Donald Smith Devices too good to be true

[Wistiti]

HR8503.

If correct rated for 51.1kV

Open file on new tab.otherwise it is black.

do you mean the hr8503 is the same as my tfb4100ad?

if so 51,1kv is really nice!!!

i'll give it a try. thank you for your help and the nice diagram!

[Mwtj]

HR8503.

If correct rated for 51.1kV

Open file on new tab.otherwise it is black.

[Wistiti]

flyback

@Mwtj can you please tell me to what kv the TFB4100ad is rated for? It seem to be bigger than the one I currently use... I think to change for this one if the spect are ok.
Thank you

[Wistiti]

OK, latest build progress. How to mount the meters: go vertical! This took me more hours than I intended to fabricate, but it works. Still have to mount the meters on the HVM board. Also, having the metal rod this close to the HV section is not good. I need to get some nylon fasteners and threaded rod instead, it exists but not at the local hardware store....

Nice and clean build!
On my side I just came from the store with some cutting board.

[tswift]

OK, latest build progress. How to mount the meters: go vertical! This took me more hours than I intended to fabricate, but it works. Still have to mount the meters on the HVM board. Also, having the metal rod this close to the HV section is not good. I need to get some nylon fasteners and threaded rod instead, it exists but not at the local hardware store....

[dragon]

TSwift said; "I think maybe you're thinking of a crowbar circuit"

Your right, my bad... split focus... that's what I get for mixing my projects with others - I'm dealing with high amperage output conversions using 350 amp 1000 volt IGBT's...

I tend to pop in and out of the forum when I get stuck on a problem to divert my attention away from the problem. Sometimes things can be seen more clearly by not looking directly at it.... anyway, I should probably refrain from posting without a clear view of the overall conversation....

Edit; On another note, I've used 8ga 700 count speaker wire for 100kv + projects with great success, I wouldn't be afraid to experiment with it.... expecially for high amperage outputs....

https://www.youtube.com/watch?v=V4l1IJJgjNc
https://www.youtube.com/watch?v=3t4pZpKSpP4
https://www.youtube.com/watch?v=WBpUSDZ3CmQ

[tswift]

Don't use speaker cable for secondary.
Stick to HV wire!
It won't get hot!

OK, not planning on changing anything. I remember what happened last time I tried to substitute wire....

[tswift]

Hopefully getting close to a workable version of the shunt regulator circuit. I changed the transistors to darlington pairs. Making the assumption that all of them are 3055's, the two being driven by the zener directly are running at about 1A collector current and the other two are running at about 11A current and about 85W. The 0.5 ohm resistors dissipate 77W. I have some 100W 1 ohm resistors on order, I can parallel these for 0.5 ohms and suitable power handling. Now the zener current is down to just over 100 mA and a 2W zener should do ok, I have some 12V 2W zeners on hand. So I think this configuration will work, I will make a breadboard version and test it.

[tswift]

Again load the file. Takes a while to charge the Caps. Adjust the speed of the simulator.

Circuit Simulator Applet

Man, that circuit simulator is dynamite! I can't believe I didn't know about that before. Anyway, you have the idea basically correct but I corrected a couple of things. I adjusted the connections to the transistor emitters, they go to ground. The whole shunt regulator literally just sits across the cap bank and shorts out excess current. I also changed the voltage source to 20V and the series resistor to 0.25 ohms. Yes the cap bank takes a large amount of time to charge when you start the simulation, this is not unlike real life when you're charging them from a small bench supply. The RC time constant is (83F * 0.25 ohms) so about 20 seconds. Go get a cup of coffee while the simulation runs. Sure enough, after about 20 seconds of simulated time, the voltage on the cap bank gets close to 12.8V and the transistors begin to gate on. If you let it continue to run it reaches a final steady-state where all the current is going through the two transistors, 13.71A each. The final voltage across the cap bank is 13.08V.

I wouldn't consider this a final circuit just yet. The zener current is not realistic, I know from experience that big power transistors like the 3055 have a very low current gain (more like 10-20) than the 100 shown in the simulation. This will burn up the zener diode. I'm sure there are other better transistor choices but it's easier to just add another NPN transistor to each one as a darlington pair. That will add another diode drop (~0.7V) to the voltage but that shouldn't really matter, it will greatly reduce the necessary base current that the zener has to supply.

