BrOdin coil - High power Big sparks!

[fh89]

Have you measured the arc current? Must be tens of amps to be doing that to the aluminum frame. Certainly not 'high voltage, but low current' anymore haha.

It might not all be arc current melting the aluminum. Maybe a streamer hit to the frame might provide enough voltage to bridge the gap, then energy from the primary is inductively coupled into the arc? Just a guess. Although, the arcs definitely do have enough current to light my grass on fire!

I have not tried measuring. Doesn't seem like an easy task- any suggestions on how that might be possible?

[futurist]

Check out Hydron's topload current measurements thread
https://highvoltageforum.net/index.php?topic=117.0

[davekni]

It might not all be arc current melting the aluminum. Maybe a streamer hit to the frame might provide enough voltage to bridge the gap, then energy from the primary is inductively coupled into the arc? Just a guess. Although, the arcs definitely do have enough current to light my grass on fire!

That's definitely my guess too.  Frame sparks often continue after tho top arc leaves the frame in your videos.

I have not tried measuring. Doesn't seem like an easy task- any suggestions on how that might be possible?

Measuring current of the secondary coil ground connection will get rather close.  Once an arc strikes, top-load voltage drops way down, so secondary current at the bottom is close to matching arc current.  My DRSSTC has a current transformer measuring secondary current, which I scope every time I run my coil.

Not worth the bother, but you could make a large CT with U-cores to measure frame current around one of the 80/20 sections.  CT would need insulation cover to avoid strikes from secondary.

[fh89]

Check out Hydron's topload current measurements thread
https://highvoltageforum.net/index.php?topic=117.0

Amazing work there, but not something I could pull off!

It might not all be arc current melting the aluminum. Maybe a streamer hit to the frame might provide enough voltage to bridge the gap, then energy from the primary is inductively coupled into the arc? Just a guess. Although, the arcs definitely do have enough current to light my grass on fire!

That's definitely my guess too.  Frame sparks often continue after tho top arc leaves the frame in your videos.

I have not tried measuring. Doesn't seem like an easy task- any suggestions on how that might be possible?

Measuring current of the secondary coil ground connection will get rather close.  Once an arc strikes, top-load voltage drops way down, so secondary current at the bottom is close to matching arc current.  My DRSSTC has a current transformer measuring secondary current, which I scope every time I run my coil.

Not worth the bother, but you could make a large CT with U-cores to measure frame current around one of the 80/20 sections.  CT would need insulation cover to avoid strikes from secondary.

I have that Ion Physics current monitor I used for primary current measurement when setting phase lead way earlier in this thread. It will have to wait though as I burned up the secondary again tonight 

First had a successful run playing the Tetris theme, making huge sparks for a coil in music mode:

But then I cranked the PW and PRF all the way up and just sent it-

Me again, for spark size scale:


Another secondary coil smoked! Grrr!

The moment the streamer hit the secondary:


Damage:

[davekni]

The moment the streamer hit the secondary:

Wow, that must be so frustrating and disappointing!  The secondary strike initiation does make for a beautiful picture, though.  Thank you for sharing that.

[AstRii]

I cannot even imagine how frustrating this must be.. but then again, patience is needed when pushing the limits
Haven't you considered a bigger topload? Better electric field distribution might solve all your issues with racing sparks and secondary being hit.

[fh89]

The moment the streamer hit the secondary:

Wow, that must be so frustrating and disappointing!  The secondary strike initiation does make for a beautiful picture, though.  Thank you for sharing that.

Yes, very frustrating, but I will rewind again!

It's really interesting how a small arc formed off the main streamer that was already arcing directly to the strike rail and jumped to the secondary. Here's the frame-by-frame:

[fh89]

I cannot even imagine how frustrating this must be.. but then again, patience is needed when pushing the limits
Haven't you considered a bigger topload? Better electric field distribution might solve all your issues with racing sparks and secondary being hit.

Yeah, it is frustrating to be sure, but like you said, it's the price to play! This isn't a tabletop coil conservatively designed to run forever!

I made a much larger 14x52" toroid that I could not get to work without major structural changes. It caused overcoupling and racing sparks, even after raising the secondary 1.5", the most I can do right now.

[futurist]

Some secondaries survive many hours of run time, but eventually they all fail

Did you try using counterpoise? In my experience it seems that it directs streamers away from the coil

[Uspring]

You always seem to have your camera on, when something interesting happens. 

