I haven't looked at electro specs closely since the mid '90s. I was involved with a product that used a conventional aluminium electro in an apparently undemanding application. The value was 10uF and variously two types were used- a 10VDC and a 25VDC [ or a bit higher - I forget]. The DC voltage across the cap was constant at a bit under 2 volts DC and was on one of the inputs to a comparator. There were issues with the product but early in the troubleshooting the input circuitry came under scrutiny and it was noticed that the capacitors were being run significantly under their 'working voltage'. The capacitor manufacturers [one Euro] were both asked for comment and both advised against the use of that style of electro under 75 to 80% of the working voltage. The reasons from both related to 'forming'. It wasn't clear whether they meant initial forming or continued forming though. To my mind it doesn't explain the seemingly satisfactory operation of electros as coupling capacitors in early transistor radios for instance. Hard facts concerning time-frames and numerical values for degradations weren't forthcoming. [BTW, the product problem was actually related to the specs for a triac being considerably improved by the manufacturer; the old snubber values were now causing the problem. ]
John K ----- Original Message ----- From: gregebert To: neonixie-l Cc: [email protected] Sent: Saturday, August 27, 2016 2:52 AM Subject: Re: [neonixie-l] Re: b7971 segment current On Wednesday, August 24, 2016 at 12:21:56 AM UTC-7, Jeff Walton wrote: >During the life of the clock, there were a couple failures of the caps in the voltage doubler When your cap(s) failed, was it catastrophic ? I've only had 1 electrolytic fail in recent history, and it was a low-voltage cap that dried-out and shorted at medium-resistance in a Heathkit device (not a clock). No smoke, etc. I've tried to prevent/mitigate cap failures in my designs by using the smallest possible fuse, keeping the caps away from any heat, staying well below the rms/ripple current spec, and using a higher voltage rating than necessary (eg 450v cap running at 340VDC). Recently, I found caps designed for solar-energy applications (TDK Epcos) that boast 85C operation for 10,000 hours, so I use them now. Most electrolytics are rated for 2000 hours. That doesn't mean the caps will fail (ie, explode) in 2000 hours; they just wont be within spec (capacitance out-of-spec, but otherwise functional). Electrolytics are a strange beast compared to other components. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/66df0632-699e-4d44-866b-a9c52e1fc701%40googlegroups.com. For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/F42BB68AED9F4B03BBA75AEBB029532C%40compunet4f9da9. For more options, visit https://groups.google.com/d/optout.
