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Phil Hobbs
Guest

Sat Jan 12, 2019 6:45 pm   



On 1/12/19 11:57 AM, bloggs.fredbloggs.fred_at_gmail.com wrote:
Quote:
On Friday, January 11, 2019 at 2:03:36 AM UTC-5, Boris Mohar wrote:
On Thu, 10 Jan 2019 20:28:11 -0800 (PST), gnuarm.deletethisbit_at_gmail.com
wrote:

We are seeing around 1 in 100 Tantalum caps fail shorted when initially powered up on the test fixture. There was a discussion here about such failures being an initial short from fabrication or created when reflowed on the 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 prevent 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 while clearing the short.

On the test fixture we can add a resistance to be bypassed with a jumper.. 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.

Any suggestions on improving this problem? It's not a big deal, but we did have one cap that failed catastrophically and actually burned the board, but not beyond repair.

Rick C.

- Get 6 months of free supercharging
- Tesla referral code - https://ts.la/richard11209

dV/dt

https://www.avx.com/docs/techinfo/VoltageDeratingRulesforSolidTantalumandNiobiumCapacitors.pdf

Author of that article is an idiotic moron from hell. Who in hell would think the voltage rating of the capacitor could possible affect peak current surge. So either that fool is an idiot or something is being lost in translation.


Take a look at Eq. 2 and the surrounding discussion. Their resistance
appears to be constant for any given series.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

Phil Hobbs
Guest

Sat Jan 12, 2019 6:45 pm   



On 1/12/19 11:11 AM, George Herold wrote:
Quote:
On Saturday, January 12, 2019 at 9:27:54 AM UTC-5, piglet wrote:
On 11/01/2019 4:52 PM, John Larkin wrote:
On Fri, 11 Jan 2019 07:33:37 -0800 (PST), George Herold
gherold_at_teachspin.com> wrote:

On Friday, January 11, 2019 at 10:00:18 AM UTC-5, gnuarm.del...@gmail.com wrote:
On Friday, January 11, 2019 at 2:38:53 AM UTC-5, Tim Williams wrote:
What rating and test voltage, out of curiosity?

Tim

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

gnuarm.deletethisbit_at_gmail.com> wrote in message
news:8c98a491-be67-4607-8317-21085d0c223f_at_googlegroups.com...
We are seeing around 1 in 100 Tantalum caps fail shorted when initially
powered up on the test fixture. There was a discussion here about such
failures being an initial short from fabrication or created when reflowed on
the 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 prevent 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 while clearing the short.

On the test fixture we can add a resistance to be bypassed with a jumper.
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.

Any suggestions on improving this problem? It's not a big deal, but we did
have one cap that failed catastrophically and actually burned the board, but
not beyond repair.

Rick C.

- Get 6 months of free supercharging
- Tesla referral code - https://ts.la/richard11209

It's a 20 volt cap on a 12 volt supply. We only see failures in test, not in the field. One engineer suggested the issue was moisture in the cap from improper handling, but he also is working on some invention where he used the term, "over unity" before I stopped listening.

I'd like to modify the test fixture to not have these failures if they can be prevented without too much work. As I said, I have a current sense resistor with a jumper so I can put any value there and jump across it once the circuit is powered up. It would add time to the test procedure though. Not interested in doing much rework on the thing. It's only 1 in 100 failures if that high. Might be 1 in 300.

How many tant's on your board? Did you change manufacturer? Tant cap quality
seems to be continually eroding.

More like it's always been continually erratic. You can switch
manufacturer and be satisfied that you have solved your reliability
problem. Then after a while the good ones turn bad.

It's really a design problem: don't detonate them and they will be
very reliable.


I was fixing a ~20 year old instrument
the other day. Problem was traced down to a tant. The board had a bunch
of 16V tant's on the 15V power rails... these days I'd use a 50V one.

Right. Tants on a supply rail should be avoided (which is usually
where you want them) or at least derated 3:1 on voltage. Keep dv/dt
under control too.



