Author Topic: A question about capacitors (real world ones, not PPC kind)  (Read 2421 times)

mbear

  • Stood Far Back When The Gravitas Was Handed Out
  • Major
  • *
  • Posts: 4497
    • Tower of Jade
So for any electrical engineers on the board, I've been seeing that a capacitor bank is used by the U.S. Navy's railgun and EMALs system. I understand that you can dump a bunch of electricity into a capacitor and then dump it all out again when you need it (like launching a shell/plane) but my question is can you use a capacitor as a battery?

In other words do if I have a capacitor do I absolutely have to open the tap to full or can I crack it to 1% and use the capacitor as a battery?

Thanks in advance!
Be the Loremaster:

Battletech transport rules take a very feline approach to moving troops in a combat zone: If they fits, they ships.

You bought the box set and are ready to expand your BT experience. Now what? (Thanks Sartis!)

guardiandashi

  • Major
  • *
  • Posts: 4826
Re: A question about capacitors (real world ones, not PPC kind)
« Reply #1 on: 23 June 2017, 10:21:01 »
Yes you absolutely can use a cap as a battery in fact there are /were some computers where the cmos settings and real time clock is powered by a cap.
basically caps in electronics are used in a number of ways. just offhand:
all dc power supplies use caps, to spread and flatten out the waveform (essentially turning a sine wave into a square wave, with a bridge rectifier essentially being a circuit that turns both sides of the sine wave into a square wave, and a reverse square wave, that are then superimposed on each other, and smoothed out.
filters, caps can pass a signal to ground, effectively removing it from the circuit
charge/discharge power sources
stable or more stable power sources.
etc.

the electronic symbol for a cap looks like -|(- or -||- basically if you look at almost any schematic you will find that all over the place.

the charge /discharge rate for caps, has to do with the ratio between the size of the cap (measured in uf) and the resistance of the circuit measured in ohms.

I could go on... but I am still 1/2 asleep.
« Last Edit: 23 June 2017, 10:47:50 by guardiandashi »

Sabelkatten

  • Lieutenant Colonel
  • *
  • Posts: 6952
Re: A question about capacitors (real world ones, not PPC kind)
« Reply #2 on: 23 June 2017, 16:13:36 »
Basically a battery stores power in chemical bonds - two materials that wants to react by exchanging electrons when connected. This means they can store a fair amount of power, but getting the power out is limited by the speed of the chemical reactions.

Capacitors store power directly - in the most basic form two plates where you push electrons into one of them and draws them out of the other. This means you can get the power in or out very quickly (the electrons are "free", sort of) but but the amount of power you can store is limited because if you put in too much you'll get a spontaneous discharge between the plates.

Regulating the power output is really the same for a battery of capacitor: put some sort of resistance in the circuit, limiting how much current can flow. Ohm's law: I = U / R.

I know there's been hybrid vehicles built with capacitors instead of batteries, but I don't think there are any being sold. As mentioned capacitors are used to store power in computers. To take a practical example we just put together a new power supply system at work where we have a microcomputer powered by a current that is occasionally interrupted due to a relay (when the relay switches between two different power sources the current can't flow). A capacitor set after the relay is charged while the relay is closed and then discharges while the relay switches to provide power to the MCU.

elf25s

  • Major
  • *
  • Posts: 4391
Re: A question about capacitors (real world ones, not PPC kind)
« Reply #3 on: 24 June 2017, 09:48:49 »
back in high school we had got an old tv with vacuum tubes as part of excercise the teacher gave us we had to take the little monster apart and name all the parts...
it was fun until some idiot burned me with a capacitor.
yah surprise!

if you work with them or planning to work with them handle with care...just little heads up
you sure cannot out run death...but sure as hell you can make that bastard work for it!

