Electronics > Projects, Designs, and Technical Stuff
Jet engine Ignition system Build with LT375 / TL494 / ZVS driver Lockup
Amper:
The IR2153 looks really nice! Iwill definetly get some and play a little.
@alsetalokin4017
Yes, its for boosting 24V system voltage to 2kV for igniting the engine.
I know how oscillators and half bridges work or i would have posted this in the beginners section. 555 and cd4093 ar not ideal at all here because i dont have an ignition coil style of transformer that is happy to be driven by only one transistor. I need resonance by push pull or it will not deliver enough power through the small transformer. Thats not really possible when talking about fixed frequency generators like the 555 that maybe wont even ave nice 50% duty, so id have to go through another bunsh of logic gates and a gate driver at least which will make things much more difficult then needed. In that case using dedicated chips like the 494 would be a much better choice and thats what im planning atm since it will give me voltage and current limit as a nice bonus.
Heat sinking was not necessary with the zvs up to over 100W of input power the TO220 has enough sink for the tiny amounts of power lost in modern low resistance fets. Thats why i like the idea so much, switching wit non resonant frequency will increase losses significantly.
Mine is adhering to all your criteria but still locks up. I have very good foil capacitors, short distances to the transformer, all wires are the exact same length, all parts are even from the same lot. Very low impedance did not have any effect in my case, i had induction heaters not start to oscillate even though they were made with copper tube and proper induction capacitors. The problematic thing is the hard turn on which might be no issue when you operate the thing by hand, you have a regulated power supply coming from the grid that is very predictable and when something goes wrong you just try again. In my case i have two of them sitting on the side of a jet engine with pumps, sensors, starter motor, ill wear ear protection and have to monitor all kinds of things, i cant afford to care about two zvs driver starting up or not because maybe the battery supplying them is not at the right voltage or impedance. in ccfl inverters its also no problem to get them running, i never had them lock up ever. There must be some thing that can be done passively.
Attached is a screenshot of what im planning as a backup right now. Obviously the layout is not done yet, just routed roughly to see if i can fit it all on a single layer aluminium pcb.
TurboTom:
Hey nice job and very good firing rate.
Are you using it on a TS-21 JFS? The original exciter box provides much less energy than your proposed 2 Joules, maybe 1/10 of that. I'm not sure how long the original spark plugs will do under these circumstances.
Having a lot of experience with high energy ignition exciters myself, I'ld recommend to either find a proper switching spark gap tube or utilize a semiconductor switch for the high voltage (several SCRs in series with a trigger transformer perform quite well). My own experiments with these surge arrester tubes (even the bigger ones) proved mediocre at best. Apparently the gas in these discharge tubes gets trapped in the electrodes, reducing pressure and thus ignition voltage within comparably short periods of time. This means, at a constant charging rate, spark energy decreases and firing rate increases.
I haven't got any experience with these ZVS drivers to power the step-up tranformer. Since the ignition exciter usually has to operate over quite a considerable range of supply voltages (while the starter motor is energized, it pulls down the battery voltage to 10V easily on a 28V system and a cold battery), I prefer a current-control flyback topology with charge voltage limiting. This, combined with a semiconductor switch and a high-current series ignition coil fires any spark plug at very high efficiency.
If you'ld like to experiment with the mentioned concepts a little bit, I may be able to provide more in-depth information.
Cheers,
Thomas
Amper:
Oh wow, i didnt expect to run into someone who knows this stuff this exact ;D
Yes, its for my TS-21 in case you havent yet you can look at one or two of my other videos on youtube to get an impression of what im trying to do.
I played around some time with smaller capacitors but i didnt expect it to require so little energy considering the insane power of whats shown on you tube. Also there is manufacturers of modern ignition systems ranging from 1J up to 12J so i thought i was in a good region. Though the way im doing it is definitely a problem in the way of having to high currents flowing, the spark plugs dont show signs of erosion yet but i guess if i used my system extensively i might have to change some things. Using an inductive coupler would be nice but im afraid tit would be very heavy and bulky. The purpose of my project is to make the entire system more light and modern wich is also the reason for mounting the ignition boxes directly to the combustor casing. If i used something similar to the original one it would cost me in the range of 1-2kg which is not acceptable.
direct switching would be a next step, maybe even using mosfets but it will not be easy driving the gate at such voltage levels and transitions though in that case even pulse shaping would be possible.
Im very interested, if you can tell me more please do so!! ;D
Grüße
Berni:
The ZVS circuit is indeed a very good and simple way of driving a transformer at pretty high powers.
One way to get around the startup problem is to power the resistors that go to the MOSFET gates separately. So you can have your main supply ramp up slowly and once that's up to voltage you suddenly apply voltage on the gates and it kicks in. Alternatively you can apply power to the resistors first. This causes enough power to move across the diodes to start the oscillator up, but can't blow it up as the resistors only provide limited current. Once its already oscillating you can ramp up the main supply as slowly as you want, you can even ramp it up slowly from 0V with a variac and it will just simply provide more and more output power as you turn it up. Its ramping both the gate supply and main supply slowly that kills the transistors.
As for it stopping osculation that is likely because your sparkgap firing loads the transformer too suddenly. The inductor limits how much power can enter the tank circuit in an instant, so when you suddenly short the transformer you suck all the energy out of the oscillating LC tank circuit and so leaves it with no energy to continue oscillating. To fix that you want to add leakage inductance to your transformer. This can be done by correct transformer design or by adding an additional inductor in series between the transistors and the transformer. This inductor will store some extra energy that can't be sucked out by the transformers secondary coils, so there is always some energy left to keep the tank circuit oscillating.
Many people build these ZVS circuits without actually understanding how they work.
Amper:
I like the additional inductor idea, i think ill give it a go tomorrow. Yes you are right, not many actually know how it works but also it is a lot ore difficult to understand then it looks at first glance. I know it for over a decade now but usually its just "yay it works lets make arcs!"
EDIT: Also i attached an image of my current approach sadly i dont have any tl494 on stock so ill have to wait before finding out what mistakes my layout has ;D Also i dont have a god way of dispensing solder paste so its not the prettiest job i guess.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version