IEC TR 63362-1:2022

IEC TR 63362-1 ®
Edition 1.0 2022-02
TECHNICAL
REPORT
colour
inside
Application of fixed capacitors in electronic equipment –
Part 1: Aluminium electrolytic capacitors
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IEC TR 63362-1 ®
Edition 1.0 2022-02
TECHNICAL
REPORT
colour
inside
Application of fixed capacitors in electronic equipment –

Part 1: Aluminium electrolytic capacitors

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.060.50 ISBN 978-2-8322-1078-4

– 2 – IEC TR 63362-1:2022 © IEC 2022
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Protection measures – insulation . 8
5 General application limits . 9
5.1 Polarity – Reverse voltage . 9
5.2 Voltage . 9
5.2.1 General . 9
5.2.2 Rated voltage . 9
5.2.3 Surge voltage . 9
5.2.4 Transient voltages . 9
5.3 Temperature range . 9
5.4 Ripple current . 10
5.5 Charge – Discharge . 10
6 Storage, transportation, and operation . 10
7 External pressure (not relevant for capacitors with solid electrolyte) . 11
7.1 Low air pressure . 11
7.2 High air pressure . 11
8 Self-recharge phenomenon (dielectric absorption) . 11
9 Flammability (passive and active) . 11
9.1 General . 11
9.2 Passive flammability . 11
9.3 Active flammability . 12
10 Internal pressure and pressure relief device . 12
11 Working electrolytes and contact with an electrolyte . 12
12 Parallel and series connection of capacitors . 13
12.1 General . 13
12.2 Voltage sharing between devices . 13
12.3 Circuit configuration . 13
12.4 Balancing resistors for voltage sharing . 14
12.4.1 General . 14
12.4.2 Voltage sharing analysis . 15
12.4.3 Resistor tolerance . 16
12.4.4 Choice of resistor value . 16
12.5 Component failure. 17
13 Clearance and creepage distances . 17
13.1 Distances inside the capacitor . 17
13.2 Distances outside the capacitor . 17
14 Capacitor mounting . 18
14.1 General conditions for mounting . 18
14.1.1 Mounting position . 18
14.1.2 Polarity indication . 18
14.1.3 Hole/pad distance . 18
14.1.4 Position of the pressure relief device . 18

14.1.5 Board holes under the insulation . 19
14.1.6 Double-sided printed circuit boards . 19
14.1.7 Case polarity . 19
14.2 Component preparation. 19
14.3 Mounting . 19
14.3.1 Discharging . 19
14.3.2 Ratings and polarity . 19
14.3.3 Lead stress . 19
14.3.4 Fixing torque . 19
14.3.5 Capacitor fixing . 20
14.4 Soldering . 20
14.4.1 Preheat temperature . 20
14.4.2 Soldering temperature and duration . 20
14.4.3 Care after soldering . 20
14.5 Transport and handling of assembled devices . 20
15 Cleaning solvents and processes . 20
15.1 General . 20
15.2 Cleaning solvents . 20
15.2.1 Halogenated solvents (e.g. CFC) . 20
15.2.2 Halogenated hydrocarbons . 21
15.2.3 Aqueous solutions . 21
15.2.4 Alcohols . 21
15.2.5 Alkaline solvents . 21
15.2.6 Other cleaning solvents . 21
15.3 Cleaning of circuit board . 21
15.3.1 Cleaning processes . 21
15.3.2 Process control during cleaning . 22
15.3.3 Process control after cleaning . 22
15.3.4 Other precautions . 22
16 Potting and gluing . 22
16.1 General . 22
16.2 Potting and gluing materials . 23
16.3 Curing process . 23
17 Selection of capacitors and failure mechanisms during overload . 23
17.1 Selection . 23
17.1.1 General . 23
17.1.2 Selection based on operating conditions . 23
17.1.3 Selection based on shapes and assembly conditions . 23
17.2 Failure mechanisms during overload (especially details under overvoltage
load conditions) . 24
17.2.1 Overview . 24
17.2.2 Failure mechanisms - details . 24
18 Disposal of capacitors . 25
Bibliography . 26

Figure 1 – Individual balancing resistors . 13
Figure 2 – Common centre connection . 14
Figure 3 – Group-balancing resistors . 14

– 4 – IEC TR 63362-1:2022 © IEC 2022
Figure 4 – Voltage sharing analysis . 15
Figure 5 – Degradation mechanisms . 24

Table 1 – Balancing examples . 17

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
APPLICATION OF FIXED CAPACITORS IN ELECTRONIC EQUIPMENT –

Part 1: Aluminium electrolytic capacitors

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
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preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
may participate in this preparatory work. International, governmental and non-governmental organizations liaising
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Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC TR 63362-1 has been prepared by IEC technical committee 40: Capacitors and resistors
for electronic equipment. It is a Technical Report.
This first edition cancels and replaces CLC/TR 50454 published in 2008. This edition constitutes
a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Complete technical revision, details of cleaning processes and failure modes added.
b) Inclusion of parts of JEITA RCR 2367D.
The text of this Technical Report is based on the following documents:

– 6 – IEC TR 63362-1:2022 © IEC 2022
Draft Report on voting
40/2881/DTR 40/2908/RVDTR
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Report is English.
A list of all parts in the IEC 63362 series, published under the general title Application of fixed
capacitors in electronic equipment, can be found on the IEC website.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
APPLICATION OF FIXED CAPACITORS IN ELECTRONIC EQUIPMENT –

Part 1: Aluminium electrolytic capacitors

1 Scope
This document establishes guidelines for the application and use of aluminium electrolytic
capacitors in electronic equipment.
The information given in this document applies to capacitors with non-solid electrolyte but can,
in its appropriate clauses, apply to capacitors with solid electrolyte as well.
Electrolytic capacitors in general – and aluminium electrolytic capacitors in particular – are an
exception in the capacitor field because of the components’ close interaction of physics and
chemistry. Therefore, aluminium electrolytic capacitors show, in various aspects, a technical
behaviour unaccustomed to the user. That could easily lead to misapplications and even to
endangering of persons and goods. The aim of this document is to minimize these risks by
providing detailed information on the specific peculiarities of the component.
2 Normative references
There are no normative references in this document.
NOTE Further information about related standards can be found in Bibliography at the end of this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
anode
positive electrode
aluminium (preferably aluminium foil) of extreme purity that is etched in most cases in order to
increase the electrode's surface and, consequently, the capacitor's capacitance yield
3.2
cathode
negative electrode
working electrolyte that is a conductive material
Note 1 to entry: Working electrolyte in the case of capacitors with solid electrolyte is a layer of manganese dioxide
MnO , conductive organic salt (e.g. TCNQ) or conductive polymer (e.g. polypyrrole, PEDOT).
Note 2 to entry: PEDOT is a thiophene-based doped polymer, which is used as a solid cathode in aluminium
electrolytic capacitors, often combined with an additional liquid electrolyte.

– 8 – IEC TR 63362-1:2022 © IEC 2022
3.3
dielectric
aluminium oxide (Al O ) which is formed on the anode’s surface by an anodizing process
2 3
3.4
contact element for the negative electrode
high-purity aluminium foil ("cathode foil") in the case of capacitors with non-solid electrolyte or
silver paste on graphite or other conductive connections in the case of capacitors with solid
electrolyte
3.5
separator
layers (preferably of special paper) that separate the anode foil from the "cathode foil" in the
case of capacitors with non-solid electrolyte
Note 1 to entry: The other purpose of the separators is to retain the working electrolyte.
3.6
polarity
polarized electrolytic capacitor
Note 1 to entry: For special purposes, so-called non-polar (bipolar) capacitors can be provided. Such special types
consist in principle of an internal back-to-back connection of two basically polarized elements.
3.7
sealing
polymer-based material to close the aluminium case
Note 1 to entry: The internal element of a non-solid electrolytic capacitor is normally encapsulated in an aluminium
case closed with a sealing material which is never perfectly gas-tight. Because of using a non-solid electrolyte, of
which, some constituents are slowly diffusing through the sealing, the electrical characteristics of the capacitor are
changing gradually over its entire life.
4 Protection measures – insulation
Capacitors can be either completely or partially covered with sleeving or coating, or not covered
at all. It should be noted that, in particular for capacitors with liquid electrolyte, the capacitor
case is not insulated from the cathode terminal. The case can be connected to the electrolyte
through the contact element for the negative electrode.
Axial leaded capacitors have a direct contact between the case and the cathode terminal. Radial
leaded capacitors have an undefined electrical contact through electrolyte or other parts inside
the case. Dummy pins are left potential-free or can be connected to the potential of the negative
terminal. Metal parts other than terminals should never make contact to conducting tracks or
metal parts of other components.
The standard sleeving must be considered as protection against contact only, and does not
offer any functional insulation. If electrical insulation is required, an additional insulation is
necessary.
Special care needs to be taken if the mounting requires electrical insulation, such as:
• other components are in touch with capacitors;
• unprotected live wires or PCB tracks are underneath the capacitors;
• capacitors are in contact with the enclosure;
• capacitors are mounted by metal clamps.
For such cases, the sleeving material needs to be agreed on case by case between the
manufacturer and the customer.

