My first and only capacitor bank

[DrewScott]

Here is my 64uF @ 4270v capacitor bank. It has 3 options on top for firing: a cylindrical coil for can crushing, a pancake coil for ring launching, and two clips for attaching wires to be exploded (with blast shield). There is a switch on top to select the desired option. It is discharged using a high voltage relay that I added tungsten contacts to so they wouldn't ablate themselves away. There is a hv diode acting as a half wave rectifier for the charging circuit. There is also a 5 megaohm hv resistor across the caps acting as a bleeder for safety, and an Incandescent bulb in series with the charging primary acting as an indicator of level of charge. It crushes cans ok, and launches rings pretty well. It will also explode wires fairly well if they are small enough.

[DrewScott]

What would be a good way to indicate when the cap bank is fully charged, other than checking the brightness of the bulb in line with the hv primary?

[Da_Stier]

Nice build, I like how the terminals on top kind of look like some lego bricks. 

The obvious solution for getting the state of charge is to just measure the voltage through a voltage divider (made from HV resistors).

You could also measure the capacitor voltage relative to the supply to get the difference between them.

If you don't want to deal with any high voltages you could also put a current shunt on the low side of the charching voltage.
This way you can measure the current which should go to 0 when the caps are fully charged.
Being in the lowside, you can simply hook up a multimeter directly across the shunt.

A more theoretical approach might also be to monitor the charging voltage and current and integrate the energy that has been transportet into the caps.

I hope this gives you some ideas on what might be interesting to try. 
Greetings,
Michael

[DrewScott]

I like the idea of the current measurement of the low end of the charging circuit. I guess that is what the bulb currently indicates (pun intended) but it would be great to have some numbers to go along with that. I did some YouTube learning about shunts and ammeters and how all that works. That'll be the next addition.

Another question: I currently have the half wave rectifier on the hv end of the charging circuit. Would it make any difference or be better if I put it on the low voltage end? And would the fact that it is half wave rectified with no smoothing cap affect the current reading?

On a different note, I'm trying to figure out more things to use this capacitor bank for. So far I've crushed cans, exploded wires, launched rings. What else could I use this for? Thanks!

[MRMILSTAR]

I built a pulsed power generator several years ago. It can store up to 24,000 joules. I use it to shrink coins, crush cans, and launch discs. I use a NST to charge the capacitor. To monitor the charge level, I use a microammeter with a 25 microamp scale. I place a 1 gigaohm HV resistor in series with the microammeter. In doing so, the meter now reads in kilovolts instead of microamps. I just watch the meter as I apply charge.

I use two meters. One meter is for monitoring the voltage level of the capacitor during charging. The other meter is for monitoring the capacitor voltage level during bleed-down. The bleed-down meter is bipolar to allow for the possibility of positive or negative residual charge on the capacitor due to voltage reversal. The charging meter is disconnected during firing and bleed-down. The bleed-down meter is only connected during bleed-down.

[Da_Stier]

Another question: I currently have the half wave rectifier on the hv end of the charging circuit. Would it make any difference or be better if I put it on the low voltage end? And would the fact that it is half wave rectified with no smoothing cap affect the current reading?

It should not make any difference on which end you place your diode. The capacitor bank acts as its own smoothing capacitor anyway.
Just make sure to place the shunt on the capacitor side of the diode.

On a different note, I'm trying to figure out more things to use this capacitor bank for. So far I've crushed cans, exploded wires, launched rings. What else could I use this for? Thanks!

You could build a coilgun and shoot "normal" projectiles.
You could build a railgun, however the energy of your capacitorbank might be a little bit on the small side for that.
You could build a Ruby laser if you connect a flashtube to it.
You could do a lot of plasma physics, which would however require a vacuum chamber.


Greetings,
Michael

[DrewScott]

Could you expand on the plasma physics? I actually am building a vacuum chamber right now for a demo fusor. It isn't quite finished yet, but it should work once it's done.

[MRMILSTAR]

Exploding fruit is another entertaining "use". Your capacitor bank may not be able to store enough energy though. Maybe a grape?

[Da_Stier]

Could you expand on the plasma physics? I actually am building a vacuum chamber right now for a demo fusor. It isn't quite finished yet, but it should work once it's done.

Sounds great, how do you plan to get your hands on Deuterium, can you just buy it where you are?

Regarding the capacitorbank, I thought about accelerating and / or compressing plasma.
You can use an electromagnet to "compress" the plasma to reach incredible energy densities, however you will generate some pretty serious EMP emissions, so be careful.
Another thing is "pulsed nuclear fusion" which is some state of the art plasma physics.

With the help of a vacuum chamber, you might also be able to do some plasma coating and metal vapour coatings.

Exploding fruit is another entertaining "use". Your capacitor bank may not be able to store enough energy though. Maybe a grape?

