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Registered Member #1169
Joined: Wed Dec 12 2007, 09:16AM
Location: Portland OR
Posts: 251
sounds good! I am actually quite excited to started. Besides it wouldn't be a hobby otherwise if you didn't drop loads of cash into something that you will get no return on!
Registered Member #141
Joined: Sat Feb 11 2006, 01:14PM
Location: Southern California
Posts: 96
Hi guys. I recently completed my miniBrute based DRSSTC built using EVR’s book and boards. This was my first solid state coil (I’ve built 5 sgtc’s). I was waiting to post until I had a few pics, but I don’t have a camera right now and figure you may be able to benefit from my experience.
First off, let me say that it was not easy, and I have a large collection of dead silicon (not because of any design flaws, but because of my mistakes), but I finally have it working right and I have replicated Dan’s 48†sparklength. There were times when I did not know what was wrong, and I was very frustrated at blowing something up every single time I turned it on.
One of the stupid mistakes I made was forgetting the 4.7uF decoupling cap across the power supply rails (c101 in the schematic). I think I missed it because it is on the half-bridge section of the schematic, but it is not part of the half-bridge board. I blew up 8 IGBT’s and 16 TVS’s before I figured out that I had forgotten a crucial part! Of course, I had to wait a week for it to arrive from Digikey.
Another thing was at some point, I melted the relay. This caused me to blow many TVS’s before I was able to figure this one out by checking the voltage at the bridge instead of at the power supply caps. Again, I had to wait a week for parts from Digikey.
Also, because of the way I laid everything out inside the base, my cooling fan did not supply adequate airflow through the mmc. They get very hot very quickly with no airflow, and as a result, I burned several up. An interesting thing is that I managed to partially melt a cap without knowing it and before I cranked the current up all the way. I could only manage about 32†sparklength with this partially melted cap, even after I cranked it up all the way. I had no idea that this was limiting my output until it finally failed completely and I replaced it. Sparklength immediately increased to 44†consistently with an occasional (once every 5 or so seconds) 48â€.
I now run 3 parallel strings of 4 series of the “normal†.15 CDE mmc caps (I had them on hand) so that they won’t get quite so hot so quickly due to my poor-airflow layout.
One final note about the testing/ fine tuning – I was able to build this coil and get great results with only a multimeter (Of course you should follow Dan’s testing/tuning instructions with freq. generator and oscilloscope if you can), and I didn’t even use the same secondary. I used wintesla and javatc to match the required resonant frequency and coupling (by adjusting # of turns and height) with a slightly smaller than specified secondary coilform, and this was accurate enough to allow me to use the original primary specifications with no additional tuning.
Hope this helps, and feel free to ask any questions.
-Freddie
p.s. I'd like to thank Daniel McCauley for taking the time to design excellent quality boards and publish professional quality books enabling a sstc n00b like me to build such an awesome coil on a first try!
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
I now run 3 parallel strings of 4 series of the “normal†.15 CDE mmc caps (I had them on hand) so that they won’t get quite so hot so quickly due to my poor-airflow layout.
No, id say Dan's design is over stressing the current capacity of the MMC, and adding more parallel strings was an appropriate upgrade. I could see problems if the MMC was enclosed and operating for hours, but if it needs a fan to cool film caps, that just sounds like too much dissipation in the capacitors for safe operation.
And from the description of the problems from missing the 4.7uF decoupling caps sounds like you have too much buss inductance with the electrolytics. My CM300 bridge actually doesnt use any film caps (nor does it require TVSs). Its just electrolytics, IGBTs, and lots of copper. This of course depends on having very high quality electrolytic caps for the bulk storage.
Registered Member #1169
Joined: Wed Dec 12 2007, 09:16AM
Location: Portland OR
Posts: 251
Wirenut wrote ...
Hi guys. I recently completed my miniBrute based DRSSTC built using EVR’s book and boards. This was my first solid state coil (I’ve built 5 sgtc’s). I was waiting to post until I had a few pics, but I don’t have a camera right now and figure you may be able to benefit from my experience.
First off, let me say that it was not easy, and I have a large collection of dead silicon (not because of any design flaws, but because of my mistakes), but I finally have it working right and I have replicated Dan’s 48†sparklength. There were times when I did not know what was wrong, and I was very frustrated at blowing something up every single time I turned it on.
