Burn in of Tantalum caps

rails? Al electrolytics? I guess

On my *power* ra ils I use these:

|0

Derating to 2/3*V_NOM takes me to my beloved 1e6 hours expected lifetime wonderland.

With a 900V part the PFC can be set up to 600V bus voltage, drivin g efficiency even higher and making good use of the

900V SiC FETs. A 500W PSU requires only 100uF of bus capacitance and works equally well in a single and t hree-phase environment.

Best regards,Piotr

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, not in the field. One engineer suggested the issue was moisture in the c ap from improper handling, but he also is working on some invention where h e used the term, "over unity" before I stopped listening.

y can be prevented without too much work. As I said, I have a current sens e resistor with a jumper so I can put any value there and jump across it on ce the circuit is powered up. It would add time to the test procedure thou gh. Not interested in doing much rework on the thing. It's only 1 in 100 failures if that high. Might be 1 in 300.

uality

nch

Wouldn't it make sense to have a surge spec for this? "Recommending" a ser ies resistor seems incredibly lame.

That's like the voltage regulator I tried to use after thoroughly reading t he data sheet. When I couldn't make it work and contacted the company I wa s told there was "additional" information on the web page... which indicate d it would never work in my application. Why wasn't that in the data sheet ???

I am going to contact the manufacturer, Kemet and see if they have any addi tional specs or data on this type of failure or info on how to deal with th e problem.

Rick C.

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Put together an automotive box last month, it can pretty much handle any input voltage, continuously, until the MOV goes up in smoke.

Fairly easy to do stuff like that when your box uses only a watt or two, though!

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Design 
Website: https://www.seventransistorlabs.com/

We normally use 24V wall warts anyway--it's the inrush torture test that's the issue.

Yup. Not hard, just necessary.

Cheers

Phil Hobbs

Users will plug in the wart and then connect the 24 volt end. Zap!

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Right it's hot plugging that can cause issues. I made a circuit power by a 48V wall wart. When unplugging it sparked enough to leave a scar, got ugly after a while.

George H.

On Thursday, 10 January 2019 23:28:14 UTC-5, snipped-for-privacy@gmail.com wrote :

owered up on the test fixture. There was a discussion here about such fail ures being an initial short from fabrication or created when reflowed on th e board. An article was linked which discussed a real world app where they powered up the board with a voltage ramp and enough series resistance to p revent the cap from creating a hard short and failing. But no information on how slow is "slow" and how much resistance is needed to prevent damage w hile clearing the short.

We can't control the ramp up time of that voltage rail other than adding more capacitance to slow it down. I suppose that is an option if we know a target ramp rate. I've asked the manufacturer of the regulator (CUI V7812

-1000) what the ramp rate is and how it varies with capacitance. We'll see if they respond.

id have one cap that failed catastrophically and actually burned the board, but not beyond repair.

Elna recommend a series resistor of 3 ohms per volt and a 3:1 voltage derat ing!

--Spehro Pefhany

Then why bother?

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

ote:

y powered up on the test fixture. There was a discussion here about such f ailures being an initial short from fabrication or created when reflowed on the board. An article was linked which discussed a real world app where t hey powered up the board with a voltage ramp and enough series resistance t o prevent the cap from creating a hard short and failing. But no informati on on how slow is "slow" and how much resistance is needed to prevent damag e while clearing the short.

er. We can't control the ramp up time of that voltage rail other than addi ng more capacitance to slow it down. I suppose that is an option if we kno w a target ramp rate. I've asked the manufacturer of the regulator (CUI V7

812-1000) what the ramp rate is and how it varies with capacitance. We'll see if they respond.

e did have one cap that failed catastrophically and actually burned the boa rd, but not beyond repair.

rating!

Quite! I guess in apps where that's acceptable they would last a lot better than ali lytics. Sounds primarily like ass covering: if you didn't take un realistic precautions it's not our fault.

Maybe tants should be mounted in sets of 8 on ballistic rated PCB. Now ever ything works until all 8 have launched.

NT

Yup, I don't use them for that reason. I use Oxi-Caps (AVX Niobium Oxide) instead. Some cost a bit more, some are less than equivalent Tantalum parts, but I've used thousands, all reflowed, and never had one fail, unless a first article had some put in backwards. (That did happen once.)

Jon

1 V is enough to do it. Supposedly, even an old voltmeter on the Ohms range could do it.

Jon

I can't seem to find a magic bullet replacement in this case. Niobium Oxide caps don't seem to be available in the voltage range. The highest I can find are rated for 10 volts.

How are Tantalum Polymer caps?

Rick C.

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