DC Power Tesla Coil

[TinselKoala]

Sorry, no, you use the second MOT, with its secondary shorted, in series with the _primary_ of the main MOT. This is just like using a big choke on the input to limit the input current. MOTs are not current-limited the way flybacks are, so if your output impedance is low, it's easy to draw so much current in the primary that breakers trip or the smoke leaks out. SO you use the second MOT primary as an input choke, just to limit the inrush current when the discharged cap bank is looking like a direct short across the MOT output. Then downstream from the MOT on the HV side you put the FWB, and then the HV choke and de-Q diode if you are using them.
I don't have another MOT so on my coil I put an ammeter around the MOT input lead, after the Variac, and I watch the peak currents and don't let it go over 15 Amps. I've still managed to blow a couple of fuses in the Variac, though. Putting the second MOT primary in the circuit with its secondary shorted will prevent the input current from going much over 10 Amps and I should be able to run continuously without problems at that point, but first I have to find the second MOT !!

[Jeg]

Hi Tinsel
If i put the second MOT as an HV choke in series with the secondary, will it also react as a current limiter? I ask because i will need a charging coil in the secondary anyway, so if it works as a current limiter i will save some space and some extra work!

What FWB stands for?

Jeg

[TinselKoala]

Hi Tinsel
If i put the second MOT as an HV choke in series with the secondary, will it also react as a current limiter? I ask because i will need a charging coil in the secondary anyway, so if it works as a current limiter i will save some space and some extra work!

I don't know if it will work that way, but you can certainly try it, although I'd be a little worried about heat buildup. I've only heard about using the second MOT's primary in series with the mains supply to the working MOT, as I described above.  But experiment, by all means... just be careful, the MOT is deadly.

What FWB stands for?

Jeg

Full-wave bridge. Made of HV high current diodes. In my MOT DC coil they are the black bell-shaped things to the left of the capacitor bank.

[Farmhand]

Hi Tinsel
If i put the second MOT as an HV choke in series with the secondary, will it also react as a current limiter? I ask because i will need a charging coil in the secondary anyway, so if it works as a current limiter i will save some space and some extra work!

What FWB stands for?

Jeg

Yeah you can do "secondary side current limiting". See the link. http://www.kronjaeger.com/hv/hv/src/mot/index.html.

The resonant charging circuit does that. http://www.richieburnett.co.uk/dcresist.html

I use a MOT secondary for the charging inductor in my resonant charging circuit. I also have a 400 mH choke made from 0.5 mm wire with removable core in series with the supply,  the two "Supply" MOT primaries are in "anti" parallel then another MOT's secondary is the charging inductor (this MOT can have it's primary shorted to reduce it's inductance). The power is limited to about 650 Watts, current about 2.7 amps in my setup at full power, the HV caps are actually 14 nF, frequency 750 kHz or so.

FWBR means a Full Wave Bridge Rectifier. My circuit uses one but it's drawn in two parts.

Cheers.

P.S. I can calculate my power input by using the electronics assistant program to tell me the energy in the HV caps and multiply by the breaks per second.

Say I dump 8000 volts from a 14 nF cap 500 times a second,  0.448 Joules times 500 = 224 Watts. And it correlates with the energy meter with a bit of losses.
The MOT secondary charging inductor will only allow the supply to charge the caps at a certain rate so the input is limited that way.

Even 6000 volts into a one turn primary with 180 secondary and extra coil turns (combined) would give a transformation to 1 million volts.  Without any resonant rise.
My setup has one primary turn and about 200 turns in the secondary and extra coils combined.

Speaking of "Q" my secondary and extra coils combined have about 3 Ohms resistance and the top load is about 16 or 17 pF I think. And the setup has about 2.5 mH in the secondary and extra coils combined. Almost a Quality factor of 4000.  http://www.circuitsage.com/tools/tool_view&tool_id=17




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[TinselKoala]

Thanks, Farmhand, what you've described is indeed the "right" way to do a DC rotary SGTC using MOTs. Is this the coil that you showed in operation earlier? What happens when you let it pull 1500 Watts input, instead of limiting to 650?

I'm working on a zero budget so I have to design from what's on hand, rather than designing to theory and then building it with the right stuff.
I'm on a 115-120VAC main, so my 15A current input (manually limited) is equivalent to 7.5 A input in your 220-240 system. But I'm only using the one MOT so my output from the FWB is nowhere near the TC primary voltage that you are getting, I think.