One of the stupid mistakes I made was forgetting the 4.7uF decoupling cap across the power supply rails (c101 in the schematic). I think I missed it because it is on the half-bridge section of the schematic, but it is not part of the half-bridge board. I blew up 8 IGBT’s and 16 TVS’s before I figured out that I had forgotten a crucial part! Of course, I had to wait a week for it to arrive from Digikey.
Another thing was at some point, I melted the relay. This caused me to blow many TVS’s before I was able to figure this one out by checking the voltage at the bridge instead of at the power supply caps. Again, I had to wait a week for parts from Digikey.
Also, because of the way I laid everything out inside the base, my cooling fan did not supply adequate airflow through the mmc. They get very hot very quickly with no airflow, and as a result, I burned several up. An interesting thing is that I managed to partially melt a cap without knowing it and before I cranked the current up all the way. I could only manage about 32†sparklength with this partially melted cap, even after I cranked it up all the way. I had no idea that this was limiting my output until it finally failed completely and I replaced it. Sparklength immediately increased to 44†consistently with an occasional (once every 5 or so seconds) 48â€.
I now run 3 parallel strings of 4 series of the “normal†.15 CDE mmc caps (I had them on hand) so that they won’t get quite so hot so quickly due to my poor-airflow layout.
One final note about the testing/ fine tuning – I was able to build this coil and get great results with only a multimeter (Of course you should follow Dan’s testing/tuning instructions with freq. generator and oscilloscope if you can), and I didn’t even use the same secondary. I used wintesla and javatc to match the required resonant frequency and coupling (by adjusting # of turns and height) with a slightly smaller than specified secondary coilform, and this was accurate enough to allow me to use the original primary specifications with no additional tuning.
Hope this helps, and feel free to ask any questions.
-Freddie
p.s. I'd like to thank Daniel McCauley for taking the time to design excellent quality boards and publish professional quality books enabling a sstc n00b like me to build such an awesome coil on a first try!
Thanks for the heads up! I just took a look at c101 on the schematic, and even though its in the schematic (but not on the board) I can see why it would be easy to miss. before i'm done building this thing i'm going to systematically check every part and compare them to the parts list to make sure that everything is there. those IGBT's are like $33 a piece and blowing up 8 of them can get very expensive.
My DRSSTC is starting to really come together now, I just ordered my 4" x 13" toroid and it should be here very soon. I'm excited because spun toroids seem hard to come by these days.
Again thank you for your suggestions, I would like to avoid as many complications as possible.
Registered Member #1169
Joined: Wed Dec 12 2007, 09:16AM
Location: Portland OR
Posts: 251
Wirenut wrote ...
Hi guys. I recently completed my miniBrute based DRSSTC built using EVR’s book and boards. This was my first solid state coil (I’ve built 5 sgtc’s). I was waiting to post until I had a few pics, but I don’t have a camera right now and figure you may be able to benefit from my experience.
First off, let me say that it was not easy, and I have a large collection of dead silicon (not because of any design flaws, but because of my mistakes), but I finally have it working right and I have replicated Dan’s 48†sparklength. There were times when I did not know what was wrong, and I was very frustrated at blowing something up every single time I turned it on.
One of the stupid mistakes I made was forgetting the 4.7uF decoupling cap across the power supply rails (c101 in the schematic). I think I missed it because it is on the half-bridge section of the schematic, but it is not part of the half-bridge board. I blew up 8 IGBT’s and 16 TVS’s before I figured out that I had forgotten a crucial part! Of course, I had to wait a week for it to arrive from Digikey.
Another thing was at some point, I melted the relay. This caused me to blow many TVS’s before I was able to figure this one out by checking the voltage at the bridge instead of at the power supply caps. Again, I had to wait a week for parts from Digikey.
Also, because of the way I laid everything out inside the base, my cooling fan did not supply adequate airflow through the mmc. They get very hot very quickly with no airflow, and as a result, I burned several up. An interesting thing is that I managed to partially melt a cap without knowing it and before I cranked the current up all the way. I could only manage about 32†sparklength with this partially melted cap, even after I cranked it up all the way. I had no idea that this was limiting my output until it finally failed completely and I replaced it. Sparklength immediately increased to 44†consistently with an occasional (once every 5 or so seconds) 48â€.
I now run 3 parallel strings of 4 series of the “normal†.15 CDE mmc caps (I had them on hand) so that they won’t get quite so hot so quickly due to my poor-airflow layout.
