Capacitor Lifetime calculation

Hi,

I have recently been servicing some equipment that has had failures of
a 1000uF 40v 85 Deg C capacitor, the equipment has been running for
about 5 years and are used in the smoothing circuit of a linear power
supply. .

I have measured the ripple current (with a true RMS meter) of about
280ma which is well within limits and can only assume that the CAN
temperature of the capacitor of around 55 deg C is too high. The
capacitor is between a transformer and the heat sink of a regulator.

My question is how do I calculate the life of the capacitor with the
temperature of 55 Deg C? I have been using the 10 Deg increase in
temperature halves the life of the capacitor rule (1.82 years in this
case) but is there a better way of showing this? I have to go to my
client and tell them they have a problem but I need some better
formula to show them (or maybe I do not?).

Any help would be greatly appreciated.

 

[exray]

q@q.com wrote:

Hi,

I have recently been servicing some equipment that has had failures of
a 1000uF 40v 85 Deg C capacitor, the equipment has been running for
about 5 years and are used in the smoothing circuit of a linear power
supply. .

I have measured the ripple current (with a true RMS meter) of about
280ma which is well within limits and can only assume that the CAN
temperature of the capacitor of around 55 deg C is too high. The
capacitor is between a transformer and the heat sink of a regulator.

My question is how do I calculate the life of the capacitor with the
temperature of 55 Deg C? I have been using the 10 Deg increase in
temperature halves the life of the capacitor rule (1.82 years in this
case) but is there a better way of showing this? I have to go to my
client and tell them they have a problem but I need some better
formula to show them (or maybe I do not?).

Any help would be greatly appreciated.

This is anecdotal but may be of some use. In one particular unit that
we constantly had to repair, the 'same' cap in a similar circuit often
failed. The factory used a 105 deg C cap and any attempt to replace it
with an 85 C unit would result in failure, often within weeks. The
actual temperature was very modest, on the order of the 55 degrees you
describe.
In speaking with a repair facility they informed me to use nothing less
than a 105 C rated cap...not because of temperature concerns but the
electrolyte and physical construction are different in such units which
apparently is an issue for longevity in this type of service.
FWIW,
Bill

 

[RonKZ650]

Yes, always replace with a 105 degree cap. Every brand is different, so there's
really no way to calculate life. Use a good capacitor is the key. Digikey sells
Panasonic "FC" series capacitors that are made for high frequency, high ripple
current and long life. In my opinion these are the best there is, and I'll bet
if they were used as replacements the life would be very many years minimum.
Don't ever use crap Taiwan capacitors life Xicon or NTE or even with 105 degree
C ratings they will fail whithin a few months.
Ron

This is anecdotal but may be of some use. In one particular unit that
we constantly had to repair, the 'same' cap in a similar circuit often
failed. The factory used a 105 deg C cap and any attempt to replace it
with an 85 C unit would result in failure, often within weeks. The
actual temperature was very modest, on the order of the 55 degrees you
describe.
In speaking with a repair facility they informed me to use nothing less
than a 105 C rated cap...not because of temperature concerns but the
electrolyte and physical construction are different in such units which
apparently is an issue for longevity in this type of service.
FWIW,
Bill

 

[Jerry G.]

Calculations of capacitor lifetime is not easily done, because of the many
variables involved. The 105 C ones do last longer than the 85 deg C ones
when used in areas that are on the warm side.

The combination of heat and the current handling of the cap is what
determines it lifespan. When the supply is under a heavy load, the debt of
the ripple filtering for the cap will be greater. Between the cycles or
charge instances of the cap, it is discharging to the load. The greater the
load, the more work the cap has to do in order to sustain filtering.
Therefore its internal heat will increase.

To increase the lifespan of the cap, you can also use a number of them in
parallel. Having a fan blowing air on capacitors, and other components also
will increase the lifespan of them. This would involve a space problem. You
can use 4 or even 6 caps in parallel to share the loading. The total sum of
the values must add up to the original value or a bit greater. The cap
voltage ratings must be the same, or a greater than the original.

You may have to mount these caps outboard from the supply unit in order to
do this. If you look at some of the very heavy duty supplies, they are using
parallel caps instead of one big one. This shares the loading, and the heat
dissipation.


