Help with Small DRSSTC
Bennem, Sun Aug 13 2006, 12:27PMI wonder if you guys can help me?
I've just completed building a small DRSSTC
Specs are:-
Secondary...7.5 x 2 inch wound with 36 AWG
primary.....2.75 inch wound with 12 AWG
Toroid ....1.75 x 6 (john Freau one)
Full bridge of 40n60A4D IGBT's (yeah over kill!)
Steve Wards driver circuit with primary feedback and OCD.
a LED peak current detector.
The coil seems to favour its 4th turn of the primary for maximum spark output at low voltage.
My problem is......the coils maximum output at full 240 volt mains in, is only 3.5 inch!
I have tried reversing the primary feed back conections, but then its spark output is even smaller.
I have also tried reversing the primary coil.....but seems to make no differance at all.
Any thoughts as what to try next?
Many thanks!
Re: Help with Small DRSSTC
robert, Sun Aug 13 2006, 12:29PM
Whats the primary capacitor value?
robert, Sun Aug 13 2006, 12:29PM
Whats the primary capacitor value?
Re: Help with Small DRSSTC
Bennem, Sun Aug 13 2006, 12:32PM
Hi Robert......My cap value is 75nf (two 0.15uf 3KV caps in series)
Bennem, Sun Aug 13 2006, 12:32PM
Hi Robert......My cap value is 75nf (two 0.15uf 3KV caps in series)
Re: Help with Small DRSSTC
Part Scavenger, Sun Aug 13 2006, 12:43PM
Are sparks alot longer at low BPS? Maybe your doubler/power cap is too small?
Maybe check the on time in the interrupter? That makes a huge difference.
Good ground?
BTW, it looks great! I've been looking forward to seeing this coil.
Part Scavenger, Sun Aug 13 2006, 12:43PM
Are sparks alot longer at low BPS? Maybe your doubler/power cap is too small?
Maybe check the on time in the interrupter? That makes a huge difference.
Good ground?
BTW, it looks great! I've been looking forward to seeing this coil.
Re: Help with Small DRSSTC
Bennem, Sun Aug 13 2006, 12:58PM
My interrupter ON time is variable from 50uS to 150uS....BPS is adjustable from 2mS to 8 mS..........playing around with the interupter seems to make very little difference to spark length with this coil.......its maximum output is 3.5 inch to ground.
My primary feedback coils (two cascaded 33 turns per coil) are only half an inch in diameter....my last coil used the comonly used 1.1 inch ones FT-114A-77.....and they worked fine!........could it be that these smaller ones might hinder performance?
My storage caps are 3 x 470uf caps in parrallel....no doubler arrangment, mains voltage is 240 volt.
Bennem, Sun Aug 13 2006, 12:58PM
My interrupter ON time is variable from 50uS to 150uS....BPS is adjustable from 2mS to 8 mS..........playing around with the interupter seems to make very little difference to spark length with this coil.......its maximum output is 3.5 inch to ground.
My primary feedback coils (two cascaded 33 turns per coil) are only half an inch in diameter....my last coil used the comonly used 1.1 inch ones FT-114A-77.....and they worked fine!........could it be that these smaller ones might hinder performance?
My storage caps are 3 x 470uf caps in parrallel....no doubler arrangment, mains voltage is 240 volt.
Re: Help with Small DRSSTC
Terry Fritz, Sun Aug 13 2006, 01:41PM
Hi,
Are you sure the primary circuit and secondary coil are running at the same frequency? You should check with a program like this:
Cheers,
Terry
Terry Fritz, Sun Aug 13 2006, 01:41PM
Hi,
Are you sure the primary circuit and secondary coil are running at the same frequency? You should check with a program like this:
Cheers,
Terry
Re: Help with Small DRSSTC
Bennem, Sun Aug 13 2006, 04:32PM
Hi Terry,
Thanks for the info,
I punched in my parameters of my coil to the JAVA TC calculator,
its frquency is 392KHZ, and gives my primary coil turns of 4.95 for the same frquency,
coupling is 0.157.
I tuned my primary at 4.5 to 5 turns......spark output is about 2 inch.....1.5 inch lower than
when it's tuned to turn 4, which seems to be its maximum.
I think i will try my driver on another coil to establish whether its a driver fault, or a coil fault.
Thanks for all the feedback!!
Bennem, Sun Aug 13 2006, 04:32PM
Hi Terry,
Thanks for the info,
I punched in my parameters of my coil to the JAVA TC calculator,
its frquency is 392KHZ, and gives my primary coil turns of 4.95 for the same frquency,
coupling is 0.157.
