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eclipse

Fri Jul 06 2007, 09:41PM

Registered Member #562 Joined: Sat Mar 03 2007, 03:36PM
Location:
Posts: 9

Hello! Everybody if my english is bad I ask even now apologies. But I try to learn it when I diccusing here. Ok but let's begin...

I have readed many websites which have talked to Microwave oven transformers and their HV circuits. And because I am interesting I will
someday want to make it myself. Of course when I will learn lot of electronics and HV physics.But I have seen some homemakers who don't care
physic and electronics just want to built it knowing anything what they are doing. So, I don't want be like them. Ok I have here some picture what I have drawn with paint and I think if you want to help me for plan this.

Ok first I ask: What do you think?

Here you can see on the left short cut and compensating system for limiting current. I think that I don't need both them just one system limiting current. I am not sure. And on the right current doubler circuit.

J. Aaron Holmes

Fri Jul 06 2007, 10:48PM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

Umm...ok...but what is your actual goal?

I think you may have forgotten to mention it after all that preamble

You say "make it", but what is "it"? The schematic you posted just looks like a mixture of a couple of the schematics you linked to, and is probably just a means to an end. Are you trying to build your own microwave oven or something?

Regards,
Aaron, N7OE

Crow187

Fri Jul 06 2007, 11:18PM

Registered Member #795 Joined: Mon May 21 2007, 06:04PM
Location: Bocholt, Germany
Posts: 35

I think too that the scematic you posted is nothig to go with ;)

I don't understand what the primary circuit is doing!?

A capacitor in direct connection to the transformer? Should it be a power correction?!

Maybe you should look at some other circuits in the web....

Lukas

Myke

Sat Jul 07 2007, 01:43AM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

The resistor on the pri side would have to be pretty huge unless it was a light bulb. I would suggesting making an inductive ballast instead of a resistive one. The capacitor is connected correctly if it was intended to be a PFC. How is the relay connected?

Coronafix

Sat Jul 07 2007, 02:27AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

The resistor is about 20W and is found in the microwave circuitry
to limit the initial current draw so it doesn't blow the breaker.
The PFC cap would have to be about 50uF but I don't think you need it,
I don't think it makes a lot of difference.
Like everyone else though, I am wondering what it is for and what it's
doing in the projects section if you're not actually building anything?

J. Aaron Holmes

Sat Jul 07 2007, 02:31AM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

Myke wrote ...

The resistor on the pri side would have to be pretty huge unless it was a light bulb. I would suggesting making an inductive ballast instead of a resistive one. The capacitor is connected correctly if it was intended to be a PFC. How is the relay connected?

EDIT: Goldsphere beat me to it by a few mins. I'm slow typing

It's not supposed to be a ballast, just an inrush current limiter that's in circuit until the relay closes and shorts across it, which happens almost immediately; the relay coil is connected directly across the input. The capacitor is indeed supposed to be a PFC. These things are explained in the links he provided

The schematic above is just a mix of two schematics he linked to.

eclipse

Sat Jul 07 2007, 06:16PM

Registered Member #562 Joined: Sat Mar 03 2007, 03:36PM
Location:
Posts: 9

Ok, let's start again. I want draw HV arcs and make jacobs ladder with it. For example:
http://www.youtube.com/watch?v=5NgUwG9O0Q0&mode=related&search=

In the primary circuit that capacitor is correcting phaseshift and it makes more impedance.
So that set a limit to current and then it doesn't break the circuit breaker. If I don't put that current could trick and break the circuit breaker. I think I don't need relay and resistor if I have this capacitor.

And circuit doubler is giving bigger voltage in the secondary circuit because I don't have another MOT so I think that system could work .

I ask you what do you like it and can I limit circuit like this? Must I take that switch on system away and use just that capacitor?

eclipse

Sat Jul 07 2007, 06:18PM

Registered Member #562 Joined: Sat Mar 03 2007, 03:36PM
Location:
Posts: 9

And of course I don't want break the MOT if it is possible. So I put also this ground to the core.

EEYORE

Sat Jul 07 2007, 06:23PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Ahhh a jacobs ladder...

I think you will need more to limit current than what you have in the primary there...You will need a hefty inductor or so (like a lightbulb), or use a variac.

A Neon Sign Transformer(much higher voltage, much less current) might be easier to work with as the MOT's voltage output will make it kinda hard to start the arc. A neon sign transformer is already current limited to a sane amount and wont blow your breaker. Just plug it in and watch it go. Plus, one screw up with a MOT and your likely dead! A NST will shock you dead too, but not like an MOT!
Matt

J. Aaron Holmes

Sat Jul 07 2007, 06:27PM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

The people in that YouTube video are being idiots. I would not use what they did as an example.

Generally speaking, power factor correction is no substitute for a ballast, and will not prevent you from tripping a breaker. MOTs are very slightly current-limited, however, which may be just enough to save you. I've heard of quite a few people running MOTs without an external ballast and getting away with it. I'm sure the MOTs run very, very hot, and that duty cycles will need to be short in order to prevent them from dying.

Also, a level shifter (voltage doubler) like this won't work for a Jacob's ladder. You're better off with just the MOT output as-is.

Cheers,
Aaron, N7OE

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