8 ft spark french tesla coil

[paulj]

Hello, My name is Paul, and I have been playing with high voltage since 2012.
I subscribed to this forum to learn more about drsstc (I have a ONE TESLA kit), and to present you some projects. (marx generator, X ray machine)

This is my largest Tesla Coil, (SGTC) it is capable for a 75 cm (29.5 in) secondary coil, to create sparks up to 2m40 (7-8 ft).

Good viewing to you, Paul, If you want more information on the specs I will get back to you.

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[Mads Barnkob]

Very good performance for a SGTC!

Please do post some pictures of the spark gap, MMC and high voltage transformers

[paulj]

Hello, Mads thank you for your compliment,

control box:



the variac is 9kw three phase model upgraded to work with one phase







 I think I can push the setting and increase the sparks up to 3m
However these capacitors (maxwell 35349  X2 : 147 nf) seem to me unsuitable for this use. on this image just after turning it off, corona seems inside the case is visible (see photos)
the chassie is provisional, I will build a nice compact case.
When I have time, I will take nice pictures for you.
If you want more details, there are still a lot of pictures.

[Bradselph]

Awesome what's the coil form size? I'm trying to get a better idea of the size because to me some coils look smaller or larger than they would be in person.

I'm curious about the power supply as well, are they Microwave transformers? 2 look to be the rare radar range transformers?

[paulj]

Hello this coil is an upgraded copy of the tesla coil by fabricio h franzoli to Brasil.

here are the specs:

4X microwave transformer (primairy in parallel, secondary on serial), so 8400v for 0,6 to 1A of current
2X maxwell 35349 capacitor bank 147nf
primary coil flat coil 1/4 in to 5-6 turn
secondary coil: 750X200mm 22 awg 1100 turn the screws are nylon, and the circles are teflon
this is very important NO WIRE INSIDE THE TUBE !!!!!!!! if not FLASHOVER hazard especially with such powers. I use KF 1280 ND for isolation (Dielectric strength 60kv/mm)  spayed inside and outside PVC tube before and after winding the copper wire, and 8 coats of polyurethane varnish to hold the thread.
toroid 900X200mm
Terry rotary spark gap, 4 mm pure tungsten electrodes  it gives a frightening roar by varying the speed of the rotor.
I don't know the number of BPS
it is a low cost spark gap, but the rotor electrode wears out very quickly despite the thickness.
I reduced the problem of stator wear a little with big busbar under, but the rotor heats up very quickly, the teflon is used so that it does not melt.

the total size of the machine is quite small, about 1.60m high.

no ballast, no filter , so 9kw power peak (RIP circuit breaker 32a  )
the primary and the secondary are not tuned there is about 5% difference, I noticed better results, sorry I do not remember the exact freqence, it seems to me that it is 80khz.
this tesla coil has been built 50% in recovery materials (trash, recycling) so she is 50% green

PS: on this picture, just after switching off, the capacitors are bright, is it corona?

Paul.

[davekni]

Fascinating capacitor glow.  The only time I've seen glow inside capacitors is shortly before failure.  This was in testing polystyrene 30kV capacitors for Marx-generator use.  Every one I tested failed, even though the EBay seller listed Marx generator as a use for them.  (In my case, glow was localized at one point of each capacitor, and only during discharge.)

Impressive coil!

[paulj]

It is curious, the capacitor are brand new (protection plastic film and safety wire).
This glow is not visible when the machine is operating at <70%,
surely their use is inappropriate, I tried to contact maxwell to have the datasheet and know their reverse voltage, but the sector was bought by Elon Musk and merged with Tesla, so no more contact

If he they explode there will be castor oil everywhere !!! slurp

We will have to think of a new bank of capacitors, out of the question to use a single specific capacitor, they are too much too rare and very expensive. (mine are from an old surplus from Los Alamos, so low cost)
It seems to have been proven 942C20P15K-F
or then doorknob, or gto snubber capacitors like those of loneoceans
https://www.loneoceans.com/labs/model82/
the phoenix coil is one of my favorites, it has spectacular results.
http://www.hvtesla.com/mmc.html

Anyway, something will be needed that can withstand big electrical constraints.

[MRMILSTAR]

Try posting the model number of your Maxwell capacitor on

https://www.pupman.com/

Some of the members have data sheets for the Maxwell capacitors. I have data sheets for the 31xxx and 37xxx series but not the 35xxx series.

[davekni]

Completely speculative, but I wonder if Maxwell intentionally included electroluminescent die in their oil in order to visually show voltage stress locations.

[paulj]

On the archives you cite I have come across cases of maxwell capacitor explosions on large dimension tesla coils, look at these photos of maxwell 31173 and 37667 having violently exploded.

the notion of reverse voltage comes up quite often in these cases.https://www.flickr.com/photos/iceowl/5437138473/
https://www.flickr.com/photos/iceowl/5812073757/

[MRMILSTAR]

On the archives you cite I have come across cases of maxwell capacitor explosions on large dimension tesla coils, look at these photos of maxwell 31173 and 37667 having violently exploded.

the notion of reverse voltage comes up quite often in these cases.https://www.flickr.com/photos/iceowl/5437138473/
https://www.flickr.com/photos/iceowl/5812073757/

Its understandable that the 31xxx capacitors exploded. They are only rated for 1 PPS which is not suitable for TC use. The 37667 capacitors are rated for up to 500 PPS and should be fine if used properly.