Yes, dv/dt is the key. I recall 1990s datasheet reccomending series R of
1 ohm per applied volt - in other words tantalum capacitor surge current
must be limited to one ampere max. Rather limits application as bypass
on beefy power rails!

piglet

So what do you use on power rails? Al electrolytics? I guess
I should 'scope the power rail turn on of all my circuits.

I use a series inductor/ multi-turn ferrite bead sometimes.

George H.


Ceramics and the occasional Alpo.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net


Guest

Sat Jan 12, 2019 6:45 pm   



On Friday, January 11, 2019 at 2:03:36 AM UTC-5, Boris Mohar wrote:
Quote:
On Thu, 10 Jan 2019 20:28:11 -0800 (PST), gnuarm.deletethisbit_at_gmail.com
wrote:

We are seeing around 1 in 100 Tantalum caps fail shorted when initially powered up on the test fixture. There was a discussion here about such failures being an initial short from fabrication or created when reflowed on the 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 prevent 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 while clearing the short.

On the test fixture we can add a resistance to be bypassed with a jumper.. 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.

Any suggestions on improving this problem? It's not a big deal, but we did have one cap that failed catastrophically and actually burned the board, but not beyond repair.

Rick C.

- Get 6 months of free supercharging
- Tesla referral code - https://ts.la/richard11209

dV/dt

https://www.avx.com/docs/techinfo/VoltageDeratingRulesforSolidTantalumandNiobiumCapacitors.pdf


Author of that article is an idiotic moron from hell. Who in hell would think the voltage rating of the capacitor could possible affect peak current surge. So either that fool is an idiot or something is being lost in translation.

Quote:


Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs (among other things) http://www.viatrack..ca

void _-void-_ in the obvious place



---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus



Guest

Sat Jan 12, 2019 6:45 pm   



On Thursday, January 10, 2019 at 11:28:14 PM UTC-5, gnuarm.del...@gmail.com wrote:
Quote:
We are seeing around 1 in 100 Tantalum caps fail shorted when initially powered up on the test fixture. There was a discussion here about such failures being an initial short from fabrication or created when reflowed on the 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 prevent 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 while clearing the short.

On the test fixture we can add a resistance to be bypassed with a jumper. 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.

Any suggestions on improving this problem? It's not a big deal, but we did have one cap that failed catastrophically and actually burned the board, but not beyond repair.

Rick C.

- Get 6 months of free supercharging
- Tesla referral code - https://ts.la/richard11209


The switching regulator is guaranteed to output 1A under fairly wide range of environmentals and circuit operational parameters like differential voltage i/o being a big one. This DOES NOT mean it limits output current at 1A. It may allow limits as high as 3A at low duty. All you know, or should know, is you don't know anything about the limit. It's the wrong part to use in this kind of test setup. But don't you worry about that. Don't deprive yourself of wasting thousands of man hours blithering about every conceivable peripheral issue that has nothing to do with fixing anything.

Phil Hobbs
Guest

Sat Jan 12, 2019 6:45 pm   



On 1/11/19 3:23 PM, John Larkin wrote:
Quote:
On Fri, 11 Jan 2019 02:16:14 -0500, Boris Mohar
borism_void__at_sympatico.ca> wrote:

On Thu, 10 Jan 2019 20:28:11 -0800 (PST), gnuarm.deletethisbit_at_gmail.com
wrote:

We are seeing around 1 in 100 Tantalum caps fail shorted when initially powered up on the test fixture. There was a discussion here about such failures being an initial short from fabrication or created when reflowed on the 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 prevent 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 while clearing the short.

On the test fixture we can add a resistance to be bypassed with a jumper. 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.

Any suggestions on improving this problem? It's not a big deal, but we did have one cap that failed catastrophically and actually burned the board, but not beyond repair.

Rick C.

- Get 6 months of free supercharging
- Tesla referral code - https://ts.la/richard11209

dV/dt

https://www.avx.com/docs/techinfo/VoltageDeratingRulesforSolidTantalumandNiobiumCapacitors.pdf



Fig 4 is interesting, especially for "one or more current surges."


