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Registered Member #4233
Joined: Sun Nov 27 2011, 09:25PM
Location:
Posts: 6
Need some guidance for sizing the tank capacitor for a tesla powered from flyback and ignition coil transformers. I understand that the primary needs to be resonant with the secondary. But Im a bit lost with dc powered tesla and the correct way to size the tank capacitor.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
You have an extra degree of freedom because the DC power source will charge any size of capacitor. The bigger the cap, the longer it'll take to charge and the slower the break rate will be.
So, using the equation for energy storage in a capacitor, and knowing the output power of your DC source, choose the capacitor size to get a reasonable break rate, maybe 100 or 200 per second.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Using a 'flyback transformer' or 'ignition coil' to power an sgtc gives less power than an NST but gives the option of higher voltage.
It is easiest to build an sgtc with components and dimensions similar to a common NST-powered sgtc and adjust the spark gap for effect
smaller gap lower charging voltage for primary capacitor less energy per bang more bangs-per-second
wider gap higher voltage rating for primary capacitor higher energy per bang (longer arcs) less bangs-per-second
For low powered sgtc such as flyback or iggy I got good results using smaller values for primary capacitor (1 to 2 nF) and pvc insulated, multistrand copper wire (cheaper than copper tubing) wound on a plastic bucket (but fine tuning is more difficult due to the insulation) at this power level cheaper ceramic disk capacitors can be used for the primary capacitor MMC and various home-made capacitors too, but an MMC of good polypropylene capacitors does give better results.
EDIT: ah, Steve beat me to it ... shows how slowly I think and type.
Registered Member #4233
Joined: Sun Nov 27 2011, 09:25PM
Location:
Posts: 6
Looks like i can estimate the output voltage by spark lenghth. But how about the current I can measure the low voltage side current. Any estimates on loses/efficiency in a flyback or ignition coil
Registered Member #3883
Joined: Fri May 13 2011, 06:30PM
Location: Norway
Posts: 87
I'm working on the same approach and was planning on calculating the caps from the energy stored in the primary on the I.C. minus some losses (10-20% perhaps?).
Now I've scoped the primary I.C., and it seems to produce a pretty decent DC pulse with no negative oscillations. Can I assume that this also will be the case on the secondary? If so I should be able to forgo the rectifier and load the caps directly, right? The secondary has a huge induction (70H IIRC), so that should prevent current from leaking back once the spark gap fires. Right? Or am I missing something?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
That'll work if one pulse from the IC is enough to charge your capacitor fully. But with a rectifier, you can use a bigger capacitor and charge it over several pulses.
Registered Member #3883
Joined: Fri May 13 2011, 06:30PM
Location: Norway
Posts: 87
True, and it will probably come to that eventually as the coil runs at appr 500Hz. It will probably make more sense to run the tesla at 100Hz or so, but without the need for a rectifier I can McGyver together a prototype just to get my bearings before I start on a more final deign.
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Sizing capacitor for a DC powered tesla coil?
