Third SSTC - Mosfet Drivers Exploding / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

Third SSTC - Mosfet Drivers Exploding

previous 1 2 3 4

Move Thread

LAN_403

zzz_julian_zzz

Thu Aug 30 2012, 01:56AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

Take my advice my friend for before I learned a lot of these in very hard way!

irfp260 is a better mosfet than a 460, well its because you are in 120VAC country.

I have used a cat 5 on my GDT, please see photo below,

Do not change your c2 and c3.
Tank capacitor means, a resonating capacitor.
Those capacitors of other coilers that have higher capacitance rating are for more space to outfrequency the secondary.
they intentionally put large capacitance (C2+C3) to detune primary circuit. (tuned means pri fres and sec fres are same) because it will suck up huge current (DRSSTC) and probably blow your FETS that are not rated on that AMPERE range. (if you want, DRSSTC, but i personally recommend you to make the SSTC fbridge work first.

In case of your sstc and kaizer's those caps (.68uf) are for DC blocking and not for matching frequency of the pri and the secondary circuits. and no, those are not for snubbing capacitor purposes although possible but the capacitance is much much low, they will not catch energy for their storage are small. you should look for 5uf at least.

my resistor is actually too big for just gate resistance, 1/4 - 1/2 watts should do fine (if there are no faults on the bridge)

Snubbing capacitors = capacitor (non polar) connected to the supply rails (+ and -) and installed nearest to the MOSFETS to snub/cut transient voltages which will destroy your FETS due to over voltages. (on my photo, the read and maroon capacitors are my snubbing caps)

Hey,,, Yes. we have the schematics from other coilers, BUT, it doesn't mean that if you follow exactly on it, there will be other things to tweak, before you can exactly replicate other's ouput/work.. The things are Layout of the driver, Layout of the bridge, Components specifications, Wires used, specially the resonator.

Every coil is a different coil.

SuperZanti

Thu Aug 30 2012, 05:55AM

Registered Member #6006 Joined: Sat Aug 04 2012, 08:50AM
Location:
Posts: 22

Well one of the biggest reasons I'm stubborn to change much on the driver circuit is also because of my PCB. It's VERY hard to cut and reroute the trace to make the 555 timer 9volts. Especially when I'm using a computer power supply which doesn't provide 9 volts. When i get some extra money I may redesign the PCB, but I think it's what I have to work with for now. And it did work for the half bridge, so is this really a necessary change?

I could change my C5/C6 to ceramic .1uf, but adding another is relatively hard. (but still doable, easier than having to cut a trace)

Other than that, I can change everything else you suggested. And I will probably try that.

I really just wish I could live with infinite money doing experiments my entire life, and figuring things out on my own. Unfortunately, I live on a college budget, and it's hard to get by as it is. So, that being said I REALLY appreciate your help, it really means a lot, so thanks.

Should the 14awg primary be directly on top of the secondary?
Finally, I made a quick update to just the bridge schematic. What do you think?

And about the bridge, you don't think zener diodes are necessary either after the resistors? And what would be a good resistor to use to drain the capacitors when the system is turned off?

How big of sparks do you think I'll be able to achieve once I get this working?

Thanks again.

Shrad

Thu Aug 30 2012, 07:06AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

you could cut a trace and solder a 9V battery holder... this would be simple enough not to require any complex modification

SuperZanti

Thu Aug 30 2012, 07:58AM

Registered Member #6006 Joined: Sat Aug 04 2012, 08:50AM
Location:
Posts: 22

I mean, I still don't want to cut traces, considering the PCB cost me $30. Especially if I don't absolutely have to. (I mean, it did work with the half bridge)

Plus, the way the board is designed, all 12v rails are connected, so I'd have to find and cut a few... to separate that circuit.

But, hey, if it comes down to it, I guess it looks like I'll have to. Last resort though.

Steve Conner

Thu Aug 30 2012, 08:27AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I can't see the point in changing the 555 supply to 9V. It should run just fine off 5V, 9V, 12V, 15V or whatever. I've run 555 circuits at all of those voltages with no issues.

Just because you're 100% sure that you wired something up right, doesn't make it so. :(

SuperZanti

Thu Aug 30 2012, 08:33AM

Registered Member #6006 Joined: Sat Aug 04 2012, 08:50AM
Location:
Posts: 22

That I'd true. I could post my pcb for everyone.
Thanks for the feedback

zzz_julian_zzz

Thu Aug 30 2012, 09:31AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

Steve's probably right about up to 15vdc supply, but I got problems when I tried that before, I don't know why, but as a friendly suggest - if you can do it, do it..
And since the logics are rated 5v, the 555 output could give a destructive pulses on the ICs, also, 9Volts battery of isolated interrupter would be easier to find. - which allow you to make it as a standard interrupter.

Can you give me the specs of your resonator, size? awg of wire used? turns if ever? so that I can at least give you reasonable spark length depending on how you successfully build your coil =)

"Should the 14awg primary be directly on top of the secondary? "
The primary should be at the bottom of your secondary, not on top.
in fact, nothing should be on top of your secondary coil other than a break out point.

Do put a capacitor in parallel of C6/C7, - this is the reason i think your coil wont work. -inadequate current reserve near the driver which they can pull of.

I think you have almost all the expensive things on this project.
you'll just have to buy 2 capacitors (C6.1/C7.1)

The bridge looks good, zener diodes are optional, but better if they are there.
since you are running on a 12volts you can make the GDT 1:1.2 means primary of 12v GDT : 15v on the secondary. -which is better ON signal to the MOSFETS. to do this, 15turns for the primary, 17 turns to the secondary.

SuperZanti

Thu Aug 30 2012, 05:52PM

Registered Member #6006 Joined: Sat Aug 04 2012, 08:50AM
Location:
Posts: 22

Since the PWM circuit runs of 12 volts that shouldn't have to be knocked down to will it? Would it be best to make both the interupter and the antenna running off the same voltage? (say if maybe I got a 12 volt inverter chip?)

I'll get back to you on all the exact specifications of my coil, as I don't have them with me right now.

When I asked "Should the 14awg primary be directly on top of the secondary? " I meant on top of the wire, not actually on the top portion of the coil. I know it goes on the bottom of the coil. I meant 'on top' as in wrapped tightly around the secondary without a space between the primary and secondary. Of course I need some insulation so it doesn't arc from the primary to secondary. Make sense?

I'll need to buy capacitors for the driver C6/C7 (can your recommend some on digikey?) as well as the capacitors for C6.1/C7.1 (could you recommend some of these as well?)

You said the diodes between the source and drain of each mosfet should be removed for simplicity sake, but would it help having these? Or should I just go with the zener diodes?

Should I still follow this design guide for the GDT?

and just have 2 less wraps on the primary side? or should I do something else?

I'm getting a new ferrite core right now, but this is the wire I made to wrap the GDT, is this good? (unfortunately i'd have to unwrap one of the wires to do a different amount of turns)

Edit: If I design a new pcb, so I can keep running on the computer power supply, would it be okay just to put 2 1.5V LEDs between the 12V input and the 555 circuit?

previous 1 2 3 4

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob