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Servicing Safety and Replacement of Electrolytic Capacitors


Senior Member
Forum Donor
Feb 8, 2022
Health Hazards
"The limited energy in capacitors (E = (1/2) C V²) restricts the duration of the shock, even if there are no circuit breakers to trip. The shock current will be limited by the body resistance, and the duration of the shock will be characterized by the time constant (τ = R C). Therefore, the total energy will be dissipated quicker when the body resistance is low, and slower when the body resistance is high. Additionally, increasing the capacitance will just extend the discharge time."[1]

E is energy in joules, C is capacitance in farads, V is voltage in volts, τ (tau) is the RC time constant in seconds, and R is resistance in ohms. A good reason why it says "do not open" on the chassis of some electronic equipment is that AC mains, capacitors or batteries can cause electric shock, and capacitors and batteries can store a dangerous charge after AC mains is disconnected. Digi-Key Electronics has calculators for safely discharging capacitors with a resistor that has the required wattage.[2][3][4] Digi-Key Electronics recommends not using a screwdriver to discharge capacitors, which implies that suitable resistors provide a safe RC time constant.[5] Converting the capacitance and voltage of a capacitor to joules is useful for knowing whether there is a risk of electric shock. 0.5 J to 10 J can be unpleasant to very painful. A safe threshold for when DC surge discharges can cause ventricular fibrillation, like disconnected capacitors can deliver, is 27 J = 27 W s (watt-seconds), and mains frequency impulse current with 13.5 J = 13.5 W s.

Reflex movements from an impulse shock of less than 13.5 W s can result in unexpected injuries. Injuries vary with contact resistance. DC might cause a single muscle contraction that prevents the hand from letting go of the circuit, but DC can jolt the hand away when the contact resistance is high. The 50 Hz or 60 Hz cycle of AC mains might give a chance to repel the hand away from the current, but the cyclical muscle contractions can be severely damaging. Currents around the let-go threshold are very painful and will help an individual with moving the hand or other inflicted body part away immediately. A safe 60 Hz RMS AC sine wave threshold for when muscle contractions become inextricable is 16 mA for men, and 10.5 mA for women. For men, this let-go threshold is 24 mA at 1 kHz, 32 mA at 2 kHz, 45 mA at 4 kHz, and 56 mA at 6 kHz. The corresponding milliamperes for women are approximately two thirds. An equivalent DC threshold is 76 mA for men, and 51 mA for women. These values are medians, so there is wide variation in how people react.[6]

Aluminum electrolytic capacitors will lose their electric charge with time, but there is dielectric absorption that brings up to 10% of the previous charge back. Charging electrolytic capacitors regularly, at least once every six months or so helps to maintain their breakdown voltage because of electrochemical reactions. This can be done by using the equipment they are installed in. High temperature or humidity where capacitors are stored, such as direct sunlight can be bad for their durability. The electrolyte in capacitors can be toxic or caustic, and becomes gas when excessive ripple current boils electrolyte that forces the pressure relief vent to open. Inhalation of lead from soldering fumes is not a considerable problem at the optimal temperature for hand soldering, but ingestion is prevented with hand hygiene. Rosin flux from soldering fumes should not be inhaled or come in contact with the skin, due to asthma and dermatitis. Recommended precautions from dross and flux in soldering fumes include ventilation, safety glasses, respirators, ESD gloves and ESD lab coats.[7][8] Computer fans can be modified by soldering them to a regulated 12 VDC adapter that has a suitable current rating. The temperature of soldering fumes is bad for the durability of a computer fan, but intake airflow can be used and computer fans are often not made for static pressure. Electrolytic capacitors, lead solder, used lead solder sponges and contaminated fume extractor filters are disposed as hazardous waste in accordance with regulations, such as the Waste Framework Directive of the European Union.[9][10][11]

Practical Calculations
"The reader is cautioned against interpreting the differences between the voltage values as a true index of the relative hazard between alternating current and direct current. Current is the proper criterion of electric shock intensity, and the hazard from the proposed reasonably safe voltages would be greatly increased if contact occurred at locations where the skin was lacerated or if local high current densities produced material breakdown of the skin. Currents of the let-go level are more than sufficient to produce very serious burns."

A safety limit for a mains frequency AC sine wave is 24 V RMS if there would otherwise be a risk of electric shock on skin that is not lacerated, and approximately 10–21 V RMS when there is conductive fluid on the skin, since there is a difference in contact area and dielectric strength of the epidermis. This limit is 12 V RMS when there is no GFCI (ground fault circuit interrupter). An equivalent safety limit for DC is 50 V, also on wet skin. These safety limits are set to half of what could generally cause electric shock in a worst-case scenario. Static electricity is safe for the skin, but the current and contact resistances can usually not be determined with accuracy when there was an injury from electricity. Therefore, voltage is used for safety limits. A multimeter can check whether the voltage in a device is safe, and a multimeter with a low-impedance mode can discharge capacitors. The effective resistivity inside the body, for electric power that can break the dielectric strength of healthy skin, is approximately 100 Ω cm (ohm-centimeters), which correlates with the electrical resistivity of intercellular fluid and the blood circulatory system.[12][13][14]

Here is the minimum dangerous capacitance for a capacitor with the minimum DC voltage, where ventricular fibrillation or respiratory paralysis can possibly occur under abnormal conditions, such as touching a set of the capacitor terminals with the tongue: 27 J = (1/2) C (50 V)² = 1,250 V C => 27 J/1,250 V = C = 0.0216 F = 21.6 mF. People normally use the milli, micro, nano and pico prefixes, so mF (1,000 times more), µF (often written uF and is 1,000,000 times more than F), nF (1,000,000,000 times more) and pF (1,000,000,000,000 times more). The minimum dangerous capacitance will naturally be lower when the voltage is higher. I have a Yamaha A-700 power amplifier with the original power supply capacitors. They are potentially deadly at the rated charge, since each is rated for (1/2) (22,000 µF/1,000,000) (69 V)² = 52.371 J. Watt-seconds are actually why electricity causes injuries as current and voltage are described in Ohm's law. The two capacitors are about 40 years old and should be measured or just replaced, since 15 years after the manufacturing date is where the end seals of electrolytic capacitors can stop working, which makes the electrolyte evaporate with time.[15][16] Touching and causing vibration on capacitors if they are soldered to a circuit board can cause deterioration of their lead seals. Film capacitors can work for 50 years or more, but they are generally too expensive at high values of capacitance, and their lower ESR can create some problems for designs that were made with electrolytic capacitors.[17]

Technical Specifications of Capacitors
"For aluminum electrolytic capacitors, the capacitance is measured under the standard measuring conditions of 20°C and a 120Hz AC signal of about 0.5V. Generally, as the temperature rises, the capacitance increases; as the temperature decreases, the capacitance decreases (Fig. 7). With a higher frequency, the capacitance is smaller; with a lower frequency, the capacitance is larger (Fig. 8)."[18]

Capacitance, dissipation factor and leakage current are used for finding out whether a capacitor is working.[19][20] An AC test voltage must be under 1.5 volts for polarized electrolytic capacitors, because they have an anodized dielectric with that breakdown voltage. Even non-polarized electrolytic capacitors are not suitable for an AC voltage application with considerable ripple current, since electric power can make the electrolyte evaporate. The anodized dielectric degrades continually if no voltage is applied. If the rated voltage (also called the working voltage) has not been applied to the electrolytic capacitor for a couple of years, then the leakage current will increase and reforming will be necessary for restoring the dielectric strength. However, the dielectric strength will not be the same as originally and the breakdown voltage will be reformed at the applied voltage.[21] This deterioration of the oxide layer can also interfere with accurate measurements, so it might be more desirable to skip measurements of electrolytic capacitors and just replace them around 30 years after the manufacturing date.