Longer lasting arcs tend to curl up after some time as you can see in your slow motion video. And that can be a problem near the strike rail. Particularly if there is some wind blowing.
Often arcs follow a previous burst since it leaves a path of hot air behind, which is thinner and thus breaks down at lower voltages. This pathway isn't very stable, though, since the arcs charges repel each other, which causes the pathway to curl like a negative string tension. It is buckling in a way. Every burst in a retracing series will be a bit more curled than the previous one. Usually arcs look for the shortest path bridging a gap, but hot air relaxes this requirement.

I suggest monitoring the current from the strike rail to ground and shutting the coil off maybe for a tenth of a second, when it is hit. That will allow the air to cool off, so that the next burst will take another route. Initial routes are much straighter than the retraced ones following a previous burst.

[fh89]

Some secondaries survive many hours of run time, but eventually they all fail

Did you try using counterpoise? In my experience it seems that it directs streamers away from the coil

Yeah, at this power level, any direct hit is going to pretty much instantly annihilate the secondary windings.  I need to prevent any secondary hits if I want this next one to last!

I assume you mean a separate counterpoise from my main 8' dedicated RF ground rod as a strike target so to speak in front of the coil? That's something I could try.

You always seem to have your camera on, when something interesting happens. 

Longer lasting arcs tend to curl up after some time as you can see in your slow motion video. And that can be a problem near the strike rail. Particularly if there is some wind blowing.
Often arcs follow a previous burst since it leaves a path of hot air behind, which is thinner and thus breaks down at lower voltages. This pathway isn't very stable, though, since the arcs charges repel each other, which causes the pathway to curl like a negative string tension. It is buckling in a way. Every burst in a retracing series will be a bit more curled than the previous one. Usually arcs look for the shortest path bridging a gap, but hot air relaxes this requirement.

I suggest monitoring the current from the strike rail to ground and shutting the coil off maybe for a tenth of a second, when it is hit. That will allow the air to cool off, so that the next burst will take another route. Initial routes are much straighter than the retraced ones following a previous burst.

Multiple cameras always running!

That's a really good idea. I should just shut it down for a moment as soon as there's a frame/strike rail hit.

[futurist]

Counterpoise from wire mesh, for example I'm using insect mesh because it's easy to store it in a roll

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There was some discussion about using counterpoise for DRSSTC here on the forum and on 4hv. In my experience my coil performs better when used in different environments if I'm using counterpoise. On the other hand it causes high current ground strikes which fry the secondaries

[Intra]

My apologies if I repeat what someone may have already wrote here.

By quick glance I could say that this secondary and it's toroid isn't quite optimal.

With that secondary length and toroid length your secondary magnetic field geometry not wide enough to spark could avoid to strike in chasiss on that spark length especially when your chasiss is completely metal and whole coil is put on wood rack alowing to strike in chasiss from bottom. Different terminal angle and length, larger toroid and longer secondary could help with this issue.
It is also good to place a toroid at least on 1/2 of toroid thickness from secondary to edge of the toroid lower plane.

For 12.75 pipe you may want to try 20awg wire with 5:1 ratio so it will be about 64.11 inch of winding length.
Also, for this possible new secondary will fit 62.3x12.4 toroid.
Primary resonance frequency in transient mode good to be 10-15% lower than secondary but in freewheeling mode it better to be even 25% lower.
Coupling is 0.154
Try this calc https://tqfp.org/calculatoria/tesla/

About how much primary windings is best. If your goal not in limiting current by primary and you run your coil in freewheeling you may do even 2.5 windings with apropriate mmc.

[fh89]

My apologies if I repeat what someone may have already wrote here.

By quick glance I could say that this secondary and it's toroid isn't quite optimal.

With that secondary length and toroid length your secondary magnetic field geometry not wide enough to spark could avoid to strike in chasiss on that spark length especially when your chasiss is completely metal and whole coil is put on wood rack alowing to strike in chasiss from bottom. Different terminal angle and length, larger toroid and longer secondary could help with this issue.
It is also good to place a toroid at least on 1/2 of toroid thickness from secondary to edge of the toroid lower plane.

For 12.75 pipe you may want to try 20awg wire with 5:1 ratio so it will be about 64.11 inch of winding length.
Also, for this possible new secondary will fit 62.3x12.4 toroid.
Primary resonance frequency in transient mode good to be 10-15% lower than secondary but in freewheeling mode it better to be even 25% lower.
Coupling is 0.154
Try this calc https://tqfp.org/calculatoria/tesla/

About how much primary windings is best. If your goal not in limiting current by primary and you run your coil in freewheeling you may do even 2.5 windings with apropriate mmc.

