[EE] Specifying the right electrolytic capacitors for long (10 year) operating life?

[Jason White-20]

Hi everyone,

I'm looking to learn about the critical parameters in specifying the
"correct" electrolytic capacitor to last a long time (10 years).

I suspect it comes down to selecting a "long life" series capacitor from a
reputable brand (perhaps Nichicon or Panasonic?) with a high hour and
temperature rating, low ESR, and significantly higher than needed voltage
rating.

I have a safety related circuit where I have no choice but to use two
"large value" electrolytic capacitors. Wide temperature range, very loose
tolerance and performance expectations from the capacitors. I'd like the
two capacitors to "last" 10 years of having power applied.

The first capacitor is being used in a RC timing delay. Consequently, the
"ripple" current would be in the single digit microamp range. I'm concerned
about this capacitor's capacitance and leakage staying in spec over
temperature and time. Low duty cycle.

The second capacitor is being used to provide bulk "high-ish voltage"
decoupling capacitance to an electric motor. The supply impedance to the
motor rail is high. I'm concerned about this capacitor's ESR and
capacitance staying in spec over temperature and time. Ripple current is
assumed to be similar to motor supply current of ~3 amps. Low duty cycle.

Tambient-max=95C

Any advice, anecdotes, or links to relevant literature would be appreciated.

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[Jason White-20]

Addendum, by low duty cycle I mean about 5 seconds of activity per hour for
the motor and timing capacitor.

The capacitors will spend most of their life exposed to something like the
following: power applied for 1 hour with 5 seconds of operation somewhere
during, 1 hour with power removed. That cycle would be repeated something
like 88000 times to get 10 years of power applied.

On Thursday, July 2, 2020, Jason White <[hidden email]>
wrote:

> Hi everyone,
>
> I'm looking to learn about the critical parameters in specifying the
> "correct" electrolytic capacitor to last a long time (10 years).
>
> I suspect it comes down to selecting a "long life" series capacitor from a
> reputable brand (perhaps Nichicon or Panasonic?) with a high hour and
> temperature rating, low ESR, and significantly higher than needed voltage
> rating.
>
> I have a safety related circuit where I have no choice but to use two
> "large value" electrolytic capacitors. Wide temperature range, very loose
> tolerance and performance expectations from the capacitors. I'd like the
> two capacitors to "last" 10 years of having power applied.
>
> The first capacitor is being used in a RC timing delay. Consequently, the
> "ripple" current would be in the single digit microamp range. I'm concerned
> about this capacitor's capacitance and leakage staying in spec over
> temperature and time. Low duty cycle.
>
> The second capacitor is being used to provide bulk "high-ish voltage"
> decoupling capacitance to an electric motor. The supply impedance to the
> motor rail is high. I'm concerned about this capacitor's ESR and
> capacitance staying in spec over temperature and time. Ripple current is
> assumed to be similar to motor supply current of ~3 amps. Low duty cycle.
>
> Tambient-max=95C
>
> Any advice, anecdotes, or links to relevant literature would be
> appreciated.
>
> --
> Jason White
>

--
Jason White
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[Harold Hallikainen-3]

I'd be concerned about using an electrolytic in an RC timer. Capacity
tolerance and leakage current could be issues. Is there any way to go to
another capacitor technology, perhaps running at a higher frequency
followed by a digital counter? I've seen electrolytic-based RC timers
never time out due to leakage current.

Harold

> Addendum, by low duty cycle I mean about 5 seconds of activity per hour
> for
> the motor and timing capacitor.
>
> The capacitors will spend most of their life exposed to something like the
> following: power applied for 1 hour with 5 seconds of operation somewhere
> during, 1 hour with power removed. That cycle would be repeated something
> like 88000 times to get 10 years of power applied.
>
> On Thursday, July 2, 2020, Jason White <[hidden email]>
> wrote:
>
>> Hi everyone,
>>
>> I'm looking to learn about the critical parameters in specifying the
>> "correct" electrolytic capacitor to last a long time (10 years).
>>
>> I suspect it comes down to selecting a "long life" series capacitor from
>> a
>> reputable brand (perhaps Nichicon or Panasonic?) with a high hour and
>> temperature rating, low ESR, and significantly higher than needed
>> voltage
>> rating.
>>
>> I have a safety related circuit where I have no choice but to use two
>> "large value" electrolytic capacitors. Wide temperature range, very
>> loose
>> tolerance and performance expectations from the capacitors. I'd like the
>> two capacitors to "last" 10 years of having power applied.
>>
>> The first capacitor is being used in a RC timing delay. Consequently,
>> the
>> "ripple" current would be in the single digit microamp range. I'm
>> concerned
>> about this capacitor's capacitance and leakage staying in spec over
>> temperature and time. Low duty cycle.
>>
>> The second capacitor is being used to provide bulk "high-ish voltage"
>> decoupling capacitance to an electric motor. The supply impedance to the
>> motor rail is high. I'm concerned about this capacitor's ESR and
>> capacitance staying in spec over temperature and time. Ripple current is
>> assumed to be similar to motor supply current of ~3 amps. Low duty
>> cycle.
>>
>> Tambient-max=95C
>>
>> Any advice, anecdotes, or links to relevant literature would be
>> appreciated.
>>
>> --
>> Jason White
>>
>
>
> --
> Jason White
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>

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[Dwayne Reid]

Hi there, Jason.

I use Tantalum capacitors for RC time delays.  Good quality
electrolytic caps might give you good results - or not.

Both bead-type and hermetically-sealed Tantalum caps have been
reliable for me for decades.  I do not have reliability data for SMT
Tantalum caps - I just haven't been using them long enough.

However, do NOT ever use a Tantalum cap on a high-current power
rail.  They fail if exposed to even a momentary over-voltage
transient.  The end result is often a hole in the PCB where the
capacitor used to be.

dwayne


At 10:38 AM 7/2/2020, Jason White wrote:

>Hi everyone,
>
>I'm looking to learn about the critical parameters in specifying the
>"correct" electrolytic capacitor to last a long time (10 years).
>
>I suspect it comes down to selecting a "long life" series capacitor from a
>reputable brand (perhaps Nichicon or Panasonic?) with a high hour and
>temperature rating, low ESR, and significantly higher than needed voltage
>rating.
>
>I have a safety related circuit where I have no choice but to use two
>"large value" electrolytic capacitors. Wide temperature range, very loose
>tolerance and performance expectations from the capacitors. I'd like the
>two capacitors to "last" 10 years of having power applied.
>
>The first capacitor is being used in a RC timing delay. Consequently, the
>"ripple" current would be in the single digit microamp range. I'm concerned
>about this capacitor's capacitance and leakage staying in spec over
>temperature and time. Low duty cycle.
>
>The second capacitor is being used to provide bulk "high-ish voltage"
>decoupling capacitance to an electric motor. The supply impedance to the
>motor rail is high. I'm concerned about this capacitor's ESR and
>capacitance staying in spec over temperature and time. Ripple current is
>assumed to be similar to motor supply current of ~3 amps. Low duty cycle.
>
>Tambient-max=95C
>
>Any advice, anecdotes, or links to relevant literature would be appreciated.
>
>--
>Jason White
>--
>http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>View/change your membership options at
>http://mailman.mit.edu/mailman/listinfo/piclist

--
Dwayne Reid   <[hidden email]>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
780-489-3199 voice   780-487-6397 fax   [phone] Toll Free
www.trinity-electronics.com
Custom Electronics Design and Manufacturing

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[Alan Pearce]

I would also be worried about using a wet electrolytic for an R/C
timer. If an R/C timer is needed then a tantalum would be a must.

>From my time on the space industry we were required to derate
capacitors to 50% of max working voltage, so on a 12V power supply
line one would use 25v capacitors. I would recommend that you use a
similar derating factor, but you could reduce the derating factor by
using Tantalum-polymer capacitors. These have two advantages, firstly
they can be run in reliability conscious applications at a lower
derating than standard caps and secondly they do not have the nasty
failure mode of going short circuit.

But coming back to the timing, maxim and the like make ICs that are
configurable timers without using R/C circuits, and OI would have
thought would be a more reliable way of doing it, after all you are
looking for a 10 year design life.

On Thu, 2 Jul 2020 at 20:29, Harold Hallikainen
<[hidden email]> wrote:

>
> I'd be concerned about using an electrolytic in an RC timer. Capacity
> tolerance and leakage current could be issues. Is there any way to go to
> another capacitor technology, perhaps running at a higher frequency
> followed by a digital counter? I've seen electrolytic-based RC timers
> never time out due to leakage current.
>
> Harold
>
> > Addendum, by low duty cycle I mean about 5 seconds of activity per hour
> > for
> > the motor and timing capacitor.
> >
> > The capacitors will spend most of their life exposed to something like the
> > following: power applied for 1 hour with 5 seconds of operation somewhere
> > during, 1 hour with power removed. That cycle would be repeated something
> > like 88000 times to get 10 years of power applied.
> >
> > On Thursday, July 2, 2020, Jason White <[hidden email]>
> > wrote:
> >
> >> Hi everyone,
> >>
> >> I'm looking to learn about the critical parameters in specifying the
> >> "correct" electrolytic capacitor to last a long time (10 years).
> >>
> >> I suspect it comes down to selecting a "long life" series capacitor from
> >> a
> >> reputable brand (perhaps Nichicon or Panasonic?) with a high hour and
> >> temperature rating, low ESR, and significantly higher than needed
> >> voltage
> >> rating.
> >>
> >> I have a safety related circuit where I have no choice but to use two
> >> "large value" electrolytic capacitors. Wide temperature range, very
> >> loose
> >> tolerance and performance expectations from the capacitors. I'd like the
> >> two capacitors to "last" 10 years of having power applied.
> >>
> >> The first capacitor is being used in a RC timing delay. Consequently,
> >> the
> >> "ripple" current would be in the single digit microamp range. I'm
> >> concerned
> >> about this capacitor's capacitance and leakage staying in spec over
> >> temperature and time. Low duty cycle.
> >>
> >> The second capacitor is being used to provide bulk "high-ish voltage"
> >> decoupling capacitance to an electric motor. The supply impedance to the
> >> motor rail is high. I'm concerned about this capacitor's ESR and
> >> capacitance staying in spec over temperature and time. Ripple current is
> >> assumed to be similar to motor supply current of ~3 amps. Low duty
> >> cycle.
> >>
> >> Tambient-max=95C
> >>
> >> Any advice, anecdotes, or links to relevant literature would be
> >> appreciated.
> >>
> >> --
> >> Jason White
> >>
> >
> >
> > --
> > Jason White
> > --
> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> >
>
>
> --
> FCC Rules Updated Daily at http://www.hallikainen.com
> Not sent from an iPhone.
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist

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[Denny Esterline-2]

> , perhaps running at a higher frequency followed by a digital counter
>

 May I suggest the CD4541B (and it's variants)
https://www.ti.com/lit/ds/symlink/cd4541b.pdf

Effectively a 555 timer with a couple counter stages added on.
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[Richard Prosser]

my 2c worth.

Tmax = 95C
What's Tmin? The ESR can increase significantly at low temperatures.

I'd also be concerned re the use of an electrolytic for an RC timer.
Tantalum or possibly even a high value MLC if a digital counter /
oscillator is not acceptable. Don't go overboard with the voltage safety
rating, a 450V cap on a low voltage circuit may not retain it's capacity.
Go for ~double if possible.

If an RC timer is required, you can get longer delays using a buffer stage
provided you protect against leakage paths (Guard rings etc). But you're
still at the mercy of the components, which is mainly the capacitor.

Select quality manufacturers & use the industrial (or military) grade rated
caps.