I tuned my primary at 4.5 to 5 turns......spark output is about 2 inch.....1.5 inch lower than
when it's tuned to turn 4, which seems to be its maximum.
I think i will try my driver on another coil to establish whether its a driver fault, or a coil fault.
Thanks for all the feedback!!
Re: Help with Small DRSSTC
Part Scavenger, Sun Aug 13 2006, 04:42PM
Hmm. What does your primary current waveform look like?
Part Scavenger, Sun Aug 13 2006, 04:42PM
Hmm. What does your primary current waveform look like?
Re: Help with Small DRSSTC
Bennem, Sun Aug 13 2006, 05:22PM
Hi Part Scavenger !
Yeah....i think i'll do some scope tests when i return to work on tuesday......have no isolating transformer at home.
Cheers.
Bennem, Sun Aug 13 2006, 05:22PM
Hi Part Scavenger !
Yeah....i think i'll do some scope tests when i return to work on tuesday......have no isolating transformer at home.
Cheers.
Re: Help with Small DRSSTC
Terry Fritz, Sun Aug 13 2006, 07:36PM
Hi,
Just a thought... If you are using primary current feedback and the CT is wired backwards it might do that. Mine does (guess how I know :O))
After the initial firing pulse makes a 1/2 inch arc, the feedback does everything possible to turn the coil off rather than on.
Cheers,
Terry
Terry Fritz, Sun Aug 13 2006, 07:36PM
Hi,
Just a thought... If you are using primary current feedback and the CT is wired backwards it might do that. Mine does (guess how I know :O))
After the initial firing pulse makes a 1/2 inch arc, the feedback does everything possible to turn the coil off rather than on.
Cheers,
Terry
Re: Help with Small DRSSTC
Bennem, Sun Aug 13 2006, 08:01PM
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!
Bennem, Sun Aug 13 2006, 08:01PM
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!
Re: Help with Small DRSSTC
HV Enthusiast, Sun Aug 13 2006, 08:28PM
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.
HV Enthusiast, Sun Aug 13 2006, 08:28PM
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.
Re: Help with Small DRSSTC
Bennem, Sun Aug 13 2006, 09:15PM
Hi Dan,
My Buss voltage goes up to 340 volts.
At full buss, spark is 3.5 inch long.
My Igbt's check ok.
Bennem, Sun Aug 13 2006, 09:15PM
Hi Dan,
My Buss voltage goes up to 340 volts.
At full buss, spark is 3.5 inch long.
My Igbt's check ok.
Re: Help with Small DRSSTC
HV Enthusiast, Mon Aug 14 2006, 12:00AM
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.
HV Enthusiast, Mon Aug 14 2006, 12:00AM
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.
Re: Help with Small DRSSTC
Bennem, Mon Aug 14 2006, 08:45AM
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.
Bennem, Mon Aug 14 2006, 08:45AM
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.
Re: Help with Small DRSSTC
vasil, Mon Aug 14 2006, 01:01PM
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).
vasil, Mon Aug 14 2006, 01:01PM
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).
Re: Help with Small DRSSTC
Steve Ward, Mon Aug 14 2006, 03:30PM
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.
Steve Ward, Mon Aug 14 2006, 03:30PM
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.
Re: Help with Small DRSSTC
Terry Fritz, Mon Aug 14 2006, 06:16PM
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
Terry Fritz, Mon Aug 14 2006, 06:16PM
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
Re: Help with Small DRSSTC
Bennem, Mon Aug 14 2006, 11:53PM
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!!
Bennem, Mon Aug 14 2006, 11:53PM
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!!
Re: Help with Small DRSSTC
HV Enthusiast, Tue Aug 15 2006, 01:23AM
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.
HV Enthusiast, Tue Aug 15 2006, 01:23AM
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.
Re: Help with Small DRSSTC
Terry Fritz, Tue Aug 15 2006, 01:35AM
Did you ever run it with the chip's output open loaded? Those darn chips always liked to burn up on me too. If they have no load on the output, they osscilate or go crazy and fry...
Cool that it seems all figured out now
Cheers,
Terry
Terry Fritz, Tue Aug 15 2006, 01:35AM
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,
Did you ever run it with the chip's output open loaded? Those darn chips always liked to burn up on me too. If they have no load on the output, they osscilate or go crazy and fry...
Cool that it seems all figured out now
Cheers,
Terry
Re: Help with Small DRSSTC
Steve Ward, Tue Aug 15 2006, 02:16AM
It seems those gate drivers dont have the best clamping diodes, ive had some "mysteriously" fail on me before, but it was usually when the design was new and i was changing stuff a lot. I havent had one fail on any of my coils that are running normally now.
