BrOdin coil - High power Big sparks!

[davekni]

They seem to be holding up so far, even at 2500A primary current limit. IIRC, the mmc is only built at 750ish Arms, so maybe these caps aren't all that bad after all?

If  750Arms is the capacitor rating, you are likely fine.  2500Apeak is 1770Arms during full current (pulse-skip operation) enable pulses.  750Arms corresponds to 18% duty cycle of 1770Arms.

I cranked the primary current limit up to 2500A because YOLO, SEND IT, LFG! I am sick of burning secondary coils up, something else break please! But nothing blew up this time, guess I'll have to wait a little longer to rebuild the bridge!

The quandary seems to be how to get arcs farther away from the coil while keeping your beautiful toroid.  Perhaps the solution is a large tapered breakout point, large enough to both add some capacitance and to move arcs farther away.  Perhaps a variation on something I'd suggested earlier:  Use a 2" x 4' x 8' styrofoam insulation board (or two laminated to get 4" thickness).  Cut into a tear-drop shape, 8' long to the point and 4' diameter at the other end.  Round edges and cover with foil.  Add a breakout rod extension past the point.  May need some counterweight at the round end of the teardrop to keep it balanced on top of your toroid.

[fh89]

They seem to be holding up so far, even at 2500A primary current limit. IIRC, the mmc is only built at 750ish Arms, so maybe these caps aren't all that bad after all?

If  750Arms is the capacitor rating, you are likely fine.  2500Apeak is 1770Arms during full current (pulse-skip operation) enable pulses.  750Arms corresponds to 18% duty cycle of 1770Arms.

I appreciate the insight as always! There's more headroom than I realized on the cap rating. Hopefully it will last a decent amount of time!

I cranked the primary current limit up to 2500A because YOLO, SEND IT, LFG! I am sick of burning secondary coils up, something else break please! But nothing blew up this time, guess I'll have to wait a little longer to rebuild the bridge!

The quandary seems to be how to get arcs farther away from the coil while keeping your beautiful toroid.  Perhaps the solution is a large tapered breakout point, large enough to both add some capacitance and to move arcs farther away.  Perhaps a variation on something I'd suggested earlier:  Use a 2" x 4' x 8' styrofoam insulation board (or two laminated to get 4" thickness).  Cut into a tear-drop shape, 8' long to the point and 4' diameter at the other end.  Round edges and cover with foil.  Add a breakout rod extension past the point.  May need some counterweight at the round end of the teardrop to keep it balanced on top of your toroid.

As silly as I know this sounds, the trade off in aesthetics just isn't worth it to me. I do appreciate the creative suggestions though! Next coil will have a properly sized toroid, but I'm content now with where this one is at. I will still experiment a bit with a slightly shorter and also a very short breakout point as well as elevating the coil, but aside from that I'm calling it a finished project.

[Mads Barnkob]

Being from a 3 phase country, its just so unreal to see someone pull 350A from a 240VAC output!

If you have forced air cooling on the MMC, it will last a long time. A thing I thought about, was to never cut the leads of axial MMC capacitors, but curl them up in a spiral, to use as a heat sink. As 66% of heat in a axial capacitor is radiated out of the ends and especially the leads. Only 33% is radiated from the round large surface.

Can I use one of your pictures to add your coil to my list of featured coils on kaizerpowerelectronics.dk ? I think I have asked about this before, but have forgot to actually add it

[fh89]

Being from a 3 phase country, its just so unreal to see someone pull 350A from a 240VAC output!

Yes, It's quite amazing that the coil can draw so much power!

If you have forced air cooling on the MMC, it will last a long time.

I think I have that covered! Six 120mm 240V fans on the MMC

A thing I thought about, was to never cut the leads of axial MMC capacitors, but curl them up in a spiral, to use as a heat sink. As 66% of heat in a axial capacitor is radiated out of the ends and especially the leads. Only 33% is radiated from the round large surface.

I did something along these lines, I soldered the leads to a thick 1/8th" x 1/2" (3mm x 12mm) copper busbars for heatsinking of the leads:
 [ You are not allowed to view attachments ]

I give up. I tried 47 times to get this attachment to work, but for some reason it just says  [ You are not allowed to view attachments ] every time, even though the first photo above works!
Photo of MMC below

Can I use one of your pictures to add your coil to my list of featured coils on kaizerpowerelectronics.dk ? I think I have asked about this before, but have forgot to actually add it

Yes, please feel free to use any of my photos! I think this one is my favorite though!