The sleeving can deteriorate depending on the environmental conditions, e.g.:
• upon exposure to high temperature, polyvinyl chloride (PVC) sleeving can become brittle
which could potentially lead to cracks;
• for polyethylene terephthalate (PET) based sleeving, exposure to high temperature and high
humidity can lead to hydrolysis.
Operating conditions for which sleeving deterioration is expected need to be agreed on case by
case between the manufacturer and the customer.
5 General application limits
5.1 Polarity – Reverse voltage
Electrolytic capacitors for DC applications require polarization.
The polarity of each capacitor is checked both in circuit design and in mounting. Polarity is
clearly indicated on the capacitor. For short periods, a limited reverse voltage can be allowed
as specified in the relevant specification by the manufacturer. Exceeding the specified reverse
voltage can induce damage by causing overheating, over-pressure and dielectric breakdown
and can be associated with open circuit or short-circuit conditions – it is the most severe failure
mechanism with aluminium electrolytic capacitors. There could even be a destruction of the
capacitor. Protections need to be used if there are reverse voltage risks (see Clause 10).
5.2 Voltage
5.2.1 General
Exceeding the capacitors' specified voltage limits can cause premature damage (e.g. by
breakdown with open or short circuit) affecting the useful life. Even destruction of the capacitor
can be the consequence.
5.2.2 Rated voltage
The rated voltage U given in the relevant specification or by the manufacturer is the value
R
permitted for continuous operation in the rated temperature range.
5.2.3 Surge voltage
For short periods, the voltage can be increased up to the surge voltage value in accordance
with IEC 60384-4, IEC 60384-18, IEC 60384-25, IEC 60384-26 and to the manufacturer's
specification.
5.2.4 Transient voltages
The surge voltage value can be exceeded for very short periods or short pulses if allowed by
the manufacturer and when in accordance with the relevant specification or detailed
specification by the manufacturer. A test method is given in IEC 60384-4, IEC 60384-18,
IEC 60384-25, IEC 60384-26.
Such special operating conditions need to be agreed on case by case between the customer
and the manufacturer.
5.3 Temperature range
The capacitors are to be used within the specified temperature range (category temperature
range).
– 10 – IEC TR 63362-1:2022 © IEC 2022
Applicable temperature ranges are given in the relevant specifications and/or in manufacturer’s
data. A general principle is that lower ambient temperature means longer life. Therefore,
electrolytic capacitors should be placed at the coolest positions wherever possible.
Exceeding the permitted temperature causes overheating and over-pressure, which can affect
the useful life and induce damage. Even destruction of the capacitor can be the consequence.
5.4 Ripple current
The sum of DC voltage and superimposed ripple voltage is specified to be within rated voltage
and 0 V at any time.
Electrolytic capacitors are not normally designed for AC application (see Clauses 1 and 17).
No excessive ripple current is allowed to pass. Exceeding the ripple current specification
reduces life and can induce overheating and over-pressure. Even destruction of the capacitor
can be the consequence.
The useful life of the capacitor is a function of the r.m.s. ripple current. Temperature, frequency
and cooling conditions as well as applied DC voltage are other factors influencing the useful
life.
5.5 Charge – Discharge
Under the conditions defined in IEC 60384-4, IEC 60384-18, IEC 60384-25, IEC 60384-26, or
in the manufacturer’s specifications, frequent charge/discharge operation is allowed.
Exceeding charge/discharge frequency leads to a high ripple current and induces damage by
overheating and overpressure or breakdown with open circuit or short circuit, leading to a
reverse voltage risk (see 5.1). Even destruction of the capacitor can be the consequence.
Rapid charge/discharge operating conditions in applications such as robotics or servo drives
need to be agreed on case by case between customer and manufacturer.
6 Storage, transportation, and operation
It is recommended to store the capacitors at temperatures between 5 °C to 35 °C and a relative
humidity of less than 75 %, and in original packaging.
Storage of the capacitors above recommended temperatures (5 °C to 35 °C) in off-duty condition
can cause an increase of the leakage current to more than 10 times the maximum limit (see
IEC 60384-4, IEC 60384-18, IEC 60384-25, IEC 60384-26). This is caused by the special
characteristics of the dielectric material (e.g. aluminium oxide in case of aluminium electrolytic
capacitors). This leakage current is not only dependent on the capacitor's design, but is also a
function of time, the applied voltage, temperature, and the capacitor’s history, such as storage
conditions and duration. Although the initial leakage current can be significantly increased after
storage, it will decrease to a stable value upon application of voltage.
Manufacturers' recommendations (reforming procedures, etc.) need to be considered after
extended storage (for more details see IEC 60384-4, IEC 60384-18, IEC 60384-25,
IEC 60384-26). High humidity and/or high temperature can impair solderability and taping.
Storage at conditions defined above has a negligible effect on capacitance, tangent of loss
angle or equivalent series resistance, and impedance.
Special care needs to be taken with respect to exposure to halogenated chemicals (see also
Clause 15). International shipments might be subjected to fumigation treatment with