I don't disagree with anything you said, but when building a coil of this size, numerous compromises had to be made because of cost and practicality, at least for me. For example, the current secondary used an entire 10lb spool of #22 wire, a longer winding length would require buying a bigger spool and the smallest next size up I can find is an 80lb spool for $1000USD! (If anybody knows where to buy magnet wire in quantities greater  than 10lbs and less than 80, let me know.)

The Toroid is too small, I agree and have experimented with a larger one, but it causes overcoupling racing sparks, even after raising the secondary 1.5", the max I can do. The toroid was also incredibly expensive, by far the most expensive part of this build at $2000USD shipped, so I'm not in a hurry to not use it now! Definitely will go bigger on the next coil!

The coil is also at the maximum height that can fit in my garage assembled. I could store each piece separately, but it is so convenient to be able to just wheel it in and out of the garage instead of carefully packing the toroid and secondary safely away where they will not get damaged, then needing to unpack and re-assemble it every time I want to run it.

Building this coil and getting so much useful feedback from the members here has been a learning experience for sure, and I will take all these suggestions to heart when the time comes to build an even better coil!

For now at least, I've pretty satisfied with the performance of this coil, especially considering all of the design compromises and less-than-ideal specs and parts chosen! After rewinding the secondary, I will consider it a finished coil. The only other thing I am planning to crank the primary current limit up a tad to 2500A, and see if there's any noticeable performance improvement.

 

[Intra]

(If anybody knows where to buy magnet wire in quantities greater  than 10lbs and less than 80, let me know.)

You can wind bifilar from two 26awg from this 6290ft $58+shipping spools https://www.ebay.com/itm/251040537280
For 12.75x64.11 need about 6299ft per spool which fits wery well and it also decrease secondary heating

have experimented with a larger one, but it causes overcoupling racing sparks, even after raising the secondary 1.5"

With 36x10 toroid and 22awg 12.75x48 coil you have 78.5k secondary impedance while with 50k or less you will have longer spark on same other parameters.
With 0.15 coupling your spark will be shorter than with 0.18, but racing sparks will gone. 0.11 is too low for 12.75 pipe.
Other option to improve perfomance you may try up voltage to 800v with pfc or rewire rectifier to doubler.

The toroid was also incredibly expensive, by far the most expensive part of this build at $2000USD shipped

Toroids can be self-made from tubes https://www.lowes.com/pd/Steelworks-3-4-in-dia-x-3-ft-L-Mill-Finished-Aluminum-Round-Tube/3053653
by tube roller https://www.ebay.com/itm/224567948035
My brand new TR-60 costs me $260 instead of $470 because I found it in my town.

For 62.3x12.4 toroid tubes in Lowes should cost about $400. I'm too far from LA, maybe you know better place to buy tubes or bender arround you.

You can make toroid even with aluminium foil tape. Check "Mon Jul 16 2012, 03:08pm" post from here https://4hv.org/e107_plugins/forum/forum_viewtopic.php?p=1&id=141872

The coil is also at the maximum height that can fit in my garage assembled. I could store each piece separately, but it is so convenient to be able to just wheel it in and out of the garage instead of carefully packing the toroid and secondary safely away where they will not get damaged, then needing to unpack and re-assemble it every time I want to run it.

I store my twins on 5 level of condominium with no elevator.

[Duane B]

That's a great coil fh89! One to be proud of. Personally, I don't think you need to change anything.

[fh89]

Brodin Coil returns from the dead yet again, this time running at 57kW peak power!


Winding jig for the 3rd secondary


1st coat of epoxy applied. Total of 3 coats applied this time.


Rebuilt and standing tall!

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!

New higher primary current has the coil drawing 350+ Amps from the 240V line!

From the DSLR

 From the GoPro

[alexhanyuan]

Can't believe you're still running those 942Cs!

[fh89]

Can't believe you're still running those 942Cs!

Well technically 940c's with higher Arms! 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?

I wanted and looked forever for some doorknob caps, but I couldn't find any with sufficient ratings in enough quantity for remotely reasonable price.

[Duane B]

Very impressive! Rising from the dead, or being born again, maybe you should call that coil the Phoenix?