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Portable transformer help! 11v to 800v

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LAN_403

Pinky's Brain

Sun Jan 23 2011, 07:33AM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

Have fun with your melting FET and batteries (there is nothing to limit the current except for leakage induction, counter EMF and winding resistance. there is very little of any of that in your case).

hboy007

Sun Jan 23 2011, 11:50AM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
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Posts: 374

the 60 .. 80A I quoted is the maximum current you can pump through two of these transformers, the output is as high as the efficiency permits. I did, however, not imply that the power overhead would be wasted. Drawing 80A from a battery is no good idea, anyway. Doubling the voltage reduces average and maximum currents, switching losses and extends battery life.

Don't try to build a self-resonating converter for capacitor charging. I build a 300W+ model myself. The charging rate is virtually uncontrollable.

Please have a look at the Unitrode UC2875 resonant controllers instead.

Steve Conner

Sun Jan 23 2011, 12:10PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

leodahsan wrote ...

Hi all again, I'm reading and checking all replies that I've found. Btw, my father found that for me:

That is an old circuit, it's been floating around for years. It's not very good, you'll never get hundreds of watts out of it.

Hboy007: My self-resonating capacitor charger worked just fine. I built it and tested it. The secret is the ballasting on the output, to limit the short-circuit current and keep the loaded Q up. A transformer with high leakage inductance would do the same.

You can terminate the charge by removing the supply to the MOSFET gates, using a comparator or the like.

hboy007

Sun Jan 23 2011, 01:15PM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
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Steve: That is just what I ended up with. I added two 1ÂµF/630V MKP caps in series. The peak current draw is still above 30A at 11.5V. The sustain charge bursts every 3-5 seconds or so are quite strong, I never figured out how to soft-start the converter shown above with a reasonable part count.

Pinky's Brain

Sun Jan 23 2011, 01:29PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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You build the same circuit? It seems to me that the combination of L4 and C1 or C2 (which are effectively the capacitance seen ny the transformer) should low pass the charging peaks.

Although I'd have to simulate it to be sure, my intuitive grasp of electronics is woeful :/

hboy007

Sun Jan 23 2011, 03:12PM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
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Well, not exactly this circuit. It's the usual Royer converter circuit but after a few tests and simulations I decided to use a really large storage choke to flatten out the current draw which consists of 6qmm copper cable wound onto a toroid transformer core.
Check out my rectifier:

looking at it now it might have been a better idea to replace R14 and R17 with RL series nets but this rectifier is very stable, immune to shorts and transients and survives regulation faults that cause overvoltage of >900V.

leodahsan

Sun Jan 23 2011, 11:06PM

Registered Member #3638 Joined: Fri Jan 21 2011, 11:56PM
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sorry i'm such a noob, hboy007, that circuit would output mine 800v 500mA or more, that I want? Thanks.

Dr. ISOTOP

Mon Jan 24 2011, 12:40AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Doesn't look like it, there are no transformers.
What you really want is a full-bridge to convert your 11VDC to 11VAC, then step it up with a ~1:73 transformer, then rectify it.

hboy007

Mon Jan 24 2011, 12:12PM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
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Posts: 374

That's the whole thing. Some "DON'T"s are included since I didn't bother at the time I designed it but I hope you will get the idea once you've worked your way into the matter.

the control header allows you to connect an external power switch, a status LED and a charge state baragraph display.

ps. "HF-Dr." should read "storage choke", just ignore the labeling. PWR_ON can be connected to the supply voltage if the voltage is stabilized by other means. I added an external boost converter for an external nice and clean 14V level after some tests. This might not be necessary if you replace the secondary coupling capacitor with a smaller value to decrease start-up current draw. Dropping C6 might be a good idea, too.

Steve Conner

Mon Jan 24 2011, 12:17PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Cool, thanks for sharing, hboy007

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