Specially using a single JFET for a high-current totem pole. ;)

Quote:

Fig 8 is crazy. Add all that stuff to every cap?


Or just limit them to the outputs of linear regulators and stuff like
that. It's the supply input that has the issue. (Our stuff has to be
able to handle being connected to two car batteries in series, because
people actually do that.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

Piotr Wyderski
Guest

Sat Jan 12, 2019 7:45 pm   



George Herold wrote:

> So what do you use on power rails? Al electrolytics? I guess

On my *power* rails I use these:

https://pl.mouser.com/Passive-Components/Capacitors/Film-Capacitors/_/N-9x371?Rl=9x371Zer3vZ1z0wm4nZ1z0wrj0Z1yz6a75Z1z0wkyvS1z0wrj4Z1z0wqtfZ1z0wqtgZ1z0wl3aZ1z0wqqeZ1z0wfauZ1z0wjx3Z1z0wrjxZ1z0wlzpZ1z0wqspZ1z0wm2pZ1z0wrjuZ1z0wli4Z1z0wrkmZ1z0wdl8Z1z0wrjeZ1z0wdjbZ1z0wrkpZ1z0wqs5Z1z0wdk4Z1yzn444Z1z0wrjaZ1z0wm2fZ1z0wrkbZ1yzofoyZ1z0wqe9Z1z0wgzrZ1z0wm4qZ1z0wrk3Z1z0wdjiZ1z0wqt2Z1z0wlf6Z1z0wdk3Z1z0wrivZ1yzoe94Z1z0wrjqZ1z0wld1Z1z0wrj6Z1z0wrkeZ1z0wlj6Z1z0wriyZ1z0wmhcZ1z0wrktZ1z0wlymZ1yzmpxgZ1z0wqr9Z1z0rvohZ1z0wm2gZ1z0whjoZ1z0wl1jZ1z0wl60Z1z0wqs2Z1yz2opmZ1z0wqe4Z1z0wqs1Z1z0wl8hZ1z0wrjfZ1z0wqe1Z1z0iz5kZ1z0wla4Z1z0wl9iZ1z0wl4uZ1z0wm2nZ1z0wqs0Z1z0wrk5Z1z0wm2mZ1z0wfgiZ1z0wqssZ1z0wkcyZ1z0wkzqZ1z0wl5wZ1z0wq3hZ1z0wm2tZ1z0wqcuZ1z0wqrtZ1z0wl8kZ1z0wm2iZ1yzsjszZ1z0wm41Z1z0wm2kZ1z0wrjdZ1z0wle6Z1z0wrjwZ1z0wqtsZ1z0wffuZ1z0wm2vZ1z0iz64Z1z0wm3iZ1z0wl35Z1z0wlhuZ1z0wff5Z1z0wm2oZ1z0wqe5Z1z0wrjoZ1z0wlalZ1z0wqd5Z1z0wfewZ1z0wkz8Z1z0wmfmZ1z0wkz0Z1z0wqt4Z1z0wrirZ1z0wqs4Z1z0wrk7Z1z0wqdqZ1z0wqqnGergjZ1ykl900Z1ykkkklSGT&Ns=Pricing|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, driving
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 three-phase environment.

Best regards,Piotr

John Larkin
Guest

Sat Jan 12, 2019 7:45 pm   



On Sat, 12 Jan 2019 08:57:05 -0800 (PST),
bloggs.fredbloggs.fred_at_gmail.com wrote:

Quote:
On Friday, January 11, 2019 at 2:03:36 AM UTC-5, Boris Mohar wrote:
On Thu, 10 Jan 2019 20:28:11 -0800 (PST), gnuarm.deletethisbit_at_gmail.com
wrote:

We are seeing around 1 in 100 Tantalum caps fail shorted when initially powered up on the test fixture. There was a discussion here about such failures being an initial short from fabrication or created when reflowed on the 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 prevent 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 while clearing the short.

