Welcome
Username:

Password:


Remember me

[ ]
[ ]
Online
Guests: 42, Members: 1 ...
HB viewing forum.php

most ever online: 333
(Members: 3, Guests: 330) on 06 Jun : 15:15

Members: 2694
Newest member: vladi mazzilli
Members Birthdays:
No birthdays today

Next birthdays
11/29 Sonic (48)
11/30 arnsfelt (35)
11/30 jaysun92 (22)
Contact
If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated within the last three months. Green bold denotes those who have donated to keep the server carbon neutral.


Special Thanks To:
  • Aaron Holmes
  • Aaron Wheeler
  • Adam Horden
  • Alan Scrimgeour
  • Andre
  • asabase
  • Austin Weil
  • barney
  • Barry
  • Bert Hickman
  • Bill Kukowski
  • Brandon Paradelas
  • Bruce Bowling
  • BubeeMike
  • Byong Park
  • Cesiumsponge
  • Chris F.
  • Chris Hooper
  • Corey Worthington
  • Derek Woodroffe
  • Dalus
  • Dan Strother
  • Daniel Uhrenholt
  • datasheetarchive
  • Dave Billington
  • Dave Marshall
  • David F.
  • Dennis Rogers
  • drelectrix
  • Dr. John Gudenas
  • Dr. Spark
  • eastvoltresearch
  • Eirik Taylor
  • Erik Dyakov
  • Erlend^SE
  • Finn Hammer
  • Firebug24k
  • GalliumMan
  • Gary Peterson
  • George Slade
  • GhostNull
  • Grant
  • GreySoul
  • Henry H
  • IamSmooth
  • In memory of Leo Powning
  • Jacob Cash
  • James Howells
  • James Pawson
  • Jeff Greenfield
  • Jesse Frost
  • Jim Mitchell
  • jlr134
  • Joe Mastroianni
  • John Forcina
  • John Oberg
  • John Willcutt
  • Jon Newcomb
  • klugesmith
  • Leslie Wright
  • Lutz Hoffman
  • Mads Barnkob
  • Martin King
  • Mats Karlsson
  • Matt Gibson
  • Matthew Guidry
  • Michael D'Angelo
  • Mikkel
  • mileswaldron
  • mister_rf
  • Neil Foster
  • Nick de Smith
  • Nick Soroka
  • Nik
  • Norman Stanley
  • Patrick Coleman
  • Paul Brodie
  • Paul Jordan
  • Paul Montgomery
  • Ped
  • Peter Krogen
  • Peter Terren
  • PhilGood
  • Richard Feldman
  • Robert Bush
  • Royce Bailey
  • Scott Fusare
  • Scott Newman
  • Stella
  • Steven Busic
  • Steve Conner
  • Steve Jones
  • Steve Ward
  • Sulaiman
  • Thomas Coyle
  • Thomas A. Wallace
  • Timo
  • Torch
  • Ulf Jonsson
  • Vaxian
  • Weston
  • William Kim
  • William N.
  • William Stehl
  • Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Forums
4hv.org :: Forums :: Electromagnetic Radiation
<< Previous thread | Next thread >>   

Electromagnetism/Capacitor Help.

Author Post
The_Happy_Duck
Thu Mar 22 2012, 03:03PM Print View
Registered Member #4089
Joined: Fri Sep 09 2011, 04:40PM
Location:
Posts: 19
Hello,
A few months ago I started a project using capacitors, needless to say I quickly found myself giving up as what I was trying to achieve didn’t seem to work correctly. I was playing with my neodymium magnets today and realised maybe I could make an electro magnet. I first wanted to use a car battery but then realised I had 24 330v capacitors, maybe I could make a strong magnetic pulse. I later found out that I would actually be creating an EMP. My lack of knowledge on the subject has slowed me down however and I have a few questions;

1. If I wanted to create a larger magnetic field would I want the iron rod to be long or wide?
2. People suggest that a thicker wire is better but is wrapping a thinner wire around to cover the same area just as effective?
3. What makes a stronger magnetic field; Larger Current or Voltage?
4. If I linked my capacitors in series what effective range would I have? (Considering the inverse square law and all that)
5. Regarding capacitors, does a higher capacitance mean that it will last for a longer period of time?
6. Would double layering the wire make the field stronger?
7. I know this is probably not possible but is there a way to direct or contain a magnetic field to limit the inverse square law’s affect?

Thank you to anyone that can answer a question.
Back to top
Forty
Fri Mar 23 2012, 02:26AM
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
Hello. I'll try to shed some light on all of your questions (under the assumption that you're trying to make a strong, pulsed magnetic field via discharge of capacitors into a coil of wire)

1. An iron core will increase the inductance of the coil and thus cause the magnetic field to change less suddenly. If you're using the pulse to induce currents into something else (such as an induction launcher) then this would be a bad thing, because induced currents depend on the rate of change of the magnetic field that's creating it.

2 and 3. The magnetic field created is dependent on the number of turns and the current. To obtain a given field strength, you can increase either one. The current is limited (aside from the source) by the resistance of the wire. The resistance of the wire decreases with more cross sectional area and, of course, less length. So to increase the current in a coil, you'd want thicker wire. With more turns comes more inductance, which again causes the current (and magnetic field) to change more slowly. So for a pulsed coil you want thicker wire, less turns, and lots of current, and for an electromagnet you'd want thinner wire, lots of turns, and less current. The voltage and the resistance of the wire will determine the peak current (roughly) by ohms law.

4. I don't think putting that many electrolytic capacitors in series is a good idea. But for a given coil, increasing the voltage (by series-ing the capacitors) will increase the current and thus increase the field. Since the capacitors will be discharging must faster because of the increased current, the pulse will be stronger.

5. Yes. The time constant for charging and discharging a capacitor through some resistance is equal to RC. So for a given load (the resistance), increasing the capacitance will increase the time constant and thus increase the time it takes for the capacitor to discharge. Another way to look at it: more capacitance=more energy stored, and if being discharged under the same circumstances, =more time to discharge.

6. Using more wires in parallel will act like a larger wire and reduce the resistance.

7. For an emp generator you can use an antenna (I've heard of all sorts of shapes) to focus and project the em signal. I'm not much of a signal or radio guy though so I don't know how you'd go about designing one. For a strictly magnetic field, using a long core extending from the coil might be a way to bring the flux out of it, but like I said in 1. that's more for an electromagnet.

What is it that you're trying to do exactly with the pulse?

Back to top
The_Happy_Duck
Sun Mar 25 2012, 10:28PM
Registered Member #4089
Joined: Fri Sep 09 2011, 04:40PM
Location:
Posts: 19
Forty wrote ...

Hello. I'll try to shed some light on all of your questions (under the assumption that you're trying to make a strong, pulsed magnetic field via discharge of capacitors into a coil of wire)

1. An iron core will increase the inductance of the coil and thus cause the magnetic field to change less suddenly. If you're using the pulse to induce currents into something else (such as an induction launcher) then this would be a bad thing, because induced currents depend on the rate of change of the magnetic field that's creating it.

2 and 3. The magnetic field created is dependent on the number of turns and the current. To obtain a given field strength, you can increase either one. The current is limited (aside from the source) by the resistance of the wire. The resistance of the wire decreases with more cross sectional area and, of course, less length. So to increase the current in a coil, you'd want thicker wire. With more turns comes more inductance, which again causes the current (and magnetic field) to change more slowly. So for a pulsed coil you want thicker wire, less turns, and lots of current, and for an electromagnet you'd want thinner wire, lots of turns, and less current. The voltage and the resistance of the wire will determine the peak current (roughly) by ohms law.

4. I don't think putting that many electrolytic capacitors in series is a good idea. But for a given coil, increasing the voltage (by series-ing the capacitors) will increase the current and thus increase the field. Since the capacitors will be discharging must faster because of the increased current, the pulse will be stronger.

5. Yes. The time constant for charging and discharging a capacitor through some resistance is equal to RC. So for a given load (the resistance), increasing the capacitance will increase the time constant and thus increase the time it takes for the capacitor to discharge. Another way to look at it: more capacitance=more energy stored, and if being discharged under the same circumstances, =more time to discharge.

