Building a capacitor bank capable of pulsing 16000 A DC

[Mike_In_Plano]

Bob's got a good proposal - The gap through the Neo is HUGE. When your magnet material goes into saturation, you'll have terrible problems with leakage flux. The best way to attack that is to have the coils in closest proximity to the Neo.

 

[trini]

Ok so more tinkering has led me to this. I can't use a pot core because of my magnet shape, but this is essentially the same thing. I have employed rounded edges wherever possible to avoid flux leakage, while the M shape of each half of the core serves to direct the lines to the gap. The tube is relatively impermeable compared to the neo so it itself provides a natural 2mm gap i have to deal with on each side of the neo. I call it a MoM core, see if you can guess why ;)

 

[mheslep]

Ok so more tinkering has led me to this. I can't use a pot core because of my magnet shape, but this is essentially the same thing. I have employed rounded edges wherever possible to avoid flux leakage, while the M shape of each half of the core serves to direct the lines to the gap. The tube is relatively impermeable compared to the neo so it itself provides a natural 2mm gap i have to deal with on each side of the neo. I call it a MoM core, see if you can guess why ;)

You don't really need or intend 0.0001 tolerances do you?

 

[trini]

no no autocad automatically does that, i'll round off to suit.

 

[Darryl]

Ive used one of these devices, only once and I did not like it one bit. I am a bit rusty on the details, but it was at ADFA (Uni of NSW, ACT Aust). It was used for the purpose you require.

It looked Like the TARDIS, a simple (lange box) with 4 red LED's and 1 (red) button on it.

The use of this thing was strickly forbidden near any sensitive electronics or computers, and the red button operated with a broom handle. (long as possible).

As for the design, it was no more than a wacking great capacitor, and large (hockey puck type) diode, (called a recirculating current diode from memory).

The red button, fired a thyrister which in tern fired a switch system I am sure was called an "IGNITRON".

I hope that helps you some.

Edit: Definetly IGNITRON
http://en.wikipedia.org/wiki/Ignitron

 

[Darryl]

Design is not too complex, I don't think. But first things first.

Safety, this is one deadly device, with such a device you DO NOT get a second chance, if you come in contact with a fully charged low value, High Tension (HT) capacitor you never get away scot free.

PLEASE: use all safety you can muster, and then some.

The system would contain 1 small HT electrolytic capacitor to generate the trigger pulse to fire the Iginitron.

And one or a bank of high capacity electrolytics, (possibly supported by various size ceramic or poly type high voltage caps for their high speed.

you will also need to design a high Ohm bleader resistors across all the capactior banks, and a shorting stick in stalled in the cabinet, these electro's can hold a charge for a very long time, and in the presence of RF fields can self charge, always store them with wire shorting out the terminals, and design bleeder resistors mabey 1meg or 10 meg for each cap.

The smaller electro connected to the THYRISTER that with triggered with dump the contents of the smaller electro into the TRIGER terminal of the Ignitron.

That will fire the Ignitron and dump the contents of the big capacitors into the recirculating diode, and onto the load.

I would mount the whole thing on a thick steel place, probably with a copper flashing over and bolted to the steal place, all sitting on a think insulating rubber mat.

I would use a solid state DC-DC converter to generate the High voltage required to charge both big and little caps.

I would have NO connection to your business electrical system when you fire the device and I would use an RF Garage door opener remote control to fire it, I would have a loud buzzer and flashing light when the device is charged, and carefull fireing procedure.

My experience is mainly from high power RF transmitters, mabey 10Kv to 15KV and 10 to 15 Amps, but that is continuous.

The normal method used to pass high current and high voltage is multiple stacked copper strap mabey 3 to 5cm wide and 25 to 50mm thick and possibly 4 or more conductors and usually only joining at the ends, not over the entire length. The conductors would also have anti parsidic radiation resistors mounted along their length, seemingly directly shorted out by the thick copper conductors.

These resisters are doing nothing until the potential difference between the ends of it (shorted by the conductor) changes from zero, this occures from the IR loss at the peak of the current (right when you want it elsewhere) so the resisters then start to pass current passing more current into the Diode and finally the load.

Be carefull :)

 

[trini]

OK so after some deliberation i have realized that a typical magnetic circuit is not the way to go with this, as basically any core i use is just going to saturate then poof there goes most of my flux out the window. Following up on the idea of the magnetic circuit wasn't a complete waste of time though, as it pointed out a very important fact to me. In the calculations thusfar, i used H = 1,600,000 Am, but my magnet is only 1 cm in length, so my required H is really just 16000. Now considering i would be using the region inside of my solenoid to determine my H, the required formula becomes:

H = u(N/l)I (im ignoring self inductance for this coil atm, it will be very minimal anyway)

where u is the AVERAGE permeability of the inside of the solenoid. By making the space inside the solenoid as minimal as possible(as shown in the diagram, note i do cover the tube area, so that the field experienced by the powder is relatively horizontal and not bending at the edges.

so the ratio of NEO to free space is about 60:40, which i would think makes my average u = [(0.6)(1.18) + (0.4)(u0)] / 2 = 0.321792

So then,

16000 = (0.321792)(4/0.012)I
I = 149.16 A

so there you have it, i only really need about 150 A(preferably DC) Surely there is some commercially available product which i can use to run this current through my wire(welding supply maybe?) So please, put forth suggestions, and also, could someone verify that 3 mm(AWG #9) wire can handle about 2-3 seconds of this current?

Note also that if i want to extend the solenoid so as to make the region the magnet experiences more uniform i can, i just have to fill the extra space with steel powder but it will drop my average permeability and thus increase my req'd current.

 

[gary350]

OK. I see what your doing now. Your trying to magnatize a magnet or re-magnatize a magnet or change the direction of the magnetic field of a magnet.

This is what you need. I built this 15 years ago here are some pictures.

http://i67.photobucket.com/albums/h292/mikeweaver/000_0022.jpg

This is a coil of wire wound with #24 enamel coated copper wire. It measures 1 1/4" inside diameter, 2 1/4" outside diameter and the coil width is 1". It has been varnished with polyurethane several times to glue all the wire together. The wire must be glued together other wise this thing will self distruct.

http://i67.photobucket.com/albums/h292/mikeweaver/000_0024.jpg

The capacitor bank is 2 capacitors in parallel. Each cap is 7400 MFD 200 VDV with max surge of 250 VDC.

The power supply that charges the capacitors is. 11 diodes in parallel each diode is rated 1 amp. 1N4007 will work fine. There is a current limiting resistor in series with the diodes it is 18 ohms 5 watts. It plugs into the wall outlet 120 volt AC.

Here is how the power supply works. If I plug this into the wall the capacitor bank will pull to many amps and burn out all the diodes so the current limiting resistor limits cap charging current to 10 amps. With 11 diodes in parallel it is rated 11 amps. It takes a few seconds for the cap bank to completely charge. Once it is charged I un-plug it from the wall.

http://i67.photobucket.com/albums/h292/mikeweaver/000_0023.jpg

Next I already have one of the alligator clips connected to one of the wires on the coil. I tough the other alligator clip to the other wire on the coil and all the current that is stored inside the caps is discharged into the coil. This produces a giant magnet field that can change the direction of the magnet field of the existing magnet or it can also super charge the magnet.

The tiny magnet inside the coil in the picture measures 1/2" thick 3/4" diameter. It has a lifting power of only about 1 lb. After I discharge the cap bank through the coil it super charges the magnet and it will lift over 250 lbs. The super magnet field has a half live of about 2 seconds so it drops from 250 to 125 lbs. in about 2 seconds, then it drops to 62, then 31, then 15, then 7.8, then 3.9, then 1.9, and so on. After about 20 seconds the magnet is almost back to normal it will lift about 2 lbs for several more hours but by tomorrow the magnet field is pretty much back to normal.

If I place the magnet in the coil in the wrong direction I can reverse the direction of the magnet field on the magnet.

If I place the magnet in the coil at a 45 deg angle I can relocate the magnet field at a 45 deg angle on the magnet.

If I place the magnet in the coil on its side 90 degs then the magnet field will be change so it comes out the side instead of the ends.

