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Registered Member #1107
Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792
Hi. I have this 12000uf 500v capacitor bank that i am dying to use and i want to build a boost converter to charge it. I want to make it similar to uzzors boost converter I want to use his design but my question is how can i get more power. I can make my own inductors and i have some nice 45a 800v isotop mosfets i would like to use. I have some knowing on how they work but i still need some help. I would like it to output at least 50-60ww but right now efficiency is not to much of a concern. Thanks.
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
45A mosfets, yikes. If efficiency is no concern than just modify the circuit for 45A peak current instead of 14A. I made an excel spreadsheet which has some calculators in it, it should help you with the math. You'll need to design a special inductor however, which will probably be the hardest. I don't know much about how it's done, just that you need to avoid saturation. You need to balance airgap size between saturation current and inductance me thinks.
Registered Member #1107
Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792
Well i mean i would like to have at least 50% efficiency but iwill have to play with that later on. As far as a inductor, can i use a flyback core or a atx psu core? I can put spacers in them to try to keep them out of saturation. How would i modify the circuit for 45 Apeak?
Registered Member #1389
Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
Why don't you use a Mazzili flyback or an SLR driven transformer to charge it instead of a boost converter? The Mazzili is probably only a little bit more complex than the boost converter, and you can easily get the power you want with a TV flyback core. You can use a comparator to cut power to the driver when the desired voltage is reached, just like the boost charger.
Registered Member #1107
Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792
well as you may of read, i cannot make a zvs with those large mosfets so i will continue to make a boost converter. Again i want to use the isotop mosfet and i am building the 555 circuit right now. Now i am assuming that the bigger the inductor the more energy it will store...am i correct?
Registered Member #1389
Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
E=LI^2, where E is energy, L is inductance, and I is current flowing through the inductor, assuming ideal parameters (no resistance, and no saturation). As long as you don't saturate the inductor core, this equation will get you the energy stored in your inductor.
Registered Member #1107
Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792
Ok thanks firefox. I got the formula but how do i figure the units and how do i set the amount of amps that i can let though. rg. the inductor is 280uh and i want 10 amps to flow through. Is that determined by the frequency? Lastly, what unit is energy in?..eg joules, amps. Sorry that im asking so many dumb questions but i am new to boost converters and i want to learn.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi. I have this 12000uf 500v capacitor bank that i am dying to use
Why is it a problem to simply use mains?
i want to build a boost converter to charge it. I want to make it similar to uzzors boost converter I want to use his design but my question is how can i get more power. I can make my own inductors and i have some nice 45a 800v isotop mosfets i would like to use. I have some knowing on how they work but i still need some help. I would like it to output at least 50-60ww but right now efficiency is not to much of a concern. Thanks.
Well, I think efficiency is your concern as once you try to scale up power level from 10 to 100W input or so, on a circuit that is 50% efficient, you'll have to get rid of 50W of heat instead of 5W from your mosfet. Since I'm sure you will not heatsink the device properly for that amount of dissipation, it will very likely just fail and make you miserable.
Many people have tried to make their point regarding these ''NE555'' boost converter and whatever circuits, but are apparently getting ignored, I'll not repeat.
It's just the way you guys are handling semiconductors is going to be a waste of time and money, and result in frustrations (I really don't want you to get frustrated).
Just to be short, building a powerful SMPS that can be loaded by a large capacitor bank (and basically shorted for a time) is not even like building a ''normal'' SMPS like PC PSU. It's a rather big engineering challenge, requiring lots of time and lots of brainbusting math to get through, that I would just try to avoid at any cost unless it's my only choice. And why in a world would I need something like that if I just want to charge a 500V capacitor bank few times to explode some potatoes?
After you guys do your homework, at some point, I'm pretty sure you guys will realize some of the pointlessness there.
If you don't believe me, just look into any inverter arc welder and it's electronics. It's pretty much what you would need for a regulated capacitor charging power supply.
If I had to charge HV capacitors some way from a low voltage source like batteries, my first choice would probably be a royer oscillator indeed. It is a very troublesome circuit, no regulation of any sorts but simplest I can think off.
As far as a inductor, can i use a flyback core or a atx psu core? I can put spacers in them to try to keep them out of saturation. How would i modify the circuit for 45 Apeak?
There is no point, because inductor in NE555 boost converter is always in saturation anyway during charging.
As long as you don't saturate the inductor core, this equation will get you the energy stored in your inductor.
The core will be saturated inevitably. If you spend some time looking at the circuit and digging up some older topics you might also find out why.
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