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Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
PJ, Nice looking wave you got there. btw, what is the scale per div of this?
Just a few friendly reminders when doing performance testing: *do not use ground targets, (not to mention that close grounded objects detune the Javatc default calculations of your coil and when arc hits it, there is a possibility of high current on the bridge that could blow your silicon) *make sure that your OCD is perfectly working. (This is very very important side of testing)
"I like that idea, but what range of impedance do you try for?" My approach is via simulations, that's how i get my desired impedance of approx 9 ohms, given the parts i only had. This is how i did it: *First i run on the simulators (lt and ps) with max voltage input to at least give me an idea what current will be flowing in my tank. (remember that most cases, the higher the V-in the better the output of the coil- well this is very rough talking, but in my observation, i confirmed this, i even compared a Half bridge of doubled mains, and Full bridge with non doubled mains, i found that the h.bridge is better in term of bridge current and spark length) *Second I vary the On-time to get the cycles i needed considering the Wave Shape (and number of cycles-ramp) and the current magnitude *Third, i hope that the simulation is correct ;) - well it never failed me hehe
"Julian, what are your primary tank cap specs for your medium sized coil?" I use these capacitors: B32654-A1154-K - i cant afford those crowned capacitors.. that is why. 6.4kvdc / 225nf (4x6)
If you dont want to blow anymore silicon, decrease pri cap.. this will lower the pri current for a given ON time., OR get bigger IGBT(cm300s would be an easy output)
Its your call if you want to follow this steps i would like to recommend you. 1. check your OCD, 2. check you bypass caps and TVS 3. check your primary capacitors (i had problems with it before - it took me 2 sets igbts to detect this huhu) 4. check your filter caps. 5. interrupter check - make sure that your interrupter does not make any unwanted signals, like excessively long ON pulse (ouch!)
To get bigger sparks @ ur own risk: 6. Lower your coupling to be able to tune lower and avoid racing sparks, maybe a ~0.13 would be fine (don't worry about it - compensate the current level with high impedance system so that the bridge wont suffer for a high current set up) - just physically raise the sec.
7. Increase impedance of your system, if you can do 300vdc, then decrease a little bit more your Pri Capacitors. - that way you lowered the tank Current more but allows you to use bigger level of V in.
8. Impedance is increased, so the ON time should be configured too.. but not too much! look into the scope or in simulations. To see if you’re hitting the OCD threshold.
9. Tune for lower primary. do this incrementally, start with 12% lower. then reach 20% WHILE observing your OCD LED.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
My CT is .01V/A and my scope as set to 5V/d. The primary was detuned like 4% for that waveform, its wierd that the waveforms look not as good as I detune though
I dont use ground targets to test with. But I always have one in the direction of the breakout just in case I get a big arc, it will strike the target and not something I dont want it to. Its a safety precaution, not what I base my data on. All of the sparks lengths in my data table are to air. If it hit the strike target i make note of it.
The OCD works just fine and is set for 740A, I can see it working on the oscilloscope as well as red LED light will turn on. I've tested it to 1000A.
I just use a online calculator for impedance and what I get is about 10.6ohms.
I think I will have to reconstruct the MMC indefinitely. I am getting way too much current compared to voltage.
I did try starting at 11% detuned and go down to 20%. At about 16% I hit over 1000A nd then kabooom. At 20% the fuses explode at around 20VAC from variac. I am using a 10A 140VAC variac
Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
there is something wrong with your system that bugs the overall operations. How did your system get pass with the 740 OCD and reach 1000A instead? how do you detune your system? 20% then fuse explodes??? hmmm.. something is wrong with it
@Physics Junkie: Thank you for sharing your table of measurements. It's an interesting read. Was that table taken with the reduced MMC? You wrote:
Impedance increases as capacitance decreases, right? Maybe slightly lower the MMC a bit more if all else does not work
Yes, you'll probably run out of primary turns somewhere along that road.
@zzz_julian_zzz:
My approach is via simulations, that's how i get my desired impedance of approx 9 ohms, given the parts i only had.