I like the idea of an exploding grape, it seems pretty silly but incredibly funny. 
Greetings,
Michael

[DrewScott]

I am only planning on building a "demo" fusor at first that won't use any Deuterium (and won't actually be fusing) as a classroom demonstration. Visually it won't look any different and will be much safer for students. Once I get that figured out, v2 might actually use Deuterium. I will cross that bridge when I get there.

[DrewScott]

 Does anyone have any experience using a capacitor bank as a power supply for a single shot induction coil?

[johnnyzoo]

I like the idea of the current measurement of the low end of the charging circuit. I guess that is what the bulb currently indicates (pun intended) but it would be great to have some numbers to go along with that. I did some YouTube learning about shunts and ammeters and how all that works. That'll be the next addition.

Another question: I currently have the half wave rectifier on the hv end of the charging circuit. Would it make any difference or be better if I put it on the low voltage end? And would the fact that it is half wave rectified with no smoothing cap affect the current reading?

On a different note, I'm trying to figure out more things to use this capacitor bank for. So far I've crushed cans, exploded wires, launched rings. What else could I use this for? Thanks!

Building a large flash lamp would be something I would try if I had such capacitors. Be careful - eye damage can occur both due to intense light/UV radiation as well as glass shrapnel in case the lamp explodes.

As for charging, I would use full-wave rectification instead of half-wave if possible. Is there a reason why you are using half-wave rectification? Multiplier circuit or something?

[DrewScott]

I am using half-wave only for simplicity. You are correct, I should probably be using full-wave. I am thinking of switching to full-wave and moving it to the low voltage side of the charging circuit. The HV transformer would still operate since it would be pulsed DC after rectification.

On a different note, I was reading this page here: https://www.stevehv.4hv.org/MOCs.htm

His bank is just over 0.57kJ. Mine is over 0.7kJ and his seems to outperform mine substantially. I am wondering what I can do to increase the performance of mine? Should I add beefier conductors to the discharge side of mine? Is my work coil not as efficient? I am using 14AWG wire for my work coil at 6 turns. He uses magnet wire with more turns. What should I work on to try and improve it?

johnnyzoo, what kind of bulb should I use for the flash lamp?

[klugesmith]

Looks good, Drew. 

On what kind of load is the competing machine outperforming yours?
Results depend on much more than stored energy, even if capacitance and voltage are identical.

Pulse timing depends on the circuit inductance, and there's probably some optimum value for each load and charge energy.  For my 52 uF can crusher I tried coils with 3, 4, 5, and 6 turns.  Also experimented with turn to turn spacing, since a longer coil induces voltage in a wider (lower-resistance)  shorted turn.

Losses from interconnect and switch resistance are probably relatively small,
compared to the effects of inductance in your capacitor bank and interconnecting wires.

[Mads Barnkob]

I am using half-wave only for simplicity. You are correct, I should probably be using full-wave. I am thinking of switching to full-wave and moving it to the low voltage side of the charging circuit. The HV transformer would still operate since it would be pulsed DC after rectification.

On a different note, I was reading this page here: https://www.stevehv.4hv.org/MOCs.htm

His bank is just over 0.57kJ. Mine is over 0.7kJ and his seems to outperform mine substantially. I am wondering what I can do to increase the performance of mine? Should I add beefier conductors to the discharge side of mine? Is my work coil not as efficient? I am using 14AWG wire for my work coil at 6 turns. He uses magnet wire with more turns. What should I work on to try and improve it?

johnnyzoo, what kind of bulb should I use for the flash lamp?

Its been quite some years since I built a MOC bank as Steve's. It was only holding 0.33kJ since I did not charge them at higher voltage and the internal bleeding resistors would also quickly bleed off the higher voltage. https://kaizerpowerelectronics.dk/pulse-power/333-joule-moc-capacitor-bank/

I think his performance is either from lower ESR/ESL capacitors and that he seems to use "sacrificial" coils compared to the more sturdy ones we have in our setups. So his magnetic field is a lot tighter with those thin wires closer together. I never ripped a can apart either Maybe US cans are thinner than in Europe?

[MRMILSTAR]

From looking at the picture of your can crusher work coil, you need to get the coupling as high as possible especially since your are only working with 700 joules. The turns of your work coil need to be even closer to the can, practically touching. This makes a big difference. My work coil consists of 3.5 turns of 9 AWG magnet wire. The coil is wound inside of a G10 holder to prevent the coil from deforming. The turns are within 0.5 mm of the can. My coil's inductance is scaled for my capacitor which is 100 uf. This results in a resonant frequency of about 8.3 Khz with can in place.

All that being said, I don't think your results will be much better even with these changes. The amount of crushing shown in your picture actually looks pretty typical for only 700 joules. Your real path to improvement is more energy.

Here are some pictures of my work coil and some results. I can cut a can in half with about 1200 joules. The 1500 joules shown in the picture was overkill.