halogenated gases (e.g. methyl bromide). These gases could penetrate the sealing and
potentially lead to internal corrosion.
Capacitors are generally housed in high purity aluminium with typically low mechanical strength.
Shocks must be avoided and the manufacturer’s packaging must always be used to transport
capacitors.
7 External pressure (not relevant for capacitors with solid electrolyte)
7.1 Low air pressure
Minimum air pressure is 8 kPa for short periods, for example 5 min accordance with
IEC 60384-4.
7.2 High air pressure
If the capacitor is operated under conditions higher than natural ambient air pressure, the
manufacturer needs to be consulted. The maximum operating pressure depends upon size and
style of the capacitor. It should be specified by the manufacturer on request. Exceeding the
specified value can damage the capacitor (e.g. destroyed cases, open pressure relief device,
short circuit, etc.).
8 Self-recharge phenomenon (dielectric absorption)
Even if aluminium electrolytic capacitors are totally discharged, these components can
afterwards develop some voltage without external influence. This self-recharge phenomenon is
known as "dielectric absorption" or as "dielectric relaxation" (can exceed 15 % of the capacitor’s
rated voltage).
The capacitor is a non-ohmic conductor and has, therefore, a non-uniform distribution of the
electric field. This is correlated with electric space charges within the dielectric layer. In the
case of open terminals, an increasing voltage is built up during the electric charges’ relaxation.
Depending on the capacitor type and its designed voltage, such self-recharge can result in
values (even several tens of volts) which could represent some risk: damage of semiconductor
devices, solder bath sparking during soldering, sparking when by-passing the terminals, and so
on.
Therefore, appropriate measures are advisable if such risks are to be avoided. In particular, for
capacitors of high capacitance and high electric charge, it is recommended, for instance, to
keep the terminals shorted or to repeat the discharge before mounting or soldering them.
9 Flammability (passive and active)
9.1 General
Aluminium electrolytic capacitors contain materials that can ignite under the influence of
external fire (passive flammability) or in the case of a defect of the component (active
flammability). Such flammable parts of the capacitor are for instance: plastic parts, sleeves,
moulding compounds, separator of the capacitors' winding element, in some cases working
electrolytes.
9.2 Passive flammability
Under the influence of high external energy, such as fire or electricity, the flammable parts can
ignite. If, for equipment safety approvals, information about passive flammability is required,
the manufacturers need to be consulted. Related information can be obtained for example from

