Whats the biggest size cap you can buy?

[Beamin]

Whats the largest size cap you have ever worked with and whats the largest you can buy / largest they could make? I would imagine they would be used for HVDC power inverters. Is there a world record biggest cap? a kilo farad would be crazy. I remember on photonic induction he had some huge box cap he would charge with high voltage and blow things up with. Mikes electric stuff has the destrucatron. The biggest I have is 1F 12 volts that I got used from someone selling car stereo parts. Haven't really played with it besides accidentally shorting it.

[RoGeorge]

I saw 4KF/2.5V listed at Mouser
https://eu.mouser.com/Power/Supercapacitors/_/N-6uivw?P=1yfs3v7
and 6KF/2.5V in the Nichicon datasheet
http://www.mouser.com/ds/2/293/e-jd-203016.pdf

[tautech]

Biggest I've worked with: 50,000 uF in a Mig welder.
The originals were horrible leaking 6x 10,000 uF single stud mount PCB¹ types, sandwiched between two alloy plates that were on insulated standoffs.

1. Not Printed Circuit Board, this muck: Polychlorinated biphenyl
https://en.wikipedia.org/wiki/Polychlorinated_biphenyl

[BNElecEng]

I recently used 2x 16v 500F modules in series. The amount of current we could pull was frightening. It's been turned into a safety video for apprentices to show them that low voltage is not a guarantee of safety.

[Cyberdragon]

The large capacitors people blow stuff up with are industrial AC capacitors, used in substations and factories I assume for PF correction. You can get them on Ebay, not sure where else though.

[frozenfrogz]

https://www.supercaptech.com/graphene-supercapacitors-2-8v-30000f-and-3v-12000f-made-in-china
http://burcev-i-co.com/news-2012-10-07-novost-2

[ConKbot]

If you want the real scary stuff, http://www.ga.com/capacitors
Have a peek at general atomics' scatter plot and the brochure below. 10kv, almost 10mf (not uf!) 350-500 kj in a single capacitor.

[SeanB]

Saw some 10uF 11kVAC capacitors at the scrap yard. Sadly they did not want to sell them to me....... would have made some nice PFC capacitors though, though they were around 1m tall, with large insulated connection posts.

[daqq]

Well, large... in terms of capacity there are maxwell that have several thousand Farads ( http://www.maxwell.com/products/ultracapacitors/threaded-weldable-cells ). In terms of energy, well, as was mentioned there are high voltage capacitors that can probably kill a person just by looking at them. The scariest are pulse high voltage capacitors that can deliver MW+ of power.

[Beamin]

https://www.supercaptech.com/graphene-supercapacitors-2-8v-30000f-and-3v-12000f-made-in-china
http://burcev-i-co.com/news-2012-10-07-novost-2

CSR Zhuzhou Electric Locomotive Company continues the development of transport means using supercapacitors having recently introduced the electric bus with the fastest charging time in the world (10 seconds thanks to supercapacitors).

10 seconds?
In Washington DC the city talked all these cab drivers into buying Nissan 100% electric cabs with a tax rebate. They showed them charging stations all around DC. Turns out those charging stations ae only for patrons of the businesses and they can't use them. They have to drive to virgina to line up to recharge their cabs which takes 30-45 minutes. They have to do this twice a day. So not only do they lose an hour to 1.5 hours or work charging they have to plan to not run out of charge to get to the recharging station as well as wait in line because all the other electric cabs have the same dilemma. I don't see how the cab drivers ever thought they could be competitive doing this. Tax break and no more gasoline costs! Gas is pretty cheap compared to the fairs they charge in DC where you have to ride a cab or take the piss ridden crime ridden down right dangerous ill maintained subways system.

[Zero999]

I worked at a defence contractor, prototyping electric armour, which contained some big, nasty,high voltage capacitors. I can't go into detail, in terms of energy, volts and amps, but it was enough to blow the human body to pieces.

[piguy101]

I've got some 2.6 kF 2.5 V supercaps that are used for regen braking of a formula style racecar at university. We've charged them up and shorted them together for giggles. Even at 2 V, the sparks can be sustained for probably around 30 seconds when shorted with some huge 0 awg wire. I'm guessing we pulled more than 1 kA and the conductors get really hot.

[Beamin]

Is it true that some caps gain their polarity based on the way they are fist charged? IE you could plug it in backwards as long as it was always used in that direction?








































































































































I wonder what capacitance is of an airplane flying at operational speeds ad heights.

[Cerebus]

I wonder what capacitance is of an airplane flying at operational speeds ad heights.

The capacitance of a hollow metal sphere (in isolation) is 4 pi epsilon₀ R, where R is the radius of the sphere, epsilon₀ is the permittivity of free space, and hopefully 4 and pi don't need explaining. So a sphere with a 1 cm radius is about 1 pF, 30 cm about 30 pF and a sphere the size of the earth about 700 uF.

Deriving a similar equation for an irregular object such as a plane is left as an exercise for the student.

[Beamin]

I wonder what capacitance is of an airplane flying at operational speeds ad heights.