6. Using more wires in parallel will act like a larger wire and reduce the resistance.

7. For an emp generator you can use an antenna (I've heard of all sorts of shapes) to focus and project the em signal. I'm not much of a signal or radio guy though so I don't know how you'd go about designing one. For a strictly magnetic field, using a long core extending from the coil might be a way to bring the flux out of it, but like I said in 1. that's more for an electromagnet.

What is it that you're trying to do exactly with the pulse?




I am actually only trying to make a strong magnet, I do not really want to make an EMP.
Thank you for the really long post, any more tips to help me?
Thank you!
Back to top
Forty
Sun Mar 25 2012, 11:01PM
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
Ah just an electromagnet then?
well just wrap as many turns of whatever enameled wire you can find around a ferromagnetic core. For a lazy approach, I'd probably just cut the top off of a transformer and use it's core as the magnetic core, and the winding with the most turns as the electromagnet. (note: don't plug the transformer back into mains after you do that, use another supply or transformer to power it)
Back to top
The_Happy_Duck
Mon Mar 26 2012, 09:35AM
Registered Member #4089
Joined: Fri Sep 09 2011, 04:40PM
Location:
Posts: 19
Yeah, I just want to make an electromagnet.

A question about the wire, You say the thicker it is the better but what is stopping you wrapping a huge wire with a Diameter of 5cm around your core. Are you saying 3 turns of that is better than 100 from a smaller wire?
Could you possibly answer question one again now, I am not sure what the best size of core Is, long or wide
I used to have a really crude charger like thing I made for my capacitors but I have realised this will no longer work, any other solutions to charging them if they are linked in series?

Thank you for all the help.

Edit; I have two neodymium magnets, N52 25mm Diameter, could these be used in this experiment somehow?
Back to top
Steve Conner
Mon Mar 26 2012, 10:31AM
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6739
The magnetic strength ("magnetomotive force") of an electromagnet is measured in amp-turns. 1 amp in 100 turns gives the same strength of magnet as 100 amps in 1 turn.

For a given MMF and copper volume, the wire gauge doesn't affect the current density and I2R losses.

So, if you want to design a strong electromagnet, you just choose the wire gauge to draw the maximum power out of whatever power supply you have available. If it's a car battery, use thick wire. If it's hundreds of volts, use thin wire. In either case, stuff as much of it as possible onto the core and provide the best cooling you can to stop the insulation melting.
Back to top
Forty
Mon Mar 26 2012, 04:05PM
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
The large wire suggestion was really more for the rapidly pulsed coil. Less turns would give you less inductance, but to still achieve a strong field you'd need lots of current, and thus thick wire.

For an electromagnet that is on for longer periods, the inductance won't really matter, so you can use many turns of thinner wire, and power it with less current to achieve a strong magnetic field.

The field created (in Teslas) is approximately B=4*pi*10^(-7)*N*I
where N is the number of turns, I is the current, and the 4*pi*10^-7 is the magnetic permeability of free space. The product of N*I gives you the amp-turns that Steve discusses

Here's a project you might find interesting that could involve the electromagnet and your permanent magnets:
The IR emitter and detector pair can be salvaged from many things (like computer mice)
Back to top
The_Happy_Duck
Wed Mar 28 2012, 09:00AM
Registered Member #4089
Joined: Fri Sep 09 2011, 04:40PM
Location:
Posts: 19
Forty wrote ...

The large wire suggestion was really more for the rapidly pulsed coil. Less turns would give you less inductance, but to still achieve a strong field you'd need lots of current, and thus thick wire.

For an electromagnet that is on for longer periods, the inductance won't really matter, so you can use many turns of thinner wire, and power it with less current to achieve a strong magnetic field.

The field created (in Teslas) is approximately B=4*pi*10^(-7)*N*I
where N is the number of turns, I is the current, and the 4*pi*10^-7 is the magnetic permeability of free space. The product of N*I gives you the amp-turns that Steve discusses

Here's a project you might find interesting that could involve the electromagnet and your permanent magnets:
The IR emitter and detector pair can be salvaged from many things (like computer mice)


Thanks for the suggestion!

