12v -> 400v inverter for caps charge / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

12v -> 400v inverter for caps charge

1 2 next

Move Thread

LAN_403

[RUS]ChaosSorcerer

Wed Jun 11 2008, 09:01PM

Registered Member #1534 Joined: Wed Jun 11 2008, 08:37PM
Location: Moscow
Posts: 4

Hi all)
...and sorry for bad english

I am experimenting with electrothermal gun(It is bases on underwater bang-spark from big caps) And I need to charge caps. Usually I use flayback-type inverter 30-40 watts, but flyback's are freakin weak and non effective (efficency ~70-80%). So I want to make a forward or push-pull inverter. But they 're much more sensitive to overload or shortcut.
But weilding inverters are all built on forward topologies - there used recuperation and PWM. So what better for caps charging and arc making: push-pull or single fet forward with recuperation solenoid?

GeordieBoy

Wed Jun 11 2008, 09:18PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

A well designed flyback converter (isolated buck-boost) is hard to beat if you only want to charge a capacitor to 400v at 30-40 J/s. Peak current mode control with one of the standard Unitrode chips would be my method of choice.

[RUS]ChaosSorcerer

Wed Jun 11 2008, 09:40PM

Registered Member #1534 Joined: Wed Jun 11 2008, 08:37PM
Location: Moscow
Posts: 4

I just using such device based on uc3845. It is simple but only simple. I want to make is smaller, more effective, more powerful and able for arcing, burning and fun like that))
So I want to make an invertor like welding device but up-step.

Some people say that flyback is immune to shortcut but of course it is not true. With small resistance secondary coil current doesn't let core to demagnetize. When building a forward you can use back-turn to demagnetize the core, but it is still need to watch forward-turn current.

kaboooom2000uk

Fri Jun 20 2008, 06:10PM

Registered Member #324 Joined: Thu Mar 16 2006, 10:28PM
Location: UK, Midlands, Buckingham, MK
Posts: 6

This depends upon your experience, but id like to suggest a simple halfbridge or as sugested, a push pull type system. Id also suggest to use IGBTs for their robustness, and high current capacity.

otherwise save youself the components and design a boost converter. These are quite reliable, and just set the duty cycle of the positive pulse to a minimum to allow for shorting tollerance or power limiting. or if your fancy you could even add an extra op-amp to measure the voltage across a current shunt and have the output set as a refererance in a comparator so it controls the duty cycle for you in realtime.

If its any help, i shall post a free circuit you can modify or make. the outputs from device A and B give signals to dive a halfbrige optocouple, or a push pull GDT. You can even just use one of the channels if you want, and freq is controled by the 1nF C1 capacitor.

You will need to place a variable resitor at the voltage divider r10 and r11. This controls the offset so the two output op-amps compair a refernce to the AC triangle wave. Channel generation in essance uses the positive cycle to generate A, and the negative cycle to generate B, crude, but effective as it gives you all the deadtime you need.

then hook this upto a opto driver for your igbt or mosfet, and you can create an efficent HF transformer driver. or welder or whatever, the possibilites are endless with simple modifications.

hope it helps, only downside it needs a dual supply. Or just use a neat dc-dc converter to overcome this.

GeordieBoy

Sat Jun 21 2008, 04:21PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

I personally wouldn't recommend using that circuit to control power electronics as it doesn't have any hysteresis built into the comparators or any latching to prevent double edges on the PWM outputs.

teslacoolguy

Sun Jun 22 2008, 05:41AM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792

For this application i would reccomend uzzors boost converter

because it is a simple circut and very effective.

lamazoid

Mon Jun 23 2008, 05:13PM

Registered Member #573 Joined: Fri Mar 09 2007, 11:26AM
Location: Russia
Posts: 14

polop

Mon Jun 23 2008, 06:00PM

Registered Member #1537 Joined: Thu Jun 12 2008, 06:44PM
Location:
Posts: 51

in the schematic tesla cool guy suggested is the hardcore mosfet nessesary if i am only going to use photo flash caps (up to 20 of them). also what is the joule per second as it stands (only need a rough guess)

...

Mon Jun 23 2008, 11:32PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

You can get away with a smaller mosfet, but the efficiency will go down. Just make sure that it has a ds rating of at least 500v.

Also, 1 joule per second is the same thing as one watt it just makes sense to call them j/s when you are charging capacitors.

polop

Tue Jun 24 2008, 10:03PM

Registered Member #1537 Joined: Thu Jun 12 2008, 06:44PM
Location:
Posts: 51

presumable it charges at 300-400v and the rating on that mosfet is 14A so it will be working under that threashhold (say 10 amps) 300 * 10 = 3000w that cant be right can some one help me inderstand the power of the circuit?

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob