resonant frequency, you will need a larger tank capacitor. you've got too many turns.
Re: Tesla Coil Help
skyler, Wed Jan 28 2015, 05:07PM
Can you guys tell us anything we need to test to give you more data on troubleshooting? We can test a bunch of stuff, and try to troubleshoot.
skyler, Wed Jan 28 2015, 05:07PM
Can you guys tell us anything we need to test to give you more data on troubleshooting? We can test a bunch of stuff, and try to troubleshoot.
Re: Tesla Coil Help
loneoceans, Wed Jan 28 2015, 06:39PM
I looked through your videos. Here are some comments.
loneoceans, Wed Jan 28 2015, 06:39PM
skyler wrote ...
Can you guys tell us anything we need to test to give you more data on troubleshooting? We can test a bunch of stuff, and try to troubleshoot.
Can you guys tell us anything we need to test to give you more data on troubleshooting? We can test a bunch of stuff, and try to troubleshoot.
I looked through your videos. Here are some comments.
- It looks like the way you measured the secondary frequency is correct (i.e. signal generator fed in the bottom of the secondary coil, and use a wire on the scope probe placed near the coil to pick up the radiated signal, and adjust the signal gen until you get max output).
- I'm not very sure what you're doing to measure the primary circuit. To measure that, short your spark gap. This will make your primary coil and capacitor connected together at both ends. Scope across the two ends of the primary coil. For the signal generator, attenuate the signal by putting a ~5 to 50k resistor on the output of the signal generator, and place that also across the primary coil. Adjust the frequency until you see the largest amplitude. You should set this to be about 5 to 10% lower than your secondary frequency.
- It looks like you really need to work on your wiring. Everything looks like it's connected with crocodile clips (these usually have very very thin wire), and are very long. Please put some effort in getting some good wire (I use 8 AWG for my 4 MOT coil for all primary connections and even that's not really good enough). So the wire that connects the capacitor to the primary coil and the coil / capacitor to the spark gap needs to be not only short, but thick, and terminated properly with proper crimp terminals. You can't cheap out and just use 18AWG wire here. I'd recommend putting these components right underneath the coil. Same goes for your spark gap - you've just wrapped thin, bare, wire around the tungsten rods with no positive contact. That's not going work at all.
- You should align the two stationary electrodes of your spark gap differently. The current configuration will cause the rotor to be near the electrodes for a significant amount of time, which can lead to the MOT simply shorting out and not sending power to charge the capacitor bank. (i.e. poor quenching).
- Your primary coil looks a bit.. dangerous. I'd try to adjust it to make it nice and rounder so it doesn't have pieces of tape separating turns. Ideally you should make more supports for them as well. 8kV from the MOT stack can short through the wooden primary table if it has any sort of moisture in it. You also cannot simply use crocodile clips for your primary connections. It needs to be a solid, beefy connection. Please put some effort into this.
- How is your capacitor bank made? Are they filled with glass bottles inside? Or are they simply made of the big plastic buckets? Did you make sure that all the connections inside are proper (electrically speaking?). I actually disagree with Kolas - glass capacitors actually work really well. You just need to build them properly. Can we have a closer look with photos of your capacitor? You might need to make a better one.
- Feel free to see how I made my 4-MOT coil here:
- Finally, I think a bigger toroid will also work, and look better. :) To conclude - you can't just slap together some wires and expect the coil to work. Put some care and thought into making the coil, otherwise you'll only reap the results of what you sow.
Re: Tesla Coil Help
Hazmatt_(The Underdog), Thu Jan 29 2015, 02:14AM
For my latest build I'm using very heavy connections, hahah 3/8" copper!
And it goes underneath the coil, and all the connections are very short.
I realize that it will be hard with your bucket configuration to keep the leads short, and get the buckets close, but try.
You might need some 8AWG "welding" cable or something heavy to make good connections, or if possible, get a large
tub to put the required cap bank in rather than the buckets, and get everything in one place.
Don't worry if your coil doesn't look perfect, they evolve over time and with experience.
My first coil was a horrendous mess, and wasn't even close to being correct. My secondary had like 50 turns of 18 AWG wire,
and it was not even close. So keep up the good work guys! and keep learning.
