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I am going to set the max peak current to about 600A, in order to avoid excessive stress on the IGBTs
Now, I have to design primary circuit...
I understand that less impedance means higher current and faster secondary voltage build-up, but, in terms of performance (spark length) which value of surge impedance should I choose? Now I am considering something between 150-200nF primary cap which gives 10-7.5 ohnm of impedance.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I choose the surge impedance to be about 10 times the inverter's output impedance, but Steve Ward's newer coils have a lower impedance and seem to work great, so now I'd say 5 times. Anything between 5 and 10 seems to work, though.
The formula I use for the inverter output impedance is (4/pi)*(DC bus voltage/current limit) but since it's just a rough estimate, you can leave out the 4/pi.
And if it were a half bridge inverter, you'd need to divide the impedance by 2.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
Goodchild wrote ...
umm.. I would go with a lower OCD value for the 60N60s I would go no more than 500A with thoses.
Steve Ward wrote this on his site about the 40N60 IGBTs
3/16/05:
A lot has changed. New secondary (6.5"x21" 30awg) and now running on primary feedback. Also a new MMC, 5 strings of 2 caps in series for .375uF. A new primary was needed to tune (requires 7 turns now). The primary is tuned to 55khz, the secondary Fr is about 75khz. Sparks easily hit 6' with measured 650A+ in the primary circuit. I tested these IGBTs to over 1000A at 95khz so this should be no problem at all. Everything runs nice and cool at 55khz and the sparks are pretty darn hot! Enjoy some pictures from today (notice the red LED on the base of the coil, indicating that the overcurrent circuit tripped). The coil was running 120bps and 150uS on period.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Mads Barnkob wrote ...
Goodchild wrote ...
umm.. I would go with a lower OCD value for the 60N60s I would go no more than 500A with thoses.
Steve Ward wrote this on his site about the 40N60 IGBTs
3/16/05:
A lot has changed. New secondary (6.5"x21" 30awg) and now running on primary feedback. Also a new MMC, 5 strings of 2 caps in series for .375uF. A new primary was needed to tune (requires 7 turns now). The primary is tuned to 55khz, the secondary Fr is about 75khz. Sparks easily hit 6' with measured 650A+ in the primary circuit. I tested these IGBTs to over 1000A at 95khz so this should be no problem at all. Everything runs nice and cool at 55khz and the sparks are pretty darn hot! Enjoy some pictures from today (notice the red LED on the base of the coil, indicating that the overcurrent circuit tripped). The coil was running 120bps and 150uS on period.
Well ya those are 40N60s there a hell of a lot better than 60N60s ive personaly tested 60N60s and they fail at about 600A to 700A
Registered Member #2481
Joined: Mon Nov 23 2009, 03:07PM
Location: ITALY
Posts: 134
Steve McConner wrote ...
I choose the surge impedance to be about 10 times the inverter's output impedance, but Steve Ward's newer coils have a lower impedance and seem to work great, so now I'd say 5 times. Anything between 5 and 10 seems to work, though.
The formula I use for the inverter output impedance is (4/pi)*(DC bus voltage/current limit) but since it's just a rough estimate, you can leave out the 4/pi.
And if it were a half bridge inverter, you'd need to divide the impedance by 2.
Well, in my case that would be around 6.5 ohm which means about 230nF...
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
Goodchild wrote ...
Mads Barnkob wrote ...
Goodchild wrote ...
umm.. I would go with a lower OCD value for the 60N60s I would go no more than 500A with thoses.
Steve Ward wrote this on his site about the 40N60 IGBTs
3/16/05:
A lot has changed. New secondary (6.5"x21" 30awg) and now running on primary feedback. Also a new MMC, 5 strings of 2 caps in series for .375uF. A new primary was needed to tune (requires 7 turns now). The primary is tuned to 55khz, the secondary Fr is about 75khz. Sparks easily hit 6' with measured 650A+ in the primary circuit. I tested these IGBTs to over 1000A at 95khz so this should be no problem at all. Everything runs nice and cool at 55khz and the sparks are pretty darn hot! Enjoy some pictures from today (notice the red LED on the base of the coil, indicating that the overcurrent circuit tripped). The coil was running 120bps and 150uS on period.
Well ya those are 40N60s there a hell of a lot better than 60N60s ive personaly tested 60N60s and they fail at about 600A to 700A
One wouldn't know from looking in the datasheets, the 60N60 are superior in almost any aspect.
Registered Member #2481
Joined: Mon Nov 23 2009, 03:07PM
Location: ITALY
Posts: 134
Mads Barnkob wrote ...
