Need specific electronic part advice
HollyMinkowski
Posts: 1,398
I want to use a propeller to control the discharging of capacitors
into small coils.
What I am trying to do is create very powerful magnetic bursts
from the tiny coils. The coils will be a few turns of #18 enameled wire
about 1" diameter. The pulses of current passing into the coils from
the caps will be of very short duration but of huge amperage. I will
be using a variable dc source to charge the caps in the range of
50 - 300v.
The duration of the pulses will be however long it takes the caps to
discharge. I wonder if there is a way to recapture some of the energy
as the field collapses and use it for the next pulse??
What sort of part could I get at a reasonable price that could be easily controlled
from a prop output pin and handle such huge current pulses?
I won't be sending more than 30 pulses per second.
If there is no low cost device then I wonder if some sort of relay
could be actuated 30x/sec? and could it stand the constant arcing
that would result...seems like it would eat up the relay contacts.
I am considering photo flash caps but I'm uncertain about whether they can
stand up to this sort of abuse? Is there a better capacitor choice? I want
about 2000uf capacity.
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"Where am I? Where am I going? Why am I in a handbasket?"
into small coils.
What I am trying to do is create very powerful magnetic bursts
from the tiny coils. The coils will be a few turns of #18 enameled wire
about 1" diameter. The pulses of current passing into the coils from
the caps will be of very short duration but of huge amperage. I will
be using a variable dc source to charge the caps in the range of
50 - 300v.
The duration of the pulses will be however long it takes the caps to
discharge. I wonder if there is a way to recapture some of the energy
as the field collapses and use it for the next pulse??
What sort of part could I get at a reasonable price that could be easily controlled
from a prop output pin and handle such huge current pulses?
I won't be sending more than 30 pulses per second.
If there is no low cost device then I wonder if some sort of relay
could be actuated 30x/sec? and could it stand the constant arcing
that would result...seems like it would eat up the relay contacts.
I am considering photo flash caps but I'm uncertain about whether they can
stand up to this sort of abuse? Is there a better capacitor choice? I want
about 2000uf capacity.
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"Where am I? Where am I going? Why am I in a handbasket?"
Comments
-Phil
Leon
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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle
They might be able to be charged faster, not sure as we needed to keep our transformer weight down and did not need faster cycle times. They were good for thousands of cycles. We would very carefully match capacitors in each bank to have the same measured capacitance believing this would increase capacitor life.
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Searider
I think 18 AWG stranded wire is about 0.0064 ohms/ft. Assuming a coil consisting of a "few turns" is about 1 foot, that means total resistance of such a coil is 0.0064 ohms. From V = IR, at 50 volts, we get a current of roughly 7700 amps. I say "roughly" because the inductance of the coil will give you a little impedance on start-up, but I think these numbers give you some idea of what you're up against. With Power = VI, then 50 volts would give you an instantaneous power output of roughly 385000 watts. A watt = a joule/second. The kinetic energy of an automobile traveling at highway speeds is roughly 300000 joules. So if you crashed a speeding automobile into your coil over the course of 1 second.... that gives you a ballpark feel for the kinds of energy your coil will be up against. At 300 volts, the situation will look less pretty.
Edit: I guess your time constants are pretty small, roughly microseconds? So maybe my car crash analogy isn't very good.
Anyway, I hope that helps,
Post Edited (ElectricAye) : 9/13/2009 9:25:33 PM GMT
I hope to charge the caps much faster than 2-4seconds, I hope a larger
power supply will allow for this.
The coils will only be a fraction of an ohm in resistance so at the voltages I want
to use the current will be astronomical and the caps should drain extremely fast
so the duration I would guess at way less than a millisecond. I suppose I could
place a coil on the work bench and suspend a similar coil above it a few inches away.
Then charge a cap and discharge it into the coil...I could watch the current
pulse in the second coil using a scope. I know where I can get a switch that
has mercury in it...maybe that could survive repeated pulses for testing the
strength of the magnetic field.
I may be making this using much too high voltage, it may be overkill, when you
do ohms law on the R of the coils the current is enormous even with low V so
maybe that's all I really need. All the DIY projects I can find that are similar
to what I'd like to build seem to leave out any details on coil design and voltages.
I want to experiment with how magnetic fields affect the brain.
www.google.com/search?hl=en&source=hp&q=persinger+coils&aq=f&oq=&aqi=
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"Where am I? Where am I going? Why am I in a handbasket?"
patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=0&f=S&l=50&TERM1=Transcranial&FIELD1=ABTX&co1=AND&TERM2=stimulation&FIELD2=ABTX&d=PTXT
The Oxford handbook of transcranial stimulation By Eric M. Wassermann, Charles M. Epstein, Ulf Ziemann
They talk about 3000v being discharged into a small 6 turn coil of #10 sized wire using a part
called a thyristor. This is way beyond anything I want to play with, I just wonder how the
coils survive this? If you do the calculations the coils are pulsed with the current used by
thousands of homes...just for 200-500Us, but still!
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"Where am I? Where am I going? Why am I in a handbasket?"
maybe I can just scale this way down to work with cheaper parts
at much lower voltage.
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"Where am I? Where am I going? Why am I in a handbasket?"
and 20,000 amp peaks... 478.00 each
That puts a quick end to any dream of making a full power project!
But looking at the simplified schematic above, if I used a cheap scr
and a v of perhaps 12 - 35v could I use ordinary cheap electrolytic caps?
It looks like the diode would prevent reverse voltage coming back
when the field collapsed in the coil?
I guess the way to vary pulse length would be to switch in/out various
amounts of capacitance, maybe 100uf to 2000uf or would that only
vary the magnitude of the current pulse?
I'd like to be able to vary the pulse length over about 200 - 500Us
After doing some more reading I discovered that the full power devices
can do things like activate the visual cortex if the coils are placed above it.
I'm not interested in that kind of power anyway...it would just be too scary
as it could do some sort of damage I'd think. But researchers report interesting
results with even weak pulses...so I'm aiming for moderate power levels.
I'm going to email or call the 3 guys that wrote that book and see if I can
squeeze any ideas about lower power circuits out of them.
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"Where am I? Where am I going? Why am I in a handbasket?"
Post Edited (HollyMinkowski) : 9/13/2009 11:20:40 PM GMT
There's some off-the-shelf technology that you might look into. For frying your brain without the use of a pan, consider this:
www.ameritherm.com/aboutinduction.php
Notwithstanding misgivings about high-voltage/high current/strong magnetic fields near MY trans-cranial space, you definitely are in scr (thyristor) territory.
Brand new high capacity scr's can be expensive but a check on e-bay, etc for surplus industrial units will get you some to play with. Also, the circuit you showed can be adjusted for some lower maximum current by changing "Lumped circuit resistance". The reference book for SCR's was the GE SCR and Thyristor Handbook.
· The abuse the coils can stand is largely dependent on their ability to dissipate the heat during discharge. A rule of thumb for thermal effects is I^2t. where I is in amps and t is in seconds. Essentially, if it survives at some nominal current, you can increase the·current as long as you reduce the time sufficiently.
Cheers,
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Tom Sisk
http://www.siskconsult.com
Post Edited (stamptrol) : 9/14/2009 1:07:03 PM GMT
Tom,
that's a very interesting rule of thumb! But could you elaborate a little on this? What exactly does your rule of thumb equal? Power not to be exceeded?
Also, is that I2t or is that I2t ?
thanks,
Mark
Does anybody want that near their cuckoo's nest!
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Tracy Allen
www.emesystems.com
One flew east and
One flew west
and one flew on transcranial stimulation
until they were burnt to a crisp.
Whatever you do, I urge you to do it with extreme caution.
Are you trying to build a rail gun?
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Please use mikronauts _at_ gmail _dot_ com to contact me off-forum, my PM is almost totally full
Morpheus & Mem+dual Prop SBC w/ 512KB kit $119.95, 2MB memory IO board kit $89.95, both kits $189.95
www.mikronauts.com - my site 6.250MHz custom Crystals for running Propellers at 100MHz
Las - Large model assembler for the Propeller Largos - a feature full nano operating system for the Propeller
····gizmodo.com/5357776/diy-rail-gun-is-terrifying-comes-with-building-instructions.
Holly?
-Phil
That guy has a massive collection of capacitors!
And the size of those wires and bars connecting the capacitors up!
Imagine touching those 2 wires together....
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"Where am I? Where am I going? Why am I in a handbasket?"
No, but they are kind of cool.
Too much like a weapon for my taste though.
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"Where am I? Where am I going? Why am I in a handbasket?"
Check this site for information of what the above combination can do:
http://www.capturedlightning.com/frames/shrinkergallery.html
Be safe,
DJ
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Instead of:
"Those who can, do.· Those who can't, teach." (Shaw)
I prefer:
"Those who know, do.· Those who understand, teach." (Aristotle)
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OMG...what a dangerous collection of stuff.
The idea of a triggered gap is interesting.
I'd never have thought of that. It's sort of an
electrically controlled mechanical device.
Using a high voltage but low amp pulse
to initiate a high current jump across a gap without
moving the parts to make the gap smaller
or increasing the voltage of the high amp
supply. You could control this with a prop
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"Where am I? Where am I going? Why am I in a handbasket?"
·· Sorry for the confusion! It's I2t and is usually found on fuse charts to predict the thermal damage potential as a given fuse is subjected to an overcurrent event.
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Tom Sisk
http://www.siskconsult.com
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