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CAPSUN ALUMINUM ELECTROLYTIC CAPACITORS(2)

Writer:sunny yangSource:szcapsun Date:2014-08-02 17:21

1.Impedance (Z)
The impedance of an electrolytic capacitor results from here below circuit formed by the following individual equivalent series components
 
Co=Aluminum oxide capacitance (surface and thickness of the dielectric)
Re=Resistance of electrolyte and paper mixture (other resistances not depending on the frequency are not considered:tabs,plates,and so on)
Ce = Electrolyte soaked paper capacitance
L = Inductive reactance of the capacitor winding and terminals.The impedance of an electrolytic capacitor is not a constant quantity that retains its value under all the conditions:it changes depending on the frequency and
the temperature.The impedance as a function of frequency (sinusoidal waveform) for a certain temperature can be represented as follows
 
Fig 1-12
-Capacitive reactance predominates at low frequencies -With increasing frequency,the Capacitive reactance Xc=1/ωCo decreases until it reaches the order of magnitude of the electrolyte resistance Re (A)-At even higher frequencies , the resistance of the electrolyte predominates:Z= Re (A-B)-When the capacitor's resonance frequency is reached (ω0),capacitive and cancel each other 1/ωCinductive reactance mutually cancel each other 1/ωCe=ωL,ω0=SQR(1/LCe)(C).-Above this frequency,the inductive reactance of the winding and its terminals (XL=Z=ωL)becomes effective and leads to an increase in impedance.Generally speaking it can be estimated that Ce≒0.01Co.
The impedance as a function of frequency (sinusoidal waveform) for different temperature values can be represented as follows (typical values)

Re is the most temperature dependant component of electrolytic capacitor equivalent circuit.The electrolyte resistivity will decrease if the temperature rises.In order to obtain a low impedance value all over the temperature range,Re must be as little as possible,but too low Re values means a very aggressive electrolyte and then a shorter life of the electrolytic capacitor at the high temperatures.A compromise must be reached.

2. Leakage current (L.C.)
Duetothealuminum oxidelayer that serves as adielectric,a small current will continueto flow even after a DC voltage has been applied for long periods.This current is called leakage current.A high leakage current flows after applying a voltage to the capacitor and then decreases in few minutes (e.g.after a prolonged storage without any applied voltage).In the course of the continuous operation , the leakage current will decrease and reach an almost constant value.After avoltage free storage the oxide layer may deteriorate,especially at high temperature . Since there are no leakage current to transport oxygen ions to the anode,the oxide layer is not regenerated.The result is that ahigher thannormal leakagecurrent will flow whenavoltageis appliedafter prolongedstorage.As the oxide layer is regenerated in use,the leakage current will gradually decrease to its normal level.The relationship between the leakage current and the voltage applied at constant temperature can be shown schematically as follows
 
Where:
VF=Forming voltage
If this level is exceeded a large quantity of heat and gas will be generated and the capacitor could be damaged.
VR=Rated Voltage
This level represents the top of the linear part of the curve.
VS=Surge voltage
It lies between VR and VF:the capacitor can be subjected to VS for short periods only 1-5 Reliability
(1)The bathtub curve luminum electrolytic capacitors feature failure rates shown by the following bathtub curve
 
Fig.1-15 Bathtub curve
a.Initial failure period:
Deficient Capacitors include any products before dispatch that may have some deficiency caused by the design, production process or used in
inappropriate environments.
b.Random failure period
        The capacitors have a low defect ratio in the period after it has been stabilized.
c.Wear out failure period
        The performance of capacitors will decrease with an increase in usage period.The malfunction rate may vary due to the structural design.

1-6 Circuit Design
 (1) Environmental and Mounting Conditions
★    Please make sure the environmental and mounting conditions to which the capacitor will be exposed to are within the conditions specified in CAPSUN’s catalog.