If I wind 2 coils and place both coils 90 deg from each other on the magnet I can force the magnet to have 2 north poles and 2 south poles 90 degrees apart.

If I wind 6 coils and place them around the magnet I can make the magnet have 6 north poles and 6 south poles.

Is this what your looking for?



Notice the contraption I built is not very fancy but it works. I was never able to find a switch that would not weld itself shut after discharging the cap bank. A push buttom to charge would be nice and a push button to discharge would be nice too.

I can not tell you for sure how many turns of wire is on this coil. #24 enamel coated copper wire is 46.3 turns per inches. Doing the math 46.3 x 23.15 = 1017 turns. There is probably about 1000 turns on the coil.

It has been too long since I did this I have forgotten just about every thing. As I recall if you reduce the coil size by half it doubles the magnet field and if you double the number of turns it doubles the magnet field. Maybe I should say it concentrated the same amount of power into a smaller space so it effectively doubles the power for a given space. Something like that.

All that is required to change a magnet or magnatize a magnet is to over come a certain power rating for each magnet. It is like trying to charge a car battery you have to excede the voltage rating of each cell by 1/2 volt to make the battery take a charge.

One more thing. The voltage at the wall outlet is 120 VAC after going through the diodes it should be about 170 VDC in the cap bank. You don't need high voltage to super charge or remagnitize a magnet you only need a strong magnet field strong enough to do the job. I not sure how much power is discharging out of the cap bank but it all comes out in one big PULSE that is what makes this device work. The caps take a few seconds to charge and a micro second to discharge.

 

[Bob S]

Gary's setup may work, but it has serious safety hazards. Any circuit that works off the 120 Vac should use an isolation transformer if possible. Also, a 3-conductor plug (hot, neutral, ground) should be used, and all equipment grounded. Lastly, if using diodes in parallel, the individual diodes should have series resistors (in this case about 120 ohms). This is because as a diode gets warmer, its forward voltage drop decreases, and it will steal current from the cooler diodes.

 

[mheslep]

I would have thought a complete air gap between the grid and the apparatus was warranted. That is charge the capacitors, disconnect from the grid, and then fire the apparatus from the capacitor.

 

[trini]

well, considering that i only need 150 A, isn't there some way i could get that kind of current without needing the capacitors at all?

 

[vk6kro]

A car battery provides currents like that to a starter motor in a car.

Alternatively, there are apparently DC welders available. There was a similar thread a couple of months ago that dealt with this.

The car battery would be the easy one.

 

[trini]

ok i have updated the design.

i will use 14 car batteries in series to get to 168 V DC. The coil will be 4 cm long, 5 layers high, making the N/l ratio 5000 using 1 mm wire[(40 x 5)/0.04]. This equates to a 9.69 Ohm resistance, making the current through my coil 17.337 A.

17.337 x 168 = 2913 J/s = 174,752 J/min

the volumetric heat capacity of copper is 3.45 J/cm^3/K
Using l = 367 m, r = 0.0005 m
c = 12,661 J/K

By holding the current while i heat the powder, i will get an even stronger final B field in my magnet. I need to heat the powder to 200 C throughout but not over that, then let it cool. I can quickly heat up the metal using an IR lamp
so if i run my Current for 1 minute, this will equate to a 13.8 K rise in my coils.

I will use jumper cables to connect the coil to the batteries, and heat the powder using a magnetron. I will need to perform tests to determine heating rates of the magnetron, what would be the best way to measure the core temperature of my powder? i was thinking a digital thermometer with a probe may work, but i need something that will give me fast readouts, as i can't let the powder get even 1 degree above 200( i may just heat to about 190 to be safe, i only need to get it to 175, to work, but 200 is optimum)

 

[gary350]

ok i have updated the design.

i will use 14 car batteries in series to get to 168 V DC. The coil will be 4 cm long, 5 layers high, making the N/l ratio 5000 using 1 mm wire[(40 x 5)/0.04]. This equates to a 9.69 Ohm resistance, making the current through my coil 17.337 A.

