How safe are leaking capacitors @ 5V? - Page 1
Forum section: electronics / beginners

author: Rick Law
author_rank: Super Contributor
timestamp: September 29, 2013, 06:35:04 pm
content: This is not a complain about quality or the lack there of, but trying to see if I can finish a project using something damaged rather than waiting for a new one.I have a 4700uF (50V) capacitor that I use for discharge testing. The first time I put over 20V to it, it vented. After I turned it off and let everything settled, I tested it at 5V-ish and it still seem to hold the charge.My intended use is to let it discharge overnight (ie:unattended). I can skip the 20plus volt part for now. My gut feel is: 5V at about 20mA is not a lot of energy, it should be ok. Besides, when discharging, energy level is reducing. So if it "held out" during the charge, the rest of the run should be ok (worst is over, ok meaning safe). Is it?Seeking your comments and thoughts about using a vented cap in the manner described above (unattended, 5V-ish, low double digit mA)...Life ends sooner or later, but there is no sense rushing into it...

author: walshms
author_rank: Regular Contributor
timestamp: September 29, 2013, 06:45:14 pm
content: Quote from: Rick Law on September 29, 2013, 06:35:04 pmLife threatening? No, probably not.Safe? Can't really say. Depends on whether it's contained or not, what the dielectric actually is, and whether it's experiencing a temperature rise and how much.It probably won't behave like a failing tantalum, but why take the chance?

author: Dave
author_rank: Super Contributor
timestamp: September 29, 2013, 06:48:44 pm
content: Why would you want to use a blown cap? Toss it away and grab a new one.If your "50V" caps blow at 20V, they probably aren't genuine, rather a very crappy counterfeit. Your best bet would be to Widlarize the whole batch, so they can never bother you again.

author: Rick Law
author_rank: Super Contributor
timestamp: September 29, 2013, 06:53:21 pm
content: Quote from: Dave on September 29, 2013, 06:48:44 pmI have only one - not a batch. I am just trying to make the most of the weekends rather than waiting for yet another week or two for a new part.

author: amyk
author_rank: Super Contributor
timestamp: September 30, 2013, 07:11:08 am
content: After it's vented its capacity will likely be a fraction of its original value, if it has any left at all. So... probably safe, but not going to be much of a capacitor either.

author: Zero999
author_rank: Super Contributor
timestamp: October 01, 2013, 03:13:49 pm
content: Quote from: Rick Law on September 29, 2013, 06:53:21 pmDon't you have a store which sells components in your area such RadioShack or Maplin? You could also go to the dump and pick up a load of old electronic equipment such as HiFi's, PCs and rip the capacitors out of themIf you can't find the desired value then connect many smaller capacitors in series.It's not worth messing around with old, damaged parts, as a new 6.3V to 10V 4700uF capacitor shouldn't be hard to find and is cheap too.

author: Rick Law
author_rank: Super Contributor
timestamp: October 11, 2013, 02:53:07 am
content: Quote from: Hero999 on October 01, 2013, 03:13:49 pmI need it @ 50V. It was a new 4700uF-50V rated and vented first time I pushed it over 20V. My need was to let it run (ie: discharges as it drive the circuit) overnight test (unattended) of a test of continual reducing voltage. I just wanted feed back from experience folks about letting it "carry-on" so I can finish a part of my project that weekend. Spending the weekend looking over old parts to remove components would not leave me enough time to finish. And I was quite sure I don't have many over 30V in my old stuff.When I was experimenting with booster boards, I had (at least) twice pushed beyond the cap's voltage and I tried continuing on with the vented cap out of curiosity "gee, it vented, but let me just turn the board back on and see if it still works." While I had seen them work, but I did not feel comfortable using a vented one with much larger capacity overnight unattended.(After my DMM tested it to be around 4700uF still...) I ended up having a go at it and I did the runs attended instead of unattended while I sleep. I cut short some of the parameters (like reducing the starting voltage from 30V down to mid-20's). I added a couple of 1000uF in parallel expecting that the vented 4700 might have reduced capacity, and I wanted the discharge to take longer...The darn thing actually held out for two days (and cummulative 1.5 nights) that weekend. Only thing was, I just didn't feel comfortable letting it go unattended. My replacement should arrive soon.

