Cost effective capacitor bank - Page 1
Forum section: electronics / beginners

author: LostElectron
author_rank: Newbie
timestamp: June 07, 2015, 11:48:56 am
content: I have been studying electronics for over a year now, but I've only made low voltage projects.And now...I am designing a power supply witch will pulse 550-600 negative volts and 100A, duty cycle 1%-5%. Mains 220V, but I think I can get 3p 480V.So, I need a capacitor bank, and here is where I am getting all my headaches. I know the theory but in real life there are just to many capacitorsI don't know witch is the best way to accomplish it.Should I step up the voltage to 600 and use high voltage capacitors in parallel?Should I step down the voltage and use a Cockcroft–Walton configuration to raise again the V?Many of you probably have made something similar. Please give me some input on your experiences.

author: Psi
author_rank: Super Contributor
timestamp: June 07, 2015, 11:55:35 am
content: Quote from: LostElectron on June 07, 2015, 11:48:56 amlol, nope. The number of people who have built something similar to that will be tiny. Probably 0.01% of people on this forum.

author: mikerj
author_rank: Super Contributor
timestamp: June 07, 2015, 12:01:29 pm
content: Quote from: Psi on June 07, 2015, 11:55:35 amAt least an order of magnitude less than that I suspect. A 60kW, 600v supply is well within the kill-you-if-you-look-at-it-wrong area, even as a low duty cycle pulse, and not the kind of thing you should be contemplating with a years experience of making low voltage projects.

author: Psi
author_rank: Super Contributor
timestamp: June 07, 2015, 12:19:57 pm
content: haha, true, it didn't occur to me that it's 60kWInfact its entirely possible that no one on this forum has built a ~60kW high voltage powersupply. Unlikely, but definitely possible.

author: dr.diesel
author_rank: Super Contributor
timestamp: June 07, 2015, 12:28:01 pm
content: I have to ask, what is this power supply powering?

author: LostElectron
author_rank: Newbie
timestamp: June 07, 2015, 02:17:59 pm
content: Quote from: dr.diesel on June 07, 2015, 12:28:01 pmPVD

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 07, 2015, 06:04:02 pm
content: Sounds like an industrial design. Have you looked at manufacturers of this type of equipment? There may be a comprehensive solution out there already; expensive yes, but available too.Otherwise, would you be interested in some consultation or contract work? Industrial equipment is no laughing matter. I've designed and built hardware that operates safely on 480V; nasty things happen when that gets lose!Tim

author: max_torque
author_rank: Super Contributor
timestamp: June 07, 2015, 07:53:41 pm
content: Where the heck are you going to find a 60kW 1ph supply??If you can't even work out which Caps to use, which lets face it, isn't rocket science, then i suspect your going to fail, possibly fatally, in your quest to make a 60kW HVDC PSU...........

author: Ian.M
author_rank: Super Contributor
timestamp: June 07, 2015, 08:35:41 pm
content: 60KW, 5% duty cycle is only 3KW average power (neglecting losses in the capacitor bank and charging circuit) If the cap bank's large enough + good enough and the charging circuit is high efficiency you could run it off a 220V 16A wall socket.The critical factor is: What's the total period of that duty cycle which its on for 5% of?

author: dr.diesel
author_rank: Super Contributor
timestamp: June 07, 2015, 09:27:14 pm
content: Quote from: LostElectron on June 07, 2015, 02:17:59 pmQuote from: LostElectron on June 07, 2015, 11:48:56 amI'm guessing you also need current limiting as well?

author: Marco
author_rank: Super Contributor
timestamp: June 07, 2015, 09:42:04 pm
content: At least some of the Tesle coil builders on 4hv.org have buildstuff like this.Worrying about capacitors is putting the cart before the horse though ...

author: LostElectron
author_rank: Newbie
timestamp: June 08, 2015, 12:36:18 pm
content: I didn't expect so many answers. Thank you guys!!Quote from: T3sl4co1l on June 07, 2015, 06:04:02 pmYes Tim there are many manufacturers making this kind of products.Guys I am not making this because I NEED to but because I WANT to. I really want to make something like this. I have never made something similar and I am loving challenge.I know 60kW is no joke, and there is going to be safety concerns and heat problems, and again, I am looking forward to learning all about it.Quote from: dr.diesel on June 07, 2015, 09:27:14 pmYep input and output but that is another story.Quote from: Ian.M on June 07, 2015, 08:35:41 pmThis is why I thought this was not so rare.Quote from: Ian.M on June 07, 2015, 08:35:41 pmExcellent question Ian.Ideal on time: between 5?s and 100?sQuote from: Marco on June 07, 2015, 09:42:04 pmThank you for the link and why about the cart??

author: Ian.M
author_rank: Super Contributor
timestamp: June 08, 2015, 01:27:08 pm
content: 100s * 100A @ 600V is 6MJ. (megajoules)That means your cap bank needs to be capable of storing energy equivalent to 6 sticks of dynamite. Get anything wrong or get unlucky and that's the size explosion you will get.If your on time had been a small fraction of a second, it might have been practical to DIY, but a bank that can safely handle 100A repetitive discharge and maintain 600V for 100 seconds is going to be big, expensive and need a carefully designed heavy duty blast shield which will probably require structural modifications to any building it is inside of.

author: Marco
author_rank: Super Contributor
timestamp: June 08, 2015, 01:32:34 pm
content: Quote from: LostElectron on June 08, 2015, 12:36:18 pm? is not a metric or SI prefix ...QuoteBecause simply making a 3 kW power supply to keep the capacitor bank fed is not necessarily a straightforward task, your CW multiplier would have atrocious power factor ... but a PFC power supply like the one I linked is a pretty complex device. How often would this thing be on?

author: wiss
author_rank: Frequent Contributor
timestamp: June 08, 2015, 05:45:14 pm
content: I guess it is 5 to 100 us, sounds like a HIPIMS supply, yes?How would you make the pulsing unit?

author: LostElectron
author_rank: Newbie
timestamp: June 08, 2015, 07:09:58 pm
content: Quote from: wiss on June 08, 2015, 05:45:14 pmYes it's microseconds and yes it's HiPIMS.Regarding the pulsing unit, I am working on it, specifically on the arc correction.Do you have experience on it??

author: Ian.M
author_rank: Super Contributor
timestamp: June 08, 2015, 07:25:33 pm
content: That makes a lot more sense. 6KJ of energy is a lot safer/saner than 6MJ. However its still double the energy of a typical rifle bullet so the potential for parts of the cap bank to depart the area at extremely high speed remains.

author: Seekonk
author_rank: Super Contributor
timestamp: June 08, 2015, 10:29:15 pm
content: Back in the 80's I was involved with a guy making plastic sheet magnets like on a refrigerator. We had three phase charging a bank of 24 electrolytics up to 300 so volts. Mercury bath ignitron fired it into a magnetic bar. Sometimes tube would short out. Then you just tipped upside down and shook it to collect the mercury on the glass walls. Welding cables would jump each time it fired. I came in second hand keeping the old design working. First real experience with relays that would fail mechanically after a few months. Did the calculations for the mechanical life and they were failing just like the data sheet said they would. Till then a million operations didn't seem possible.

author: wiss
author_rank: Frequent Contributor
timestamp: June 09, 2015, 10:56:28 am
content: Quote from: LostElectron on June 08, 2015, 07:09:58 pmNo, I've mounted one in its rack once, and seen a blown free-wheeling diode in another...They are not small, and not cheap...