On the test fixture we can add a resistance to be bypassed with a jumper. 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.

Any suggestions on improving this problem? It's not a big deal, but we did have one cap that failed catastrophically and actually burned the board, but not beyond repair.

Rick C.

- Get 6 months of free supercharging
- Tesla referral code - https://ts.la/richard11209

dV/dt

https://www.avx.com/docs/techinfo/VoltageDeratingRulesforSolidTantalumandNiobiumCapacitors.pdf

Author of that article is an idiotic moron from hell. Who in hell would think the voltage rating of the capacitor could possible affect peak current surge. So either that fool is an idiot or something is being lost in translation.



But voltage derating does make tantalums reliable.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics


Guest

Sat Jan 12, 2019 7:45 pm   



On Saturday, January 12, 2019 at 9:27:54 AM UTC-5, piglet wrote:
Quote:
On 11/01/2019 4:52 PM, John Larkin wrote:
On Fri, 11 Jan 2019 07:33:37 -0800 (PST), George Herold
gherold_at_teachspin.com> wrote:

On Friday, January 11, 2019 at 10:00:18 AM UTC-5, gnuarm.del...@gmail.com wrote:
On Friday, January 11, 2019 at 2:38:53 AM UTC-5, Tim Williams wrote:
What rating and test voltage, out of curiosity?

Tim

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

gnuarm.deletethisbit_at_gmail.com> wrote in message
news:8c98a491-be67-4607-8317-21085d0c223f_at_googlegroups.com...
We are seeing around 1 in 100 Tantalum caps fail shorted when initially
powered up on the test fixture. There was a discussion here about such
failures being an initial short from fabrication or created when reflowed on
the 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 prevent 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 while clearing the short.

On the test fixture we can add a resistance to be bypassed with a jumper.
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.

Any suggestions on improving this problem? It's not a big deal, but we did
have one cap that failed catastrophically and actually burned the board, but
not beyond repair.

Rick C.

- Get 6 months of free supercharging
- Tesla referral code - https://ts.la/richard11209

It's a 20 volt cap on a 12 volt supply. We only see failures in test, not in the field. One engineer suggested the issue was moisture in the cap from improper handling, but he also is working on some invention where he used the term, "over unity" before I stopped listening.

I'd like to modify the test fixture to not have these failures if they can be prevented without too much work. As I said, I have a current sense resistor with a jumper so I can put any value there and jump across it once the circuit is powered up. It would add time to the test procedure though. Not interested in doing much rework on the thing. It's only 1 in 100 failures if that high. Might be 1 in 300.

How many tant's on your board? Did you change manufacturer? Tant cap quality
seems to be continually eroding.

More like it's always been continually erratic. You can switch
manufacturer and be satisfied that you have solved your reliability
problem. Then after a while the good ones turn bad.

It's really a design problem: don't detonate them and they will be
very reliable.


I was fixing a ~20 year old instrument
the other day. Problem was traced down to a tant. The board had a bunch
of 16V tant's on the 15V power rails... these days I'd use a 50V one.

Right. Tants on a supply rail should be avoided (which is usually
where you want them) or at least derated 3:1 on voltage. Keep dv/dt
under control too.



Yes, dv/dt is the key. I recall 1990s datasheet reccomending series R of
1 ohm per applied volt - in other words tantalum capacitor surge current
must be limited to one ampere max. Rather limits application as bypass
on beefy power rails!


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

That's like the voltage regulator I tried to use after thoroughly reading the data sheet. When I couldn't make it work and contacted the company I was told there was "additional" information on the web page... which indicated 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 additional specs or data on this type of failure or info on how to deal with the problem.

Rick C.