author: Greyersting
author_rank: Regular Contributor
timestamp: October 11, 2013, 03:03:21 am
content: I doubt it will be enough to KILL you.

author: Rick Law
author_rank: Super Contributor
timestamp: October 11, 2013, 03:45:13 pm
content: Quote from: Greyersting on October 11, 2013, 03:03:21 amWhere there is a will, there is a way. But first thing first, lets beef up the life insurance. One can be immortal to be the first...

author: Halfdead
author_rank: Contributor
timestamp: October 12, 2013, 12:46:57 pm
content: You're joking right?

author: dr_p
author_rank: Frequent Contributor
timestamp: October 12, 2013, 02:10:45 pm
content: are you really, really, really, REALLY sure you didn't power it backwards? An electrolytic with -20V on it will crap out FAST.

author: fluxcapacitor
author_rank: Frequent Contributor
timestamp: October 12, 2013, 09:50:49 pm
content: Youve already said you didnt feel comfortable about leaving it unattended,it can lead to one of those moments where you say to yourself "i knew i shouldn`t have done that" .

author: RSTPhysics
author_rank: Newbie
timestamp: October 12, 2013, 10:33:38 pm
content: It's not going to be life-threatening... If you're the least worried about it, make sure there aren't any flammable or easily ignitable materials around it and you'll be safe.

author: madsci
author_rank: Regular Contributor
timestamp: October 13, 2013, 05:34:22 am
content: There is a chance it could fail short circuit and damage the circuit it is in....what other damage this may cause depends on the nature of the device.Vented = shit canned.

author: pickle9000
author_rank: Super Contributor
timestamp: October 13, 2013, 06:37:58 am
content: If you have to ask the question (regarding safety) the answer is easy "No I shouldn't do it". No mention of safety glasses? It's not going to take your head off but eye damage or fire is a real possibility.At least make sure you don't leave it unattended. I'm my shop no bench was to be powered up without a person in the room.

author: Rick Law
author_rank: Super Contributor
timestamp: October 14, 2013, 02:38:15 am
content: Quote from: dr_p on October 12, 2013, 02:10:45 pmYeah, I am really really really sure of that. I checked that many times and the circuit has been running for a while at around 10volt. Each time I rerun, I check again so I was really sure. What I am not sure is which capacitor actually did the venting.Since I was trying to do a test as voltage decrease, I ran a bunch of caps in parallel. The 4700uF was the second one in a chain of 6 (470, 1000, 1000, 220, 4700, 330), the smoke came from the 4700 end and it did looks like it came from the 4700. Careful inspection later (after the runs I was going to do) shown the 330 is the one that looks a little bulge out on the top whereas the 4700 looks absolutely normal - the 330 is the only "reused" cap whereas all the other ones are new.In any event, my need for that is done, I ran it attended and finished the runs I wanted to do. I plan to order a replacement 4700 should I want to run that test again. I was actually fairly confident about it. The tests started with the caps fully charged and starts discharge as I run the test. I lowered the desire voltage to around 22. I know that when it didn't vent again at the start, once started, as the cap discharges and the voltage will continue to decrease and as the voltage decreases the less likely it will vent. While it made logical sense to me (that the high risk of vent/spark is at the start), I was interested in thoughts from those more experienced.My concern was not really life or death. I know a 4700uF@30V doesn't really have enough energy to burn down my desk. I hate the smell, and I did not want the smoke alarm going off at night or sparking - and I was hanging on the hope that I could do over night run unattended. Rather than waiting another week for parts, I decided to go with it and just babysit the silly thing. It worked out.ThanksRick

author: geraldjhg
author_rank: Regular Contributor
timestamp: October 14, 2013, 01:13:38 pm
content: hithrow it away and find a discarded crt monitor for partsnot may low voltage high uf but funin in doubt discard it, its not worth the time spentold caps are generally bad till proven goodand for that you need time scope etc etcsaludos