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Are you sure? This is basically describing what I initially thought would happen until you stated otherwise:
Reasonably so. The "corrections" I made were due to the wrong assumption of switching between +170V and -170V rails.
Kizmo wrote:
Interesting thing is that the primary current can be larger than this math suggests too. All depends on your load conditions and tuning point. I think under some conditions the secondary can back drive the primary resulting higher currents.
The only condition I can think up for this is a short cut secondary. That would not cause any losses but reduce primary inductance, i.e. higher primary frequency. Cycles are then shorter and rampup is faster. It is a small effect since coupling is low. A sensibly tuned secondary which isn't short cut avoids this.
Registered Member #599
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
Something like this happened when i first ran my big coil. More than likely the tuning was way off but with secondary in place i was able to trip the over current protection which did not happen when i tested it without secondary.
Who knows, might have been something else too.. :)
Hey everyone, hope you don't mind the slightly necropost. I do have new content to add though, I'm quite happy to announce!
I've been studying C++ programming lately and have learned enough to write a basic calculator program for the formulae discussed in this thread. I've tested it on all my PCs, which are windows 7 and 8.1, so I cannot guarantee that it will work on any other platform or OS. Please let me know what you think.
Here's the link to download the .rar EDIT: Fixed the link, now points to the correct release file! Sorry folks!
Just for reference; here are the formulae I used: Ipk = V / (2Pi * Lpri * fres) N = Vlimit / Vbus (half bridge) N = (Vlimit / Vbus) / 2 (full bridge) Where: N = number of switched half cycles. Vlimit = chosen peak tank voltage.
Registered Member #3704
Joined: Sun Feb 20 2011, 01:13PM
Location: Vermont, U.S.A.
Posts: 92
That one works much better Sigurthr, thanks! Now I've got a stupid question: How would one determine the percentage to derate their capacitor by? Guess I'm not quite sure how to figure that out in this case.
Regards, Matt
EDIT: I just assumed 60% for sake of argument and got the following for my Tesla coil:
Seems legit to me! Thanks a lot, this will help a lot!
It's just an amount you want in the voltage overhead for the cap. I use 10% generally, but it really depends on cap type. If your MMC is rated for 30kV then you could probably go to 5% as that would leave 1500V overhead.
The reason I put the figure in there at all is that it is an easy way to adjust the outputs of the program without changing multiple inputs. For example: if you put in 0 derating and it says you can't run more than 500uS bursts without exceeding the cap rating, but the peak current is well over what your bridge can handle, for example maybe 1200A, you can re-run the program with various derating factors to find a new maximum usable burst length that doesn't exceed your bridge's current capability.
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DRSSTC Peak Primary Current formula?
