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poor Tesla Coil performance

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loveHV

Wed Dec 10 2008, 06:27PM

Registered Member #1854 Joined: Wed Dec 10 2008, 06:09PM
Location: West-Flanders Belgium
Posts: 88

hi i am new

i am building a ISSTC for a couple of months now and he's finally finished. The driver is based on uzzors pll driver only it has protection diodes over the FETS and a 10 ohm resistor in series with the FETS and 12V ZENERS over the gates.

but i had lots of problems in the beginning i started with a bag of 14 IRFP450's and now the only 2

and now there is a problem wich i can't find any solution for.

The performance of my tesla coil is really depressing i only get like 2mm sparks at most.
I've tried to changed the coupling but all i got was a 2mm spark instead of a 1 mm spark

my GDT core is one from an old B&W flyback and the windings are 2.5mmÂ² insulated wire. and the turn ratio is 10 windings on primary and 7 on secondary's

i have some photo's of the setup

the first one is all i got from the tesla coil and that were little arcs in a lightbulb

the second one is my GDT

the third one is my primary

the fourth one is the whole setup

well, hope you can help me

Dago

Wed Dec 10 2008, 08:51PM

Registered Member #538 Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181

Impossible to say what ALL is wrong with your coil but at least your GDT is totally useless. The core is made from the wrong material, the windings aren't wound together (=huge parasitic inductance), and it (might) have an air gap if you haven't removed it and it looks like theres unconnected wire ends (??). You will most likely get only something out of it that doesn't resemble a square wave even remotely, huge ringing etc. It would be easy to check it with an oscilloscope and I really suggest you and everyone else who is making a SSTC gets one, it just makes things A LOT easier, otherwise its just guesswork.

LithiumLord

Wed Dec 10 2008, 09:16PM

Registered Member #1739 Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261

Yeah, tweaking an SSTC without a scope is completely pointless, it's like doing the boards for it with your eyes closed.
Also, to prevent further blown components, do the low-power tests. If your coil is to give any nice sparks on higher voltages, 20% of the target supply voltage should be enough to see any noticable performance. If you see no, there's no point in further voltage increase.
Also, you can have problems in the PLL setup - however first you need to fix the GDT issues. But before it all - get a scope to do all the upcoming measurements.

loveHV

Wed Dec 10 2008, 10:07PM

Registered Member #1854 Joined: Wed Dec 10 2008, 06:09PM
Location: West-Flanders Belgium
Posts: 88

ok so primary and secondary windings of the GDT must be twisted together no problem

is it possible to remain that same core because i don't think i have an EMI-filter core.

ive scoped the GDT a while ago in school.
when it was unbalasted i got the most crazy waveforms but when it was ballasted i got a Sine

something like this:

@ lithiumlord

ok low power testing but what do you mean by low power, first i was testing with half wave rectified mains but the circuitbreaker always flipped when i tested it so i putted an transformer in between now im testing at 66V DC filterd is that low power or do i need to go lower ?

besides the GDT (i'll try to take care of that)

anything else that need adjusting ??
(i know the coupling on that picture isn't good the windings are now closer together and lower)

Arcstarter

Wed Dec 10 2008, 10:09PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Yes, just get a ferrite toroid from a computer psu, monitors and televisions occasionally have them on the ground connection from the plug. Just get the three wires, put them all in a drill and slowly wind them together , forming a single 'braid' of three wires. After that just put 10 or more turns around a ferrite toroid. That will minimize parasitic inductance, which will reduce ringing. You should also cut the secondary former so that the topload is about level with the last winding.

If you have an oscilloscope, check the output of the pll, and see if it locked. If it did, it will be a clean square wave. I have had problems with this driver, but with 12 volts in i could draw an arc about an inch. I don't have a scope to check with though.

loveHV

Wed Dec 10 2008, 10:16PM

Registered Member #1854 Joined: Wed Dec 10 2008, 06:09PM
Location: West-Flanders Belgium
Posts: 88

ok thanks

yes the output of the PLL is square i tchecked that at school.

i also have a little problem with interference. how do you compress it
my neigbours can hear the sound of my intterupter on their radio

and next to my coil there is a car standing in my garage. could the tesla coil do damage at the car electronics ?

Arcstarter

Thu Dec 11 2008, 12:26AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

loveHV wrote ...

ok thanks

yes the output of the PLL is square i tchecked that at school.

i also have a little problem with interference. how do you compress it
my neigbours can hear the sound of my intterupter on their radio

and next to my coil there is a car standing in my garage. could the tesla coil do damage at the car electronics ?

I doubt it would do any damage to cars. Car electronics are inside the metal chassis, which will act as a Faraday cage, and pretty much shield from any RFI. To make the rfi pretty much disappear, you can make a Faraday cage around the coil, which is grounded by a thick wire to a long stake in the ground.

Remember, this will require different tuning than just open air. Also, this might interfere with feedback, so that could take some tweaking.

teslacoolguy

Thu Dec 11 2008, 02:08AM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792

Arcstarter wrote ...

Yes, just get a ferrite toroid from a computer psu, monitors and televisions occasionally have them on the ground connection from the plug.

Oh no. Those toroids are usually iron power and are pretty much useless for a gdt. One option you can try if you dont have a ferrite toroid, is to take the ferrite transformer from a computer psu or monitor or whatever and seperate the 2 ferrite core halvs and unwind all the existing windings and then wind 10 turns of the tri wire around the empty bobben and then ungap the transformer and that should work. In order to seperate the 2 core halvs and trust me it is painstaking but you have to boil the transformer in water and when it is really hot the 2 halvs should come apart without to much problem. But be careful because they do break really really eazy. I hope this helps.

loveHV

Thu Dec 11 2008, 05:50AM

Registered Member #1854 Joined: Wed Dec 10 2008, 06:09PM
Location: West-Flanders Belgium
Posts: 88

powerd iron cores are usually yellow aren't the grey core's ferrite?

because i've cracked some PSU's open yesterday and, i have 3 types of cores now:

yellow

green

grey (wich i think is ferrite because its 2 windings where sitting on the L & N of the mains)

are they all iron powderd ?

teslacoolguy

Thu Dec 11 2008, 06:04AM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792

Yes, the gray ones are usually ferrite but they are usually to small to be of any use when used for filtering mains. Try to get as many windings as you can on it and see what kind of gdt output waveforms you are getting. Remember to use twisted pairs leading to and away from the gdt because you want as little stray inductance as possible because all that causes is ringing and then the mosfets won't switch properly and that could lead to premature failure.

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