Here's a pic of a coil I'm building for a customer
Hazmatt_(The Underdog), Thu Jan 29 2015, 02:14AM
For my latest build I'm using very heavy connections, hahah 3/8" copper!
And it goes underneath the coil, and all the connections are very short.
I realize that it will be hard with your bucket configuration to keep the leads short, and get the buckets close, but try.
You might need some 8AWG "welding" cable or something heavy to make good connections, or if possible, get a large
tub to put the required cap bank in rather than the buckets, and get everything in one place.
Don't worry if your coil doesn't look perfect, they evolve over time and with experience.
My first coil was a horrendous mess, and wasn't even close to being correct. My secondary had like 50 turns of 18 AWG wire,
and it was not even close. So keep up the good work guys! and keep learning.
Here's a pic of a coil I'm building for a customer
Re: Tesla Coil Help
Sigurthr, Thu Jan 29 2015, 02:38AM
Also, you can't measure the primary circuit resonance with the secondary not in place. The mutual inductance of the secondary will affect the resonant frequency of the primary, and vice versa.
I find most builders have better results by plugging data carefully into JavaTC to model the expected approximate resonance points than they do by trying to measure it directly. I say give the program a go.
Sigurthr, Thu Jan 29 2015, 02:38AM
Also, you can't measure the primary circuit resonance with the secondary not in place. The mutual inductance of the secondary will affect the resonant frequency of the primary, and vice versa.
I find most builders have better results by plugging data carefully into JavaTC to model the expected approximate resonance points than they do by trying to measure it directly. I say give the program a go.
Re: Tesla Coil Help
Kolas, Thu Jan 29 2015, 06:40AM
I'm not going to say anything that hasn't already been said.
I agree that might be a Huge help to you now.
What you guys need to do is an "asbuilt" using your current configuration.
While much better performance comes from synthetic materials, Glass capacitors are certainly the cheapest route. I don't like them but they will do you well. Expect some bottles to break.
MOT's are very resilient and don't care much about be shorted.
Beef up your wiring, its just too small a gauge, everyone is saying it.
Remember the ring down is hundreds of amps. And those charges need "room" to move. I'd like to say that the primary winding should be the smallest in the system, but that is likely not going to happen. Every bit of wiring that isn't "coupled" to the secondary is leakage inductance. and yes, 1 inch matters. The entirety of the primary should no be used. The larger your hookup conductors, the lower their inductance.
I think the biggest problem is the size of your tank cap. 24 NF is TOO SMALL!!! You're pumping all this power, and you've got a tiny tank cap. The first thing I think you should do is at least double the size. Doing this will let you decrease the number of primary turns. Java TC will let you determine the resonant frequency of the primary. It is very important to try and calculate it out.
I like that you youngsters are playing around with this tech. Keep it up, and _Don't ever quit!_
The moral of my story.... get more tank capacitance. Try to calculate the capacitance for about 10 turns on the primary. Just like Matt said.
The look of your coil is secondary to it's function. So don't worry about that. Machine techniques evolve with time. Once this one is functional, I'm sure the next one will be quite pretty.
Kolas, Thu Jan 29 2015, 06:40AM
I'm not going to say anything that hasn't already been said.
I agree that
might be a Huge help to you now.What you guys need to do is an "asbuilt" using your current configuration.
While much better performance comes from synthetic materials, Glass capacitors are certainly the cheapest route. I don't like them but they will do you well. Expect some bottles to break.
MOT's are very resilient and don't care much about be shorted.
Beef up your wiring, its just too small a gauge, everyone is saying it.
Remember the ring down is hundreds of amps. And those charges need "room" to move. I'd like to say that the primary winding should be the smallest in the system, but that is likely not going to happen. Every bit of wiring that isn't "coupled" to the secondary is leakage inductance. and yes, 1 inch matters. The entirety of the primary should no be used. The larger your hookup conductors, the lower their inductance.
I think the biggest problem is the size of your tank cap. 24 NF is TOO SMALL!!! You're pumping all this power, and you've got a tiny tank cap. The first thing I think you should do is at least double the size. Doing this will let you decrease the number of primary turns. Java TC will let you determine the resonant frequency of the primary. It is very important to try and calculate it out.
I like that you youngsters are playing around with this tech. Keep it up, and _Don't ever quit!_
The moral of my story.... get more tank capacitance. Try to calculate the capacitance for about 10 turns on the primary. Just like Matt said.
The look of your coil is secondary to it's function. So don't worry about that. Machine techniques evolve with time. Once this one is functional, I'm sure the next one will be quite pretty.
Re: Tesla Coil Help
skyler, Thu Feb 05 2015, 04:17PM
Thanks everyone for the help. Got the coil to work better with a little bit of your suggestins and something else- the ballast.
At first, I had a tiny MOT as the ballast and I replaced it with a bigger MOT and it worked so much better. I then took the ballast off, and the spark gap didn't even fire properly until I just let it free slow down. At some speeds, I got strange giant arcs.
So in general, I am using a MOT with secondary shorted as power ballast.
The question: What does the ballast have an affect on the coil other than the power output?
skyler, Thu Feb 05 2015, 04:17PM
Thanks everyone for the help. Got the coil to work better with a little bit of your suggestins and something else- the ballast.
At first, I had a tiny MOT as the ballast and I replaced it with a bigger MOT and it worked so much better. I then took the ballast off, and the spark gap didn't even fire properly until I just let it free slow down. At some speeds, I got strange giant arcs.
So in general, I am using a MOT with secondary shorted as power ballast.
The question: What does the ballast have an affect on the coil other than the power output?
Re: Tesla Coil Help
Hazmatt_(The Underdog), Fri Feb 06 2015, 03:36AM
It's basically going to limit the surge current and act like a resistor. The voltage drop across the inductor is V = L di/dt, where di/dt is the rate change of current over time.
The resistance the circuit "sees" or reactance, is Xl = 2*pi*f*L, so you can see how this translates to a resistance, and how the resistance interacts with the current di/dt by the relationship
V = Xl di/dt = 2*pi*f*L di/dt
The amount if inductance that you have can also be varied by changing the degree of shorting of the secondary due to the mutual inductance and coupling of the transformer.
k = M/(sqrt(L1L2))
If you measure the inductance of the primary when the secondary is open, the inductance will be higher then when the secondary is shorted. So if we control this with a large rheostat, we can control the degree of the effective inductance reflected back to the primary, but this is just theory.
It would take a substantial rheostat to control the secondary of the MOT because we're dealing with a 20:1 ratio or so, so you would need a 250W rheostat at maybe 500 ohms or 1000 ohms, which would be an interesting experiment.
You would be changing the secondary reactance and resistance which changes the primary impedance by the impedance ratio.
Anyway, there are some intersting things going on with the transformer as a current ballast.
Hazmatt_(The Underdog), Fri Feb 06 2015, 03:36AM
It's basically going to limit the surge current and act like a resistor. The voltage drop across the inductor is V = L di/dt, where di/dt is the rate change of current over time.
The resistance the circuit "sees" or reactance, is Xl = 2*pi*f*L, so you can see how this translates to a resistance, and how the resistance interacts with the current di/dt by the relationship
V = Xl di/dt = 2*pi*f*L di/dt
The amount if inductance that you have can also be varied by changing the degree of shorting of the secondary due to the mutual inductance and coupling of the transformer.
k = M/(sqrt(L1L2))
If you measure the inductance of the primary when the secondary is open, the inductance will be higher then when the secondary is shorted. So if we control this with a large rheostat, we can control the degree of the effective inductance reflected back to the primary, but this is just theory.
It would take a substantial rheostat to control the secondary of the MOT because we're dealing with a 20:1 ratio or so, so you would need a 250W rheostat at maybe 500 ohms or 1000 ohms, which would be an interesting experiment.
You would be changing the secondary reactance and resistance which changes the primary impedance by the impedance ratio.
Anyway, there are some intersting things going on with the transformer as a current ballast.
Re: Tesla Coil Help
Kolas, Mon Feb 09 2015, 05:26AM
this sounds a lot like the beginning of a variable reactor. which may not be entirely impossible.
Kolas, Mon Feb 09 2015, 05:26AM
this sounds a lot like the beginning of a variable reactor. which may not be entirely impossible.
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