Modifying ramp time in mains synced QCW

[dru]

Hi
In a mains synced QCWDRSSTC, is the max on time for the interruptor ~8ms? I wanted to increase the pulse duration, but since both the power supply and interruptor are synced with mains I don't know if it's possible. Would I have to completely swap the power supply circuit out for a buck converter to get longer ramps? Ideally I would want 20ms ramps, I guess I'm just wondering if there are any modifications I could make to the circuit I have before I make a new one.

[Hydron]

Uh, don't you mean max-on time of 4ms? I don't see how you can use more than a quarter mains cycle (ramp from 0 to peak of the sine wave).

If you move to 50Hz country you could get 5ms

[dru]

Uh, don't you mean max-on time of 4ms? I don't see how you can use more than a quarter mains cycle (ramp from 0 to peak of the sine wave).

If you move to 50Hz country you could get 5ms

haha yes I thought I put 4ms my bad. Yeah that's what I figured, I don't think there's much I can do other than build a QCW coil that runs on large dc bus instead of mains. I've been meaning to do that anyway. Interesting idea about lowering mains frequency, I wonder if there are any practical circuits that can do that I'll have to look into it. Each supply has its own variac right now, but both output 60hz.

[Max]

[...] lowering mains frequency, I wonder if there are any practical circuits that can do that [...]

Electrically? No, nothing simple. You'd need a VFD and then you're better off building a buck.
However, there is a mechanical solution that's pretty simple (and shouldn't be too expensive if buying used): motor, gearbox, another motor (generator).

Kind regards,
Max

[Rafft]

Hi
In a mains synced QCWDRSSTC, is the max on time for the interruptor ~8ms? I wanted to increase the pulse duration, but since both the power supply and interruptor are synced with mains I don't know if it's possible. Would I have to completely swap the power supply circuit out for a buck converter to get longer ramps? Ideally I would want 20ms ramps, I guess I'm just wondering if there are any modifications I could make to the circuit I have before I make a new one.

you got confused with stacatto-interrupted vs qcw.

they both operate by ramping the power supply. same principle, but are entirely different beasts.

stacatto interrupt relies on ac line freq(60Hz or 50Hz). you could get longer on-times with lower freq ie 50Hz. can get shorter and longer from quarter wavelenth to almost a half.

qcw on the other hand, has the variable ramp duration 1~20mS(or more). and does not rely on ac line frequency. what it gets from ac line, is charging the bulk capacitor(dc bus voltage) and chopped up by the buck to get a ramped DC power. and qcw electronics gets more complicated because of that 

there is a new video out there w/c shows how a qcw coil operates. better explanation than mine.

[Hydron]

[...] lowering mains frequency, I wonder if there are any practical circuits that can do that [...]

Electrically? No, nothing simple. You'd need a VFD and then you're better off building a buck.
However, there is a mechanical solution that's pretty simple (and shouldn't be too expensive if buying used): motor, gearbox, another motor (generator).

Kind regards,
Max

I wonder if you can make a ramp by using a motor-generator, with a separately excited DC generator being used to ramp bus voltage via field current control... (maybe totally impractical, last time I looked at rotating machines was years ago at uni!)

[davekni]

I wonder if you can make a ramp by using a motor-generator, with a separately excited DC generator being used to ramp bus voltage via field current control... (maybe totally impractical, last time I looked at rotating machines was years ago at uni!)

I suspect a larger (ie. 100A) automotive alternator could work through a rectifier bridge.  At high engine RPM they can output well over 100V.

[Max]

I wonder if you can make a ramp by using a motor-generator, with a separately excited DC generator being used to ramp bus voltage via field current control... (maybe totally impractical, last time I looked at rotating machines was years ago at uni!)

I guess you could...

Actually, one manufacturer of wind turbines used to do something like this. The generators had a three phase field winding. By providing that with an AC current of specific frequency, plus the mechanical frequency (rotation speed), they could always assure 50Hz output. The advantage is that they only need a VFD to power the field, instead of one for the full generated power. However, with VFD prices dropping, this model lost most of its competitivity.


