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1
Hobby Sites / Re: Ultra High Voltage Lab (UHVLab) | website | youtube
« Last post by AstRii on Today at 09:33:18 PM »
Very cool, i dont have mysite fully up either.

Thank you, glad you liked it!

I stopped spending time on developing my own websites and just use Wordpress, gives me much more time to work with the electronics and there is always a plugin or theme for the features you want, like mobile friendly site

Hey Mads, I actually use Wix.com, I would never find the time to write the HTML, css, js and PHP and who knows what else.. Wix also allows you quite easy editor to create mobile friendly site. I will definitely make it more responsive soon.
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With the width of your bus bars you could probably increase the spacing quite easily by drilling one of the mounting holes off-center. That would allow you to move the bus bar on the outer terminal further out, increasing the spacing considerably.

You will also need a pre-charge resistor for the dc bus. The inrush current of charging up such a large capacitance directly from the mains is massive, and will very likely cause problems.

I also think that a 10A breaker for such a high power coil is a little small. I managed to trip the breaker on my 3 phase 16A outlet in a matter of seconds with my skm400 coil and I suspect your inverter might do the same :)
And a type C breaker won't help do mucht to protect the semiconductors. if anything goes wrong the bus capacitance is likely enough to kill them by it self. I'd recommend just not installing a breaker on your coil directly, since all it would protect is the cabelling and that is already protected by the breaker in the distribution box.

Thanks TMax that's actually a good idea, I'll take note and see what to do when my fat heatsink arrives. Actually the holes are already off-center but I forgot that the widht of the busbars was changed last minute bruh :(

For the circuit breaker it's true that it doesn't add a lot of protection. I think I will go with the 10A one for the test phase and that evaluate to skip it when everything work as it should if necessary.
 
I agree with you about the pre-charge resistor, there is no way it will work if I attach it to 400VAC directly. For now I will be using a variac to be able to run it at a lower bus voltage. When everything works I will put 3 pre-charge resistors that get shorted after some seconds by a relais and regulate power via on-time.
3
Voltage Multipliers / Re: My Switches Don’t Switch
« Last post by abstruse1 on Today at 07:51:08 PM »
Vtroxi, thanx for your elaborate explanation of what I need to do.  I'll have to read it carefully since some of it is over my head, but I can probably figure a lot out.  Stay tuned.
4
With the width of your bus bars you could probably increase the spacing quite easily by drilling one of the mounting holes off-center. That would allow you to move the bus bar on the outer terminal further out, increasing the spacing considerably.

You will also need a pre-charge resistor for the dc bus. The inrush current of charging up such a large capacitance directly from the mains is massive, and will very likely cause problems.

I also think that a 10A breaker for such a high power coil is a little small. I managed to trip the breaker on my 3 phase 16A outlet in a matter of seconds with my skm400 coil and I suspect your inverter might do the same :)
And a type C breaker won't help do mucht to protect the semiconductors. if anything goes wrong the bus capacitance is likely enough to kill them by it self. I'd recommend just not installing a breaker on your coil directly, since all it would protect is the cabelling and that is already protected by the breaker in the distribution box.
5
Hi to everyone, hope you are all doing well,

I'm now in the process of building a new DRSSTC and I have a question about my inverter design.
My inverter is based on two GD600HFY120C2S, see datasheet in attachement, running at around 560VDC from 3 phase supply. For the bus capacitance I'm using a 2s2p configuration of 4700uF 400VDC caps. The input of the 3 phase 80A rectifier is protected by 10A type C circuit breaker for added safety.

The gap between + and - it's now 2mm, this is okay for 560VDC but I was wondering if this could be a problem because of transients voltages.

If a transient comes it will be limited at the voltage necessary to fill the gap between + and - . In this way I can protect my IGBTs, maybe at the cost of loosing my 3 phase rectifier but it's cheaper and easy to change. The problem is that in this case the arc will also make the bus caps discharge and I have the feeling that is is not good and could kill the IGBTs in some strange way   :(

I'm now trying to decide between leaving it this way or putting a insulator layer / milling away some copper to enlarge the space between rails.

What do you think will be the better solution ?

Here is my Inverter so far, it's still missing the heatsink:




I also  made a small and simple circuit to safely discharge the main caps. The basic idea is to have an emergercy stop switch that will both open the 3 phase supply and put a power discharge resistor between + and - , this will also work if the 230V driver circuit it's un-plugged.

You can check it here:
6
Few months ago I had to fix one of my Tesla coils but during the repair I realized that I've never wrote down any details about the build. I found myself thinking "why did I use this? and why did I built it this way?". I completely lost track of my build. So I decided to document everything I do, so that in the future I will be able to track down my progress and my decisions while building some electronics project. I realized that making a website is probably the best way to document my work, as this can also serve as a "guide" for others.
I always wanted to share my knowledge with other people. I always enjoyed writing educational texts and scripts. This website is making it possible.

Any feedback is appreciated!

note: I haven't yet designed the website for mobile phones, but it is on my to-do list.

