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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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2nd Dec 2017, 9:18 pm | #41 |
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Re: Electrolytic capacitor fails after 1 hour in service!
You keep saying they're a reputable brand.
Reputable manufacturers know exactly what their reputation is worth, and their prices carry a premium because of it. Reputable manufacturers know what damage counterfeits do to their reputation, and faulty units that get stolen. They very much want to track down and destroy the sources of these parts. It is to the advantage of the rest of us if you contact the manufacturer and some action is taken to get the duds off the market. Please contact them. Reputable manufacturers also know that occasional units fail, and they handle these events in a way which preserves their reputation for standing behind their products. They are also likely to be interested in understanding the cause of the failure and this improves their parts, so please contact them. David
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2nd Dec 2017, 10:27 pm | #42 | |
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Re: Electrolytic capacitor fails after 1 hour in service!
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It is a big deal in the aviation industry how to dispose of faulty parts, often they end up getting recycled & sold as refurbished. Sometimes they mutilate them before dumping. There was a story about a helicopter blade(these things are worth 100's of thousands of $) being mutilated with multiple holes drilled in it. Someone found it, filled the holes with Bondofil, repainted it with a masterful black gloss coat and on sold it. At least with axial electros the polarity is self evident due to the rubber seal. But radial ones it relies on the plastic cover being put on and labelled correctly. Check the physical size of the caps against others, if its a mislabeled 16V one it should be physically smaller than a 63V one of the same capacity. One thing I found recently with radial electros, if they have leaked electrolyte in the past (which can sometime not be easily optically visible) if meter probes are placed on the rubber base, 2 or 3mm apart, they conduct because the electroltye is on the rubber's surface. I recently repaired a video monitor where a film of invisible electrolyte had coated the board in an area of a few square inches and corrupted the function of some high impedance circuits in a color processor circuit.The board also had a matt looking conformal coating which I think was microscopically porous. Standard pcb cleaner had no effect at all, in the end warm water managed to remove it. Another electrolytic nightmare. |
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2nd Dec 2017, 10:56 pm | #43 | ||
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Re: Electrolytic capacitor fails after 1 hour in service!
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Quote:
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2nd Dec 2017, 10:57 pm | #44 |
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Re: Electrolytic capacitor fails after 1 hour in service!
It sounds too me like the capacitor shouldn't have failed, but the way to find out what's going on is to replace with another one the same and see if it fails again. If it does, then either there's something odd about the circuit which is damaging the capacitor, or you've got a bad batch of capacitors. Then you can try one of the same ratings but from a different supplier or manufacturer and see if that helps.
Decoupling a gate driver chip is hardly arduous duty for a big electrolytic like that, and you'd know pretty quickly if its ripple current rating was being exceeded: it would get really, really hot. In the case of ripple current, it's the heat that does the damage. That's why higher voltage rated capacitors tend to have higher ripple current ratings for the same capacitance. They're in bigger cases so they dissipate the heat better. Chris
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2nd Dec 2017, 11:00 pm | #45 | |
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Re: Electrolytic capacitor fails after 1 hour in service!
[QUOTE=Argus25;996322]
Quote:
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3rd Dec 2017, 12:34 am | #46 |
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Re: Electrolytic capacitor fails after 1 hour in service!
When a blade comes off a helicopter, you can't autorotate to a nice landing, and ejector seats aren't a common fitment...
This is a high probability of killing people. Then there are all the fake drugs. What if something you need to stay alive gets replaced with fake labelled aspirin? David
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3rd Dec 2017, 2:10 am | #47 | |
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Re: Electrolytic capacitor fails after 1 hour in service!
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It seems practically everything in our world has been faked; currency, artworks, watches, DVD's, nearly every electronic part, drugs, nothing is spared, perhaps only cathode ray tubes. I haven't seen a fake one yet, but I wish somebody would try then we might get some spare parts ! Ps: the helicopter that got that refurbished rotor was shown on TV lifting a heavy object (I think a crashed plane out of bushland) and amazingly despite the holes in the main rotor, it didn't break, it was discovered later. I've attached a pdf of a brief Fake Part story I had a while back. Last edited by Argus25; 3rd Dec 2017 at 2:26 am. Reason: add attachment |
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3rd Dec 2017, 6:20 pm | #48 | |
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Re: Electrolytic capacitor fails after 1 hour in service!
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I'm also on the hunt for bigger values; there seem to be a lot of ex-Soviet bloc types that are NOS or pulls from military equipment but the unit cost is very high indeed...
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Al Last edited by Al (astral highway); 3rd Dec 2017 at 6:31 pm. |
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3rd Dec 2017, 6:37 pm | #49 |
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Re: Electrolytic capacitor fails after 1 hour in service!
That may be where you're going wrong. The risk of fake components is lowest from authorised distributors who have regular turnover and direct interaction with the real manufacturer. Grey market things get cheaper and riskier.
Real mil-spec stuff appears affordably on the surplus market, and there's this chief petty officer Pertwee chap whose prices are quite reasonable. David
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3rd Dec 2017, 7:16 pm | #50 | |
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Re: Electrolytic capacitor fails after 1 hour in service!
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Ah, intriguing, David! Who is chief petty officer Pertwee?
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3rd Dec 2017, 10:45 pm | #51 | |
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Re: Electrolytic capacitor fails after 1 hour in service!
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I'm actually involved right now dealing with 1N825A diodes, bought from a big distributor in the US, which are in a different package (DO35) than ordered and certified (DO7). I'm pretty confident that the diodes are genuine, but the paper trail is not quite what it should be - and our customer is not impressed because the different package, with different internal construction, invalidates qualification tests done some years ago. |
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3rd Dec 2017, 11:39 pm | #52 |
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Re: Electrolytic capacitor fails after 1 hour in service!
CPO Pertwee (played by John Pertwee, btw), as us 'olduns' will remember, was a character in 'The Navy Lark', a radio comedy set on and around 'HMS Troutbridge'. He was in Charge of the stores in the series, and various items would 'dissapear' and be sold by said CPO Pertwee on the black market. If challenged he would deny all knowledge of such deals.
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3rd Dec 2017, 11:43 pm | #53 | |
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Re: Electrolytic capacitor fails after 1 hour in service!
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One good one I saw recently was a mosfet with a higher RDSon than the original part. The fakers didn't know that in the circuit is was in, it had little heat sinking because the design always had it off or fully enhanced carrying 20A. So the fake part melted, but probably in other circuits they would have gotten away with it. This is how they get away with it a lot of the time of course, they are aided by the good Engineers who build with conservative design rules and the parts slip through unnoticed and appear to work ok. |
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4th Dec 2017, 1:35 pm | #54 | |
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Re: Electrolytic capacitor fails after 1 hour in service!
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Unfortunately, someone made a blunder on the Web site, indicating the DO35 suffix as obsolete, and DO7 as current. To most users it is immaterial, probably why the error was never picked up. To us and our customer, it is important. I caught it and queried it. Unfortunately the error crept as far as the Certificate of Conformance we received, which indicates that even genuine parts from a genuine manufacturer can be misrepresented. Microsemi have confirmed from a photo I sent, that the diodes, sold as DO7, are DO35 - and although they have not yet received a return, they haven't shouted that they are bogus. But they're amending their on-line data. So Al's capacitor - he's doing all of us a favour by alerting the manufacturer. |
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