This a good idea to get some ballparks. Primary current is much affected by arc loads, though. And this is diffcult to add to a simulation, since there is no good arc model around. It would have to describe the growth of the arc during rampup.
To recap, the effect of arc load on primary current is determined by a) The Lsec/Lpri ratio: A lower ratio leads to lower currents. b) The tuning: Getting the primary and secondary resonant frequencies closer together will lower the pri current. This is a moving target, since the growing arc changes the secondary resonant freq. Optimal tuning is a compromise between differing arc loads during rampup. c) The coupling constant: The effect is somewhat involved. On the one hand increased coupling will make the arc load more "visible" to the primary, thus lowering primary current. On the other hand, it will have the effect of lowering the lower poles frequency, which is the frequency your coil operates at (if there is not much notching). This will have a detuning effect, which counteracts the intended decrease in pri current (see b). At larger arc loads this detuning effect will disappear again, but your IGBTs may have blown up before that.
To make things even more involved: An increasing arc load will not indefinitely lead to lower primary currents. At some point these will rise again, e.g. in the case of a ground arc.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
zzz_julian_zzz wrote ...
there is something wrong with your system that bugs the overall operations. How did your system get pass with the 740 OCD and reach 1000A instead? how do you detune your system? 20% then fuse explodes??? hmmm.. something is wrong with it
How did system get past 740A and reach 1000A? It doesnt. What I meant is I've tested my OCD between 500 A and 1000A. And now I have it set to 740A. The OCD works as it is supposed to. I can see the red LED light and current limit to 740 A on my oscilloscope.
How do I detune? Increase the primary tap point every quarter turn (lowering primary resonant frequency) and record results.
@Uspring. The table was taken with the new MMC .1999 uF ~ .2uF
On the one hand increased coupling will make the arc load more "visible" to the primary, thus lowering primary current.
So basically, lower K=higher Ipri and higher K=lower Ipri? I have somewhat noticed this in my data, but only a slight increase. It is much more clear at high power levels. I have raised my secondary even more to k=.136 and I'm noticing that current is higher already.
Julian, I agree with you in the respect that something is clearly wrong somewhere. My first hunch is DC bus voltage doubler, I might try without the V doubler if problems persist. I am surprised that I am not seeing anywhere near similar results from the identical systems that I based this build from ( mine is a mix between wards drsstc1 and mccauleys drsstc2
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
the mini brought caps its current at 500A I think you are pushing it to the hairy edge you are not giving your self any head room for arc strikes. reducing your mmc is only half the equation, increase the number of primary turns if you can along with reducing the mmc capacitance. you could also add another set of mosfets for better power handling.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
teravolt wrote ...
the mini brought caps its current at 500A I think you are pushing it to the hairy edge you are not giving your self any head room for arc strikes. reducing your mmc is only half the equation, increase the number of primary turns if you can along with reducing the mmc capacitance. you could also add another set of mosfets for better power handling.
you mean minibrute? minibrute is not what I am talking about nor is the minibrute anything like my system. mccauleys drsstc1&2 are much larger than the minibrute and were based off of steve wards original drsstc1, just like mine. the minibrute is closer to mccauleys drsstc3, if not its exactly the same. I'm not ready to completely rebuild an entire new system all over again without even knowing what the problem is in the first place. Honestly I shouldn't have to. This system has worked for others, I'd like to figure out why its not working out for me.
For fun, I rasied secondary more and tuned to 9 turns, maximum detuning for my primary which is 18.5% at 64kHz, k=.13. Heres the data from that:
Above photo: OCD limiting current to 740A. Bad looking waveform. IGBT Blown. @300V and +50PW I should be getting massive sparks.
Thank god it was just one IGBT, since I only have one left. Now you see why I will not be tuning lower than 6%? whatever the problem is, i'm going to slap myself when I figure it out...
Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
What IGBTs are you using? can you give us your schematic?
