Help with Small DRSSTC / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

Help with Small DRSSTC

previous 1 2 3 next

Move Thread

LAN_403

Bennem

Sun Aug 13 2006, 08:01PM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

Hi Terry,
Yeah, i've tried reversing my primary feedback CT connections.
That was my first thought too.
I have been given an idea by Steve Ward....i will try switching to secondary feedback.
Seems that guys like 'Reaching' and 'Derek woodroft' have built their small coils with secondary feedback and had success.

cheers!

HV Enthusiast

Sun Aug 13 2006, 08:28PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Try the following:

1. Check your IGBTs first. If you are running a full-bridge or half-bridge, you may have killed some already. Typically, if you kill 1/2 the bridge, you will get only a small amount of output like you are seeing. Trying ohming out C-E with multimeter and check for high-ohms.

2. Ball park Tuning - Actually measure. Simple to do with just some sort of signal generator (even 555's work), and an LED and one resistor.

3. How much bus voltage do you have? Remember, if you primary is tuned much lower than the secondary, you may need considerable input voltage to get decent arcs. With my DRSSTC III system (which puts out more than 50" now), my arc length is less than 5" even at 200VDC bus voltage. Its only after this point that the streamer really grows.

1. What voltage input are you running and what is your measured bus voltage.

Bennem

Sun Aug 13 2006, 09:15PM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

Hi Dan,

My Buss voltage goes up to 340 volts.
At full buss, spark is 3.5 inch long.

My Igbt's check ok.

HV Enthusiast

Mon Aug 14 2006, 12:00AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Yeah, check those IGBTs, you may have one side (full-bridge i.e.) thats toast and that will do it.

If not that, then try checking the tuning.

SECONDARY RESONANT FREQUENCY

1. Attach 1k ohm resistor to base of secondary and feed into + input of signal generator. - input of signal generator doesn't have to attach to anything. Hook oscilloscope to secondary base end of 1k resistor. Oh yeah, put two opposing LEDs in series with this connection. Adjust signal generator frequency until LED is brightest. Remember series resonance is when circuit is lowest impedance (i.e. short circuit) so LED will be brightest at resonance. Use this to roughly determine your resonant frequency. Make sure your topload is on it as well and its in the spot where you would normally run the coil.

PRIMARY RESONANT FREQUENCY

1. Disconnect everything from the primary coil, primary capacitor. Connect the primary coil and primary capacitor in parallel. One end connects to GND of the signal generator. The other end through the LEDs and 1k ohm resistor. Parallel resonance is where impedance is at its highest, therefore, adjust signal generator frequency until LED is dimmest.

These will get you good ballpark numbers to compare resonant frequencies. Try this if your IGBTs are both okay.

If you have an oscilloscope, you can monitor voltage at the resistor as well to get a more accurate number, but shouldn't be necessary.

Bennem

Mon Aug 14 2006, 08:45AM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

Cheers Dan for the advice!

I have no signal generator at present.....guess i'll have to run up a '555' timer one, and check the frequencies of the primary and secondary coils.

Thanks to all you guys for responding!.......i now have a few things to try out

Is the tunning more 'critical' on a smaller DRSSTC than a larger one?
On my last coil, i could tune it anywhere on its fourth turn and get the same spark length, laters, i de-tuned it 20% and got longer sparks due to streamer loading, of course the buss voltage had to be higher before break out would occur.

vasil

Mon Aug 14 2006, 01:01PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

I remeber that Steve said that is not enough for primary resonant circuit to switch only the primary or CT connections once time. Try reversing the primary, CT and GDT connections in the same time (just try /error thing).

Steve Ward

Mon Aug 14 2006, 03:30PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

I remeber that Steve said that is not enough for primary resonant circuit to switch only the primary or CT connections once time.

Im not sure if maybe i said it wrong, but you are partially right. Reversing the primary coil (of the tesla coil) connections wont change the feedback phasing (like it will with secondary feedback). But, changing the CT connections (or removing the CT, flipping it over and putting it back on the wire, effectively reversing the primary of the CT) will give the desired 180* shift in feedback phasing.

Terry Fritz

Mon Aug 14 2006, 06:16PM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Hi,

For an H-bridge, if both sides were wired to the GDT "in phase". Then there would really be little or no primary current flow. But the voltage on the primary would swing from +340 to -340 which might be enough to cause small acrs from capacitive coupling. So the only thing I can think of at this point is maybe both sides of the H-bridge are running "in phase" instead of "out of phase"...

Cheers,

Terry

Bennem

Mon Aug 14 2006, 11:53PM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

Weh hey!!.....i found the fault,
It turned out to be faulty driver ic's UCC37321, both turned out to be faulty!
Now i have 3 inch spark at 35 volt buss voltage,
I wanna turn up the buss, but its late and have to think of my neighbors,
i spent the whole weekend trying to de-bug it, think i need a new driver board now!.....lol

Anyway, thanks guys for all your help!!

HV Enthusiast

Tue Aug 15 2006, 01:23AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Well, you're not done yet. Now you need to find out why the drivers are bad. I'm guessing you probably ran the circuit at 100% duty instead of a light duty with an interrupter.

previous 1 2 3 next

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