The capacitance of a hollow metal sphere (in isolation) is 4 pi epsilon₀ R, where R is the radius of the sphere, epsilon₀ is the permittivity of free space, and hopefully 4 and pi don't need explaining. So a sphere with a 1 cm radius is about 1 pF, 30 cm about 30 pF and a sphere the size of the earth about 700 uF.

Deriving a similar equation for an irregular object such as a plane is left as an exercise for the student.

What about a neutron star?

[Cerebus]

What about a neutron star?

What's the exact radius and exact mass, allowing for relativistic effects?

[Kevman]

A lot of Arcade machines have one or more giant capacitors in them because they drove stupid amounts of 5v logic from linear PSUs.

Ataris, for instance, usually have a 'big blue'- 27,000 uF 25V. The Paperboy I was trying to troubleshoot was drawing something like 12A for each of its 2 logic boards, all for 7000s logic and RAMs and POKEYs and such.

Stupid Paperboy. It's still broke 

I just noticed that screw terminal cap of that size costs $30 on Digikey but the Snap in is $4.62? Screw terminals are 5x the cost of the rest of the cap? 

[T3sl4co1l]

Physically largest, or largest value (farads)?

Value in a single part, some kind of supercap.  If you don't mind a nonlinear C(V) curve, then batteries.

The physically largest, practical, cap might be the Navy's array of caps for their railgun.  They aren't directly visible, but they fit into multiple shipping containers.  They are likely polypropylene film capacitors, on the order of 50mF and 2kV (or more than that, I forget, I'd done the calculation once).  They're all connected in parallel with kickless cables, so can reasonably be counted as a single large capacitor.

The physically largest, bar none, is probably a galactic cluster with many AGNs, spewing out conductive plasma that permeates the cluster; the conductivity is very low (in everyday terms), but nonzero, so over very long time constants (millions or billions of years -- the speed of light is still a factor in this, mind, so it's not slow in that sense!), it should behave as a capacitor with respect to the surrounding universe.  The extents of such a conductive region are on the order of millions of light-years, for which you can calculate the capacitance-to-infinity of such a sphere.

Tim

[AndyC_772]

Are there not some very large capacitors used by power distribution companies for power factor correction of inductive loads?

[Cyberdragon]

Are there not some very large capacitors used by power distribution companies for power factor correction of inductive loads?

yes, we have mentioned these in this thread. Industrial PFC caps are the caps people also use to blow things up with on youtube.

[frozenfrogz]

They're all connected in parallel with kickless cables, so can reasonably be counted as a single large capacitor.

I have heard that term before but have no clue as to what »kickless« means - enlightenment would be highly appreciated! 

Edit: My guess would be that it has something to do with reduction of induced electro-magnetic fields due to the way the cables are wound, but even Google could not help me out - all results are for sourcing cables without telling me what makes these special :/

[ConKbot]

Found this on an image search for kickless cable.

http://image.ec21.com/company/m/mj/mj0/mj0293/upimg/04_02.jpg

Looks like the cables are constrained so they aren't flopping all over the place due to Lorrentz forces. Even a small capacitive spot welder can have the cables jump on discharge, I'd hate to see what a railgun could do.

[T3sl4co1l]

Yup!  They're useful anywhere a lot of amps are present, especially transient loads, and those requiring low inductance.

You can put an induction coil on the far end, hook it up to an induction heater power supply, and not know anything is different (the power supply settings are nearly the same).

The ones we used for that were made of probably a hundred twisted pairs, run together in parallel, and bathed in water for cooling.  We had problems with arcing at the leads, because they weren't well insulated (the metal blocks seemed to be separated by a wafer of G10 (mechanical FR-4), while water flushes over the gap).

A twisted pair runs about 300nH/m, but a hundred in parallel is less than 3nH/m.

Both properties -- the reduction of physical kick, and the minimal inductance -- are key in a railgun.

They are definitely kickless cables, because they don't move, by themselves, at all!  In the video, the gun recoils, and the cables are moved by it.

Needless to say, there are multiple points at which a 60MJ is not a cheap device.  Just a few meters of this cable, for an induction coil, runs a few thousand bucks.  Though come to think of it, the cables are probably the cheapest major component in that project...

Tim

[G7PSK]

I don't know what capacity it was but I once had a welding transformer that weighed close to 700 KG with a power factor correcting capacitor mounted on the side weighing just over 200KG. The welder was a two operator unit each operator could pull 540 amps at 95 volts continuously. I purchased it from a sale in a shipyard very cheaply as no one else wanted it. 

[Beamin]

What about a neutron star?

What's the exact radius and exact mass, allowing for relativistic effects?

Exactly 25 miles in diameter and a mass of 758,983,123,843,690,275,636,256,346,932,456,469,297,357 AMU: That's assuming ~10^23 of neutrons is equal to one gram and the star is a few times bigger then our sun but I might be off by a few orders of magnitude/ decimal places. I was surprised how many decimal places that actually is given the universe only has 10^80 "things" in it and holds 10^120 plank volumes.