ClarkeMarek

  • Captain
  • *
  • Posts: 1958
  • The original
Re: A question about capacitors (real world ones, not PPC kind)
« Reply #4 on: 24 June 2017, 10:48:02 »
back in high school we had got an old tv with vacuum tubes as part of excercise the teacher gave us we had to take the little monster apart and name all the parts...
it was fun until some idiot burned me with a capacitor.
yah surprise!

if you work with them or planning to work with them handle with care...just little heads up

Yep.  Dangerous little squirts if you're not careful.  Hence why I was told to wait a few seconds(or minutes, depending) for the things to power down before messing with them.
"Son, if dynamite was dangerous, do you think they'd sell it to an idiot like me?"~Al Bundy
Five rounds, rapid!

guardiandashi

  • Major
  • *
  • Posts: 4826
Re: A question about capacitors (real world ones, not PPC kind)
« Reply #5 on: 24 June 2017, 11:28:23 »
Yep.  Dangerous little squirts if you're not careful.  Hence why I was told to wait a few seconds(or minutes, depending) for the things to power down before messing with them.
honestly in the grand scheme of things the caps in an old tube style tv aren't the most dangerous parts in it.  that particular honor actually goes to the picture tube.  as it if not properly grounded can and will charge back up to its operating voltage which can be anywhere from ~18kvolts up to 50k+ volts depending on the size of the tube it might only store a few miliamps, but if it gets you just the right way...

Tymers Realm

  • Lieutenant
  • *
  • Posts: 1292
Re: A question about capacitors (real world ones, not PPC kind)
« Reply #6 on: 24 June 2017, 14:43:04 »
Oh I can recall what can happen when you put a Cap in backwards.
I was working for a maintenance place and unintentionally put a fairly large Cap for a power supply in wrong. The fact it went boom quite nicely shortly after a burn-in started scared everyone where I was working at.

Sabelkatten

  • Lieutenant Colonel
  • *
  • Posts: 6952
Re: A question about capacitors (real world ones, not PPC kind)
« Reply #7 on: 24 June 2017, 14:57:15 »
honestly in the grand scheme of things the caps in an old tube style tv aren't the most dangerous parts in it.  that particular honor actually goes to the picture tube.  as it if not properly grounded can and will charge back up to its operating voltage which can be anywhere from ~18kvolts up to 50k+ volts depending on the size of the tube it might only store a few miliamps, but if it gets you just the right way...
It's actually fed through a couple of caps, those are the ones that hold the voltage up. The elements of the vacuum tube will discharge quite fast. But the basic rule is still "don't touch anything for several hours after unplugging it, and the first thing you should touch it with is the voltmeter probes!".

Oh I can recall what can happen when you put a Cap in backwards.
I was working for a maintenance place and unintentionally put a fairly large Cap for a power supply in wrong. The fact it went boom quite nicely shortly after a burn-in started scared everyone where I was working at.
Do it in a small room and watch the smoke! :D

elf25s

  • Major
  • *
  • Posts: 4391
Re: A question about capacitors (real world ones, not PPC kind)
« Reply #8 on: 24 June 2017, 14:59:39 »
honestly in the grand scheme of things the caps in an old tube style tv aren't the most dangerous parts in it.  that particular honor actually goes to the picture tube.  as it if not properly grounded can and will charge back up to its operating voltage which can be anywhere from ~18kvolts up to 50k+ volts depending on the size of the tube it might only store a few miliamps, but if it gets you just the right way...
ohhh dont remind me about those...
if we as kids even knew how bloody dangerous these things were even with covers on we would had never come near them
btw i was the only kid in my neighborhood who knew how to fix these old heat producing monsters... so instead calling  a shop my neighbors called me.
yah older than i appear. and yah i remember when transistor radios were a thing...expensive little crappers when they came out and reception of the stations was not too good...
you sure cannot out run death...but sure as hell you can make that bastard work for it!

Matti

  • Major
  • *
  • Posts: 5085
  • In Rory we trust
Re: A question about capacitors (real world ones, not PPC kind)
« Reply #9 on: 24 June 2017, 16:05:22 »
Oh I can recall what can happen when you put a Cap in backwards.
I was working for a maintenance place and unintentionally put a fairly large Cap for a power supply in wrong. The fact it went boom quite nicely shortly after a burn-in started scared everyone where I was working at.
Capacitor can be put on whichever way. Electrolyte capacitor on otherhand...
You know what they say, don't you? About how us MechWarriors are the modern knights errant, how warfare has become civilized now that we have to abide by conventions and rules of war. Don't believe it.