 (2) Operating Temperature,
      Equivalent Series Resistance(ESR),Ripple Current and Load Life
★    MTTF(Mean-Time-TO-Failure) means the useful life at room temperature  25℃

Load life:
    If the capacitor's max. operating temperature is at 105℃(85℃), then after applying capacitor's rated  voltage (WV) for L0  hours at 105℃(85℃),the capacitor shall meet the requirements in detail specification.where L0 is called   "load life" or "useful life (lifetime) at 105℃(85℃)".
Lx= L0 x 2 (To-Tx) /10 x K-△Tx / 5
where △Tx=△T0x ( Ix/ I0)2 Ix>I0,K=4;
Ix≦I0,K=2
Ripple life:
    If the capacitor's max. operating temperature is at 105℃(85℃), then after applying capacitor's rated   voltage (WV) with the ripple current for Lr hours at 105℃(85℃), the capacitor shall meet the requirements in detail specification. where Lris called "ripple life" or "useful ripple life (ripple lifetime) at 105℃(85℃)" .
         Lx  = Lr x 2 (To-Tx) /10 x K(△To -△Tx) /5
         where △Tx=△T0x ( Ix/ I0)2
         Ix>I0,K=4; Ix≦I0,K=2
        The (ripple) life expectancy at a lower temperature than the specified maximum temperature may  be estimated by the following equation,but this expectancy formula does not apply for ambient  below +40℃.

L0= Expected life period  (hrs) at maximum operating temperature allowed
Lr= Expected ripple life period (hrs) at maximum operating temperature allowed
Lx= Expected life period (hrs)  at actual operating temperature
T0= Maximum operating temperature (℃) allowed
Tx= Actual operating ambient temperature (℃)
Ix= Actual applied ripple current (mArms) at operating frequency f0(Hz)
I0= Rated maximum permissible ripple current IR(mArms) x frequency
 multiplier (Cf) at f0 (Hz)
※Ripple Current calculation: no need Temperature Multiplying Factor
※Ix Should be 80% equal or more of Io
△T0= Maximum temperature rise (℃) for applying I0(mArms) =5
△Tc =Temperature rise (℃) of capacitor case for applying Ix (mA/rms)
△Tx= Temperature rise (℃) of capacitor element for applying Ix(mArms)
=Kc△Tc=Kc(Tc-Tx)
where Tcis the surface temperature (℃) of capacitor case Tx  is ditto.Kc  is transfer coefficient between element and case of capacitor from table below
 

频率(HZ

50

120

300

1K

3K

10K

50K

10~50 V.DC

0.95

1.00

1.03

1.05

-

1.09

1.12

63~80V.DC

0.90

1.00

1.06

1.10

-

1.18

1.22

100~250V.DC

0.80

1.00

1.12

1.22

-

1.30

1.33

350~525V.DC

0.80

1.00

1.20

1.50

1.6

-

-


 ★ The formula of Equivalent Series Resistance (ESR)
The operating frequency of ESR, DF, f & C must be the same, usually,
they test at 120 Hz.
ESR=DF/2πf C…………(2)
Where  DF: Dissipation Factor(tanδ)
f : Operating frequency(Hz)
C: Capacitance(F)
★ Estimation of life considering the ripple current
The ripple current affects the life of a capacitor because the internal loss (ESR)
generates heat.The generated heat will be:
P = I2R-------(3)
Where  I : Ripple current(Arms.)
       R: ESR( Ω)

At this time the increase in the capacitor temperature will be:
△T= I2R / AH------(4)
        Where  △T: Temperature increase in the capacitor core(degree)
               I : Ripple current(Arms)
               R: ESR(Ω)
               A: Surface area of the capacitor (cm2)
               H: Radiation coefficient(Approx.1.5~2.0×10-3 W/ cm2.℃)
The above equation (4) shows that the temperature of a capacitor increases in
proportion to the square of the applied  ripple current and ESR, and in
inverse proportion to the surface area. Therefore, the amount of the ripple   
current determines the heat generation, which affects the life. The values of
△T varies depending on  the capacitor types and operating conditions.
The usage is generally desirable if △T remains less than 5℃.The measuring
point for temper-ature increase due to ripple current is shown below
 
(3) Application
★Aluminium Electrolytic Capacitors are normally polarized.Reverse voltage or AC Voltage should not be applied.When polarity may flip over, non-polar type  capacitors should be used, but the non-polar type cannot  be used for AC circuits.

(4) Applied Voltage
★Do not exceed the rated voltage of capacitor
(5) Insulation
★Aluminum Electrolytic Capacitors should be electrically isolated from among thefollowing points
(3) Soldering
a.Aluminum case, cathode lead wire, anode lead wire and circuit pattern
b.Auxiliary terminals of snap-in type, anode terminal, outward terminal
soldering and circuit pattern.