My 6.5 KVA SGTC uses 6 of the Maxwell 37667 capacitors in series-parallel. I've been using them for several years with no problem. Since they are only rated for 15% VR (30% max), 35 KV, and 500 PPS the key is to derate them. Since I use a 2 x 3 configuration, my voltage rating is 70 KV with a total capacitance of 45 nF. I also only run it at 240 PPS. The power supply is a 14.4 KV pole transformer.

I have a Maxwell application note that explains how derating the voltage extends the life. It is quite a dramatic affect. According to the application note, the life time is increased according to a 5th-power relationship to the peak voltage versus the maximum rated voltage. I did a back-of-the envelope calculation for my capacitor bank and expected usage. The results were that my expected life time for the capacitor bank was something like 40 years! It will be up to my heirs to replace any failed 37667s. 

[MRMILSTAR]

With regard to that capacitor glow. Have you confirmed that the capacitors have not leaked any oil? Glowing capacitors does not sound good and portends a short life I fear.

[MRMILSTAR]

On the archives you cite I have come across cases of maxwell capacitor explosions on large dimension tesla coils, look at these photos of maxwell 31173 and 37667 having violently exploded.

the notion of reverse voltage comes up quite often in these cases.https://www.flickr.com/photos/iceowl/5437138473/
https://www.flickr.com/photos/iceowl/5812073757/

The cracked Maxwell 37667 shown in the archived picture appears to have been part of a DRSSTC. I wonder if the coil was operating at over 500 PPS? The 37667 is only rated for a maximum of 500 PPS.

I caused a hairline crack in the case of one of my Maxwell 37667 several years ago because I likely exceeded the maximum current specification of 25K amps. My initial 2 x 3 capacitor bank design was too compact and I had several flash-overs between the capacitor buss bars. The stress caused a hairline crack in the case causing oil loss. After re-designing the 2 x 3 capacitor bank to provide more spacing I haven't had any problems since. That was several years ago.

Here is a picture of the re-designed capacitor bank.

[paulj]

Hello, the capacitors are not leaking at the moment.

Indeed for this glow, I fear damaging them, when I have enough money, I will pass on a mmc.

[paulj]

Hello everyone, I just contacted general electrics for 35349 capacitor to get the datasheet, they kindly sent it to me.

The reverse voltage seems a little low to me 25% and could perhaps explain during high power mode the presence of corona, what do you think ?, Paul.

here are the specs:
sales_35349.pdf

[MRMILSTAR]

The specs on that capacitor look fine to me. The one important spec that they don't cite is the maximum rated pulses per second (PPS).

[paulj]

Hello, I was unable to get more information. I assume that given the amount of corona produced, Maxwell 34349 this is not good.

For large capacitors, Condenser Products Company produces large capacitors dedicated to the enormous electrical constraints of tesla coils, I am thinking of the large magnifier by Ed Wingate. i might ask for a quote, but customs might be a problem.

the MMC seems to me to be a good solution.

apart from the 942c20p15k-f, in France we have the EUROFARAD brand. (these capacitors equip Loneoceans coils)


I use 202k 2nf doorknob 40 kv TdKs on my marx generator, but it will take a lot for a MOT coil, I have a seller who can provide me a lot, but I think them rather suitable for DRSSTC.

[paulj]

Good morning all

general atomics couln't answer me, so the number of PPS of my capacitors is unknown BUT:

I know the maximum lifetime of its DC capacitors and the number of charge / discharge cycles it can perform. (IN the PDF datasheet attached previously)

Can I simulate rough life of my capacitors if it is operating at 200 BPS?

Paul I am tempted to calculate, but as in alternating current the values change enormously.

[MRMILSTAR]

It sounds like your in a 50 Hz power country. Since you have a synchronous rotary spark gap, you could remove 2 of your flying electrodes to make it a 100 PPS coil. This would give you 2 charge-discharge cycles per sine wave cycle instead of 4. This would put less stress on your capacitor by halving the PPS rate and doubling your charge-discharge cycle lifetime. This should be easy to do. Try it and see if the glowing disappears.

I can't answer your question about relating charge-discharge cycles to PPS rating. I suspect that they are only loosely related.

[paulj]

So after reflection, without information on the working frequency of these capacitors and their abnormal luminessence inside the plastic box visible at high power, I think that the maxwell 35349 can be used to produce long electric arcs temporarily (see my photos) but that they are not suitable for tesla coils. (except on small models)

They only have 10 minutes of use, I know I bought these new capacitors with original film package and safety wire.. so I'm thinking of selling it to someone who would use it. for an application such as a voltage doubler, or a cutting laser?

I will maybe post an ad soon and pass on a MMC cornell Dublier