check to see if capacitor is full

Current circuit for testing.

lcd says its at 2.47-2.5 volts. its not that bright its got 2k ohms for contrast.

Pretty sure my voltage divider is working as intended.

the 2 resistors in the divider is both 1k ohms respectively.

IMG_20150613_111439[1].jpg

the 2 resistors in the divider is both 1k ohms respectively.

What would they be if your capacitor was charged to 50V dc ?

2k ohms.

or 1k ohms sin paralell

R1 = ? R2 = ?

Grieva: 100ohms?

100 Ohm can't be right. And answering a question with a question, hmm..

If you answer that question and elaborate on how you came to that answer, we might be able to get what you aren't getting yet.

pretty sure this is wrong but…

50v to 5v is 1700ohm and 190ohm

what i did is simply used a calculator

https://learn.sparkfun.com/tutorials/voltage-dividers/all?print=1

because apparently im stupid and cant figure out how to get vout without resistors.

You replied while i was typing.
Don’t get too frustrated and think you are “stupid”, as that has not been established yet.
But you do need to communicate enough for anybody to be able to help you out.
This is what i had typed before you re-replied:

I don’t think so, but the ratio would get you on the safe side.

However you would put an almost 2000 (2K) Ohm resistance on your capacitor with 50 volts.
Put Ohm’s law to that an see what current will flow, i’ll tell you the capacitor will run empty quite fast.

I’d choose some other values, and keep an eye on the standard values available.
1700 isn’t and 190 is neither.

You want to end up on the safe side, so choosing the lower value resistor to be a bit higher would be a good choice if you come up with different values (that depends on the ratio you need).
@Grieva: Can you tell us what ratio you need ?

i know those arent standard, but i was answering a question.

so now that i got the voltage to drop how can charge a capacitor and check if its full.

Here we go again...

"How do I charge a capacitor ?"

"To what voltage ?"

"I don't know,. I don't have a rail gun yet."

For the THIRD TIME, you cannot ask for a design of a circuit for which NO DESIGN CRITERIA have been presented. How many times do we have to tell you this ?

to 95% of its capacity. goign full risks damage.

i want to just know how charging it would work with wires and such. wouldnt the voltage increase AFTER the capacitor would indicate its near full?

95% of WHAT VOLTAGE ?

How do you expect to design a circuit to measure 95% of an UNKNOWN voltage ?

Apply power to the capacitor, and it will charge. You might want to limit current to the capacitor, and that will reduce the charging speed. You already know how to check if it is full, as you would read the value that represents 100 % of the 5 volt maximum readout you created with the voltage divider.

Ah, some mistake there. Why do you think 100 % of the capacity means taking a risk ? That's not true. I think you are mixing up some things here.

@raschemmel: SHOUTING isn't going to help.

Nothing is going to help

@MAS3, All caps of ONE word is not SHOUTING.

SHOUTING IS WHEN THE ENTIRE SENTENCE IS ALL CAPS. (occassionally there is an "!" at the end too)

95% of WHAT VOLTAGE ?

How do you expect to design a circuit to measure 95% of an UNKNOWN voltage ?

to 95% of its capacity. goign full risks damage.

I think the OP is confusing "voltage capacity" and "voltage rating"

as the title says i wanna know how you can check if a capacitor is fully charged. like programming wise and a basic schematic.

something like this. when you hear the cpacitors charge the meter goes up for what i assume is the voltage.

Mock rail gun (just model with no functionality) how can you detect how much the capacitor is charged and such.

Apply power to the capacitor, and it will charge. You might want to limit current to the capacitor, and that will reduce the charging speed. You already know how to check if it is full, as you would read the value that represents 100 % of the 5 volt maximum readout you created with the voltage divider.

This is not relevant to the OP's original post , which was how to tell if a cap (that is one of the primary components of a rail gun) is fully charged. The voltage divider questions addressed measuring a voltage greater than 5V. Explaining how to measure a cap that is charging to 5V has no relevance to this thread. The whole object of this thread is to find out how to measure a cap that is charging to a voltage (which remains unknown to this day) in order to determine when the cap has charged to 95% of it's capacity (which , as I stated, cannot be known until the actual voltage (not 5V) of the rail gun cap is known. Obviously the rail gun is not going to work with a cap that is only charged to 5V. Since we cannot seem to obtain the actual operating voltage of the rail gun cap from the OP , this line of questioning is pointless.

Why ?

Because the circuit design is supposed to be based on the DESIGN CRITERIA, which , as I pointed out, has not been presented yet. Granted, a 5k pot across rail gun charging circuit power supply could be used to adjust the 95% threshold for a level detector comparator circuit. Probably, instead of posting here and going around and around in circles, the OP should just Google "Capacitor charging" and read this. And then you will be ready to proceed with this.

edit: never mind for now

raschemmel you forget i am completely new to this. and your questions to a newcomer is very confusing. you also confuse that im going to be putting small capacitors in my rail gun i want to build. Again i only want to test charging a capacitor to gain a basic understanding on how to wire it up.

i only say 95% because i did not want to risk any damage. if 100% does not pose any risk then thanks for clarifying.

yes im confusing voltage rating and voltage capacity, if you can clarify that would be fantastic.

what do you mean by the actual voltage. i dont know what you mean? do you mean AC or DC? in that case, it will be DC.

im going to do a quick setup sometime later today and please let me know if everyth9ing is set up correction, suggestions, corrections and pointers are always welcome.

How about just waiting so long that capacitor is full. After reading some posts here, I think it is the best way.

Did you say a rail gun. If the OP is an absolute beginner in electronics, I think he may hurt him/her self with those kind of things.

If you exceed the voltage rating, you will blow up (literally) the capacitor. So your capacitor should always have a much higher rating than what you plan on using. You cannot charge a capacitor with a higher voltage than that what is available. But you can charge multiple capacitors, and then stack them to get an also stacked voltage.

That will pose another risk to personal damage, and certainly in your case, being all new to this. You need to understand the components in order to understand the risks, and they are considerable here.

i am a beginner but i am not stupid. i am very cautious about touching anything. and i always discharge the capacitors with my screwdriver(by touching both power and ground simutaniously)

MAS3 - thanks but i am aware of the capacitor danger. Like i said i always discharge them.

i also procured myself a disposable camera and now have a 330v 160uF capacitor. i found a camera shop that is willing to give me literally boxes full of cameras. So therfor i struck gold on that. I also have the flash/transformer too!!

Also your comment about having a much higher rating, can you please clarify? i dont want to misunderstand.

I also would like to take this opportunity in helping me understand this better and i am learning a good deal. i was never a good reader in terms of understanding, i was always a man who learns by doing it and making mistakes.

Thank you to all. I know i can be difficult, but i appreciate it.

You might be able to discharge a capacitor with a screwdriver if it was a small cap charged to a low voltage but the video you linked shows the rail gun charging to 289 V. If you had a large cap charged to 300 V and did something like discharge it by shorting the terminals, energy would vaporize the screwdriver and splash thousands of particles of molten metal in your eyes and face. I think that would qualify as "stupid". Your supposed to have a power resistor connected across the terminals with a push button in series , labeled "DISCHARGE".

In all honesty, from what I have seen so far, and from the questions you have asked , this project is beyond your skill level and too dangerous for you to attempt. This is very similar to children playing with matches.