N.B. to every experimenter: if you don't already have this book on your bookshelf, you are making a BIG mistake. No other source I have ever found does as good a job of explaining basic circuits all the way up through how transistors really work, into digital logic design. It's well worth your time and money.

https://www.amazon.com/The-Art-Elect...=maggicom0e-20

[Wistiti]

Sadly, yes wood conducts much better than you would think. At low voltages 12V up to house current 120V/240V it's not enough to matter but as you reach tens of kilovolts it definitely does matter. You need some kind of plastic or ceramic material. Sadly pretty much all the substitutes cost more and/or are harder to work with than wood. You can use a wood baseplate and build upward from it with good enough insulators like Mwtj is doing. You might try using a non-conductive baseplate like a big HDPE (polyethylene) kitchen cutting board. You can get these up to maybe 18x24 inches in size and at least 1/2 inch thick. Then you can drill holes in it just like wood to mount your components, that should work OK for minimal cost. I like acrylic because it also looks good and has desirable properties at HV/HF (high dielectric strength and low dissipation factor), but (A) it's expensive and not available at your local store like a cutting board and (B) it takes a lot of time and care when constructing to make sure it looks pretty when you're done. So probably I would suggest polyethylene cutting boards, you could use one big one, or if all you can find are smaller ones, use a bigger wood backplate and mount the smaller HDPE cutting boards on it, even better would be to use standoffs so there is an air gap of 1 inch or so between the wood and the plastic boards. Divide your circuit into components (the HVM driver, multiplier, PPV's, and LV section) like I have done and mount each part on its own cutting board. As long as there is 1/2 inch of polyethylene between the wood and anything with HV it will probably work OK at voltages up to maybe 100KV. Adding a 1 inch air gap and ensuring at least 2 inches between any HV surface and anything metal or wood should let you get closer to 200KV.

thank you for the hint Twsift! Maybe it is the reason why my side seems to not produced so much hv...

I'll have to go shopping for some cutting board!

[tswift]

Mwtj, Tswift, What have you experienced with wood as the support of the project? Does it conduct the hv?
What should I use instead?
thank you!

Sadly, yes wood conducts much better than you would think. At low voltages 12V up to house current 120V/240V it's not enough to matter but as you reach tens of kilovolts it definitely does matter. You need some kind of plastic or ceramic material. Sadly pretty much all the substitutes cost more and/or are harder to work with than wood. You can use a wood baseplate and build upward from it with good enough insulators like Mwtj is doing. You might try using a non-conductive baseplate like a big HDPE (polyethylene) kitchen cutting board. You can get these up to maybe 18x24 inches in size and at least 1/2 inch thick. Then you can drill holes in it just like wood to mount your components, that should work OK for minimal cost. I like acrylic because it also looks good and has desirable properties at HV/HF (high dielectric strength and low dissipation factor), but (A) it's expensive and not available at your local store like a cutting board and (B) it takes a lot of time and care when constructing to make sure it looks pretty when you're done. So probably I would suggest polyethylene cutting boards, you could use one big one, or if all you can find are smaller ones, use a bigger wood backplate and mount the smaller HDPE cutting boards on it, even better would be to use standoffs so there is an air gap of 1 inch or so between the wood and the plastic boards. Divide your circuit into components (the HVM driver, multiplier, PPV's, and LV section) like I have done and mount each part on its own cutting board. As long as there is 1/2 inch of polyethylene between the wood and anything with HV it will probably work OK at voltages up to maybe 100KV. Adding a 1 inch air gap and ensuring at least 2 inches between any HV surface and anything metal or wood should let you get closer to 200KV.

[soundiceuk]

Basic circuit corrected.

[Mwtj]

It's really simple, I pretty much described it. Even the base resistor is essentially optional. External pass resistors would go between the transistor collector and +V, and should be suitable resistance and power dissipation for the application. In this case, at 12V the desired dissipation might be 30A, so Ohm's law means we need 0.4 Ohms resistance and 360W power handling. Of course all the cables and connectors need to handle 30A as well, and the traces on the PCB need to be very beefy and probably solder reinforced.



Full discussion:
design - High power equvalient for a zener - Electrical Engineering Stack Exchange

For even more power dissipation these could be made in single 30A modules, like a brick. Just parallel multiple units to reach the desired dissipation. Designing a PCB for it would be great!

Again load the file. Takes a while to charge the Caps. Adjust the speed of the simulator.

Circuit Simulator Applet

[soundiceuk]

Don't use speaker cable for secondary.

Stick to HV wire!

It won't get hot!

[radioionics]

Well, I have to find another flyback. Mine seem to not output enough. If someone have a suggestion for another easily available hv source im all ears open. I have another Tv to dismantle...

Bruce I see in your last schematic you use lithium battery instead of cap... witch kind are them?

Thank you!

LiPO lithium ion | eBay