Large Dual Resonant Solid State Tesla Coil
Large Dual Resonant Solid State Tesla Coil
Embedded Files
Quick Summary
Quick Summary
I joined the IEEE club at WPI as a freshman, and they offered to provide funds for a Tesla Coil I wanted to make. After a few weeks of planning and building, this is what I ended up with:
I joined the IEEE club at WPI as a freshman, and they offered to provide funds for a Tesla Coil I wanted to make. After a few weeks of planning and building, this is what I ended up with:
Please see the Interrupter page for an Update
Please see the Interrupter page for an Update
When I arrived at WPI my freshman year, I spotted the IEEE club and joined right away. They mentioned that they like Tesla Coils in their introductory meeting, so I showed them the first one I made and asked if they'd be willing to give funding for me to make a newer, bigger, and better one. They were very enthusiastic and asked me to finish it for WPI's annual Spark Party, which was less than two months away. I put on my thinking cap and went into high-gear for Tesla Coil Building.
When I arrived at WPI my freshman year, I spotted the IEEE club and joined right away. They mentioned that they like Tesla Coils in their introductory meeting, so I showed them the first one I made and asked if they'd be willing to give funding for me to make a newer, bigger, and better one. They were very enthusiastic and asked me to finish it for WPI's annual Spark Party, which was less than two months away. I put on my thinking cap and went into high-gear for Tesla Coil Building.
Design Process / Goals
Design Process / Goals
The goal for this Tesla Coil was originally 4 foot sparks (which was shattered after 7 feet!). Based off of that, I chose beefier components than my last coil. Mainly the 1200v IGBT half bridge modules with "Sehr grosse Robustheit" written in their datasheet and the 350v, 15 millifarad, 50 A rms bus capacitors.
The goal for this Tesla Coil was originally 4 foot sparks (which was shattered after 7 feet!). Based off of that, I chose beefier components than my last coil. Mainly the 1200v IGBT half bridge modules with "Sehr grosse Robustheit" written in their datasheet and the 350v, 15 millifarad, 50 A rms bus capacitors.
Before I could get funding, however, I had to design the coil in full and plan out exactly what I was going to need. I started by drawing out the heart, which is the H-Bridge inverter.
Before I could get funding, however, I had to design the coil in full and plan out exactly what I was going to need. I started by drawing out the heart, which is the H-Bridge inverter.
The IGBTs were to be mounted on a large heat sink, which was going to be the entire size of the paper pictured. The bus capacitors were going to be configured as a voltage doubler for a rated 700V! The area shaded in red is 5mm copper bus bar, which were designed in AutoCAD and laser cut. Not shown: bleeder and balancing resistors.
The IGBTs were to be mounted on a large heat sink, which was going to be the entire size of the paper pictured. The bus capacitors were going to be configured as a voltage doubler for a rated 700V! The area shaded in red is 5mm copper bus bar, which were designed in AutoCAD and laser cut. Not shown: bleeder and balancing resistors.
It's safe to say that this one went through a few revisions.
It's safe to say that this one went through a few revisions.
General Bridge Schematic:
General Bridge Schematic:
Bridge.pdfD9-D16 almost aren't needed, due to the fact that I only plan to run the coil at a bus voltage of 400V max. Any transients created will be well within the 1200v limit.
D9-D16 almost aren't needed, due to the fact that I only plan to run the coil at a bus voltage of 400V max. Any transients created will be well within the 1200v limit.
After the IGBTs and bus caps were selected, it was time to do MMC calculations. Since the 942C series of capacitors aren't cheap, I wanted to make a rugged capacitor bank that could last for a long time.
After the IGBTs and bus caps were selected, it was time to do MMC calculations. Since the 942C series of capacitors aren't cheap, I wanted to make a rugged capacitor bank that could last for a long time.
4 capacitors in series results in 8kvDC, 1400Vrms de-rated at 65kHz. 15 strings in parallel (brought down from 16 in the plans) allows for some pretty hefty primary currents - 202Arms!
4 capacitors in series results in 8kvDC, 1400Vrms de-rated at 65kHz. 15 strings in parallel (brought down from 16 in the plans) allows for some pretty hefty primary currents - 202Arms!