– 12 – IEC TR 63362-1:2022 © IEC 2022
IEC 60384-1, which refers to the needle flame test (IEC 60695-11-5) for testing the passive
flammability of capacitors. The severities and requirements for different categories of
flammability are listed in IEC 60384-1.
9.3 Active flammability
In rare cases, the component can ignite caused by heavy overload or some capacitor defect.
One reason could be that during the operation of an aluminium electrolytic capacitor with non-
solid electrolyte, there is a small quantity of hydrogen developed in the component. Under
normal conditions, this gas permeates easily out of the capacitor. But under exceptional
circumstances, higher gas amounts can develop and can catch fire if sparking occurs at the
same time.
As explained above, a fire occurrence cannot be totally excluded. Therefore, it is recommended
to use special measures in critical applications (e.g. additional encapsulation of the equipment
for mining applications).
10 Internal pressure and pressure relief device
(Not relevant for capacitors with solid electrolyte).
During the operation of the aluminium electrolytic capacitor with non-solid electrolyte, some gas
develops in the component. Under normal conditions, this small amount permeates without any
problems slowly out of the capacitor. But in cases like an overload, application of reverse
voltage, or a malfunction of the capacitor can cause a higher gas production that cannot be
covered by the normal permeation and leads to a considerable overpressure in the component.
This high internal pressure can lead to the rupture of capacitor sealing/body/casing. The
relevant detail specifications will indicate whether the capacitor is equipped with a specific
pressure relief device ("safety vent") which opens at a relatively low pressure and, therefore,
limits the abovementioned risk of rupture.
The test of the proper function of this pressure relief device is specified in IEC 60384-1. The
test methods described therein prove whether the pressure relief device covers the majority of
the fault events.
In rare cases, such as extreme overload or ignition of gas inside the capacitor (through sparking
caused by breakdown), a fully functioning pressure relief device does not react in time.
Therefore, capacitors exposed to such limit conditions need to be shielded. The same applies
in the case of testing the pressure relief device.
When using the capacitors, care needs to be taken to ensure that the proper function of the
pressure relief device is not impaired, for instance by mounting measures such as clamps or
glue and potting compounds (see also 14.1.4, Position of the pressure relief device).
11 Working electrolytes and contact with an electrolyte
(Not relevant for capacitors with solid electrolyte).
Capacitors with non-solid electrolyte contain high purity aluminium foils and separators that are
impregnated with a suitable electrolyte. To give the electrolytic capacitor a long and stable life,
the ingredients must be very pure. Impurities such as halogens (e.g. chloride) or foreign metals
must be kept as low as possible.
The electrolyte is a biodegradable liquid based on a stable solvent with a high boiling point as
the main ingredient (common solvents are γ-butyrolactone or ethylene glycol). Furthermore, the

electrolyte consists of an acid base system and other added chemicals that are dissolved in it.
It has a low toxicity, but prolonged inhalation of vapours or ingestion should be avoided.
However, it is advisable to avoid contact with the skin or the eyes. Exposure of electrolyte on
the skin must immediately be treated by rinsing with water. Exposure to the eyes must be
treated by flushing for 10 min by rinsing with water. Medical attention should be sought if
problems persist. Inhalation of electrolyte vapours or aerosols from electrolyte must be avoided.
If vapour of electrolyte is present, the air in the room must be ventilated. Smoke from burning
electrolyte is irritating but does not contain dioxins or similar highly toxic substances. If
electrolyte gets on cloth, it can be washed with water.
12 Parallel and series connection of capacitors
12.1 General
Connection of aluminium electrolytic capacitors in series/parallel banks gives rise to the
following considerations. Subclauses 12.2 to 12.5 provide guidelines for parallel and series
connection of capacitors. Individual differences in component characteristics for different
manufacturers need to be considered. Detailed information for balancing resistors can be
obtained from manufacturers.
12.2 Voltage sharing between devices
This factor is influenced by the leakage current difference between the individual capacitors in
the chain. It is very important that the leakage current differences are compensated for at the
design stage as fairly small differences can cause problems.
This is normally evidenced at turn on as an overvoltage condition on the components with the
lowest leakage currents and can lead to premature failure.
Depending on the circuit configuration of the bank and failure mode, other components which
were initially unaffected could at this stage be subjected to voltages considerably in excess of
the ratings and will also fail.
This leakage current difference is normally controlled by the use of resistors across each of the
individual components, or in the case of a common centre connection, by only two resistors.
12.3 Circuit configuration
There are two major configurations to consider when constructing a series/parallel bank of
capacitors. The advantages and disadvantages of each are outlined below but the final choice
needs to be made by the equipment designer:
a) Option 1: Individual balancing resistors (see Figure 1)

Figure 1 – Individual balancing resistors
Advantages
If one capacitor fails and becomes short circuit, then the capacitor in series with it will almost
certainly fail but the other capacitors in the bank should be unaffected.