- Do you guys know of any way I could charge these 24 capacitors in series? I'm not sure if I have to apply 7920v or just 330v (which would take a long time to charge). I have this disposable camera which charges a 330v capacitor and I am not sure if I can use that.
- Which capacitors would be best to use? One with a high voltage rating or one with high capacitance? (For example; 3000 capacitors at 1kv and 100pF, would this be good even though it is 300nF overall?)
- Can transformers be used in some way?

Thank you for putting up with my lack of knowledge on this subject, I really appreciate it.
Back to top
Forty
Wed Mar 28 2012, 02:13PM
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
If you're making an electromagnet, and not a pulsed coil, then I don't see why you need the capacitors. Just power it with a 12v battery.

Charging that many electrolytics in series probably wouldn't work too well. They have a series resistance to them.

The camera charger makes 330 volts. so it can't charge anything higher than 330 volts, but it could charge all the capacitors in parallel.

The energy stored in a capacitor is 0.5*C*V^2
and time constant (seconds to charge to 63% or discharge by 37%) is equal to RC. With that you can answer your second question.

Transformers can be used for lots of things, but since I have no idea what it is you're trying to do, I can't tell if you might have a use for them.

Are you making a pulsed electromagnetic coil or an electromagnet? You said electromagnet but then you went back to talking about capacitors so I don't know.
Back to top
The_Happy_Duck
Wed Mar 28 2012, 04:04PM
Registered Member #4089
Joined: Fri Sep 09 2011, 04:40PM
Location:
Posts: 19
Forty wrote ...

If you're making an electromagnet, and not a pulsed coil, then I don't see why you need the capacitors. Just power it with a 12v battery.

Charging that many electrolytics in series probably wouldn't work too well. They have a series resistance to them.

The camera charger makes 330 volts. so it can't charge anything higher than 330 volts, but it could charge all the capacitors in parallel.

The energy stored in a capacitor is 0.5*C*V^2
and time constant (seconds to charge to 63% or discharge by 37%) is equal to RC. With that you can answer your second question.

Transformers can be used for lots of things, but since I have no idea what it is you're trying to do, I can't tell if you might have a use for them.

Are you making a pulsed electromagnetic coil or an electromagnet? You said electromagnet but then you went back to talking about capacitors so I don't know.


Sorry, I was sort of referring to both because they seemed similar.
I think I am going to go the EMP route, the reason I wanted to use capacitors in a magnet was because I thought It would give me a very large instantaneous magnetic pull (Or push)
I am guessing an increase in Voltage will produce more of an effect than an increase in capacitance from your equation? But what you are saying is that an increase in either will produce a more powerful effect?
Thanks,
Back to top
Forty
Wed Mar 28 2012, 07:19PM
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
use this to simulate a coil

I'd pick a fixed inner diameter and length (the size of something you might wrap the wire around), a magnet wire size that you have, and then adjust the outer diameter slider and record the R and L values for each number of layers. Then take that table of values to here:


and then you can play around with the voltage and capacitance values to see what the pulse will look like. Increasing R (more turns or thinner wire), Increasing L (more turns or larger diameter), or Increasing C will make the pulse longer and affect the peak current. And Increasing V will just affect the peak current.

The number of turns from the first sim, along with the peak current from the second, and times the permeability of free space will roughly give you the magnetic field strength with no core.
Back to top
The_Happy_Duck
Thu May 10 2012, 02:13PM
Registered Member #4089
Joined: Fri Sep 09 2011, 04:40PM
Location:
Posts: 19
Hello,
Sorry for bumping an old thread but I have not had chance to start this project due to exams.

I am still a little confused on the calculations,
I am also not sure how current works with capacitors.

Just out of curiosity I am going to list a few assortments of capacitors; I hope you can tell me which set would be the most effective to use in an EMP, creating the largest radius possible. I also hope you could tell me how your worked it out. (I am comparing these by cost, not a good measure I know)

3000 Capacitors; 1000pF 1KV
35 Capacitors; 330uf 0.160KV
10 Capacitors; 150uF 0.5KV

(Please note I am not going to start building anything until I know what I am doing, especially with these quantities.)
Thank you for all the help.
Back to top
Forty
Thu May 10 2012, 07:22PM
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
the banks would hold
1.5J
147.84J
187.5J

Could probably make a coilgun with the 3rd one, but i doubt any of them would be suited for an emp pulse.

something like a defibrillator capacitor, a bunch of microwave oven capacitors, or any other high energy discharge/pulse capacitor would be better suited for the fast pulse you need for an emp. Playing around with any of those would be extremely dangerous though, so I wouldn't recommend that you do it without a lot more experience.
Back to top
The_Happy_Duck
Fri May 11 2012, 09:38AM
Registered Member #4089
Joined: Fri Sep 09 2011, 04:40PM
Location:
Posts: 19
I actually meant by '3000 capacitors' that each one had 1000pF and 1KV, was this taken into account? I was comparing tiny ones to larger ones. I am guessing you were using the equation; 0.5*C*V^2?

Edit; I did the calculation and got the same answer, never mind

Can you take a look at this for me?;
http://www.sourcingmap.com/300uf-15kv-30kw-threaded-ceramic-door-knob-high-voltage-capacitor-p-200473.html?currency=GBP&utm_source=google&utm_medium=froogle&utm_campaign=ukfroogle
My calculations say that this would output 33,750J, I don't think that can be correct.
What am I getting wrong here?

Also could you give me some indication of what a good energy output would be?
Back to top
Mattski
Fri May 11 2012, 02:42PM
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 522
wrote ...
Can you take a look at this for me?;

My calculations say that this would output 33,750J, I don't think that can be correct.
What am I getting wrong here?

Your calculation is fine, the problem is that the specs are wrong. No way is that capacitor 300uF, it's probably 300pF. So instead of 34 thousand joules it's 34 thousandths of a joule.
Back to top
The_Happy_Duck
Fri May 11 2012, 06:38PM
Registered Member #4089
Joined: Fri Sep 09 2011, 04:40PM
Location:
Posts: 19
Mattski wrote ...

wrote ...
Can you take a look at this for me?;

My calculations say that this would output 33,750J, I don't think that can be correct.
What am I getting wrong here?

Your calculation is fine, the problem is that the specs are wrong. No way is that capacitor 300uF, it's probably 300pF. So instead of 34 thousand joules it's 34 thousandths of a joule.


Ah, ok thank you.
Another thing, I thought one joule was a tiny amount of energy?
I thought it was not used in electric bills because it is so small so instead they used kWh's?
Back to top
Harry
Fri May 11 2012, 07:19PM
Registered Member #4081
Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139
Correct, 1 joule is nothing. A kWh is 3.6 million joules, for perspective.
But it is the rate of energy transfer that is important with EMP's, and in general, capacitor experiments. A 1000J could be used in 1 second in a heater at 1000W, but in a 100 microsecond capacitor experiment it will reach (1000j/0.0001) 10 000 000W or 10 million watts, realistically this figure is lower because of resistance and inductance in circuits.
Back to top
The_Happy_Duck
Fri May 11 2012, 08:19PM
Registered Member #4089
Joined: Fri Sep 09 2011, 04:40PM
Location:
Posts: 19
Harry wrote ...

Correct, 1 joule is nothing. A kWh is 3.6 million joules, for perspective.
But it is the rate of energy transfer that is important with EMP's, and in general, capacitor experiments. A 1000J could be used in 1 second in a heater at 1000W, but in a 100 microsecond capacitor experiment it will reach (1000j/0.0001) 10 000 000W or 10 million watts, realistically this figure is lower because of resistance and inductance in circuits.


I am guessing that discharge time varies with capacitance?
Back to top
The_Happy_Duck
Sat May 12 2012, 02:40PM
Registered Member #4089
Joined: Fri Sep 09 2011, 04:40PM
Location:
Posts: 19
Another question regarding these capacitors,
Would something like this be suitable;


I am thinking it would not make a very good EMP due to the capacitance but I am not sure, all of these capacitors with over 1 Farad seem to hold a good yield. I am still searching for those big blue capacitors which everyone with washer launchers seem to own.
Back to top

Moderators: Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Bjørn, Dave Billington, Steve Conner, Wolfram, Mads Barnkob

Jump:     Back to top

Powered by e107 Forum System
 
Legal Information
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.