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My One MOSFET Driverless Tesla Coil with 555 Interrupter

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Shaan

Sat Aug 15 2015, 08:13AM

Registered Member #5528 Joined: Sat Jun 30 2012, 06:53AM
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Posts: 14

Hi jdub. Good to hear that ^^

I am using separate 12v supply for the interrupter, the mosfet takes 160V. The interrupter circuit is below.

NE555+IRF540N Interrupter

shaan

jdub1581hv

Fri Aug 28 2015, 12:08AM

Registered Member #55219 Joined: Tue Jun 09 2015, 11:21PM
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Posts: 80

Alright.. I just got my MOT rewire done 56v ac out after bridge rect about 100v, and a new coil built ...
4"dia 1400 turns of #28..

Thanks for the interrupter schematic also, was different than mine.
I was trying to follow the wiring in your vids for the int.

Is it sinking the current from base or supplying it?

I think this is how you have it, is that correct? (see img)

Shaan

Fri Aug 28 2015, 06:00AM

Registered Member #5528 Joined: Sat Jun 30 2012, 06:53AM
Location:
Posts: 14

Hi jdub.

Looks like you've done it right.

In on state the mosfet in the interrupter shorts the voltage at the switch mosfet's gate pin to ground resulting in no net current flow and in off state should let the gate turn on and the oscillation take place for very short periods of time. Even 5% off-time of the interrupter is more than enough for good break-up. Higher off-time (i.e. higher on-time for the switch mosfet) will do nothing more than overheat the switch mosfet.

Keep it going.
Awaiting your sparks. ^^
shaan

Perezx

Sat Aug 29 2015, 05:18AM

Registered Member #54263 Joined: Thu Jan 15 2015, 09:54AM
Location: Perth
Posts: 35

What is the reason of using D1+Q3? You can use something like 1.5KE15 to protect FET's gate.
And I suggest adding a HF capacitor ro the source-drain of FET. Something lke 1-10nf, if you find right capacitance, you'll get close to E-class and bigger sparks.

Shaan

Sat Aug 29 2015, 08:41AM

Registered Member #5528 Joined: Sat Jun 30 2012, 06:53AM
Location:
Posts: 14

I am no expert but I guess D1 clamps the gate-source voltage to its zener voltage and Q3 in off state simulates another fast diode besides MUR160 clamping the source-gate voltage to -0.7V, and in on state "tries" to limit mosfet drain current to (0.7 divided by the source resistance) amperes. So a 0.1R instead of a 1R is better if interrupter is actively limiting on time to less than 5% of total pulse length and we want long interrupted sparks.

Also, I have tried adding many different value capacitors between drain and source. Something strange happened (I don't know what exactly), and as a result about a dozen of the expensive HV mosfets are dead. Hence the D-S cap-omission. ^^

jdub1581hv

Sat Aug 29 2015, 05:26PM

Registered Member #55219 Joined: Tue Jun 09 2015, 11:21PM
Location:
Posts: 80

Shaan wrote ...

Also, I have tried adding many different value capacitors between drain and source. Something strange happened (I don't know what exactly), and as a result about a dozen of the expensive HV mosfets are dead. Hence the D-S cap-omission. ^^

I have also had issues trying to add a "tank" cap .. That's really the only thing I don't like about this circuit..
I've tried both serial and parallel with pulse rated caps and the circuit just fails to oscillate. Though perhaps adding another UF diode from source to drain might help?

Aside from that I got the interrupter going with results very similar to your 1st vid, about 1 1/2 inch streamers. I have do shorten all my leads and redesign my primary and topload.
I didn't get enough 1/4" copper tubing to make a primary for my big coil, was short by 5 turns or so :/..

I used some older parts I was willing to destroy:
IRF740 mfet
2sc3598 npn bjt
39k 3w resistor
5w 15v zener
0.22 2w resistor

Going to replace the IRF740 with a SD20n60 now that I have the rest working well. :)

Shaan

Sun Aug 30 2015, 08:18AM

Registered Member #5528 Joined: Sat Jun 30 2012, 06:53AM
Location:
Posts: 14

Nice to hear that!

Show us some porn of your setup if possible. :)

Regarding the cap: I think the primary is resonating with the parasitic capacitor(s) inside the MOSFET, which is variable and nonlinear. But, when we run this circuit freely then the system automatically chooses its resonant frequency depending on the combination of the parasitic capacitance, the primary inductance and the secondary feedback.

Although in this mode the operation is far from optimum and probably much inefficient, it seems "guarranteed" to work to some extent with almost any configuration, with high initial pulses and then coming down to its normal and inefficient state, generating huge waste heat. Much like a typical "slayer exciter".

The addition of an interrupter will let the first few high-current pulses go through the system and then shut it down for some time for the PS cap to recharge. The average power drain and waste heat will be minuscule but apparently the spark length will be double or more than without and interrupter. In my case I got it tripled. ^^

jdub1581hv

Sun Aug 30 2015, 01:05PM

Registered Member #55219 Joined: Tue Jun 09 2015, 11:21PM
Location:
Posts: 80

Well it's no Sasha Gray, but here's the setup with the SD20n60 ...

Diode is a FMLG13 (from Projection TV) Ultra fast 300v 5a.
Other diode(base 39K) is there for adding straight ac for 1/2 wave if I wanted to..
Been trying different caps, this setup seems to work best for me (so far)..
Coil is a fresh wound 700t * 3 1/2" with #28 and HDD platter for top load.
Primary is 12t 14awg speaker wire using only one strand.

Still need to get rid of my long leads, but it's working well.
I also went back to a standard 555 oscillator with duty adj (had a hard time with freq on the one you provided).

I'll try and make a vid once I get things cleaned up a bit.. Maybe a family photo as well (10+ coils now from 2" tall to 2' tall)...

1440939859 55219 FT172138 20150830 054054

1440939859 55219 FT172138 20150830 054131

1440939859 55219 FT172138 20150830 054203

Shaan

Mon Aug 31 2015, 06:12AM

Registered Member #5528 Joined: Sat Jun 30 2012, 06:53AM
Location:
Posts: 14

Hey! that looks good!

please post the interrupter schematic you are going to use.

thanks.

Perezx

Mon Aug 31 2015, 08:59AM

Registered Member #54263 Joined: Thu Jan 15 2015, 09:54AM
Location: Perth
Posts: 35

Shaan wrote ...

the system automatically chooses its resonant frequency depending on the combination of the parasitic capacitance, the primary inductance and the secondary feedback.

This is not the best way.

Working frequency depends on secondary (+ topload + ambience) frequency. Primary circuit has to follow in order to form a resonant overall circuit. The most efficient primary also has to switch on/off at Zero Voltage and Current (thus called ZVCS) and put maximum amount of energy during single pulse. This ideal circuit is said to be working in E-class.
You can read Stewe Ward's "Class E SSTC" article on this site: stevehv.4hv.org, he shows the way how to check your setup.
Of course, all research about DS capacitor should be done with a lower voltage. I use 24V DC, which is enough to get small streamer.

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