Electrolytic capacitors sometimes blow up -- due to heat, old age, or lack of use(?).
I have some old studio flashes used for photography and they contain some high voltage electrolytic capacitors. I use them once in a long while. But if they ever blow up, it would be very unpleasant.
Could someone reassure me that it is not going to happen, or suggest a solution?
I would say that generally speaking they heat up before exploding so perhaps fixing a very low temp thermal fuse to the outside/top of the cap, wired into the supply rail would help but I somehow doubt a guarantee. They all should have a vent, like any pressure vessel, but obviously they don't all or those fail to work. I've seen the bolied electrolyte mess in a part of a lab and hole in the ceiling where a techie replaced a large ps one, the wrong way round.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
It's not going to happen.
Happy now?
It is fairly important to use them regularly, like once or twice every couple of months, to keep the internal chemistry formed. The quality of those old capacitors is probably much better than average, and I wouldn't worry about them blowing up. You probably wouldn't want to sit and stare at them for hours at a stretch, but I wouldn't hesitate to use them like yhou say you do.
The caps in flashes generally charge via an inverter circuit. Compared to other types of supply that have electros hanging across the end of them, the inverter supply is likely to be quite high impedance, and will charge the caps relatively slowly. This being the case, it is highly unlikely that they would fail in any 'explosive' way. If they were to fail at all as a result of being 'woken up' after a long period of slumber, they would most likely fail short circuit, in which case, the inverter will probably just groan a bit, and shut down.
Arfa
By any chance, do you have any cites for that? Thanks.
Photo-flash caps are typically "good chemistry" and also typically charged quite slowly from a relatively LV supply (batteries). Consider how much energy must be transmitted into those caps from the batteries before they have enough energy to physically explode. That is not quite the same as making a bright flash. Not gonna happen. However if you have rapid recovery mains-supplied flash units, you *may* be able to make them explode - that would require multiple-failures, however. Not just the caps failing.
Also keep in mind that most caps "blow up" because they are connected at the wrong polarity and-or are subjected to a very high over- voltage. Note "multiple failures" above. Mostly they just short or heat up and open, or leave a sloppy mess.
Peter Wieck Wyncote, PA
I agree. It's not like they are sitting there on a stout rail inside some
1000 watt power amp. Also consider the quality of the cap itself which is probably pretty high.
I have 44 years of experience at Bell Laboratories, dealing with reliability and other electronic-related quality issues like electromagnetic compatibility. I also have done electronics repairs for 50 years, putting myself thru college doing tv repairs, which I still do.
I agree 100% with the other posters. If the capacitors were to get leaky enough to start to heat up internally, they would most likely load down the power supply and reach a steady-state condition short of exploding.
Exploding usually results from rapid heating when whatever internal mechanism exists for releasing the hot gasses does not get a chance to react due to sudden, rapid heating. If the capacitors are being charged from a lower voltage - almost always the case - there simply is not enough energy capability to heat them fast enough to cause an explosion before the venting can take effect. As I and several other posters said, those capacitors were not the dime a dozen type manufactured today.
H. R.(Bob) Hofmann
If it's a line powered flash, you can increase the input voltage slowly to allow the cap to reform after non-use.
This might be more difficult with an inverter type though.
I think that the cap he is referring to, is the energy discharge source for striking the xenon flash tube, in which case, they are not charged from a low voltage battery supply - rather from a high voltage supply derived from an inverter circuit, which is itself powered by the low voltage and impedance batteries.
Given that the (largely) urban myth stories about unused electrolytics exploding, generally refer to those strapped across high voltage supplies, I would guess that this is what prompted the OP's question.
Arfa
Geez, twice a month? I let them sit 5 years and there is no problem, except a slightly longer initial charge time. :)
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The electrolytics in electronic flashes do seem to take rather a long time to recharge the first time they're used after sitting for a while. Whether this is due to deforming, or completely discharging, I don't know.
My experience in restoring the Polaroid #355 flash is that the electrolytic caps, though almost 40 years old, are rarely bad.
They will blow up if connected backwards to a source of sufficiently high current, but to blow up in normal use would be extremely unusual, I'd be much more worried about a meteorite crashing through your roof to kill you in your sleep than that.
"James Sweet" hath wroth:
Yeah. That's lots of fun. See videos at:
Seems to be a fun thing to do. I couldn't find a video of a large electrolytic explosion, just the small ones.
Start worrying:
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Do you remember the insurance company, which offered every girl with name Mary protection against the risk of immaculate conception?
Regards, H.
"peter" hath wroth:
Dunno. There's quite a bit on the topic of old electrolytic caps in the cazapitor section of the Repair FAQ at:
Photoflash:
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
I would not worry about the caps blowing up. I you have good quality flashes, most likely the caps are properly rated to be very safe. It is very rare that these caps blow up. Usually they will fizzle out. They are supposed to have a release.
If a cap was to blow up, the case of the flash should be strong enough to not break opened or be destroyed.
--
JANA _____
I have some old studio flashes used for photography and they contain some high voltage electrolytic capacitors. I use them once in a long while. But if they ever blow up, it would be very unpleasant.
Could someone reassure me that it is not going to happen, or suggest a solution?
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