RP

On Fri, 3 Jul 2020 at 08:14, Alan Pearce <[hidden email]>
wrote:

> I would also be worried about using a wet electrolytic for an R/C
> timer. If an R/C timer is needed then a tantalum would be a must.
>
> >From my time on the space industry we were required to derate
> capacitors to 50% of max working voltage, so on a 12V power supply
> line one would use 25v capacitors. I would recommend that you use a
> similar derating factor, but you could reduce the derating factor by
> using Tantalum-polymer capacitors. These have two advantages, firstly
> they can be run in reliability conscious applications at a lower
> derating than standard caps and secondly they do not have the nasty
> failure mode of going short circuit.
>
> But coming back to the timing, maxim and the like make ICs that are
> configurable timers without using R/C circuits, and OI would have
> thought would be a more reliable way of doing it, after all you are
> looking for a 10 year design life.
>
> On Thu, 2 Jul 2020 at 20:29, Harold Hallikainen
> <[hidden email]> wrote:
> >
> > I'd be concerned about using an electrolytic in an RC timer. Capacity
> > tolerance and leakage current could be issues. Is there any way to go to
> > another capacitor technology, perhaps running at a higher frequency
> > followed by a digital counter? I've seen electrolytic-based RC timers
> > never time out due to leakage current.
> >
> > Harold
> >
> > > Addendum, by low duty cycle I mean about 5 seconds of activity per hour
> > > for
> > > the motor and timing capacitor.
> > >
> > > The capacitors will spend most of their life exposed to something like
> the
> > > following: power applied for 1 hour with 5 seconds of operation
> somewhere
> > > during, 1 hour with power removed. That cycle would be repeated
> something
> > > like 88000 times to get 10 years of power applied.
> > >
> > > On Thursday, July 2, 2020, Jason White <
> [hidden email]>
> > > wrote:
> > >
> > >> Hi everyone,
> > >>
> > >> I'm looking to learn about the critical parameters in specifying the
> > >> "correct" electrolytic capacitor to last a long time (10 years).
> > >>
> > >> I suspect it comes down to selecting a "long life" series capacitor
> from
> > >> a
> > >> reputable brand (perhaps Nichicon or Panasonic?) with a high hour and
> > >> temperature rating, low ESR, and significantly higher than needed
> > >> voltage
> > >> rating.
> > >>
> > >> I have a safety related circuit where I have no choice but to use two
> > >> "large value" electrolytic capacitors. Wide temperature range, very
> > >> loose
> > >> tolerance and performance expectations from the capacitors. I'd like
> the
> > >> two capacitors to "last" 10 years of having power applied.
> > >>
> > >> The first capacitor is being used in a RC timing delay. Consequently,
> > >> the
> > >> "ripple" current would be in the single digit microamp range. I'm
> > >> concerned
> > >> about this capacitor's capacitance and leakage staying in spec over
> > >> temperature and time. Low duty cycle.
> > >>
> > >> The second capacitor is being used to provide bulk "high-ish voltage"
> > >> decoupling capacitance to an electric motor. The supply impedance to
> the
> > >> motor rail is high. I'm concerned about this capacitor's ESR and
> > >> capacitance staying in spec over temperature and time. Ripple current
> is
> > >> assumed to be similar to motor supply current of ~3 amps. Low duty
> > >> cycle.
> > >>
> > >> Tambient-max=95C
> > >>
> > >> Any advice, anecdotes, or links to relevant literature would be
> > >> appreciated.
> > >>
> > >> --
> > >> Jason White
> > >>
> > >
> > >
> > > --
> > > Jason White
> > > --
> > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > > View/change your membership options at
> > > http://mailman.mit.edu/mailman/listinfo/piclist
> > >
> >
> >
> > --
> > FCC Rules Updated Daily at http://www.hallikainen.com
> > Not sent from an iPhone.
> > --
> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> --
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>

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[Jason White-20]

Tmin= -55C (very cold)

Thanks everyone for the RC timer advice. I will use an alternate chemistry.
What about the motor capacitor?

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