How do i charge a capacitor? - Page 1
Forum section: electronics / beginners

author: shane_95
author_rank: Regular Contributor
timestamp: July 04, 2012, 08:15:04 am
content: I have a 16v 10uf (thats micro ferrets, yes?) and i want to charge it up, how do i do that?

author: Simon
author_rank: Unknown
timestamp: July 04, 2012, 08:17:36 am
content: apply a voltage to it. Do not try to charge it up to 16V, leave 20-50% margin so say 12V. Simply connect to a battery or other power source

author: shane_95
author_rank: Regular Contributor
timestamp: July 04, 2012, 08:24:41 am
content: Quote from: Simon on July 04, 2012, 08:17:36 amoh ok that easy is it :p i only have 9v but ill give it ago. I got a bread broad so im just mucking around with it having a bit of fun

author: Simon
author_rank: Unknown
timestamp: July 04, 2012, 08:29:18 am
content: what exactly are you trying to achieve ?

author: Rerouter
author_rank: Super Contributor
timestamp: July 04, 2012, 08:29:42 am
content: micro "farads" and if its an electrolytic type (round cylinder) take good note of which side is positive and negative,

author: Simon
author_rank: Unknown
timestamp: July 04, 2012, 08:30:53 am
content: Quote from: Rerouter on July 04, 2012, 08:29:42 amVery good point, I nearly missed taking an eye out with an exploding 2200 uF capacitor i connected back to front

author: shane_95
author_rank: Regular Contributor
timestamp: July 04, 2012, 08:39:13 am
content: Quote from: Simon on July 04, 2012, 08:29:18 amnothing, just being bored

author: notsob
author_rank: Frequent Contributor
timestamp: July 04, 2012, 09:02:06 am
content: I would suggest safety glasses, as you are learning and haven't experienced it yet, electrolytic caps will blow up if hit with a large overvoltage (with lots of acrid smoke)

author: shane_95
author_rank: Regular Contributor
timestamp: July 04, 2012, 09:10:15 am
content: Quote from: notsob on July 04, 2012, 09:02:06 amim only using a 9v battery and the cap is rated at 16v, i dont think it will go, well i hope not

author: Simon
author_rank: Unknown
timestamp: July 04, 2012, 09:13:46 am
content: any voltage revered on a cap produces jets of acid

author: shane_95
author_rank: Regular Contributor
timestamp: July 04, 2012, 09:20:00 am
content: *puts safety glasses on* ok, don't revise the weirs. *thinks to self* red to the + and black to the - got it

author: vk6zgo
author_rank: Super Contributor
timestamp: July 04, 2012, 10:26:54 am
content: I wouldn't sweat on it!The cases of people being injured by reversed electrolytic capacitors are very few & far between!Most such caps will get quite hot if reverse connected for a fair length of time,(minutes)& vent fairly graciously.Some older types,& cheaper new types may go bang,but it isn't the horrific danger some people allege it to be.It all depends on the circuit the caps are in.I have found caps which have been wired in reverse in Sony picture monitors,due to a mistake in the silk screening of the overlay on the non copper side of the PCB.The thing worked for 15 years like that!!I am fairly doubtful if your 9v battery could source enough current to cook the electrolytic in any case.OK,you've got your electrolytic charged up--what are you going to do next?Here's an idea,why not learn about RC time constants?Find a 1MegOhm resistor.Now if you look in a book on Electronics,(they are those funny things with a lots of bits of paper between two hard bits),you will find a formula something like this: t = CR,where R is in Ohms,C is in Farads & t is in seconds.If you use this formula, t = 10 seconds,for C=10 microfarads,& R=1 MegOhm.Let's try it:With the cap fully charged,place both the 1M resistor & your Digital multimeter across the capacitor terminals,time how long the cap takes to discharge till the voltage across it looks like zero volts.What do you notice?What's this---It took 50 seconds! what's wrong?Back to the book!You will find that the voltage across C should drop to approximately 37% of the original voltage in the timeperiod : t=CR ,so that after that time has elapsed,the voltage across the C will be, (in your case) 37% of 9 volts, or around 3.33 volts.*The voltage in theory,never quite reaches zero,but is near as dammit there at time=5CR.At this point,you will probably have found that the times don't quite coincide with those calculated.Why do you think that is so?Hint: Think cap accuracy , DMM input impedance,& battery voltage .*PS: in my first edit,I forgot to change the figures,& missed them again in the subsequent edits,so instead of making it easier to read,I just made it incorrect.It should now be both clear & correct.

author: T4P
author_rank: Super Contributor
timestamp: July 04, 2012, 03:47:12 pm
content: Some electrolytics caps are used as AC bypass filter caps therefore whether they are flipped around or not it doesn't really matterUnless it's the input to an opamp2V tops in reverse before any cap goes

author: vk6zgo
author_rank: Super Contributor
timestamp: July 04, 2012, 09:30:20 pm
content: Quote from: DaveXRT on July 04, 2012, 03:47:12 pm*I have seen this figure quoted as gospel on this forum a number of times,but it has not been my experience in over 40 years of working in Electronics.

author: T4P
author_rank: Super Contributor
timestamp: July 05, 2012, 01:45:56 am
content: Well ... apparently, i don't think them caps can survive 1V in reverse

author: SeanB
author_rank: Super Contributor
timestamp: July 05, 2012, 04:58:25 am
content: The 2V rating depends....... In low frequency use yes, in power switching no.

author: T4P
author_rank: Super Contributor
timestamp: July 05, 2012, 05:26:44 am
content: Quote from: SeanB on July 05, 2012, 04:58:25 amI see what you mean, in low frequency there's hardly any ripple current but in power switching never because of the ripple currentAfter all they are used as AC bypass caps