Kind regards,
Max

[Mads Barnkob]

Line-synced "QCW" is limited by the relatively short on-time of the mains waveform. My DRSSTC4 was not really a success, due to this fact and also that without DC bus capacitance to supply peak current, it presented itself close to a dead short on the mains supply. It was pretty good at dimming light and destroying electronics with its transients

https://kaizerpowerelectronics.dk/tesla-coils/kaizer-drsstc-iv/

[dru]

Line-synced "QCW" is limited by the relatively short on-time of the mains waveform. My DRSSTC4 was not really a success, due to this fact and also that without DC bus capacitance to supply peak current, it presented itself close to a dead short on the mains supply. It was pretty good at dimming light and destroying electronics with its transients

https://kaizerpowerelectronics.dk/tesla-coils/kaizer-drsstc-iv/

/>

Yes I got similar results with mine haha, I've been through at least 20 pairs pf IGBTs despite many tests indicating the transistors were properly switching. I used TVS diodes and varistors in the circuit but even with those my fuses just kept blowing. I was suspecting it may have something to do with my larger variac, as it's connected directly to the circuit with no isolation. The smaller variac has a 12VAC isolation transformer. Although it was a cool project and I managed to get around 34" straight discharges, it really requires too much maintenance and luck for proper operation and I've spent too much time fixing it. I did look in to methods of generating lower frequency A/C, and I found some solutions but nothing really viable other than the gears. One was to just make an inverter that operates at a lower frequency, but pure-sine inverters are difficult to build and even if I did the max amperage may not be enough. I also saw some SCR circuits that required a complex control circuit, and I haven't worked much with SCRs so I trashed that idea. As for the gears and motors, I've been taking some time before I build the next coil to see if I can get a proper generator running. I'm limited by a few things: I am in an apartment complex so noise is an issue, I'm indoors so no gas powered generators, and I don't have an amazing selection of motors on hand. I do have a lot of stepper motors, which could maybe be used to drive a gear based generator if used unidirectionally. I also have dozens of smaller dc brushless motors, and a couple larger ones but these will only generate DC of course unless I drive them with an alternating direction (not sure that's practical given the gears are plastic and switching directions at high torque would probably annihilate them). I do have some microwave plate motors (synchronous), which I tested and were able to generate around 300vac, but they are quick to break if driven to hard so I don't know about them. I'm enjoying this challenge because I'm learning a lot about motors and mechanical processes which I usually stay away from, it's bringing back a lot of my high school physics knowledge. The other motors I have left to try are a couple of those ac fan motors with the huge coils of wire (I generally like taking this coil and winding a Tesla coil with them haha), I few universal motors from blenders, a beastly treadmill motor, and several large extruders, 2 stepper and one DC not sure what kind for inclining treadmill. In the long run I would like a nice isolated A/C supply, because I worry about the noise I'm sending into the mains lines and also as I mentioned I'm in an apartment building so I don't want to blow any circuits. I wish I had as much motivation on my college apps as I do for this haha. I'll probably start building a true QCW soon, so my focus will shift to that unless I make some progress on a generator. Thanks for all the advice everyone

[dru]

I'm attaching a link to a folder in google drive that contains some videos of odd behavior
I was observing from the coil leading up to its catastrophic failure. Some are from a month ago, so long before death but I did have to switch out driver circuitry and change coils, primary and secondary. Excuse the very random toploads.
The folder is large, the videos taken in red light are the most interesting. I'm excited to see what differences there will be with a true QCW coil. My theory for the chirps and wild discharges is that the antenna was malfunctioning or the control circuit was receiving multiple rapid fire signals in succession due to emf. I'll go through some of the videos and extract single discharges and slow them down, then upload those as well. Currently uploading over ethernet though it still says ~20 mins until they're all up.
https://drive.google.com/drive/folders/1Htzwx3LpMvtKuoW0uTBubvDszXDsh2hP?usp=sharing

[davekni]

Quite a list of motors.  None seem reasonable for QCW, however.  Need electromagnet field for ramp control.  If you can find an automotive alternator (perhaps used at a junk yard), one of your motors could be used to spin it up.  Alternator inertia would likely provide sufficient energy for a QCW ramp.  Spin-up motor could be smaller, just energetic enough to overcome alternator friction and drag and get it to high rotational speed.  Tread mill motors should have plenty of power for that.  Perhaps an old larger automotive pulley on the motor, standard automotive belt to alternator.

Or, with proper control, perhaps a encoderless brushless DC motor driver could be used to spin up the alternator directly, then disconnected before QCW ramp.