 
Also, here is a photo dump of all of my construction photos (some of these photos show mistakes that were later corrected):
https://1drv.ms/u/s!Ap7oF5iAXsqR_Q4Ll1D90VbZBSRI?e=13UIZi

[futurist]

Wow those are really impressive streamers!

That 350A current draw reminds me of mr. Photon, a plug straight to the National Grid?

[Kizmo]

This is just so cool to see!

Pulse skipping driver on a big coil, lovely!

[fh89]

Wow those are really impressive streamers!

That 350A current draw reminds me of mr. Photon, a plug straight to the National Grid?

This is just so cool to see!

Pulse skipping driver on a big coil, lovely!

Really appreciate it coming from you guys! Been busy with other projects, but hope to get the coil fired up again soon and get some more video!

[Kizmo]

This makes my brute force approach (BiggerDR) to seem like waste of silicon.

[patracy]

I've enjoyed reading about this coil.  So much that I went out and purchased a few of those CM600's myself.  Now to find a driver and a few other bits.  Maybe I can offload some of the stuff I have to start funding that build.

[fh89]

Well after a long hiatus, BrOdin coil is back, with yet another new and improved secondary coil. The last secondary coil (secondary #3) burned up yet again with racing sparks.

Aftermath:


So secondary #4 was wound with a few changes to hopefully eliminate the racing sparks for good. I applied a base coat of epoxy on the bare secondary and wound the new coil while the epoxy was still slightly soft so that the wire would hopefully sink in slightly and provide extra insulation. 3 coats of epoxy were applied on top giving a thick and even finish. Coupling was also reduced to .141 by starting the winding higher up on the form.







1st runs on new secondary:

Had to cut it short because it was a little too breezy for comfort and the wind was blowing the streamers toward the secondary. I did not want to risk smoking another one so soon, so shut it down to fight another day.

I was also tripping my 100A breaker for the first time. This did not happen before, even when drawing 350A+ for 30ish seconds. Now the breaker is tripping after 12 - 15 seconds at maximum power, so I must be getting more power throughput and drawing more current. Didn't have time to set up the ammeter this time around but will get a measurement next time for sure!

[davekni]

Impressive run!

I'm guessing that another much-larger-diameter ground strike rail around the primary would further improve survival of your secondary.  If I recall correctly from previous videos, your racing spark issues were often triggered by a normal arc from the top hitting your existing strike rail and/or case first.  That may be making enough local hot plasma and distorted electric field to then trigger racing arcs.  A new strike rail could be a separate loop set into place after moving your coil to operating position.  Avoids issues with a larger diameter initial base during transportation.
Of course, this is just my guess at something to help.  I added larger ground strike rails to my DRSSTC at the same time as more varnish layers and slightly reduced coupling.  Can't say which of those changes were most effective at fixing my initial racing-arc issues.

Hope you find a good day when wind is blowing away from your coil.  May further extend arc length.

[fh89]

As always, great suggestion Dave. I'm going to run with this one, seems like cheap insurance to prevent yet another very time-costly part from going up in smoke yet again. Getting pretty good at winding secondary coils, but I wouldn't mind waiting a few years to put my skills to the test again!

[Mads Barnkob]

That is some movie special effects level video production you are getting with that doom machine of a Tesla coil! Sparks flying from the base and setting stuff on fire.

I wish I could be there in person to feel that beast running.

I guess you have removed all my doubt about if I should build some freewheeling drivers or not

[fh89]

That is some movie special effects level video production you are getting with that doom machine of a Tesla coil! Sparks flying from the base and setting stuff on fire.

I wish I could be there in person to feel that beast running.

I guess you have removed all my doubt about if I should build some freewheeling drivers or not

Thanks, Mads! This video was shot on my new Samsung s22+ in 4k, looks miles better than my gopro or DSLR. I would love to see more large coils with freewheeling drivers, I'm sure you could build something impressive!

[fh89]

This one is frustrating. Might be a while before the frustration wears off to give it another go. So much work into a secondary coil only to get maybe a minute of total runtime on it. Not sure what exactly happened, but looks like primary to secondary flashover? Or looks like it could be the strike rail flashing over to the secondary? And it happened I turned the pulse frequency down, maybe pulling it out of tune? All suggestions and comments to prevent this next time welcome.

[Maju]

Hi

It must be incredibly frustrating 

Leaving aside the potential tuning and coupling issues, the first thing I would try is to cover the primary. 1 cm plexiglass plate in the shape of a circle with a minimum radius of 10cm greater than the primary with a safety ring. It's even better when it's a full disc where the secondary does not go through the big hole but is standing on it. I know that for these voltages 1 cm of plexiglass is a rare obstacle. But in my experience it helps, the ionized air above the primary is somewhat cut off from the secondary.

