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300 volt dc power supply

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lo_key_cmos

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I am looking for a super simple circuit for a 300 to 320 volt dc power supply. I made a bank of 50 photo flash capacitors for various experiments and projects. the flash circuit from the cameras just dont have the ooomph to charge them all up. Besides its much more fun to build my own. It doesnt really matter if its powered by ac or dc. i have a huge box of wall worts(3 to 18 volts) and i have some transformers and bridge rectifiers in my collection. It would be super awesome if it used parts i can get at radio shack, but not necesary. I have a good amount of electronics experience, but i cant seem to find a decent simple schematic on line. any help from my fellow electronic enthuiasts would be totally appreciated! Thanks guys! :)
 

Sceadwian

Banned
Someone's gonna blow something up! =) Good luck =-\ and wear saftey glasses, in the case of that many caps at 350 volts body armor might be a good idea too. I've dead shorted one of those before and they give a pretty healthy bang, 50 is easily lethal.

The flash circuit should be able to charge the bank just fine, it'll just take about 50 times longer. If you want a decent simple schematic how about the one you already have? You should be able to reverse engineer the flash circuit you have, finding a bigger transformer might be a problem though.

Do a google search of this website and look for high voltage supply you should find plenty of examples floating around here, this isn't the first time someone's wanted to do this.

If I'm not mistaken you should be able to use a few diodes and capacitors to voltage double and rectify 120 volt mains power, but you'll want to do some kind of current limiting, you're definitely into dangerous voltage and energy potentials.
 
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lo_key_cmos

New Member
is there anything i can do to make it charge much faster? or is it just an unovercomable limitation? does amperage play a factor in charging speed?
 

Nigel Goodwin

Super Moderator
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Yes, charging speed is directly related to current - essentially you're storing energy, and just like filling a bucket with water the higher the flow of water (current) the faster it will fill.
 

Sceadwian

Banned
Yeah amperage is the trouble with those flash charge circuits, they don't produce much, they're not supposed to. You could feed the flash charge circuit a slightly higher voltage, but then you're getting into dangerous territory as it will charge faster, but may blow out components, or worse over charge the capacitors, I do NOT want to be around when a 360 volt capacitor internally shorts and explodes. I did some quick math in LTspice and a bank of 50 80uF capacitors will have 800 joules stored. Discharged through a 1 ohm resistance that will take 10ms and provide a peak power of 90kw's. I've never been able to determine what the internal resistance of photo flash caps are though which would effect delivered quiet a bit depending on what it's discharged into. Try connecting a few old junk mini speakers to one if you wanna see something interesting =) Just don't aim it at anyone =O
 
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tcmtech

Banned
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:D So my bank of 30 2300uf 450volt capacitors is really just some mischief waiting to happen? :D
 

Sceadwian

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That's not even funny, that's 5500 joules. Those are 'ideal' estimates though. Doesn't account for parasitics in the caps themselves, or other losses.
 

tcmtech

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I know. I was just teasing. :D

But I really do have at least 30 or more capacitors that size.
I was planning to make a low cost EMP generator with them at one time.
use a couple of 2kv 2200 amp SCRs and a properly constructed coil.
Massive Capacitive discharge device! :eek:

Just cant come up with a justifiable use for it. :p
 

crutschow

Well-Known Member
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A 110 to 220v transformer should give about 300v when rectified.

Use a resistor in series with the capacitors to limit the initial charge current.
 

Willbe

New Member
:D So my bank of 30 2300uf 450volt capacitors is really just some mischief waiting to happen? :D
Probably. The skin punctures at >600v so your skin resistance might save your life. Even if the current doesn't pass through your head or chest it still might cause nerve damage.
5500 J = 3900 ft-lbs, ~90x the energy in a fatal dose of radiation. It's 70 hp if it discharges in 0.1 second.
Supposedly 1 J can be fatal.
 
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tcmtech

Banned
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Yea I know all that stuff too. Glad you guys are trying to keep me alive! Thanks! :)

Believe it or not I have had saftey training on high voltage systems.
I worked at the coal mines as a student worker for my first college degree. I had to be trained in to be safe around stuff up to 23Kv 400 amps 3 phase. :eek: (Dragline power cords)
I was still grunt labor but privilaged grunt labor! :p
 

Sceadwian

Banned
Oh don't tease tcmtech, I wanna play with stuff like that =) Although 400 volts is just getting started really, using capacitors for high current pulses is usually done through high voltage though cause parasitic's tend to keep the discharge of lower voltages smoothed out a bit with a large capacitance, I guess it's a big problem with railgun design.

Destruct-o-tron

You gotta respect something that can shrink coins.
 
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tcmtech

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Wow! If I stack my capacitors in three sets of 10 I should get an actual equivalant of 690 uf at 4500 volts. :eek: :D
I can kick his crushers ass! (theoreticaly that is) :p

Another dangerous and rather pointless toy to add to my collection! :D :)
 

Sceadwian

Banned
Won't work =) The series resistance of 10 photo flash caps in series would completely nerf the discharge. This is why surge generators use very expensive capacitors. Electrolytics are horrible in series.
 
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tcmtech

Banned
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Um... I dont have photo flash caps I got these. My count was way off. I have 4 banks of 16 not 2. Plus they are 2400uf :D

And a 600 amp DC contactor. :D

It shoud still do something! with 6 banks of ten and a theoretical cappacity of 1440 uf at 5250 VDC peak. :eek:

Could be wrong too! :p
 

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Sceadwian

Banned
That's 19 thousand joules now =O time to discharge through a total resistance of 1 ohm down to 50 volts is about 350ms, starting power is upwards of 240kw's =O The question is what do you do with it =) You could make one hell of a railgun with those banks, but you'd need to time their discharge through a series of separate stages. Wanna send me one of those banks? I'll try not to kill anyone, I promise.
Well I hope =)
 

lo_key_cmos

New Member
Sceadwian, can you recommend a certain diode and capacitor value for a voltage multiplier? i know what a voltage multiplier is, and i am under the impression that the output is exponential depending on how many stages, but is it possible to calculate component values so a specific output can be achieved? ty
 

tcmtech

Banned
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I would go with 1 or 2 uf AC capacitors and just use regular 400 volt 1 amp diodes.

Bigger capacitors will charge it up faster but if your multipler is up to high you could easily over charge the capacitors and BOOM! Capacitor explosions are like cherry bombs!
Plus they can shoot metal shards and foul smelling confette all over!

Giving a little more charge up time will allow you a better chance to monitor your charging voltage. Once you know exactly where your system levels off then you could step up to bigger ones.
 

tcmtech

Banned
Most Helpful Member
Watch your local salvage yard for the big industrial VFD units.
All the capacitors I got like these in the picture came from a 100hp units. I got them for free too! The salvage yards can't send capacitors to the smelters. (PCB laws from way back.)
So I have my scrap buddies call me when a big lot come in. I happily haul them away for free!
 

lo_key_cmos

New Member
i found a super easy way to charge up my caps quite quickly. it took a couple spare transformers i had laying around. i forgot what they where rated for already, but when i put the secondaries together with 110 into the primaries of one i get 298 volts out of the "primary" of the second transformer. along with a $2.59 bridge rectifier from radio shack and a 20 watt light bulb from a junk microwave as a limiter it charges within a couple minutes and works great!
 
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