Homemade Capacitors ~50kV

[Krumlink]

mickey mouse capacitors?!?

I just want to know how to test my 500pf caps in somthing that I can verify easily. I need to test 20 of them...

 

[Sceadwian]

You really should try glass bottles. Go buy a six pack of beer (or soda) and clean them out real good afterwards. Never done it myself but I see people using those kinds of capacitors on the net frequently. Glass is a significantly better dielectric than plastic.

 

[kchriste]

You really should buy some proper high voltage caps:
https://www.electricstuff.co.uk/marxgen.htm
This guy has a pretty detailed site, but don't forget:
BE VERY CAREFULL!

 

[Krumlink]

Thats where I got the schematic from! Ive searched that site through and through!

Im underage! I cant buy beer! I Cant drive either!!!

 

[Krumlink]

Also, I have decoded my Transformer's coils. It says I need a 18kHZ signal for my xformer. Do I have to have this? I dont want to build all that, I just want to hook my xformer up to some Voltage and at least get that firing...

As a last ditch effort to get 10kV, what kind of transformer is this?
**broken link removed**
Its labeled as T1. What pinout/what can I get that from or one like it? I have a monitor circuit board, so I should have somthing like that in there.

 

[Oznog]

No kidding. The cap's only rated for a few hundred volts at most. I wouldn't be surprised at less than 100V.

More of a point, a cap with air in it will break down quickly. Air breaks down into a corona at high voltage or high dV/dT rates. That corona will chemically and or thermally destroy the saran wrap. You try to generate a pulse with a Marx generator and you can expect it to break down on the first shot... well it's not going to make it to 50KV in the first place.

 

[Oznog]

That transformer is used all the time in zenon camera flashes.
Can put out like 300V at very low current.

Are you seriously trying to get 10KV out of plastic party cups? I haven't seen your cups but I doubt they'll hold that.

 

[Krumlink]

I redesigned the capacitor to use polystyrene after I looked at its breakdown voltage. Go to Homemade caps not working. I wana only have to look at one thread

 

[Krumlink]

The site I got the idea off of said that he got them up to 33kV before they broke down. I still cant get it working. Any more tips?

 

[Nigel Goodwin]

Should have keep your CRT and used that!, they make a nice high voltage capacitor between the aquadag and final anode - I've known them hold their charge for over five years!.

 

[JimB]

Should have keep your CRT and used that!, they make a nice high voltage capacitor between the aquadag and final anode - I've known them hold their charge for over five years!.

The same idea occured to me. They would make excellent capacitors.

JimB

 

[Krumlink]

I cant figure out how to hook up my flyback transformer. Any help and tips?

 

[Nigel Goodwin]

I cant figure out how to hook up my flyback transformer. Any help and tips?

You need to essentially duplicate the drive circuit in the TV, a high frequency (15,625Hz for 625 lines), high voltage, switching circuit - with the transformer (and load) tuned correctly.

How are you trying to connect it?.

 

[Hero999]

For some reason my 500pf homemade capacitors are not holding their charge once charged. What is the reason behind this? They are made out of plastic party cups with aluminum wraped around the out side. They are then put into another party cup that is also aluminum wraped but the lead facing the other way. They are then put into another party cup to insulate the outside. What is the problem?

Perhaps it's sparking through?

That would make sense, we did try to tell you that this isn't a good idea.

You could try immersing the whole thing in transformer oil.

 

[Krumlink]

I went to my local TV repair guy and he helped me find the HV coils and HVGND and stuff. We also found a driver circuit that will run the transformer.

They arent holding charge, because they are discharging into the air, so I have to either create a vacuum or fill it with a dielectric fluid (any suggestions as to what fluid? I was going to use Mineral oil)

 

[Krumlink]

This is the transistor I am using:
**broken link removed**

That should work when substituted with this schematic right?

Also, THe IRF830 is a N channel MOSFET, while the C5296 is NPN. Is Nchannel NPN?

 

[Nigel Goodwin]

They arent holding charge, because they are discharging into the air

They aren't holding charge because they are totally useless capacitors!

They are also too small to hold much charge anyway.

What voltage are you hoping for from your LOPTX?, the circuit is fed from too small a voltage to give much. In a TV/Monitor it probably provides 25KV or so, but you're only feeding it a fraction of it's normal input voltage, so you 'might' get 2.5KV to 5KV?.

BTW - thread moved to **** Chat, as it doesn't meet the criteria for the Electronic Projects forum

Moderator.

 

[Hero999]

They arent holding charge, because they are discharging into the air

That would make sense but have you checked the cups for any signs of electrical damage?

, so I have to either create a vacuum or fill it with a dielectric fluid (any suggestions as to what fluid? I was going to use Mineral oil)

Please re-read my previous post.

Also, your schematic looks wrong.

Why is the LM7808 connected incorrectly?

There is nothing on the input and the power is applied to the output, did you check the datasheet?

Even if you used the LM7808 correctly, the chances are it will current limit when the transistor turns on, you don't really need a regulated supply for something like this. I'd go for a 9V 2A transformer with a large 4700:mu:F capacitor on the output.

 

[Nigel Goodwin]

There is nothing on the input and the power is applied to the output, did you check the datasheet?

You need to look again!

The input is clearly shown, and it's connected the correct way round!.

 

[Hero999]

You're right, it's drawn backwards!

The 555 is powered from 8V and the flyback driver is powered from an unregulated 10V to 25V. Please disregard my comments relating to the regulator and current limiting.