Another solution (extreme, but not so stupid with your scale and probably the most effective) is this:
https://www.youtube.com/watch?v=pJzOi0dfyfE

I saw another interesting solution on the secondary but I did not test it and I would have to find a photo on the internet 

[fh89]

Hi

It must be incredibly frustrating 

Leaving aside the potential tuning and coupling issues, the first thing I would try is to cover the primary. 1 cm plexiglass plate in the shape of a circle with a minimum radius of 10cm greater than the primary with a safety ring. It's even better when it's a full disc where the secondary does not go through the big hole but is standing on it. I know that for these voltages 1 cm of plexiglass is a rare obstacle. But in my experience it helps, the ionized air above the primary is somewhat cut off from the secondary.

Another solution (extreme, but not so stupid with your scale and probably the most effective) is this:
https://www.youtube.com/watch?v=pJzOi0dfyfE

I saw another interesting solution on the secondary but I did not test it and I would have to find a photo on the internet 

I would be interested in seeing that other solution. I would hate to put so much time and effort into the grooved secondary only to have it burn up again.

Looking closer at the damage and frame by frame, I am pretty sure it was a strike rail to secondary flashover.

The primary is fully covered by a polycarbonate disc, but the disc was destroyed in this incident and I have to get a new one made.

[Mads Barnkob]

This one is frustrating. Might be a while before the frustration wears off to give it another go. So much work into a secondary coil only to get maybe a minute of total runtime on it. Not sure what exactly happened, but looks like primary to secondary flashover? Or looks like it could be the strike rail flashing over to the secondary? And it happened I turned the pulse frequency down, maybe pulling it out of tune? All suggestions and comments to prevent this next time welcome.

With reference to this thread ( https://highvoltageforum.net/index.php?topic=113.0 ) about DRSSTC inverter vs. secondary impedance, a inequality equation is proposed. When I ran the numbers of all my DRSSTCs builds, my DRSSTC1 stood out with a higher impedance on the inverter side than the secondary side. DRSSTC1 has been harder to tune and does NOT like low BPS.

Others coils do not exhibit the same low BPS hatred, not that they love it, its pretty small sparks, but at least they do not make flash-overs / racing sparks from it.

So what do you get on either side of this equation? Vmax/Imax < k*sqrt(L/C) ?

Another possibility, however not that documented and what ultimately led Kizmo to make the space wound coil was the "whiplash" theory. That there could be a wave front travelling so fast, from a heavy ground strike, that it fails at within the lower 20% of the secondary coil. I collected some information about that here (scroll down to the whiplash part): https://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/grounding-circuit-protection-and-emi/

[Hydron]

I also ran it frame by frame, saw something light up beneath the primary a few times but not immediately before the big secondary<->strike-rail arc.
There looks to be another arc underneath the coil on the first flashover frame - do you know what this is? Could it be primary<->strike-rail?

As for mitigation, not sure winding in grooves (or spaced winding with fishing line or something between turns) would directly help with a strike-rail<->secondary arc (rather than secondary<->secondary, which spaced windings should majorly mitigate), though I guess it could keep the voltage gradient down a bit at the bottom of the coil. What might help is something to make the ends of the strike rail less sharp, as that seems to be the starting point - could be as simple as a brass knob/ball on each end of the gap?

Alternatively, it might be possible to make a strike rail hit trip the OCD - just put a CT on the braid going to the strike rail, and set it up so that it would trip an OCD in the traditional (non-freewheeling) style. Note it would only need a handful of turns compared to the normal CT for OCD - you'd be trying to trip on any strike rail arcs at any current level that's distinguishable from interference from the operating coil. This would be a bit of a pain to do with a UD+, as you'd need to dig into the source VHDL to add the feature and also patch in a second OCD circuit/input, but it's far from impossible.

[Maju]

I would be interested in seeing that other solution. I would hate to put so much time and effort into the grooved secondary only to have it burn up again.

Looking closer at the damage and frame by frame, I am pretty sure it was a strike rail to secondary flashover.

The primary is fully covered by a polycarbonate disc, but the disc was destroyed in this incident and I have to get a new one made.

Finding a photo with this solution is very difficult (the photo was very old), but it is about pasting by covering Epoxy plexi discs on the secondary (with cooper) every several centimeters.
Something like this:


Your covering plate is way to small. You should do something like Phillip Slawinski did. Look on his oversized primary cover plate - it covers whole primary with safety ring: