Safely testing 22 kV capacitors

[Roy L. Fuchs]

Hm... So... DO you think that they are now useless, or simply a little
out of spec?

They are probably fine. The spec is there so that the original
purchaser knows what to expect from them at their rated specs. They
are likely slightly lower in value, but they probably don't have any
holes punched through them, since they get used in systems where they
are used within their voltage spec.

They may be slightly off their original mark, or they my be right on
the money. Either way, maxwell makes some of the best HV pulse caps
in the world.

 

[Ignoramus26172]

They are probably fine. The spec is there so that the original
purchaser knows what to expect from them at their rated specs. They
are likely slightly lower in value, but they probably don't have any
holes punched through them, since they get used in systems where they
are used within their voltage spec.

They may be slightly off their original mark, or they my be right on
the money. Either way, maxwell makes some of the best HV pulse caps
in the world.

Thanks Roy. That's encouraging. I will try to get appropriate HV
equipment and then will test the caps. I may keep one for myself.

i

 

[Dave Hinz]

Why not keep them and start trying to shink coins?
http://205.243.100.155/frames/shrinkergallery.html

I was thinking of that, actually. Iggy, what would you need for some of
these?

This site has been recently edited to take out most of the technical
details. I suspect it was a bit too dangerous for the average user.

The Wayback Machine (www.archive.org) will have the old version of the
site, of course.

 

[Michael A. Terrell]

Maybe Ignoramus is within his rights.

But Win has a very good point. In any event, if Ignoramus alienates Win
and just a few other knowledgeable regulars here, his (Ignoramus's)
experience will be badly degraded.

So he may want to think seriously about Win's protest.

--Mac

Just think if those Win and those other people got fed up and had
Goggle remove all of their archived posts? Then the archives would be
nearly useless. All that would remain would be newbies asking
incomplete questions, flames, and idiotic remarks.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Roy L. Fuchs]

Just think if those Win and those other people got fed up and had
Goggle remove all of their archived posts? Then the archives would be
nearly useless. All that would remain would be newbies asking
incomplete questions, flames, and idiotic remarks.

There was a time when they archived regardless of the flag setting.

With all the money google has, one would think that they would have
several hundreds of terabytes of archival data online and available.
One would think they would have other service providers using their
servers as the master archive.

That is still no excuse for a poorly planned web interface to
Usenet.

 

[Ignoramus26172]

I was thinking of that, actually. Iggy, what would you need for some of
these?

I think that I would need all my caps, and some way to vent the copper
gas from exploding copper coils. In other words, too violent for me.

I want to keep one or two caps at most. I think that I could build a
coke can crusher (you can do a google search for "can crusher
capacitor"), using materials readily available, such as solid copper
wire, fiberglass, pvc pipes, and steel balls. I think that 2 uF at 18
kV could be enough to deform the cans.

i

 

[Rich Grise]

Big Van DeGraf machines produce microamps! Charging a uF to 20,000 V at
one uA will take 20,000 seconds. And, that's one of those 6 foot tall
jobs with a 6" wide belt.

How about a Wimshurst machine?

http://www.google.com/search?q=wimshurst

But wtih any kind of static generator, you'd need some kind of voltage
limiting, wouldn't you? It wouldn't do to destroy the caps while trying
to test them! Is there such a thing as a calibrated spark gap? Maybe
a shunt regulator from an old, old TV - or the whole HV section, but
again, it'd have to be calibrated somehow.

Cheers!
Rich

 

[Ignoramus26172]

You need to get a collection of EEM catalogs. Back in the 1993 edition,
the Victoreen pages in the Resistor section says that it's most
likely a MAXI-MOX rated at 22.5 kV. Rated at 4.5 watts if it's a
MOX-3-13, epoxy coated or 7.5 watts for a MOX-3-12 silicone coated.

Mark, thank you VERY much for looking it up.

i

 

[Bruce L. Bergman]

I was thinking of that, actually. Iggy, what would you need for some of
these?

Well of course it is! That's what makes it fun... And as I recall
he had huge warning signs plastered all over the site, too. And
triggered the shrink blast from outside the garage while standing
behind a healthy barricade like a truck.

That's why I tell all my customers the old saw that is SO true:
"I'm a trained professional - If you see me running, try to keep up."

The Wayback Machine (www.archive.org) will have the old version of the
site, of course.

But usually minus all the pictures.

--<< Bruce >>--

 

[Ignoramus26172]

Bruce,

I like the saying that there are no old, bold captains.

i

 

[Winston]

Iggy, does that transformer output alternating current or
direct current?

--Winston

 

[Ignoramus26172]

Iggy, does that transformer output alternating current or
direct current?

AC, as it turns out.

i

 

[Cydrome Leader]

I think that I would need all my caps, and some way to vent the copper
gas from exploding copper coils. In other words, too violent for me.

I used to crush quarters. "copper gas" is the least of the problem you
will encounter, and not the reason the solenoids explode.

20 kV is low for quarter crushing.

If it matters, I used 14uF of 50kV energy discharge caps. 30-35kV worked
the best, although inductance is of the circuit is as important as the
voltage.

I didn't dare to connect a scope up to measure the waveforms.

I want to keep one or two caps at most. I think that I could build a
coke can crusher (you can do a google search for "can crusher
capacitor"), using materials readily available, such as solid copper
wire, fiberglass, pvc pipes, and steel balls. I think that 2 uF at 18
kV could be enough to deform the cans.

Use pipe not wire for can crushing.

 

[Ignoramus26172]

I used to crush quarters. "copper gas" is the least of the problem you
will encounter, and not the reason the solenoids explode.

20 kV is low for quarter crushing.

If it matters, I used 14uF of 50kV energy discharge caps. 30-35kV worked
the best, although inductance is of the circuit is as important as the
voltage.

I didn't dare to connect a scope up to measure the waveforms.

That means I do not have enough capacitors.

Use pipe not wire for can crushing.

Thanks... So, what would you say, would 1 uF at 22kV crush a can?

i

 

[Bert Hickman]

That means I do not have enough capacitors.




Thanks... So, what would you say, would 1 uF at 22kV crush a can?

i

Nice catch!

For can crushing you need a minimum of about 400 Joules, and for coin
crushing at least 2000 Joules. I happen to use a bank rated at 140 uF at
12 kV. I also use Maxwell energy discharge caps, but mine are Series C
100 kA high current type. Because mine are rated for only 20% voltage
reversal, I only take the bank up to about 9500 volts (6300 Joules) for
coin crushing. For can crushing, I only go to about 3500 Joules (mainly
to reduce wear and tear on the spark gap switch).

Using all of your 15 caps in parallel would give you a capacitor bank
capable of delivering ~3 kJ, so you are in the right ballpark. However,
can crushing (especially) and coin crushing can cause highly oscillatory
discharges. Rapid voltage reversals are very stressful on a HV
capacitor's dielectric system, and most of Maxwell's pulse caps are only
rated for 10-20% voltage reversal (at faceplate voltage), so you don't
want to run these caps anywhere near their full faceplate voltage if you
are doing can or coin crushing - they WILL prematurely fail. And, you
definitely don't want to be anywhere near the caps when the energy from
the other 14 capacitors dump everything they've got into a single
faulting cap... :^)

Looking at the "Frankenstein" insulator style used on your caps, they
are likely not rated for more than 2 - 5 kA peak (the folks at General
Atomics can probably provide you with their actual specs):
http://www.gaep.com/capacitors.html).

Running more caps in parallel will help to share the peak current seen
by each capacitor. If you plan to do any coin shrinking, treat the coil
like a small bomb, with copper shrapnel being ejected at hyper velocities.

There's more information on my site:
http://205.243.100.155/photos/shrinker5.pdf (1 page summary)
http://205.243.100.155/frames/shrinker.html (more gory details)

And, always remember to be afraid - very afraid - of the energy stored
in these caps. They will not give you any second chances. =:^[

Bert
--
-------------------------------------------------------
We specialize in UNIQUE items! Coins shrunk by huge
magnetic fields, our "Captured Lightning" Lichtenberg
Figure sculptures, and Out-of-Print technical Books.
Visit Stoneridge Engineering: http://www.teslamania.com
-------------------------------------------------------

 

[Robert Nichols]

:For can crushing you need a minimum of about 400 Joules, and for coin
:crushing at least 2000 Joules. I happen to use a bank rated at 140 uF at
:12 kV. I also use Maxwell energy discharge caps, but mine are Series C
:100 kA high current type. Because mine are rated for only 20% voltage
:reversal, I only take the bank up to about 9500 volts (6300 Joules) for
:coin crushing. For can crushing, I only go to about 3500 Joules (mainly
:to reduce wear and tear on the spark gap switch).
:
:Using all of your 15 caps in parallel would give you a capacitor bank
:capable of delivering ~3 kJ, so you are in the right ballpark. However,
:can crushing (especially) and coin crushing can cause highly oscillatory
:discharges. Rapid voltage reversals are very stressful on a HV
:capacitor's dielectric system, and most of Maxwell's pulse caps are only
:rated for 10-20% voltage reversal (at faceplate voltage), so you don't
:want to run these caps anywhere near their full faceplate voltage if you
:are doing can or coin crushing - they WILL prematurely fail. And, you
:definitely don't want to be anywhere near the caps when the energy from
:the other 14 capacitors dump everything they've got into a single
:faulting cap... :^)
:
:Looking at the "Frankenstein" insulator style used on your caps, they
:are likely not rated for more than 2 - 5 kA peak (the folks at General
:Atomics can probably provide you with their actual specs):
:http://www.gaep.com/capacitors.html).
:
:Running more caps in parallel will help to share the peak current seen
:by each capacitor. If you plan to do any coin shrinking, treat the coil
:like a small bomb, with copper shrapnel being ejected at hyper velocities.
:
:There's more information on my site:
:http://205.243.100.155/photos/shrinker5.pdf (1 page summary)
:http://205.243.100.155/frames/shrinker.html (more gory details)
:
:And, always remember to be afraid - very afraid - of the energy stored
:in these caps. They will not give you any second chances. =:^[

Ever thought about the effect that might have on a nice chunk
of plutonium?

 

[Tim Williams]

Ever thought about the effect that might have on a nice chunk
of plutonium?

Not much- plutonium (and manganese) are the most resistive metals, IIRC.
They would induction melt great, though. Both of these facts have the same
reason: the more resistive a metal is, the less bEMF it makes and the more
induction power it consumes, with less reaction force (Lenz' law).

Basically, the discharge's energy would go into heating up the block of
pluotonium, with little force, if any. Although I wonder if you could melt
or vaporize the surface, what with conductivity, skin effect and
instantaneous power being what they are.

Tim

 

[Winfield Hill]

Bert Hickman wrote...

For can crushing you need a minimum of about 400 Joules, and
for coin crushing at least 2000 Joules. I happen to use a bank
rated at 140 uF at 12 kV. I also use Maxwell energy discharge
caps, but mine are Series C 100 kA high current type. Because
mine are rated for only 20% voltage reversal, I only take the
bank up to about 9500 volts (6300 Joules) for coin crushing.

I thought you used four 70uF 12kV caps in series parallel,
for a 70uF 24kV rating? The coin crushing is where you
count on the wire coil disintegrating within the first half
cycle, with the arc rapidly extinguishing to limit reversal
the voltage? Or are you charging to a smaller fraction of
the 24kV bank faceplate rating?

How much of the energy is taken up by the coin crushing and
coil stretching?

For can crushing, I only go to about 3500 Joules (mainly to
reduce wear and tear on the spark gap switch).

That's using 140uF? That would be two paralleled 70uF 12kV
caps from your bank, charged to 7kV, or about 60% of the cap's
faceplate rating? Implying only 35% voltage reversal while
staying under a 20% limit? Is that with a 3-turn coil, which
would be about 1uH? What's the Q of the 13kHz resonance?

Using all of your 15 caps in parallel would give you a capacitor
bank capable of delivering ~3 kJ, so you are in the right
ballpark. However, can crushing (especially) and coin crushing
can cause highly oscillatory discharges. Rapid voltage reversals
are very stressful on a HV capacitor's dielectric system, and
most of Maxwell's pulse caps are only rated for 10-20% voltage
reversal (at faceplate voltage), so you don't want to run these
caps anywhere near their full faceplate voltage if you are doing
can or coin crushing - they WILL prematurely fail. And, you
definitely don't want to be anywhere near the caps when the energy
from the other 14 capacitors dump everything they've got into a
single faulting cap... :^)

So, sticking to 60% of the faceplate rating, that'd be 13kV
allowed on the full 15 x 1uF = 15uF cap bank, which would be
only 1.3kJ available, where 3.5kJ is needed for can crushing?

Looking at the "Frankenstein" insulator style used on your caps,
they are likely not rated for more than 2 - 5 kA peak (the folks
at General Atomics can probably provide you with their actual
specs): http://www.gaep.com/capacitors.html).

For a 3-turn 1uH coil and 140uF caps at 7kV, that's 83kA peak
in your case, Bert? 83kA/15 = 5.5kA. But a higher voltage
would allow using more inductance and lower peak currents.

Running more caps in parallel will help to share the peak current
seen by each capacitor. If you plan to do any coin shrinking, treat
the coil like a small bomb, with copper shrapnel being ejected at
hyper velocities.

There's more information on my site:
http://205.243.100.155/photos/shrinker5.pdf (1 page summary)
http://205.243.100.155/frames/shrinker.html (more gory details)

And, always remember to be afraid - very afraid - of the energy
stored in these caps. They will not give you any second chances.
=:^[

Bert

 

[Ignoramus24006]

Bert, thank you for yout very interesting post. I am not interested
in coin shrinking, however, I am interested in can crushing.

I would like to know if I can do some meaningful experiments with can
crushing if I keep only two caps. (1 uF, 22 kV). I do not want to keep
more. Perhaps somehow getting a "better", faster spark would help with
getting higher instantaneous amperages?

I have a bottle of argon, perhaps I can somehow inject it into the
spark gap to trigger the spark?

As for oscillation and the implied necessity to reduce voltage, what
woul dbe the appropriate voltage to charge the caps to?

i

 

[Bert Hickman]

Bert Hickman wrote...



I thought you used four 70uF 12kV caps in series parallel,
for a 70uF 24kV rating? The coin crushing is where you
count on the wire coil disintegrating within the first half
cycle, with the arc rapidly extinguishing to limit reversal
the voltage? Or are you charging to a smaller fraction of
the 24kV bank faceplate rating?

Although my capacitor bank is capable of being configured for 24 kV (+/-
12 kV with cases of all four caps grounded), I presently use only half
of the bank since it provides excellent results and is completely
compatible with previous charging/control/safety hardware from the
earlier bank that used three 54 uF 15 kV GE caps. [The previous GE caps
weren't up to the task and they began catastrophically failing. Ruptured
cases, gunky arc-blackenned Geconol dielectric fluid oozing onto the
floor.... it wasn't pretty.] The pair of Maxwell caps have delivered
well over 6000 trouble free shots over the last few years.

How much of the energy is taken up by the coin crushing and
coil stretching?

It's really hard to say... but I'd be surprised if even 50% of the
energy actually ends up going into shrinking the coin. Considerable
energy goes into explosively ejecting coil fragments. A fellow shrinker
in Texas has calculated fragment velocities of up to 5000 fps.

That's using 140uF? That would be two paralleled 70uF 12kV
caps from your bank, charged to 7kV, or about 60% of the cap's
faceplate rating? Implying only 35% voltage reversal while
staying under a 20% limit? Is that with a 3-turn coil, which
would be about 1uH? What's the Q of the 13kHz resonance?

Yes, with a maximum bank voltage of 7.1 kV (for can crushing). BTW,
that's the MAXIMUM energy I use - but can crushing can be done with
considerably less energy. Since the work coil remains intact during can
crushing, I assume a high Q load (100% worst case voltage reversal).
Under this scenario, the capacitor dielectric system would see a peak
voltage swing of about 14.2 kV, which is an ~18% voltage reversal based
on the 12 kV faceplate rating of the caps.

I haven't measured the actual circuit Q, but anticipate it's at least
15-20, with most of the losses coming from the spark gap. BTW, can
crushing is quite hard on spark gaps - lots more evaporated metal than
with coin crushing. I recently bought a Pearson Model 301 50 kA wideband
current transformer to allow for isolated current measurements, but
haven't had a chance to hook it into the system as yet.

Also, my current coin shrinker is really not very "efficient" for
crushing cans since its operating frequency is comparatively low. The
system actually oscillates at about 11 kHz (including loop inductances
from cabling, capacitors, and spark gap switch). The compressive force
on the can is a function of skin depth, which at 11kHz is about 0.024".
Since a typical aluminum beverage can only has a wall thickness of about
..0035" (about 1/6th of the skin depth), most of the work coil's magnetic
field passes through the can, leaving only a small portion to do
crushing. Using a lower capacitance, higher voltage bank would work
significantly better for can crushing.

However, the current 140 uF system is almost ideal for crushing coins
(from an esthetic and practical standpoint). Lower capacitance/higher
voltage systems begin encountering coil flashover problems once you go
beyond ~20-25 kV. The coins also begin to develop "toroiding" (i.e.,
having thicker edges versus the interior). For example, here's a Silver
Eagle 1 Oz coin shrunk with higher voltage lower capacitance shrinker in
Texas:
http://205.243.100.155/photos/HVStuff/[email protected]

So, sticking to 60% of the faceplate rating, that'd be 13kV
allowed on the full 15 x 1uF = 15uF cap bank, which would be
only 1.3kJ available, where 3.5kJ is needed for can crushing?

Using 60% voltage derating should work assuming these caps are rated for
20% reversal. And, since it uses a higher operating frequency, can
crushing should be considerably more "efficient". 400 Joules should be
more than sufficient to demonstrate the effect.

For a 3-turn 1uH coil and 140uF caps at 7kV, that's 83kA peak
in your case, Bert? 83kA/15 = 5.5kA. But a higher voltage
would allow using more inductance and lower peak currents.

Yes. However, increasing the inductance lowers the operating frequency,
reducing can crushing "efficiency", so there's a trade-off. YMMV...

Running more caps in parallel will help to share the peak current
seen by each capacitor. If you plan to do any coin shrinking, treat
the coil like a small bomb, with copper shrapnel being ejected at
hyper velocities.

There's more information on my site:
http://205.243.100.155/photos/shrinker5.pdf (1 page summary)
http://205.243.100.155/frames/shrinker.html (more gory details)

And, always remember to be afraid - very afraid - of the energy
stored in these caps. They will not give you any second chances.
=:^[

Bert

Bert
--
-------------------------------------------------------
We specialize in UNIQUE items! Coins shrunk by huge
magnetic fields, our "Captured Lightning" Lichtenberg
Figure sculptures, and Out-of-Print technical Books.
Visit Stoneridge Engineering: http://www.teslamania.com
-------------------------------------------------------