check to see if capacitor is full

ambitious i know but i have the will and curiosity to do it.

But not the basic training or intellectual capacity to understand what you are doing.

I'd be concerned for other peoples' safety, except that coil guns are a dud concept that won't actually work.

im not oging to be firing this at anyone, its for educational purposes.

im doing a rail gun. and in order to do that i need to learn other tricks.

you comment doesnt provide any useful information.

Capacitors don't have a specfic "capacity". They store charge. The capacitance is the amount of coulombs of charge that they store, and it is proportional. It's a ratio. So many coulombs per volt.

A theoretical "ideal" capacitor has no limit to the charge it can store and the voltage potential.

Real capacitors have a voltage rating, which indicates the voltage at which the dielectric will break down or be degraded. It is generally recommended that you choose capacitors with a voltage rating substantially above the actual voltage you expect it to experience. I don't know where this "95% capacity" notion comes from exactly. I suppose it depends on the specific application.

Suppose you have a 100 microfarad capacitor rated at 300 volts. It will store 100 micro-coulombs of charge for each volt that it is charged to. If you charged it to 200 volts, it would have 20,000 micro-coulombs of charge in it.

You measure the amount of charge in a capacity by measuring the voltage.

Do you know the difference between a coil gun and a rail gun ?

My advice would be to buy a voltage display, about $4 on ebay, and use that to display your voltage, exactly the way it does in the video.

except that coil guns are a dud concept that won't actually work.

coil gun (AKA Gauss Rifle)

100uF , 500V Cap



Q = C * V | Q = charge in Coulombs, C = capacitance in F, V = Voltage in volts

J = C*V | J= Joules, C = Coulombs, V = Volts

Q(C) = C(F)*V(V) = 100uf * 300V Q = 0.03 Coulombs (30 mC)

J= C*V | J= Joules, C = Coulombs, V = Volts 0.030 C * 300 V J = 9 joules

One joule in everyday life represents approximately: the energy required to accelerate a 1 kg mass at 1 m·s−2 through a 1 m distance in space.

FYI, a AAA battery weighs about 0.5 g.

SOOOO useful.

because of this it clicked for me what the 2 numbers mean. this the proper way to put in a capacitor? and where would i put my a0 pin to detect and confirm that the capacitor is full.


I guess yes, and nowhere on that breadboard as it is now.
Where did your voltage divider go ?

This answer is as incomplete as the question was.

here you go.

when i fire it up the voltage reader starts at 2.4 then drops to 0 in a few seconds. its running on 5v and capacitor is 100uf / 25v.


The photo is not well focused and too dark (you might want to stick some dark tape to the Arduino's USB connector). I doubt your Huawei P6 smartphone is the best suited device to take this picture. Can't see very well what's going on there. But i can see that this is not even close to what you asked or what you showed 1 picture ago. Because of this photo i can't see how the resistors are connected. But i can see that this is not a capacitor charging form the power supply, and your description doesn't tell the story that would show such setup either. You have built an entirely different piece of hardware here (more like a filter), You connected the input A0 to the marked pin of the capacitor. That pin should go to GND, and that's why the mark clearly says -. You want to sense the other pin of the capacitor.

Start again, and show a better photo next time please.

hold up, how did you know my phone was a huawei p6?

anyways, i subbed the a0 wire with orange for asthetics. i also took your advice and covered the usb port to help remove the light.

please review the new photo attached.


You are communicating more than you think you are...

That picture is better. But it still shows something else than what you think you have built. This is what you have built:

Compare it to the schematic you received before, it is different and does something completely different.

Back to your original question...

I'd recommend the following: Put your multimeter across the capacitor and time how long it takes to charge. Then, just assume it going to take the same amount of time every time it's charged. Add some time in your software... i.e. If it takes 2 seconds to charge, program the Arduino to charge it for 2.2 seconds or more. (You can't "overcharge" a capacitor as long as you don't over-voltage it.)

As someone else already pointed out, a "regular" small capacitor is going to charge-up "instantly" when directly connected across the power supply. But, a large capacitor bank for a rail gun is probably going to take a bit longer, and in fact you'll probably need to slow down the charging (maybe with a resistor) so that you don't damage your power supply or battery.

mas3 where do you go to make those schematics, is it a program?

and also how did you know i have a huawei p6?

picture uploaded with a capacitor and 2 1k resistor.

since there was only 1 other picture...


Grieva: and also how did you know i have a huawei p6?

No secrets here mate.

You and your rail gun are being watched....

my rail gun doesnt exist yet. not sure if this capacitor is even charging...either that or my volt reader isnt working right...

is there a working code/setup to detect the voltage through pins? im pretty sure mine isnt working right.

Your circuit is all messed up.

Your cap is backwards. (it will explode eventually)
Your voltage divider should be in parallel with the cap.
The cap should not be IN SERIES with the voltage divider.
The +5V should connect to the + side of the cap and the input side of the voltage divider.
The black stripe with the “-” symbols should be connected to ground.

This is what MAS3 was trying to tell you.
This is also a good example of the inexperience with electronics that makes you dangerous.
The cap polarity was clearly explained yet you still got it backwards.
If you did this with a HV cap at 300V it would explode .

See attached corrected schematic.


what are you smoking. the capacitor is connected to power and ground correctly. the strip is ground you cant miss it.

You MUST be blind.

since i cant even get this right at all, maybe you can show me a working example because reading text and a schematic is CLEARLY not working out.


Grieva, is the program. I use it also for quick schematics for the forum.

Ok, my mistake, the cap polarity is correct but the voltage divider is wired wrong.

I see you used orange for NEG and GREEN for POS, so that threw me off but the voltage divider is connected to the wrong side of the cap. It should be in parallel with the cap, connected to the side that has the green wire. (the + side) (poor choice of wire colors Typically GRN = GND, ORANGE, & RED = POS) In Europe they like brown (+) & blue (-)

See my schematic. Google "SCHEMATIC CAPTURE"

what are you smoking.

I quit smoking (cigarettes) on my birthday last April. (about 2 months ago)

i have no idea what the different colors of cables are for other than black and red.

i upped a new picture.