17.337 x 168 = 2913 J/s = 174,752 J/min

the volumetric heat capacity of copper is 3.45 J/cm^3/K
Using l = 367 m, r = 0.0005 m
c = 12,661 J/K

By holding the current while i heat the powder, i will get an even stronger final B field in my magnet. I need to heat the powder to 200 C throughout but not over that, then let it cool. I can quickly heat up the metal using an IR lamp
so if i run my Current for 1 minute, this will equate to a 13.8 K rise in my coils.

I will use jumper cables to connect the coil to the batteries, and heat the powder using a magnetron. I will need to perform tests to determine heating rates of the magnetron, what would be the best way to measure the core temperature of my powder? i was thinking a digital thermometer with a probe may work, but i need something that will give me fast readouts, as i can't let the powder get even 1 degree above 200( i may just heat to about 190 to be safe, i only need to get it to 175, to work, but 200 is optimum)

Car batteries are over kill most batteries are rated 600 to 1000 cold cranking amps. I just bought a 750 amp battery 2 weeks ago $78.00 plus tax. So your going to have $1201.00 worth of batteries with 14 in series. A D size flashlight battery produced 8 amps. Many of the new D size rechargable batteries will produce 30+ amps. I know of some D batteries that produce 50 amps. The battery on my RC model airplane produces about 40 amps.

 

[vk6kro]

You can get non-contact thermometers that would give a reading in about a second.

But I'd agree that 14 car batteries are not a good idea.
All for one great splat? You could buy a DC welder for that and have something useful afterwards.

Why not redesign it so you use only one car battery? You probably have easy access to one car battery and a set of jumper leads.

This thread has been going for nearly a month. Why not just do something?

 

[gary350]

Why not design it to use capacitors. You can get more amps out of a cap bank than batteries.

 

[trini]

thanks for the continued replies peeps, correct me if I'm wrong, but the reason i thought i'd need 14 batteries is because i need a minimum of 16.57 A in a 9.69 ohm resistance = 160 V minimum.

also i have to wait for some orders to arrive before i can proceed anyway (mould, mould release agent) and i still have to go get my magnetrons, so I'm using this time to work out all the kinks possible.

I am not an electrical engineer so this is very unchartered territory for me. also, by following the thread you see why it is a good thing i waited, i went from needing a $1500 capacitor and charger setup, which could have potentially killed me, to needing a car battery or perhaps even just a few D batteries.

while it is true that i can get more amps out of a cap bank, my material achieves 95% saturation above 1600000 Am. anything above that will not make my residual B field material much stronger anyway.

let me include a bit of permanent magnet theory for those of you who are unfamiliar:

when making a compression molded magnet, one first compresses the powder(epoxy coated) to a certain density (in my case 7.6 g/cm^3), then saturates the magnet powder in the desired direction. The powder is then heated so as to activate the epoxy which then spreads and holds the powder particles in place.

when i use AC, after i pulse, the magnet's internal b field will balance itself out and end up at its Br value of about 0.872 T, so no matter how many amps i pump into it, once that current stops it's still going to end up at around 0.872 T(this also explains why your magnet will only be 'supercharged' for a while before going back to it's original Br value), so when i begin heating, I'm 'gluing' this 0.872 T into place.

if i use a dc current, i can hold the B field above 0.872 T(what this means is that the arrangement of magnet particles are aligned at this point such as to achieve a field over 0.872. remember, even when you 'supercharge' your magnet, all you're doing is temporarily realigning the particles inside each domain), and 'glue' it into place while it is in this 'supercharged' state. so DC clearly has it's advantages.

 

[gary350]

You get a continious stream of amps out of a battery, you don't need that to charge a magnet. A pulse will do the job. It is like compairing a fire hose to a shotgun blast. You can charge a lot of amps into a capacitor bank over several seconds, when it discharges all those amps come out in a micro second like a shotgun blast. The huge pulse of amps produces a giant magnet pulse in the coil. 1 pulse is all it takes to charge a magnet. It is not much different than a flash on a camera the flash goes off in a micro second and produces plenty of light to take a picture. If your building your own magnet you can pulse the cap bank over and over if you want. If you dump a bunch of iron filings on a sheet of cardboard then pulse the coil with the cap bank all the iron filings instantly line up. It takes only 1 pulse to line them up. I'm not sure your idea of continious magnet field will do a better job or not. If the magnetic particles are mixed in with thick glue then the glue will slow down their movement they will not line up very quick.