Here's a full cad rendering of what I planned the coil to look like:
Here's a full cad rendering of what I planned the coil to look like:
Secondary Coil Construction
Secondary Coil Construction
With a primary capacitance of ~550nF and wanting 4-7 turns on the primary max, in order to match resonance, the secondary was planned to be around 3.5' of 6" diameter PVC with 2600 turns of 26 AWG wire. To make it, I had to redesign my coil winder to have enough torque. I tried using the original stepper motor I had mounted, but it was simply no match for the pipe. I decided to scrap the idea of putting a shaft down the middle of the pipe and instead got two lawn mower wheels I had to act as rollers. I then added gears to one of the wheels and rotated it with the stepper motor, which you can see in the following video:
With a primary capacitance of ~550nF and wanting 4-7 turns on the primary max, in order to match resonance, the secondary was planned to be around 3.5' of 6" diameter PVC with 2600 turns of 26 AWG wire. To make it, I had to redesign my coil winder to have enough torque. I tried using the original stepper motor I had mounted, but it was simply no match for the pipe. I decided to scrap the idea of putting a shaft down the middle of the pipe and instead got two lawn mower wheels I had to act as rollers. I then added gears to one of the wheels and rotated it with the stepper motor, which you can see in the following video:
Secondary_winding.MOVThe stepper motor had issues with overheating, so I had to change the design. After all, stepper motors are used for precise, calculated turns, not continuous rotation. What I really needed was a gear motor. So, that's exactly what I added. On the left wheel, I added hot glue to reduce the pipe slipping during rotation. Once I finished winding, I covered the coil in two coats of epoxy resin to protect it from scratches and also to give it a mirror-like finish.
The stepper motor had issues with overheating, so I had to change the design. After all, stepper motors are used for precise, calculated turns, not continuous rotation. What I really needed was a gear motor. So, that's exactly what I added. On the left wheel, I added hot glue to reduce the pipe slipping during rotation. Once I finished winding, I covered the coil in two coats of epoxy resin to protect it from scratches and also to give it a mirror-like finish.
The topload was then made from 7" semi-rigid aluminum duct formed into a toroid. I made it screw mounted for easy transport.
The topload was then made from 7" semi-rigid aluminum duct formed into a toroid. I made it screw mounted for easy transport.
Primary Coil
Primary Coil
Once I finished the secondary, it was time to wind the primary. I modeled supports in Autocad and had them laser cut along with the bridge copper busbar. I first found the center of the circle pine board by drawing two perpendicular bisectors, and then traced out a 4" circle with a compass. I then hot glued the 6 supports 60 degrees apart. I didn't have a protractor, so the perfect angle was simply found using trigonometry. All that was left was to basically snap the 3/8" copper tubing into place. I couldn't find a long enough continuous pipe, so I had to "splice" another tube to it by soldering.
Once I finished the secondary, it was time to wind the primary. I modeled supports in Autocad and had them laser cut along with the bridge copper busbar. I first found the center of the circle pine board by drawing two perpendicular bisectors, and then traced out a 4" circle with a compass. I then hot glued the 6 supports 60 degrees apart. I didn't have a protractor, so the perfect angle was simply found using trigonometry. All that was left was to basically snap the 3/8" copper tubing into place. I couldn't find a long enough continuous pipe, so I had to "splice" another tube to it by soldering.
Here's the finished product. Note the outer ring bound about the last turn. This is a strike rail connected to ground, which is there to protect the primary coil from getting hit with an arc.
Here's the finished product. Note the outer ring bound about the last turn. This is a strike rail connected to ground, which is there to protect the primary coil from getting hit with an arc.
Multi-Mini-Capacitor Bank
Multi-Mini-Capacitor Bank
The capacitance of the MMC works with the inductance of the primary coil to make the resonant tank circuit of the Tesla Coil. It needs to be able to withstand high voltages and extremely high currents. I decided to go with 15 parallel strings of 4 capacitors in series for a total of ~563nF @ 202.5 A rms - essentially indestructible.
The capacitance of the MMC works with the inductance of the primary coil to make the resonant tank circuit of the Tesla Coil. It needs to be able to withstand high voltages and extremely high currents. I decided to go with 15 parallel strings of 4 capacitors in series for a total of ~563nF @ 202.5 A rms - essentially indestructible.
The plan was to have a stacked design; three pieces of wood would be stacked using threaded rods. Each outlined rectangle is where a capacitor would be ziptied down. Each string of capacitors would then be tied to the sheet metal plates, which I cut by hand.
The plan was to have a stacked design; three pieces of wood would be stacked using threaded rods. Each outlined rectangle is where a capacitor would be ziptied down. Each string of capacitors would then be tied to the sheet metal plates, which I cut by hand.
H-Bridge Inverter
H-Bridge Inverter
As stated above, all of the H-Bridge components were to be mounted on a large heat sink to maximize heat dissipation. From the plans, marks for mounting holes were penciled in and then drilled. Snubber capacitors were placed directly on the IGBTs to minimize transient spikes. Copper bus bar was used to minimize resistance and maximize current flow. Two large bus capacitors were mounted on the part that is sticking out (not pictured here).
As stated above, all of the H-Bridge components were to be mounted on a large heat sink to maximize heat dissipation. From the plans, marks for mounting holes were penciled in and then drilled. Snubber capacitors were placed directly on the IGBTs to minimize transient spikes. Copper bus bar was used to minimize resistance and maximize current flow. Two large bus capacitors were mounted on the part that is sticking out (not pictured here).
