how do i convert 220VAC to 220VDC?

coolfox

Member
2010-09-13 2:32 pm
i'm trying to drive my eht transformer with 220Vdc which sounds crazy:D i used bridge rectifier with 1N4007 to regulate network and a filter capacitor about 100uf/400V.. isn't that true?at the end of this line i must get it ? could you please explain me clearly how do i get 220V DC from network[help=?]%[/help] i'm stuck!
 

bob91343

Member
2010-03-11 10:43 pm
First, you can't drive a transformer with dc. Second, if you connect a rectifier and capacitor, you will get the peak voltage (without load) and that will be the rms ac voltage times the square root of two, so you get from 220 Vrms over 300 Vdc.

If you attempt to put dc into a transformer winding, the core will saturate and you will get a very high current, and probably burn out something. Or cause a fire.
 
Transform to 157V then recitifie it. You'll get about 220V.
DC is 3 times more dangerous than AC THERE IS NO CHANCHE TO LET THE POWER CORD GO ONCE YOU TOUCHED IT!
I won't recommend to use such DC voltages. For instance you need about 10kVDC to make an arc of 3cm. But only 220VDC to do the same ;)
 
i'm trying to drive my eht transformer with 220Vdc which sounds crazy:D
No, that doesn't sound crazy.
It is crazy.
You need to study and learn a lot more before you do something stupid and kill yourself. The questions you asked show how little you know about this stuff, so maybe playing around with high voltages (high DC voltages in fact) is a bad idea.
 

coolfox

Member
2010-09-13 2:32 pm
i dont drive directly the eht with DC..there is a 555 trigger on the network line driving the ırf830 mosfet's Gate and the primer winding of the eht transformer is to the mosfet's Drain..yes there is about 300Vdc on the drain and i can't drive the mosfet still.. i succeed that when i give about 128Vdc to drain and give the 555 's supply voltage externally..i don't expect to extend the cm too much(may be 6 cm) but though i couldn't make it , this plug/jack structure sounds me practical..
 
I just don't get what you want to do. A 555 is a counter wich only needs 16Vdc? Primary winding of the transformer is 300Vdc? Do you understand how a transformer works? The there is a magnetic flux created between the two windings wich is only possible with alternating currents. This way you are heating your transfo. If you do this for to long the insulation will start to melt and not much later you'll end up with a fire.
 

coolfox

Member
2010-09-13 2:32 pm
ofcourse i know how a transformer works..my circuit is a simple flyback driver circuit with 555.. i use the 555 as an square wave generator in a eht's desired spec. at low levels. 555 generates ttl and this is connected to mosfet's gate.. mosfet creates an alternate at the eht's primer..then transformer works..
in my first test i used an external supply ;about 12Vdc for 555 and 128Vdc to" mosfet drain" (i said eht before,sorry..).. this works very well..there is an 3-4 cm arc..
then i tried to drive 555 over network . i regulated with bridge rectifiers and reduced the voltage with and power resistors and used filter caps to minimize peaks to 14Vdc ( i think there is a problem) .. this structure works on its own..
lastly i try to get 220Vdc (which is about 300Vdc) after the bridge rectifier and filter capacitor to mosfet drain.. from that point nothing works ...
 
He isn't going to kill himself with a flyback transformer, but he may kill himself when the transformer dies and there's 230v all over the place. Anyway, all it takes is a bridge rectifier and a capacitor. BUT i wouldn't run anywhere close to 300v DC into your typical flyback transformer. You're going to kill it as soon as you plug it in. I'd run 100 volts at the very extreme, it's best that you don't go over 40v if you want that transformer to survive for any reasonable length of time.

Anyway, here's why your circuit does not work. When wiring a bridge rectifier to the mains you will still have phase on one of the leads (depending what orientation you plug it in), meaning everything may be floating 230v above ground, which is NOT a good idea.

You need isolation between the 555 and power MOSFET. For best results drive a smaller mosfet with the 555 and have that output into a drive transformer from an old ATX power supply. At the other side of the transformer you wire your power MOSFET. This should work, but again, i wouldn't run it straight off the mains, you will damage the high voltage transformer.

@ BrianVG: AFAIK 50Hz AC is more dangerous than DC, i'll try to remember where i read that.
 
AC more dangerous because it disrupts your cardiac rhythm?

DC more dangerous because it makes your muscles contract and force you to hang on to it? I believe there used to be an old technician's trick (DON'T TRY THIS AT HOME) of touching a potentially live DC circuit with the outside of a finger (i.e. the side with the fingernail) so that the resultant muscle twitch (if it was live) would pull the finger away - much safer than touching with other side and grabbing the circuit.

Oh, and RF will give you a nasty deep burn which takes months to heal.
 
What is your desired end result? Why do you want to start with 220VDC?

You won't rectify a 220 volt utility line and directly filter it and get 220VDC. You'll get 1.414 times that. See Root Mean Square.

If you must get 220VDC for some reason from 220VAC you can use higher than the critical inductance (for whatever your load current is) after the bridge rectifier and before the filter capacitor. Unfortunately it's not necessarily useful for doing what you've described so far because you need an isolation transformer anyway to avoid killing yourself by accidentally coming in contact with the primary circuitry, it may as well be wound so you can hit the voltage you want with just a bridge and not have to hold a certain minimum current on the output to keep it from floating up to the peak voltage. Unless for some really strange reason you need a few kilowatt flyback converter, which is just wrong, it's easy enough to use lower voltages on the primary.
 
Last edited:
1. Always use an isolation transformer when doing things like this. It can save your life. It is for a reason that it is FORBIDDEN on this site to post schematics of, or encourage the use of, "live" power supplies.

2. If the voltage is too great, you might saturate the flyback transformer. As a stopgap measure, you can take it apart and enlarge the air gap.

3. Make sure you don't blow up the MOSFET, it will see voltages much higher than the 300VDC you feed it.

4. Open the windows, if you smell ozone, the concentration is already way beyond the healthy limit! (Yeah, it does smell kinda good :) )
 
Last edited:

star882

Member
2007-03-19 8:41 pm
It is common for electronic air filters to use a flyback transformer driven from rectified mains to create the several kV needed for operation. I have actually done a high voltage flyback design (ion generator) that consisted of a mains based "current source" (series capacitor ahead of rectification) powering a self-oscillating flyback circuit.
 

wakibaki

Banned
2008-01-08 11:51 pm
txfrmr.jpg

Danger! These voltages can kill. You have been warned.

w
 
Don't start a war about AC or DC. I think we all know voltages above 42V can easily run through your body and cause damage, not to mention the currents that are flowing.

I hope that coolfox knows what he's doing.

Ashes to ashes, dust to dust, if one doesn't get you, the other one must!

AC/DC, both can kill ya, no worries mate!

Doesn't make a difference in da afterlife!
 
Using more input voltage with a flyback circuit does not give more output voltage, it merely reduces the time to charge the flyback inductor. Output voltage is mainly dependent on rate of fall of the primary current as per v = LdI/dT Output voltage is limited by the blocking voltage of the primary current switch not to mention transformer insulation. If you want DC voltage ring around the scrap yards for an Xray power supply beware these kill from a distance, 60Kv + at over an amp, they are the size of a bar fridge, for AC a pole transformer is an option, on a more compact scale a 15Kv neon sign transformer can handle 30mA and make a nice jacobs ladder.