--

Fact:
In consumer TV sets and computer monitors, if cooling fans were properly
installed at the time of installation, there would be about a possible 80%
decrease of component failure over the TV set's lifespan.

TV sets that are installed in book cases and wall units, have a higher rate
of failure than ones that are installed on an open table with more than 4
feet of clearance on all sides and the top.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


<q@q.com> wrote in message
news:r1j06017jli5h82j77v4bbl266e5famo07@4ax.com...
Hi,

I have recently been servicing some equipment that has had failures of
a 1000uF 40v 85 Deg C capacitor, the equipment has been running for
about 5 years and are used in the smoothing circuit of a linear power
supply. .

I have measured the ripple current (with a true RMS meter) of about
280ma which is well within limits and can only assume that the CAN
temperature of the capacitor of around 55 deg C is too high. The
capacitor is between a transformer and the heat sink of a regulator.

My question is how do I calculate the life of the capacitor with the
temperature of 55 Deg C? I have been using the 10 Deg increase in
temperature halves the life of the capacitor rule (1.82 years in this
case) but is there a better way of showing this? I have to go to my
client and tell them they have a problem but I need some better
formula to show them (or maybe I do not?).

Any help would be greatly appreciated.

 

[Cornholio]

How about using some tantalum caps instead? They stand up to heat
better and by paralleling 2 or 3, the ESR is reduced which will keep
internal heating to a minimum as well as ripple.


On Tuesday, 23 Mar 2004 22:51:24 -500, "Asimov"
<Asimov@-removethis-bbs.juxtaposition.dynip.com> wrote:

"Jerry G." bravely wrote to "All" (23 Mar 04 11:14:09)
--- on the heady topic of "Re: Capacitor Lifetime calculation"

Another problem not mentioned so far is the peak current. This factor
is directly proportional to capacitance. Increasing the capacitance on
the principle that the ripple will be reduced can sometimes be
deterimental. Believe it or not hundreds of amperes can flow through a
supply filter capacitor as a pulse of current from the rectifier. It
is this pulse which causes a lot of stress aging. Typically the pulse
has a short duration but it can easily get out of control if the
designer neglects this aspect of supply rectification. What should be
done concurrently to increasing capacitance is to add a small length
of wire (just milli-ohms!) to reduce the peak current.

An alternative non-intuitive solution is to simply reduce the
capacitance value and tolerate a much larger ripple but following the
rectifier filter with a voltage regulator. As long as the ripple
doesn't dip below the regulator voltage compliance it will eliminate
the ripple almost completely. However the more important result is
that the supply rectifier and filter capacitor(s) will be far less
stressed by the peak current. Their service life and reliability will
then also increase by a large measure.


JG> From: "Jerry G." <jerryg50@hotmail.com

JG> Calculations of capacitor lifetime is not easily done, because of the
JG> many variables involved. The 105 C ones do last longer than the 85 deg
JG> C ones when used in areas that are on the warm side.

JG> The combination of heat and the current handling of the cap is what
JG> determines it lifespan. When the supply is under a heavy load, the
JG> debt of the ripple filtering for the cap will be greater. Between the
JG> cycles or charge instances of the cap, it is discharging to the load.
JG> The greater the load, the more work the cap has to do in order to
JG> sustain filtering. Therefore its internal heat will increase.

JG> To increase the lifespan of the cap, you can also use a number of them
JG> in parallel. Having a fan blowing air on capacitors, and other
JG> components also will increase the lifespan of them. This would involve
JG> a space problem. You can use 4 or even 6 caps in parallel to share the
JG> loading. The total sum of the values must add up to the original value
JG> or a bit greater. The cap voltage ratings must be the same, or a
JG> greater than the original.
JG> You may have to mount these caps outboard from the supply unit in
JG> order to do this. If you look at some of the very heavy duty supplies,
JG> they are using parallel caps instead of one big one. This shares the
JG> loading, and the heat dissipation.


JG> --

JG> Fact:
JG> In consumer TV sets and computer monitors, if cooling fans were
JG> properly installed at the time of installation, there would be about a
JG> possible 80% decrease of component failure over the TV set's lifespan.

JG> TV sets that are installed in book cases and wall units, have a higher
JG> rate of failure than ones that are installed on an open table with more
JG> than 4 feet of clearance on all sides and the top.