Its always good to at least attempt to figure out why something fails, rather than just stuff new parts in. I can think of some people who have that mentality... its pretty sad how much stuff they destroy.
Steve Ward, Tue Aug 15 2006, 02:16AM
It seems those gate drivers dont have the best clamping diodes, ive had some "mysteriously" fail on me before, but it was usually when the design was new and i was changing stuff a lot. I havent had one fail on any of my coils that are running normally now.
Its always good to at least attempt to figure out why something fails, rather than just stuff new parts in. I can think of some people who have that mentality... its pretty sad how much stuff they destroy.
Re: Help with Small DRSSTC
Terry Fritz, Tue Aug 15 2006, 03:26AM
Hi,
Gate drive chips are made to be as "hot" as possible. Maximum current in as little as time as they dare. Thus the "poles and zeros" are tight and designed for a "load". Nobody drives an open load so they don't "dumb down" the chips to handle open load. So if you drive power into an open load, the chip will die figuring out "how"... No big deal though...
We may kill a few here and there as we experiment, but in the actual application which uses 99.9% of the 100's of thousands used per day, there is no issue at all...
If the chip was run open, all is expalined right there... It's just a fleck of sand after all
Cheers,
Terry
Terry Fritz, Tue Aug 15 2006, 03:26AM
Hi,
Gate drive chips are made to be as "hot" as possible. Maximum current in as little as time as they dare. Thus the "poles and zeros" are tight and designed for a "load". Nobody drives an open load so they don't "dumb down" the chips to handle open load. So if you drive power into an open load, the chip will die figuring out "how"... No big deal though...
We may kill a few here and there as we experiment, but in the actual application which uses 99.9% of the 100's of thousands used per day, there is no issue at all...
If the chip was run open, all is expalined right there... It's just a fleck of sand after all
Cheers,
Terry
Re: Help with Small DRSSTC
Bennem, Tue Aug 15 2006, 05:30AM
Yes i did run the driver without a load (CT ) when i was first testing its start up waveforms,
so, the UCC ic's don't like it without a load?
Perhaps thats the reason they failed?
I also found a dry jointed clamping diode connected from the UCC output and the 15 volt rail.
Cheers.
Bennem, Tue Aug 15 2006, 05:30AM
Yes i did run the driver without a load (CT ) when i was first testing its start up waveforms,
so, the UCC ic's don't like it without a load?
Perhaps thats the reason they failed?
I also found a dry jointed clamping diode connected from the UCC output and the 15 volt rail.
Cheers.
Re: Help with Small DRSSTC
Steve Conner, Tue Aug 15 2006, 09:32AM
Glad you found the fault Bennem!
Terry: I've run the UCC driver chips in my DRSSTC drivers open-circuit for hours, and never had any problems. I don't think running without a load should do them any harm. There were only two times I ever killed any:
When I ran them without clamp diodes and they latched up. They survived that if I turned the power supply off quickly. >.<
When the power supply that I was running them off went crazy due to RF pickup from the Tesla coil, and increased its output voltage to more than the chips are rated to take.
Steve Conner, Tue Aug 15 2006, 09:32AM
Glad you found the fault Bennem!
Terry: I've run the UCC driver chips in my DRSSTC drivers open-circuit for hours, and never had any problems. I don't think running without a load should do them any harm. There were only two times I ever killed any:
When I ran them without clamp diodes and they latched up. They survived that if I turned the power supply off quickly. >.<
When the power supply that I was running them off went crazy due to RF pickup from the Tesla coil, and increased its output voltage to more than the chips are rated to take.
Re: Help with Small DRSSTC
HV Enthusiast, Tue Aug 15 2006, 10:35AM
I have to agree with Steve on this one. I run these drivers open circuit (no load) all the time for testing and never have any problems. Sometimes if you don't have a good tantalum (10uF for example) to bypass the chips, they will oscillate, but other than that, I've never seen one fail on the bench no load.
HV Enthusiast, Tue Aug 15 2006, 10:35AM
wrote ...
Terry: I've run the UCC driver chips in my DRSSTC drivers open-circuit for hours, and never had any problems. I don't think running without a load should do them any harm. There were only two times I ever killed any:
Terry: I've run the UCC driver chips in my DRSSTC drivers open-circuit for hours, and never had any problems. I don't think running without a load should do them any harm. There were only two times I ever killed any:
I have to agree with Steve on this one. I run these drivers open circuit (no load) all the time for testing and never have any problems. Sometimes if you don't have a good tantalum (10uF for example) to bypass the chips, they will oscillate, but other than that, I've never seen one fail on the bench no load.
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