Sabelkatten

  • Lieutenant Colonel
  • *
  • Posts: 6952
Re: A question about capacitors (real world ones, not PPC kind)
« Reply #10 on: 25 June 2017, 03:06:02 »
Capacitor can be put on whichever way. Electrolyte capacitor on otherhand...
Just to confuse things some electrolyte caps are not polarized, while some non-electrolyte caps are. Standard rule: if there is some kind of marking near one of the legs, check the datasheet!

Aokarasu

  • Captain
  • *
  • Posts: 2013
  • Commander, Musei Yuuchi
Re: A question about capacitors (real world ones, not PPC kind)
« Reply #11 on: 26 June 2017, 07:09:36 »
The anti-collision light on top of the F-16 vertical stab had a power supply that stepped up the voltage to something in the multi-thousands, via capacitors and such. The procedures in the technical orders specified waiting two minutes after power being removed from the circuit before disconnecting the cannon plug to the power supply.

Simon Landmine

  • Lieutenant
  • *
  • Posts: 1223
  • Enthusiastic mapmaker
Re: A question about capacitors (real world ones, not PPC kind)
« Reply #12 on: 26 June 2017, 08:18:59 »
I remember the Signals section in cadets had some obsolete field radios with beer-can-sized capacitors in them. They used to have fun out of hours charging them up and then discharging them with a wire coat-hanger attached to the end of a wooden broom-handle. Not a great idea, but they did make a good bang and spark.
"That's Lieutenant Faceplant to you, Corporal!"

Things that I have learnt through clicking too fast on 'Move Done' on MegaMek: Double-check the CF of the building before jumping onto it, check artillery arrival times before standing in the neighbouring hex, and don't run across your own minefield.

"Hmm, I wonder if I can turn this into a MM map."

elf25s

  • Major
  • *
  • Posts: 4391
Re: A question about capacitors (real world ones, not PPC kind)
« Reply #13 on: 26 June 2017, 12:32:38 »
I remember the Signals section in cadets had some obsolete field radios with beer-can-sized capacitors in them. They used to have fun out of hours charging them up and then discharging them with a wire coat-hanger attached to the end of a wooden broom-handle. Not a great idea, but they did make a good bang and spark.
funny that...we as kids used to do same thing whenever we could get away with that at summer camp...
now keep in mind we were about 9 and 10 age range at the time.
love former eastern block summer camps....
you sure cannot out run death...but sure as hell you can make that bastard work for it!

Matti

  • Major
  • *
  • Posts: 5085
  • In Rory we trust
Re: A question about capacitors (real world ones, not PPC kind)
« Reply #14 on: 26 June 2017, 14:51:39 »
funny that...we as kids used to do same thing whenever we could get away with that at summer camp...
now keep in mind we were about 9 and 10 age range at the time.
:o
Did anyone got hurt?
You know what they say, don't you? About how us MechWarriors are the modern knights errant, how warfare has become civilized now that we have to abide by conventions and rules of war. Don't believe it.

elf25s

  • Major
  • *
  • Posts: 4391
Re: A question about capacitors (real world ones, not PPC kind)
« Reply #15 on: 26 June 2017, 18:32:49 »
:o
Did anyone got hurt?
amazingly enough no
but we did learn how to hunt ...how to prep food you caught... and tracking skills along with how to play nasty game of find and catch with other groups of kids...
you may say it was an abreaveted boot camp before we got drafted manditory for boys voluntary for girls at age 18.
whenever my group got loose from camp we would find old cars or tracktors along with some old electronics or what passed for electronics at the time and just wreck havoc.
to be honest i am amazed that none of us got killed after we got our hand on few dozen old tvs that used tubes and crt monitors...btw capacitors on those things still worked after being exposed to elements for week before we found them.
you sure cannot out run death...but sure as hell you can make that bastard work for it!