If i were you, i will scrutinize and search for the culprit in my bridge first. tuning is not that critical in exploding silicons (given for 740 AMPS for a 4 inch sparks???? NO WAY!) - well maybe that is if you don't do what you're doing and tuning is far away to be considered) BUT i know you have ideas on how the system works, its just a problematic part(s) in the bridge. Look for it before you fire it again. Is your mains 120VAC? or 220 VAC? do you have a variac? wattage? thanks.
I hope you can find the missing piece in your system. your posted parameters in JAVATC seemed to be just great. And if your problem is only tuning or coupling, then the coil will work properly but with 2-3 ft sparks.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
zzz_julian_zzz wrote ...
What IGBTs are you using? can you give us your schematic?
If i were you, i will scrutinize and search for the culprit in my bridge first. tuning is not that critical in exploding silicons (given for 740 AMPS for a 4 inch sparks???? NO WAY!) - well maybe that is if you don't do what you're doing and tuning is far away to be considered) BUT i know you have ideas on how the system works, its just a problematic part(s) in the bridge. Look for it before you fire it again. Is your mains 120VAC? or 220 VAC? do you have a variac? wattage? thanks.
I hope you can find the missing piece in your system. your posted parameters in JAVATC seemed to be just great. And if your problem is only tuning or coupling, then the coil will work properly but with 2-3 ft sparks.
IXGN60N60C2D1 schematic is the 2nd gen DRSSTC from easternvoltage research, I dont own the rights so I'm not going to post it. If you have a copy of Dan's book it's in there, but for the most part its exactly the same as steve ward's drsstc1 with a bit more fanciness to the power supply and gate driver. It uses the same circuitry as the UD1.3b but it uses UCC mosfets drivers. I am using a full bridge. Basically, my design specs are identical to steve wards drsstc1 except I am using EVR's driver circuit. but its really all the same.
My mains is 120V. Variac is a 140VAC 10A Powerstat 1400VA. its good for the job. But note that I am using a Voltage doubler configuration with my DC Bus caps. so at 140Vin I get about 390-400V at the bridge. I have a shunt cap from the negative terminal of the DC bus to ground, as well as on the bridge output to ground for protection, just like this
I got outside and did some full variac testing. I tuned back to 75kHz and didnt mess with it. I left K at .13 The best results I get is with 400Hz PRF 60uS PW at Vin. About 30-36" streamers both to air and to ground target. The OCD hardly tripped and the Ipri stayed at about 700A. Tomorrow I am going to increase the coupling back to about .15ish to see if I can lower current a little to allow for longer PW without racing sparks. Below are two short videos, sorry for the shakiness I wasnt recording the vids. It was windy and very cold so I didnt have to worry about the electronics overheating at all
For the moment I may just be at my limit for performance, I really dont know. Ill check the bridge components like you said. I'm going to try lower Ipri as much as I can to allow for longer PW. This would mean: finding where coupling can be at its highest without racing sparks, lower tank cap just a tiny bit (I dont want to have to make a new primary), possibly construct a double toroid topload with slightly lower capacitance, but only if I need to change overall natural frequency to keep in good tuning range with the primary.
Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
Physics Junkie wrote ...
IXGN60N60C2D1 schematic is the 2nd gen DRSSTC from easternvoltage research, I dont own the rights so I'm not going to post it. If you have a copy of Dan's book it's in there, but for the most part its exactly the same as steve ward's drsstc1 with a bit more fanciness to the power supply and gate driver. It uses the same circuitry as the UD1.3b but it uses UCC mosfets drivers. I am using a full bridge. Basically, my design specs are identical to steve wards drsstc1 except I am using EVR's circuit board. but its really all the same.
2nd Generation DRSSTC from Dan, I have the book, but uhh... the feedbacking circuit samples the signal from the Secondary isn't??? if this is the case, then detuning the Pri will not work properly for the system. It must be sampled from the primary.
As for the 2 circuits, EVR's utilize the soft cut of the interrupter signal when D-FF is on a negative edge, S.wards, utilizes a positively edge triggered.
using a full bridge of this IGBTs could give sparks up to 5ft (if system is properly configured) Thanks.
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Strike rail arcs to secondary. -coupling & tuning-
