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Seriesed Electrolytic Capacitor Charging Dilemma (lots of caps...)

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MikeT1982

Sat Apr 14 2007, 10:26PM

Registered Member #621 Joined: Sun Apr 01 2007, 12:37AM
Location:
Posts: 119

Well here goes, hopefully you guys can help me out here before I do this and end up hurting myself possibly LOL. I have been a long time tinkerer, but never good at the math calculations and all, but have submitted to having to do them for this project as it is my most complicated thing I've ever done. I am making a capacitor discharge Pulse Forming Network to flash a decently large quartz Xenon Helical coiled flashlamp to pump a ruby rod in a laser project. Now from my research I have learned that for this type of application where the Capacitors need to charge and discharge quickly the safest bet would be to use Film type capacitors but I wanted to save money and love the look of the Nippon blue Electrolytic can looking capacitors. So I got online to the Electrostore.com and purchased 16 Nippon Caps, each being rated at 400 Volts DC and 3,900 Microfarads. I decided on 16 because I plan to series them all for a 6,400 volt capacity and about 244 uF total capacitance. Now keep in mind I must admit I am new to the formulas and had to find them and work them out but that's what it comes too. The mathmatical energy formula gives me about 3,900 Joules of Energy when charged to 5656 volts DC. My flashlamp is a 10,000 Joule max per pulse. Now I am still looking into the proper inductor and designing it....I have yet to learn of Henries and all, that's next I'm not worried about that now, I'm willing to draw this project out for a year if it takes me that. So anyways I have read that it's risky to do as I plan and series electrolytic caps...so seriesing 16 must not be any better!!! I only plan to flah the lamp once every 3-5 minutes or so with a manually activated series injection transformer (a small cap dumped through a pushbutton activated 12v coil Kilovac 12kv vacuum relay into a EG&G Series Injection Trigger Transformer) circuit as it will be air cooled, not water cooled or automatic rapid pulse triggering like I witnessed in the expirmental YAG lasers at Anderson Lasers when I visited. So given I am not pressed on time, do you guys think I can safely use these Electrolytics in series? I plan on using my Fluke meter to get an internal resistance measurement of each one cap by connecting it and letting it level out and I hope they are similar.....if I get this measurement how can I go about figuring what value and wattage I need for my Voltage Equalizing resistors? I've heard use 1/10th the internal resistance value of each cap and so on...but no really concrete answers. I am afraid that because I using a Rectified Neon Sign Transformer to charge them that my resistors may eat all of the weakling's current....Dick Anderson pointed this out to me so what I did was buy 2 more Franceformers, each rated at 4,000 Volts RMS AC and 30 mA. I will parallel them for 4,000 Volts AC and 90 mA, then run it into a rectifier bridge for 5656 volts DC.....in theory.....but hopefully it'll get me past at least 5 kilovolts real world. So since I have no time limit, I guess I could say I am trying to decide on a resistor value (and I will put one across each cap's terminals) that will help keep my blue caps from blowing up!! Shoot I have to run since I'm at work, but any suggestions/input is greatly appreciated, thanks ahead of time!!

ragnar

Sun Apr 15 2007, 02:42AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
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Posts: 1425

6400V 244uF -- be aware you're building a deathtrap.

MikeT1982

Sun Apr 15 2007, 04:49AM

Registered Member #621 Joined: Sun Apr 01 2007, 12:37AM
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Posts: 119

Yes definitely man, I know that this much power is more than deadly, I plan on treating the capacitors like tubes of nitroglycerin. I am wiring with 15kV GTO wire, and will wire each capacitor shorted untill completely installed and covered with a zero clearance THICK piece of plexiglass SCREWED into place and overlapping each edge by a few inches so that it is impossible for any body part to come into contact with any of their terminals.

Electroholic

Sun Apr 15 2007, 04:58AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

just put bleeder resistors on... something around 20 or 30k >5W across each cap.

Hazmatt_(The Underdog)

Sun Apr 15 2007, 05:32AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Wait a minute here.... you think that some 14 awg GTO wire is gonna survive 4KJ ?!

*shakes no* there's no way.

...

Sun Apr 15 2007, 05:53AM

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

Are you sure that your tube needs 5kv? Unless it is like 10" long I think you only need about 2kv tops... It wouldn't surprise me if the tube will self trigger at 5kv. The 2" long tube out of a ssy-1 yag laser laser breaks down at well under 2kv... Also, I have my doubts that the tube will like having 10kj pumped into it without water cooling, regardless of how low you have the pulse rate set.

In any case, just drop a 30k 5w resistor across each cap.

Your NST (90ma/5kv) should have plenty of power, you will burn about 100w in the resistors (at 400v) which leaves about 400w for charging the caps, so they will charge in about 30 seconds.

Also, please tell me that you are using the gto wire for the low current charging and not the connections between the caps to the tube... You need to use big copper plates for between the caps, and some thick (at least 10awg, preferably like 6awg) wire between the caps/tube. If you want a 1ms pulse you are running at 2.5KA...

Also, I might suggest that you start with a slightly lower power laser (an ssy-1 is a great first project, $125 for a complete head that just need a 20j/800v cap and camera trigger transformer to give tons of power)

have fun and don't blow yourself up

BTW, if you break your posts up into a few more manageable pieces people are more likely to read them.

MikeT1982

Sun Apr 15 2007, 07:12AM

Registered Member #621 Joined: Sun Apr 01 2007, 12:37AM
Location:
Posts: 119

Thanks a TON for the replies. I apologize for my rambling and run on sentences I'll fix that in the future posts LOL! The flashlamp I have is a quartz one and Dick said it is about 40" when uncoiled as it is one of those helical ones that look like Arby's curly french fries LOL. Hopefully it won't self trigger or break down, that is defnitely one thing I fear at the high voltage, but am hoping it's length saves me. About the GTO wire, yup I was planning on using it only for the the charging aspect, but was unsure of whether the simple low time duration of the pulse would allow it to withstand the huge current pulse...THANK YOU for clearing that up as now I will use some 4 gauge car audio cable I have if you say I have to for the flahlamp leads. 2.5 KILOAMPS!!!! JESUS!!!!!!!!!! Wow I didn't realize that much current. Instead of joining the caps with the GTO wire I will use metal plates as you said too. Thanks a ton again man for the wake up call. I have a habit of biting off projects larger than I can chew but gradualllllllly and carefully getting a nice result LOL! Oh, about the smaller lasers!...Dick Anderson showed me a baby YAG laser he built out of a small Eye surgery unit head and a little cigarette pack sized power supply and it ran off a 9 volt battery. If I had done my research and realized what I could do with a baby pulsed solid state laser like that I definitely would have man, it was neat he shot a few baloons from across the room for me LOL.

Bored Chemist

Sun Apr 15 2007, 08:17AM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

Will electrolytic caps produce a pulse fast enough to pump a ruby laser?

Steve Conner

Sun Apr 15 2007, 09:18AM

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

Sure, you can series electrolytics. I built a Tesla coil power supply that uses 14 450V electrolytics in series to smooth 5kV.

The only thing to watch is that the metal can of an electrolytic is connected to the negative terminal, and the blue heatshrink is unlikely to stand 6kV! Extra insulation will be needed for series strings. You need to be careful about this: all these kilojoules will make a nasty mess if anything arcs over.

The GTO wire would probably stand the pulse fine, since you're only doing it every 5 minutes, but the relatively high resistance of it would waste energy.

BC: Who knows how fast the pulse needs to be for ruby? Surely it depends on what peak power you actually want from the laser, and whether you are using a Q-switch or not. I imagine that 244uF at 6kV would make a hell of a pulse no matter if it was electrolytic or plastic film.

Marko

Sun Apr 15 2007, 11:36AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

3,900 Joules of Energy when charged to 5656 volts DC. My flashlamp is a 10,000 Joule max per pulse.

Wow... how does a 10kJ flashlamp look like??

Considering these ones are rated about 50 kJ

Blowing holes in 10mm steel instantenously?

Be safe with those things..

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