This is also the same reasons that I started my website, to document for myself and share my experiences with others. All I learned was from other amateur websites or forums, so its all about sharing :)

I stopped spending time on developing my own websites and just use Wordpress, gives me much more time to work with the electronics and there is always a plugin or theme for the features you want, like mobile friendly site
7
Electronic Circuits / Re: Problems with Franzoli electronics' easy flyback driver
« Last post by futurist on October 25, 2021, 07:14:25 PM »
Hi and welcome to the forum

Please read forum rules before posting
https://highvoltageforum.net/index.php?topic=31.0

In order for someone to help you please show you have done some troubleshooting on your own and provide more information about your circuit, like photos of the circuit and scope shots
8
Electronic Circuits / Problems with Franzoli electronics' easy flyback driver
« Last post by Anon_v3 on October 25, 2021, 07:01:28 PM »
Made the circuit on a pcb and everything works but the audio modulation part. When I bridge the test jumper I get gnarly arcs from the flyback but probing the lm311 with my scope the audio signal seems to me nonexistent. Link to the schematic is below. Anything wrong with it or is it my mistake?
https://franzolielectronics.com/easy-flyback-i/
9
Voltage Multipliers / Re: My Switches Don’t Switch
« Last post by Vtroxi on October 25, 2021, 04:38:37 PM »
Hi,

Your problem is caused by your lack of a decent driving circuitry for your IGBT.
A function generator cannot provide enough current to quickly charge the gate of an IGBT.
When you are trying to switch at several kHz, the transistor is most likely not really turning on at all.

What you need is a so called gate driver. This is a circuit which acts as a current amplifier to charge
the gate in order of a few microseconds or even nanoseconds (the necessary rise time of the gate voltage depends on your switching frequency but it should generally be as fast as possible).
This gate driver can be realized as a push-pull stage with a NPN and PNP BJT transistor or you can simply use one of the many available integrated circuits, which are very easy to use (IXYS has some quite powerful ones, capable of up to 20Apk of charging current - that's probably a bit overkill for your project :D ). They usually feature an input with a specific hysterieis - this means that any voltage in a given range is enough to make the output of the driver turn high (most of the time a few volts is enough).

A gate driver IC also needs a ceramic filtering capacitor (~100nF) across it's supply and ground pin.
This filters the HF currents that the IC is drawing in operation.
In addition to that you should add a small resistance like 2-10 ohms in series with the IBGT gate and the output of the gate driver. This limits the charging current and helps to reduce unwanted oscillations of the gate signal.

When you are only planning to use one transistor, you should use it as a low side switch, meaning the emitter is connected to ground, the supply is connected to the (+) connection of your load and the (-) connection of the load is connected to the collector of the IGBT.
The signal output of the gate driver goes via a gate resistor to the gate and the GND pin of the gate driver is connected to the emitter.

The advantage of a low side switch is that you can use an unisolated driving signal with ground reference.
(High side switches require more complicated concepts like bootstrapping, isolated power supplies or gate drive transformers...).

Another important aspect is the gate voltage. Most gates of IGBT bricks should be switched at around 20V which is is also the input voltage of your gate driver.

And one last thing: you said that you are planning to switch a transformer.
Because a transformer is an inductive load, you need to protect your transistors against high voltage spikes which can appear at the inductor turn off.
This should be accomplished by snubber networks or simply snubber capacitors.
Snubber networks consist of a series resistor (which is sometimes left out) and a capacitor.
These absorb the voltage spikes and protect your transistors.
There are also lot of guides on snubber design online.

I hope I could help with my explanation.

Best regards,

Vtroxi
10
Vacuum Tube Tesla Coils (VTTC) / Re: Mains Staccato / T-200 VTTC
« Last post by 304er on October 25, 2021, 01:58:47 AM »
Hi Duane,

Thanks again.
Yeah this old fella does pretty good. It actually has a very inefficient primary, but does pretty good as is seen. That said, tuning...tuining....said twice on purpose is key despite other problem areas of this coil design. Getting the grid leak set up was very challenging on this fella while also getting the tank capacitance right at the same time. Dozens and dozens of trys changing things.

That said, why one would not design new better primary and this includes feedback...well for nostalgia sakes for me here :^) And actually...I enjoy a good challenge...

I like the some old with new here.

Oh...the flashing on the transformer is on some threads sticking out from the core clamp bolts. I have wrapped one wire lead to this which the whole core is grounded and bent the other wire lead straight up the side of the little neon bulb as a little antenna for my fun little RF detector.
I do something similar on my 304 VTTC also, which is a "green" neon bulb.

Mentioning my 304, this coil now has always been about getting better, good efficient design.
That said tuning is still very challenging to getting right.
Not sure if you have seen the other videos of it yet, but it "uses" at times most of the yard stick hanging behind it. Pretty good for just a single MOT and a single tube and no over voltage input. Using 120v in to MOT.

Oh... the very temporary 27" was achievable because of the vacuum variable capacitor this has in parallel with the 2 mica tank caps.
I had extra wiggle adjustment left to put on more proper capacitance needed using this VVC.

Chris Reeland
Ladd Illinois USA

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