One final note about the testing/ fine tuning – I was able to build this coil and get great results with only a multimeter (Of course you should follow Dan’s testing/tuning instructions with freq. generator and oscilloscope if you can), and I didn’t even use the same secondary. I used wintesla and javatc to match the required resonant frequency and coupling (by adjusting # of turns and height) with a slightly smaller than specified secondary coilform, and this was accurate enough to allow me to use the original primary specifications with no additional tuning.
Hope this helps, and feel free to ask any questions.
-Freddie
p.s. I'd like to thank Daniel McCauley for taking the time to design excellent quality boards and publish professional quality books enabling a sstc n00b like me to build such an awesome coil on a first try!
Wirenut what did you use for your high current bus bar? sheet of copper? wires? if so what gauge. Also i would love to see some pics once you get a working camera.
Registered Member #141
Joined: Sat Feb 11 2006, 01:14PM
Location: Southern California
Posts: 96
Wirenut what did you use for your high current bus bar? sheet of copper? wires? if so what gauge. Also i would love to see some pics once you get a working camera.
I used fine stranded 8ga. wire that I purchased from a local car stereo shop. One of the reasons I like this type of wire is because it is very flexible. Lead length from the power supply caps to the bridge is about 4" on one side and about 8" on the other, so I imagine it's not the lowest inductance design, but it seems to work. As Steve W. mentioned above, this high inductance design may be the reason I was blowing IGBTs when I was missing the snubber cap. I also used this wire for the connections from the bridge to the mmc and also for the leads to the primary. This wire gets warm, but not warm enough for me to want to change it.
Believe me, I would love to post some pics, and will as soon as possible. I'll try to borrow a camera from a friend this weekend.
Registered Member #1169
Joined: Wed Dec 12 2007, 09:16AM
Location: Portland OR
Posts: 251
Wirenut wrote ...
Wirenut what did you use for your high current bus bar? sheet of copper? wires? if so what gauge. Also i would love to see some pics once you get a working camera.
I used fine stranded 8ga. wire that I purchased from a local car stereo shop. One of the reasons I like this type of wire is because it is very flexible. Lead length from the power supply caps to the bridge is about 4" on one side and about 8" on the other, so I imagine it's not the lowest inductance design, but it seems to work. As Steve W. mentioned above, this high inductance design may be the reason I was blowing IGBTs when I was missing the snubber cap. I also used this wire for the connections from the bridge to the mmc and also for the leads to the primary. This wire gets warm, but not warm enough for me to want to change it.
Believe me, I would love to post some pics, and will as soon as possible. I'll try to borrow a camera from a friend this weekend.
How much inductance is too much? Is that something i'm going to have to "tinker" with until things stop blowing up? I don't think McCauley actually mentions how he designed his bus bar. Is there an effective way to shield the wires from inducing currents in other components?
Registered Member #154
Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260
I used copper sheeting cut down in size, to connect my bus to my bridge on my last DRSSTC. I 'm not sure if my layout is as 'low inductance friendly' as it should due to my copper sheets not close to one another, but it seems to work fine, and no blown IGBT's yet (touch wood....lol)
Registered Member #141
Joined: Sat Feb 11 2006, 01:14PM
Location: Southern California
Posts: 96
How much inductance is too much? Is that something i'm going to have to "tinker" with until things stop blowing up?
I don't think so as long as you don't forget the snubber cap like I did. I think the rule of thumb is to try to keep the connections between the large electrolytics and the half-bridge as short as possible. I think to best way to do this is to put the caps and bridge head to head, but the caps I used were massive (nearly 1' long) so I had to put them sort of side by side with the bridge to get everything to fit inside the base.
Is there an effective way to shield the wires from inducing currents in other components?
I just used tightly twisted pair wires for the connections from the current transformers and to the gate transformer.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
wrote ...
No, id say Dan's design is over stressing the current capacity of the MMC, and adding more parallel strings was an appropriate upgrade. I could see problems if the MMC was enclosed and operating for hours, but if it needs a fan to cool film caps, that just sounds like too much dissipation in the capacitors for safe operation.
Actually, not correct on two points.
Firstly, the design of the MMCs in the miniBrute are not being overstressed during specified operational parameters. They are designed to be used with a cooling fan as described in the design. When used with the shown cooling arrangement, the temperature of the MMC capacitors are well within the temperature limits (derated) of the components.
Secondly, just because a fan is required doesn't mean the capacitors are being overstressed. Technically, the caps don't care whether a fan is used or not. All they care about is what temperature they are operating at.
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