– 14 – IEC TR 63362-1:2022 © IEC 2022
Disadvantages
More complex construction, many resistors to be fitted. Additional cost of resistors.
b) Option 2: Common centre connection (see Figure 2)

Figure 2 – Common centre connection
Advantages
As the number of capacitors in parallel increases, so the effective capacitance at the top
and bottom of the bank will tend to equalise; this will give better balancing during transient
conditions.
Also, the average total leakage current at the top and bottom of the bank will become closer
giving improved balancing under steady-state conditions.
Only two resistors required. In some cases, the difference between the leakage currents at
the top and bottom of the bank can be so small as to render the use of resistors unnecessary.
Disadvantages
If one capacitor goes short circuit, the other half of the bank will be exposed to the full
voltage and can cause several further failures.
Of course, combinations of the above basic configurations are in use too, as shown in
Figure 3. Capacitor banks can be subdivided into groups of option 2 (common centre
connection).
Figure 3 – Group-balancing resistors
The consequent advantages and disadvantages of both options apply when using the circuit
diagram as shown in Figure 3.
12.4 Balancing resistors for voltage sharing
12.4.1 General
When aluminium electrolytic capacitors are connected in series, the voltage ratio across the
series capacitors will be equal to the ratio of their insulation resistances (or to the reciprocal
ratio of their leakage currents, respectively), see 12.1. As there are remarkable spreads of
leakage currents to be taken into consideration, it is advisable to use balancing resistors to
control the voltage sharing across each device.

12.4.2 Voltage sharing analysis
Consider the circuit consisting of two capacitors in series (C and C ) with balancing resistors

1 2
(R and R ) shown in Figure 4.
1 2
Figure 4 – Voltage sharing analysis
If a voltage U is applied across this capacitor and resistor network then, when equilibrium is
reached, the currents I , I , I and I will flow as shown.

c1 c2 r1 r2
The sum of the currents through the top half of the network will equal the sum of the currents
through the bottom half of the network, thus:
I + I = I + I
(1)
c1 r1 c2 r2
The voltage at the mid-point, denoted by U , will be given by:
m
U = I × R
(2)
m r1 1
Combining equations (1) and (2) gives:
U = (I − I + I ) × R
(3)
m c2 c1 r2 1
Furthermore, since I can be defined as:

r2
UU−
( )
m
I = (4)
r2
R
It can be shown that:
I −I ×R×R
( ) UR×
c2 c1 1 2
U +
(5)
m
RR++RR
( ) ( )
12 12
This shows that the mid-point voltage U is dependent on the difference in capacitor leakage
m
current (I – I ), the applied voltage U and the values of the resistors used.

c2 c1
Since the values of the balancing resistors will normally be equal, we can set both R and R

1 2
equal to R and simplify the equation to give:
=
– 16 – IEC TR 63362-1:2022 © IEC 2022
II−×R
( ) U
c2 c1
(6)
U +
m
This clearly demonstrates that the mid-point voltage U deviates from the ideal value of U/2 by
m
an offset voltage (I – I ) × R/2, which is determined by the resistor value and the difference
c2 c1
in leakage currents between the two capacitors.
12.4.3 Resistor tolerance
The effect of different resistor values (varying within normal tolerance) can be shown by
examining equation (5).
For example, suppose the resistors have a ± 5 % tolerance and one resistor is on bottom limit
and the other on top limit. We can set R = 0,95 × R and R = 1,05 × R, which gives:

1 2
II− ××R 0,9975
( )
U× 0,95
c2 c1
(7)
U +
m
In this case, the ideal mid-point voltage of U/2 is reduced by 5 % and the offset voltage due to
leakage current difference is slightly reduced by a factor of 0,997 5.
12.4.4 Choice of resistor value
Equation (6) can also be rearranged to determine the value of balancing resistor necessary for
a given set of conditions, thus:
(2×−UU)
m
R=
(8)
(II− )
c2 c1
To calculate the maximum resistor value required, set U to
...