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Registered Member #4603
Joined: Wed Apr 25 2012, 07:33PM
Location: Austria
Posts: 159
Thanks!
Yes, of course.
I tuned the coil to the upper pole. Just moved the primary tab a bit lower to get a higher primary frequency and that forced the coil to oscillate to the upper pole. The frequency went up to >400kHz. The UD always showed the OCD LED running on such high frequencies. That was the main problem... I did not realize that the UVLO was the problem until i scoped the 24V of the UD board. The voltage dropped significantly. I added 6000µF to the 24V rail and set the UVLO to about 20V - then it worked Now i am going to build a casing for the coil so that i can run it outside with more power/longer ramptime and higher voltage on the bridge.
Hey fantastic job there and it looks like you’re getting about the same performance as my QCW was. I’m glad to see the QCW driver is working well!
As you have found, upper pole tuning works better for QCWs where the added streamer pulls the coil more in tune, as opposed to lower pole operation, though ideally I would run the coil with the primary tuned lower but driving at the upper pole. This is a bit difficult with the direct feedback UD driver without some modifications.
The wires and heatsink / heating are usually not a problem though especially in the low-duty cycle cases likeT what RateReducer and my coils are doing. This becomes much more relevant in high duty cycle operation, though of course some proper litz wire is always good. And as you found out, it wasn't the OCD kicking in but the UVLO due to the large drive required. The modifications I made to the UD2.7C were inspired exactly because of the UVLO and gate drive power required I was seeing in QCW use, though I wind my GDTs for +-20V operation just to reduce the total gate drive power required. I presume you are using the full 24V gate drive on your 8-bridge?
Looking forward to more sparks when you move the coil down to the floor! The composite photo of the sparks hitting the walls is very cool. Good luck!
Registered Member #4603
Joined: Wed Apr 25 2012, 07:33PM
Location: Austria
Posts: 159
Hi loneoceans!
Yes, there is huge difference between upper and lower pole tuning. Tuned to the upper pole the streamers are much longer but not as thick like on the lower pole tuning. I use 24V, yes. With the added electrolytic caps and UVLO adjusted to 20V it works. A casing for the coil is in the works The casing will consist of 4 levels. The cap(s) for the buck will be 30.000µF @ 400V - that should do ^^
Registered Member #4603
Joined: Wed Apr 25 2012, 07:33PM
Location: Austria
Posts: 159
Made some progress on the casing.
I am worried about the distance primary - bridge and GDT. Is the distance shown on the 2nd pic to close? Now i am still able to move the last plate, the threaded rods are not cut yet. I just want to keep the casing as small as possible...
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RateReducers QCW DRSSTC