JG> --

JG> Greetings,

JG> Jerry Greenberg GLG Technologies GLG
JG> =========================================
JG> WebPage http://www.zoom-one.com
JG> Electronics http://www.zoom-one.com/electron.htm
JG> =========================================


JG> <q@q.com> wrote in message
JG> news:r1j06017jli5h82j77v4bbl266e5famo07@4ax.com...
JG> Hi,

JG> I have recently been servicing some equipment that has had failures of
JG> a 1000uF 40v 85 Deg C capacitor, the equipment has been running for
JG> about 5 years and are used in the smoothing circuit of a linear power
JG> supply. .

JG> I have measured the ripple current (with a true RMS meter) of about
JG> 280ma which is well within limits and can only assume that the CAN
JG> temperature of the capacitor of around 55 deg C is too high. The
JG> capacitor is between a transformer and the heat sink of a regulator.

JG> My question is how do I calculate the life of the capacitor with the
JG> temperature of 55 Deg C? I have been using the 10 Deg increase in
JG> temperature halves the life of the capacitor rule (1.82 years in this
JG> case) but is there a better way of showing this? I have to go to my
JG> client and tell them they have a problem but I need some better
JG> formula to show them (or maybe I do not?).

JG> Any help would be greatly appreciated.


... I worked hard to attach the electrodes to it.

 

[Max Harding vk3jin]

check capacitors with a ESR meter.can be checked in circuit.
<q@q.com> wrote in message
news:r1j06017jli5h82j77v4bbl266e5famo07@4ax.com...

Hi,

I have recently been servicing some equipment that has had failures of
a 1000uF 40v 85 Deg C capacitor, the equipment has been running for
about 5 years and are used in the smoothing circuit of a linear power
supply. .

I have measured the ripple current (with a true RMS meter) of about
280ma which is well within limits and can only assume that the CAN
temperature of the capacitor of around 55 deg C is too high. The
capacitor is between a transformer and the heat sink of a regulator.

My question is how do I calculate the life of the capacitor with the
temperature of 55 Deg C? I have been using the 10 Deg increase in
temperature halves the life of the capacitor rule (1.82 years in this
case) but is there a better way of showing this? I have to go to my
client and tell them they have a problem but I need some better
formula to show them (or maybe I do not?).

Any help would be greatly appreciated.

 

[do_not_spam_me]

q@q.com wrote in message news:<r1j06017jli5h82j77v4bbl266e5famo07@4ax.com>...

how do I calculate the life of the capacitor with the
temperature of 55 Deg C? I have been using the 10 Deg
increase in temperature halves the life of the capacitor
rule (1.82 years in this case) but is there a better
way of showing this?

The rough rule of thumb I've seen is:

estimated lifespan = (rated lifespan) x (2^(max temp - actual
temp)/10)

So if max temp = 105C, actual temp = 55C, and rated lifespan @ max
temp = 2000 hours, then lifespan = 2000(2^(105-55)/10) = 64,000 hours.
I haven't seen any common electrolytics rated for less than 2,000
hours, but many are rated for 3,000-4,000 hours, and a few for 7,000.

 

[do_not_spam_me]

"Jerry G." <jerryg50@hotmail.com> wrote in message news:<c3poto$ct3$1@news.eusc.inter.net>...

Fact:
In consumer TV sets and computer monitors, if cooling fans
were properly installed at the time of installation, there
would be about a possible 80% decrease of component failure
over the TV set's lifespan.

I don't think I want my TV to match the reliability of the old Zenith
Flat Tension monitor, which included a fan. Except for a failed
vertical capacitor and some loose wirewraps that needed soldering, my
TV (made in Japan) has been fine over the past 20+ years.

 

[do_not_spam_me]

"Jerry G." <jerryg50@hotmail.com> wrote in message news:<c3poto$ct3$1@news.eusc.inter.net>...

Fact:
In consumer TV sets and computer monitors, if cooling fans
were properly installed at the time of installation, there
would be about a possible 80% decrease of component failure
over the TV set's lifespan.

I don't think I want my TV to match the reliability of the old Zenith
Flat Tension monitor, which included a fan. Except for a failed
vertical capacitor and some loose wirewraps that needed soldering, my
made-in-Japan TV has been fine over the past 20+ years.