Goodchild wrote ...
Mads Barnkob wrote ...
Goodchild wrote ...
umm.. I would go with a lower OCD value for the 60N60s I would go no more than 500A with thoses.
Steve Ward wrote this on his site about the 40N60 IGBTs
3/16/05:
A lot has changed. New secondary (6.5"x21" 30awg) and now running on primary feedback. Also a new MMC, 5 strings of 2 caps in series for .375uF. A new primary was needed to tune (requires 7 turns now). The primary is tuned to 55khz, the secondary Fr is about 75khz. Sparks easily hit 6' with measured 650A+ in the primary circuit. I tested these IGBTs to over 1000A at 95khz so this should be no problem at all. Everything runs nice and cool at 55khz and the sparks are pretty darn hot! Enjoy some pictures from today (notice the red LED on the base of the coil, indicating that the overcurrent circuit tripped). The coil was running 120bps and 150uS on period.
Well ya those are 40N60s there a hell of a lot better than 60N60s ive personaly tested 60N60s and they fail at about 600A to 700A
One wouldn't know from looking in the datasheets, the 60N60 are superior in almost any aspect.
I made the same remark looking at the datasheets. Both the nominal and peak currents are the same for the two devices...
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Ive had questionable results when pushing the IXYS 60N60 parts, they seemed to explode when the older fairchild parts did not. I suspect the die size is actually smaller for the IXYS compared to the fairchild.
You can always give it a try and see how it works.
But as ive said before, im no longer into pushing parts way beyond their specifications, it doesnt get you anywhere in the long run. Unless you really go through the thermal transient modeling (which unfortunately the 60N60 datasheet is screwed up) and prove that the delta Temp on the die is quite safe, then you guys are mostly just pulling numbers out of your ass.
My thoughts on surge impedance: faster rise time seems to be more efficient at producing the longest sparks for a given power consumption. You are ultimately limited by the silicon and other resistive losses. I think the guideline Conner gave is pretty good if you dont have any other idea of where to start. If you are seeking to minimize peak current, then you likely want a higher surge impedance, but too high means that you cant dump as much energy into the sparks (the system is held back). I have found that i can achieve a moderate spark length with a high Z primary at some low current, and when using a low Z primary it takes more peak current to get the same spark. The only difference is that the low Z primary still has the ability to go much beyond and produce even bigger sparks, at a cost of even higher primary current.
Going further, it seemed to me that small coils could never be optimized for a really fast energy transfer in the same way that big coils could be. So small coils are often detuned so that they only excite 1 pole frequency which allows the secondary voltage to grow un-bounded before spark breakdown (it essentially removes the notch). But, on big coils i found that i didnt need to detune the primary to get good performance, and tuning it for a "notched" waveform yields a better net energy transfer to the secondary, making operating more efficient than the detuned method.
Its difficult to explain this in a short forum post. For anyone interested, i suggest you read up on Antonio's theoretical description of the DRSSTC
Its sort of a pre-requisite to really understanding the subtleties of DRSSTCs, they can really be quite complex if you want them to be. Or, just tune for maximum smoke if you dont want to be bothered with all the thinking.
I also recommend Antonio's DRSSTCD program, just be mindful that with any simulation: garbage in = garbage out. It takes a bit of interpretation and working with a real system to know whether or not the results are realistic when you have a spark shooting off the top of your coil (which is, afterall the hardest part of all of this analysis).
Registered Member #2481
Joined: Mon Nov 23 2009, 03:07PM
Location: ITALY
Posts: 134
Steve Ward wrote ...
Ive had questionable results when pushing the IXYS 60N60 parts, they seemed to explode when the older fairchild parts did not. I suspect the die size is actually smaller for the IXYS compared to the fairchild.
Steve, I have found two different 60N60 parts from IXYS...
IXGN60N60: datasheet dated 2000. Datasheet quite poor (no graphs), max peak current is 200A, 1ms @ 25°C
IXGN60N60C2: datasheet dated 2009. Two times faster than the older part (half the gate charge) and max peak current is 300A, 1ms @ 25°C
By extrapolation of the output characteristic, I assume that with a collectror current of 300A Vce is about 4.5V (Vge=15V). So, a peak current of 300 A with a period of 1ms means a pulse with energy of 1.35J.
Considering a pulse of 700A with a Vce of 10V (rough estimate) and a duration of 100us the dissipated energy is 0.7J... In theory, no problem of junction over heating...
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DRSSTC: choosing the "right" surge impedance