Here it is set up on the base board of the coil. The fans from the far side of the MMC also blow onto the heat sink, killing two birds with one stone.
Here it is set up on the base board of the coil. The fans from the far side of the MMC also blow onto the heat sink, killing two birds with one stone.
Driver Board
Driver Board
For this coil, I chose to use Loneocean's UD2.7c driver board, which is sort of like the de facto standard in the Tesla Coil universe. It employs phase lead to ensure ZVS, and has over current detection circuitry. It takes a signal from the interrupter (which is typically a ~100us pulse) to make a spark. During these 100us, it activates the push-pull MOSFETs driving the gate drive transformer connected to the gates of the IGBTs. It times the switching of the gates in accordance with the zero crossings in the primary circuit.
For this coil, I chose to use Loneocean's UD2.7c driver board, which is sort of like the de facto standard in the Tesla Coil universe. It employs phase lead to ensure ZVS, and has over current detection circuitry. It takes a signal from the interrupter (which is typically a ~100us pulse) to make a spark. During these 100us, it activates the push-pull MOSFETs driving the gate drive transformer connected to the gates of the IGBTs. It times the switching of the gates in accordance with the zero crossings in the primary circuit.
There is one key detail to pay attention to when connecting the gate drive transformers to the gates of the IGBTs. In order for the coil to resonate in this push-pull circuit, Q1A and Q2B must be on at the same time, opposite of Q2A and Q1B. If Q1A and Q1B turn on at the same time, there is a direct current path across the capacitor bank through the IGBTs, likely causing component failure. To avoid this, I double and triple checked the timing using a 4-channel oscilloscope, pictured below.
There is one key detail to pay attention to when connecting the gate drive transformers to the gates of the IGBTs. In order for the coil to resonate in this push-pull circuit, Q1A and Q2B must be on at the same time, opposite of Q2A and Q1B. If Q1A and Q1B turn on at the same time, there is a direct current path across the capacitor bank through the IGBTs, likely causing component failure. To avoid this, I double and triple checked the timing using a 4-channel oscilloscope, pictured below.
From the connections on the right, the green and red signals should be synced, and opposite from blue and yellow.
From the connections on the right, the green and red signals should be synced, and opposite from blue and yellow.
On Another note, I added Zener diodes to protect the gates from overvoltage, and series termination resistors to dampen overshoot and ringing.
On Another note, I added Zener diodes to protect the gates from overvoltage, and series termination resistors to dampen overshoot and ringing.
Before running the coil with the secondary in place, I tested the primary circuit to make sure it oscillated correctly. The yellow trace is the collector to emitter voltage of one of the IGBTs, and green is primary current. It was working perfectly; the primary current would "ring up" with each cycle. One issue, however, is the ringing present. From the photo on the right, it can be seen that the unexpected ringing is near twice the frequency of the Tesla Coil's resonant frequency. From this, I suspected that the capacitance from the snubber capacitors was resonating with the inductance of the busbars. After some calculations, one easy fix I found was to simply double the capacitance of the snubber capacitors by placing two more caps on the busbar. Shoutout to the High voltage forum community for helping me debug: https://highvoltageforum.net/index.php?topic=1820.msg13736#msg13736
Before running the coil with the secondary in place, I tested the primary circuit to make sure it oscillated correctly. The yellow trace is the collector to emitter voltage of one of the IGBTs, and green is primary current. It was working perfectly; the primary current would "ring up" with each cycle. One issue, however, is the ringing present. From the photo on the right, it can be seen that the unexpected ringing is near twice the frequency of the Tesla Coil's resonant frequency. From this, I suspected that the capacitance from the snubber capacitors was resonating with the inductance of the busbars. After some calculations, one easy fix I found was to simply double the capacitance of the snubber capacitors by placing two more caps on the busbar. Shoutout to the High voltage forum community for helping me debug: https://highvoltageforum.net/index.php?topic=1820.msg13736#msg13736
After adding the caps, I ran the same test as above, and the ringing appears to be fixed. Another present issue, however, is the switching transients. This still has to be fixed by tuning the phase lead on the driver board. It isn't that big of a deal though, because the spikes only reach 300v, well within the 1200v IGBT rating. I could also add varistors across the collector and emitter to help protect against overvoltage.
After adding the caps, I ran the same test as above, and the ringing appears to be fixed. Another present issue, however, is the switching transients. This still has to be fixed by tuning the phase lead on the driver board. It isn't that big of a deal though, because the spikes only reach 300v, well within the 1200v IGBT rating. I could also add varistors across the collector and emitter to help protect against overvoltage.
For reference, I am 6'4"
For reference, I am 6'4"
Videos from Spark Party 2021
Videos from Spark Party 2021
imperial March.mp4mountain King.mp4nyan cat.mp4ClownMusic.MP4Page updated
Google Sites
Report abuse