+- Get 6 months of free supercharging
+- Tesla referral code - https://ts.la/richard11209

Tim Williams
Guest

Sun Jan 13, 2019 2:45 am   



"Phil Hobbs" <pcdhSpamMeSenseless_at_electrooptical.net> wrote in message
news:UbydnY9XafeWvafBnZ2dnUU7-bfNnZ2d_at_supernews.com...
Quote:
Or just limit them to the outputs of linear regulators and stuff like
that. It's the supply input that has the issue. (Our stuff has to be
able to handle being connected to two car batteries in series, because
people actually do that.)


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/


Guest

Sun Jan 13, 2019 9:45 am   



Quote:
(Our stuff has to be
able to handle being connected to two car batteries in series, because
people actually do that.)


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


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

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


Yup. Not hard, just necessary.

Cheers

Phil Hobbs

John Larkin
Guest

Sun Jan 13, 2019 5:45 pm   



On Sun, 13 Jan 2019 00:17:17 -0800 (PST), pcdhobbs_at_gmail.com wrote:

Quote:
(Our stuff has to be
able to handle being connected to two car batteries in series, because
people actually do that.)


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

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

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

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

George Herold
Guest

Sun Jan 13, 2019 6:45 pm   



On Sunday, January 13, 2019 at 10:58:37 AM UTC-5, John Larkin wrote:
Quote:
On Sun, 13 Jan 2019 00:17:17 -0800 (PST), pcdhobbs_at_gmail.com wrote:

(Our stuff has to be
able to handle being connected to two car batteries in series, because
people actually do that.)


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

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

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

Yup. Not hard, just necessary.

Cheers

Phil Hobbs

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

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.
Quote:

--

John Larkin Highland Technology, Inc

lunatic fringe electronics


speff
Guest

Sun Jan 13, 2019 7:45 pm   



On Thursday, 10 January 2019 23:28:14 UTC-5, gnuarm.del...@gmail.com wrote:
Quote:
We are seeing around 1 in 100 Tantalum caps fail shorted when initially powered up on the test fixture. There was a discussion here about such failures being an initial short from fabrication or created when reflowed on the 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 prevent 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 while clearing the short.

On the test fixture we can add a resistance to be bypassed with a jumper. 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.

Any suggestions on improving this problem? It's not a big deal, but we did have one cap that failed catastrophically and actually burned the board, but not beyond repair.

Rick C.


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

--Spehro Pefhany

John Larkin
Guest

Sun Jan 13, 2019 8:45 pm   



On Sun, 13 Jan 2019 09:45:25 -0800 (PST), speff <spehro_at_gmail.com>
wrote:

Quote:
On Thursday, 10 January 2019 23:28:14 UTC-5, gnuarm.del...@gmail.com wrote:
We are seeing around 1 in 100 Tantalum caps fail shorted when initially powered up on the test fixture. There was a discussion here about such failures being an initial short from fabrication or created when reflowed on the 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 prevent 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 while clearing the short.

On the test fixture we can add a resistance to be bypassed with a jumper. 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.

Any suggestions on improving this problem? It's not a big deal, but we did have one cap that failed catastrophically and actually burned the board, but not beyond repair.

Rick C.


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

--Spehro Pefhany


Then why bother?


--

John Larkin Highland Technology, Inc

lunatic fringe electronics


Guest

Mon Jan 14, 2019 3:45 am   



On Sunday, 13 January 2019 19:26:43 UTC, John Larkin wrote:
Quote:
On Sun, 13 Jan 2019 09:45:25 -0800 (PST), speff <spehro_at_gmail.com
wrote:
On Thursday, 10 January 2019 23:28:14 UTC-5, gnuarm.del...@gmail.com wrote:

We are seeing around 1 in 100 Tantalum caps fail shorted when initially powered up on the test fixture. There was a discussion here about such failures being an initial short from fabrication or created when reflowed on the 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 prevent 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 while clearing the short.

On the test fixture we can add a resistance to be bypassed with a jumper. 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.

Any suggestions on improving this problem? It's not a big deal, but we did have one cap that failed catastrophically and actually burned the board, but not beyond repair.

Rick C.


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

Then why bother?


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 unrealistic precautions it's not our fault.

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


NT

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