 

[trini]

the glue is dry until i begin heating, so it won't affect alignment. what you're saying is true with regards to a pulse doing the same job, however there is a limit to the B field of a magnet. This limit is reached when all the particles in all the domains line up in the same direction. According to the information i have been provided with, a field of 16,000 Am will line up 95% of particles in my magnet. even if i pulsed 1000 A through my coil continuously, my final B field would not be very much stronger than if i used 17 A.

What i will concede however is that a pulsed current may 'shake' any particles which don't align themselves initially into place, but i can achieve the same effect by flicking the power on and off a few times before holding it.

EDIT:
quick question, if i have a power supply which delivers 10kV with an internal resistance of 4Mohm, would i still get 10000/9.69 = 1000 A when i connect it to a 9.69 ohm resistor, or does the internal resistance of the supply somehow limit this?

 

[vk6kro]

quick question, if i have a power supply which delivers 10kV with an internal resistance of 4Mohm, would i still get 10000/9.69 = 1000 A when i connect it to a 9.69 ohm resistor, or does the internal resistance of the supply somehow limit this?

The internal resistance of a power supply appears in series with the voltage of the supply.

So, it appears in series with the load as well.

Current = 10000 volts / 4000009.69 = 2.5 mA

 

[trini]

Ok so due to school starting back recently and a huge delay in getting everything ready, i had to put this off for a while. Now that i have some better wire to use, i have new requirements to work with.

I got AWG#34 wire, which did wonders in reducing my required current to just 2.4 A, however the resistance of this wire is 235 ohm. Now this implies(since I'm using DC) that i need a voltage or 564 V.

Any ideas on a DC power supply to drive this thing?

564V 2.4 A(minimum)

 

[mheslep]

... Now this implies(since I'm using DC) that i need a voltage or 564 V.

Any ideas on a DC power supply to drive this thing?

564V 2.4 A(minimum)

This is simply to charge the capacitors right? Any kind of bench ~2kw high voltage supply is going to cost you probably $3/Watt. However, since you SHOULD be using an isolation transformer anyway, better yet just get a variac (1.5kw, $100 tops) and then follow it with a http://www.tpub.com/neets/book7/27c.htm" (~800V breakdown , 4A diodes, minimum) . The resulting pulse train will charge the caps nicely. You'll have to start the variac at very low voltage to not trip the breaker on the grid side of the variac, or put in some other kind of current limiter.
I don't recall seeing as part of your plan a way to safely dump the charge on these capacitors without firing the entire mechanism, say into a resistive load. Hopefully you've thought of that. Those caps should no more be left alone and idle with that kind of energy than you would leave cups of gasoline lying around. Think about a fire starting for instance, an electrical fire energized by the capacitors. Pulling the plug out of the wall or flipping the breaker won't stop that.

Enclose the entire output of the variac / diode bridge properly. If you are not absolutely sure about the risks and safety measures required for HV forget the variac/bridge and buy the certified DC supply. If that's not affordable drop this project and move on.

 

[trini]

Oh no this isn't for the capacitors, I'm using dc to magnetise the material, so you gave me my answer in your first paragraph lol, thanks!

 

[mheslep]

Oh no this isn't for the capacitors, I'm using dc to magnetise the material, so you gave me my answer in your first paragraph lol, thanks!

Please also see my edits above.

 

[Bob S]

The drawing in post #62 is good, because it minimizes unnecessary air gaps, but I do have some comments:

1) the two coils are very hard to wind, because the breaks between the two halves of the core are in the middle of the coils.
2) The breaks in the core are where the magnetic field is highest, so will have a maximal effect on the field.

The breaks should be moved 90 degrees to the center on the right and left of the sample, because that is where the magnetic flux is least. This would permit winding the coils on single pieces of the core.

I do not understand your drawing. Are you magnetizing across the diameter?

Are you planning on inserting the sample into the opening in the side of the complete assembled core including windings? It might be more efficient magnetically to place the sample in a wound coil, and inserting this assembly into the magnetic core without coils.

Bob S