(6) Conditions of use
★    Aluminum Electrolytic Capacitors must not be used under the following conditions:
      a.Damp conditions such as water, saltwater spray, or oil spray or fumes.High  humidity or humidity  condensation situations
      b. Ambient conditions that include toxic gasses such as hydrogen sulfide,  sulfurous acid, nitrous acid, chlorine, ammonium,etc.
      c. Ambient conditions that expose the capacitors to ozone,ultraviolet  rays  and radiation
      d. Severe vibration or shock that exceeds the conditions specified the capacitors.in the catalog or specifications sheets
(7) Recommended design considerations
★    When designing a circuit board. Please pay attention to the following:
      a. Make the hole spacing on the PC board match the lead space of the capacitor.
      b. There should not be any circuit pattern or circuit wire above the capacitors.
      c. In case the capacitor's vent is facing the PC board,make a gas release  hole on PC board.
      d. Do not install screw terminal capacitor with end seal side down.When you install a screw terminal capacitor in a horizontal mount,the positive terminal must be in the upper position.
      e. Do not locate any wiring and circuit patterns directly above the capacitor's vent.1-7 Caution for Mounting
(1) Caution before assembly
★    Aluminum Electrolytic Capacitors cannot be recycled after mounting and applying electricity in unit. The  capacitors that are removed from PC board for the purpose of measuring electrical characteristics at aperiodical inspection should only berecycled to the same position.
★    Aluminum Electrolytic Capacitors may accumulate charge naturally  during  storage. In this case, discharge through a 1KΩ resistor before use.
★    Leakage current of Aluminum Electrolytic Capacitors may be increase  during long storage time. In this case,the capacitors should be subject  to voltage treatment through a 1KΩ resistor
before use.
(2) In the assembly process
★    Please confirm ratings before installing capacitors on the PC board
★    Please confirm polarity before installing capacitors on the PC board side
★    All CAPSUN's cp wires of electrolytic capacitors are without lead (Pb).
★    Soldering conditions(temperatures, times) should be within the specified conditions which are described in the catalog or specification sheets
★    If it is necessary that the leads must be formed due to a mismatch of the lead space to hole space on the board,bend the lead prior to without applying too much stress to the capacitor.
★    If soldering capacitor has to be withdrawn from the PW board by  soldering iron, the capacitor should be removed after the solder has melted sufficiently in
        order to avoid stress to the capacitor or lead wires.
★    Soldering iron should never touch the capacitor's body.

(4) Flow soldering
★    Do not dip capacitor's body into melted solder.
★    Din of flow soldering for the capacitors should be limited at 260℃,10sec.
★    Flux should not be adhered to capacitor's body but only to its terminals.
★    Other devices which are mounted near capacitors should not touch the capacitors.
(5) Reflow soldering condition
★    For reflow, use a thermal condition system such as infrared radiation or hot blast. Vapor heat transfer systems are  not recommended.
★    Observe proper soldering conditions(temperature, time, etc.Do not exceed the specified limits.
★    Repeated reflowing :
        *Avoid reflowing twice if possible.
        *If repeated reflowing is unavoidable,contact us after measuring the first and the second reflow profiles and reflow interval at your side.
        *Do not attempt to reflow three times
 
(6) Lead free type reflow soldering condition
★    For reflow, use a thermal condition system such as infrared radiation or hot blast.Vapor heat transfer systems are not recommended.
★    Observe proper soldering conditions(temperature, time, etc.Do not exceed the specified limits).
★    Repeated reflowing:
        *Avoid reflowing twice if possible.*If repeated reflowing is unavoidable,contact us after measuring the first and the second reflow profiles and reflow interval at your
★    Do not drop capacitors on the floor, nor use a capacitor that was dropped.
★    Be careful not to deform the capacitor during installation.
★    Please confirm that the lead spacing of the capacitor matches the hole spacing of the PC board prior to installation.
★    The snap-in type of capacitors should be mounted firmly on the PC board without a gap between the capacitor body and the surface of PC board.
★    Avoid excessive force when clinching lead wire during auto-insertion process.
★    Avoid excessive shock to capacitors by automatic insertion machine,  during mounting, parts inspection or centering operations.
★    Please utilize supporting material such as strap or adhesive