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Re: Burn in of Tantalum caps
On Friday, January 11, 2019 at 2:38:53 AM UTC-5, Tim Williams wrote:
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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 fro
m 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 resi
stor 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.  N
ot interested in doing much rework on the thing.  It's only 1 in 100 failur
es if that high.  Might be 1 in 300.  

  Rick C.

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

Re: Burn in of Tantalum caps
On Friday, January 11, 2019 at 10:00:18 AM UTC-5, snipped-for-privacy@gmail.com w
rote:
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ed on  
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r.  
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t in the field.  One engineer suggested the issue was moisture in the cap f
rom improper handling, but he also is working on some invention where he us
ed the term, "over unity" before I stopped listening.  
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n be prevented without too much work.  As I said, I have a current sense re
sistor with a jumper so I can put any value there and jump across it once t
he 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 fail
ures if that high.  Might be 1 in 300.  

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

George H.    
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Re: Burn in of Tantalum caps
On Friday, January 11, 2019 at 10:33:41 AM UTC-5, George Herold wrote:
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 wrote:
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ly  
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owed on  
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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.  
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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 fa
ilures if that high.  Might be 1 in 300.  
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ity
  
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Just the one tantalum.  It may well be rather overkill but it's too late no
w.  The board has been in production for 10 years and I don't want to make  
any changes that might require new EMI testing.  No change to the manufactu
rer.  

I was making these units at a facility which did everything including shipp
ing.  They were not reporting failure information it seems.  Once when I wa
s there someone mentioned that when they had any problems the first thing t
hey did was replace this part.  I thought that was an odd thing to do.  The
y didn't mention that they saw some number of shorts on the power rail.  Th
at is one of the things the test procedure tests for, shorted supplies.  


  Rick C.

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

Re: Burn in of Tantalum caps
On Fri, 11 Jan 2019 07:33:37 -0800 (PST), George Herold

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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.


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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.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: Burn in of Tantalum caps
On 11/01/2019 4:52 PM, John Larkin wrote:
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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


Re: Burn in of Tantalum caps
On Saturday, January 12, 2019 at 9:27:54 AM UTC-5, piglet wrote:
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com wrote:
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lly
uch
lowed on
here
stance
to
mper.
ding
 know a
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.  We'll
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 we did
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ard, but
, 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.
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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.
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uality
nch
  
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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.  

Re: Burn in of Tantalum caps
On 1/12/19 11:11 AM, George Herold wrote:
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Ceramics and the occasional Alpo.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Burn in of Tantalum caps
George Herold wrote:
 
> So what do you use on power
rails?  Al electrolytics?  I guess
 
On my *power* ra
ils I use these:
 
https://pl.mouser.com/Passive-Comp
onents/Capacitors/Film-Capacitors/_/N-9x371?Rl=9x371Ze
r3vZ1z0wm4nZ1z0wrj0Z1yz6a75Z1z0wkyvS1z0wrj4Z1z0wqtfZ1z
0wqtgZ1z0wl3aZ1z0wqqeZ1z0wfauZ1z0wjx3Z1z0wrjxZ1z0wlzpZ
1z0wqspZ1z0wm2pZ1z0wrjuZ1z0wli4Z1z0wrkmZ1z0wdl8Z1z0wrj
eZ1z0wdjbZ1z0wrkpZ1z0wqs5Z1z0wdk4Z1yzn444Z1z0wrjaZ1z0w
m2fZ1z0wrkbZ1yzofoyZ1z0wqe9Z1z0wgzrZ1z0wm4qZ1z0wrk3Z1z
0wdjiZ1z0wqt2Z1z0wlf6Z1z0wdk3Z1z0wrivZ1yzoe94Z1z0wrjqZ
1z0wld1Z1z0wrj6Z1z0wrkeZ1z0wlj6Z1z0wriyZ1z0wmhcZ1z0wrk
tZ1z0wlymZ1yzmpxgZ1z0wqr9Z1z0rvohZ1z0wm2gZ1z0whjoZ1z0w
l1jZ1z0wl60Z1z0wqs2Z1yz2opmZ1z0wqe4Z1z0wqs1Z1z0wl8hZ1z
0wrjfZ1z0wqe1Z1z0iz5kZ1z0wla4Z1z0wl9iZ1z0wl4uZ1z0wm2nZ
1z0wqs0Z1z0wrk5Z1z0wm2mZ1z0wfgiZ1z0wqssZ1z0wkcyZ1z0wkz
qZ1z0wl5wZ1z0wq3hZ1z0wm2tZ1z0wqcuZ1z0wqrtZ1z0wl8kZ1z0w
m2iZ1yzsjszZ1z0wm41Z1z0wm2kZ1z0wrjdZ1z0wle6Z1z0wrjwZ1z
0wqtsZ1z0wffuZ1z0wm2vZ1z0iz64Z1z0wm3iZ1z0wl35Z1z0wlhuZ
1z0wff5Z1z0wm2oZ1z0wqe5Z1z0wrjoZ1z0wlalZ1z0wqd5Z1z0wfe
wZ1z0wkz8Z1z0wmfmZ1z0wkz0Z1z0wqt4Z1z0wrirZ1z0wqs4Z1z0w
rk7Z1z0wqdqZ1z0wqqnGergjZ1ykl900Z1ykkkklSGT&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, 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
 


Re: Burn in of Tantalum caps
On Saturday, January 12, 2019 at 9:27:54 AM UTC-5, piglet wrote:
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com wrote:
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lly
uch
lowed on
here
stance
to
mper.
ding
 know a
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.  We'll
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 we did
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ard, but
, 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.
Quoted text here. Click to load it
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.
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uality
nch
  
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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.

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

Re: Burn in of Tantalum caps
On Thursday, January 10, 2019 at 11:28:14 PM UTC-5, snipped-for-privacy@gmail.com
 wrote:
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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.  
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  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.  
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id have one cap that failed catastrophically and actually burned the board,
 but not beyond repair.  
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The switching regulator is guaranteed to output 1A under fairly wide range  
of environmentals and circuit operational parameters like differential volt
age 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 kno
w, is you don't know anything about the limit. It's the wrong part to use i
n this kind of test setup. But don't you worry about that. Don't deprive yo
urself of wasting thousands of man hours blithering about every conceivable
 peripheral issue that has nothing to do with fixing anything.

Re: Burn in of Tantalum caps
:
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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.  
Quoted text here. Click to load it
  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.  
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id have one cap that failed catastrophically and actually burned the board,
 but not beyond repair.  
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Elna recommend a series resistor of 3 ohms per volt and a 3:1 voltage derat
ing!

--Spehro Pefhany  



Re: Burn in of Tantalum caps
wrote:

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Then why bother?


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: Burn in of Tantalum caps
On Sunday, 13 January 2019 19:26:43 UTC, John Larkin  wrote:
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ote:

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

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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

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