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Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Here are my plans:
First I’d like to try audio-modulated 450W ClassE SSTC. The audio modulation will be based on modulating the main power source (I do not care about the power consumption) which I think should make the best quality sound. The coil at the moment is powered by 50Hz (220VAC) which is very nicely and loudly reproduced. The plan is to make a simple amplifier 10Hz-20KHz providing same voltage and at least 400W and connect it instead the wall AC. Check the movie for the 50Hz sound...
Next I plan to increase the power consumption to at least 2KW (by adding more motor caps). I already performed few experiments with high power (max 1000W) some time ago (my previous posts) but with different primary and out of tune. Now I made a new primary and improved the tuning (using 70nF resonant cap) and the pictures and the movie show my latest 450W model in action. For the 2KW experiment I'll have to make some chnages regarding the TVS cooling.
The weakest point in the construction are the TVS. When the coil is tuned properly than the heating of the TVS at 450W is relatively low (you can easily keep them only warm by a small fan) but if out the tune they are the most exposed parts. I use 10x2-in-series uni-polar 440V 5W TVS. For the 2KW project I plan to use another 10x2 and maybe I put them into oil bath like I did it already before.
Here is the movie with 50Hz sound:
Here is my latest scheme of 450W model, picture of the gate IGBT driving pulses (must be as short as possible!) and few pics of the 450W coil in action
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
I see nobody likes me…
But anyway, I’ve made some progress regarding the Ghetto I. I finally achieved what I thought is impossible. The TVS are keeping the RT even after 5 minutes of run. The double BUP314 also does not know is alive and both without the fan running! The main change is that I played with the coupling by shifting the primary little bit up. I’m afraid of going higher, at least not until I have the protection plastic disk there. (Last time when an arc strikes the primary my HV diode protecting the transistor died). But it does not seem necessary anyway, because almost all the energy is now processed by the coil. I’ll start adding new motor caps this weekend and increase the power to 1000W. I also designed the audio amplifier based on my NPN high voltage TV screen transistors so hopefully the audio modulation will work…
Now few more pictures of the construction and the sparks of course…
So this 450W and plan 4 times more!
this is just a funny picture of a flower on the topload which is made by overlay of two photographs before (light) an after the coil is on (dark with sparks). BTW: the flower burned completely after few seconds...
Registered Member #538
Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181
I dont think you are running in class-E. Your schematic is also very confusing because its hard to make out which crossing lines are connected and which ones are not.
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
jmartis wrote ...
What is the purpose of the diode IN SERIES with the igbt and the capacitor in parallel with the diode?? IMO they do nothing, just waste power.
That's a good point. It was ment as kind of spikes buffer helping litle bit the transistor. But most likely it is a nonsence which can be removed from the circuit...
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
New progress: Today I add a protection disk from an LP (following the ghetto style ). I had to build a resistive cutter first to cut the hole inside. It seems it works fine, so I could increase the coupling again. I also add another 25uF cap and increased the total power of the coil. The TVS are still only warm and the whole construction is amazingly robust even if put different things on the top capacitor which usually shifts the resonant frequency.
I was also thinking of different type of audio-modulation before I finish the big amplifier. Actually I would need some help with this: The idea is based on strange behavior of my coil. When I increase the PW I’m decreasing the power of the coil (it is exactly opposite how the bridge concept respond) Just to make it more clear - it means that how shorter are the pulses so bigger are the sparks! So my point is to drive the PW by “inverted†audio-signal in a limited range (1-3us). Do you guys have any idea how to do it? It would be great to keep the TL494 for this kind of PW modulation.
Here are some pictures of the protection LP disk and sparks with increased coupling and power…
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
PWM and Class-E don't mix...
And I'm worrying that with a very large breakout from the coil, the Q may suffer so much that maintaining class-E operation would be quite impossible... I'm also worrying that at such a low frequency, Class-E is pointless, and a halfbridge would be more rewarding.
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Ghetto I (450-2000W Class "TVS" SSTC)