The IEC 60384-1 and IEC 60384-4 standards for aluminum electrolytic capacitors are a measurement frequency of 100 Hz or 120 Hz for capacitance and dissipation factor, at a temperature of 20 °C.[22] The IEC 60068-1:2013 standard for film capacitors is a measurement frequency of 1 kHz for capacitance and dissipation factor. MKT, MFP and MKP film capacitors with a rated capacitance ≤ 1 μF have additional measurement frequencies of 10 kHz or 100 kHz for dissipation factor.[23] The capacitance (IEC 60062) should normally be the same and the voltage can be higher, but not lower than the capacitor that is being replaced.[24] This also depends on finding the right physical dimensions, including lead spacing for the replacement. LCR meters or a program called Room EQ Wizard use an AC test signal. The dissipation factor also called tan(δ) is needed for testing the condition of capacitors accurately. Accurate measurements also provide an impression of authenticity if an authorized distributor was not used. However, there can still be defects because of the acceptance quality limit (ISO 2859-1, IEC 60410 and JIS Z 9015-1).[25] A multimeter can check for an internal short circuit or open circuit in a capacitor, which are failure modes.[26] A resistance reading that stays low is a short circuit, and one that starts and stays high is an open circuit. A working capacitor that is discharged will have a resistance reading that starts low and rises to infinity. Multimeters can give cursory measurements if they use a pulsed DC test signal for capacitance. ESR = tan(δ)/(2 π f C), where f is the measurement frequency in Hz.


Figure 1: "A capacitor’s total complex impedance is represented on a real-complex plane as the vector sum of a real component, (the ESR) and a complex (reactive) component representing the ‘ideal’ capacitor that things like ESR mess up in all actual components. The angle between the total impedance and its complex component is called the ‘loss angle,’ and is a figure used to summarize the ratio between the ideal and non-ideal components of a capacitor’s overall impedance."[27]

Replacement of Capacitors and Related Components
"The expected life time shall be about fifteen years at maximum as a guide in terms of deterioration of the sealant."[28]

Rosin or resin flux that is halide-free, respectively called ROL0 or REL0 (IPC J-STD-004) is used because of chemical reactions of halides or other fluxes that are harmful for aluminum electrolytic capacitors or other electronic components. Eutectic Sn63/Pb37 solder is optimal for restoration of vintage electronic equipment, since the RoHS Directive of the European Union only came into effect for products that were originally marketed on July 1, 2006 or later. RoHS means lead-free in this context. The soldering iron tip should always be tinned in order to prevent oxidation. Polarized electrolytic capacitors should be installed with the correct polarity, because reverse polarity can cause a catastrophic failure and open the pressure relief vent. Applying pressure during soldering can cause excessive wear on solder pads and the weight from gravity is enough. Movement of the parts to be soldered during solidification does not ensure the necessary solderability.

ELNA states that the sleeves of aluminum electrolytic capacitors should not be considered as an insulation, and that the aluminum case is connected to the cathode terminal through the electrolyte, which has uncertain resistance.[29] PCBs (printed circuit boards) should be horizontal during soldering, so that gravity provides adhesion and concave solder joints along the periphery of through holes. The optimal dwell time is less than 3 seconds.[30] Jim Smith recommends preapplying separate flux on areas to be soldered, since oxidation prevents intermetallic bonding.[31] 30 °C to 50 °C more than the liquidus temperature of the solder is recommended, in order to ensure that enough heat energy is available for the metallurgical bond.[32] Nichicon states that film capacitors must not be used if there are more than two directly connected in series, and recommends using isopropyl alcohol for cleaning PCBs.[33]

[1] Scott, Mark A. "Working Safely with Hazardous Capacitors". IEEE Industry Applications Magazine (Volume 25, Issue 3, May–June 2019).
[2] Sculley, D. RC Time Constant. Tufts University.
[3] Digi-Key Electronics. Capacitor Safety Discharge Calculator.
[4] Digi-Key Electronics. Time Constant Calculator.
[5] Awalt, Ashley. How to Safely Discharge a Capacitor. Digi-Key Electronics.
[6] Dalziel, Charles F. "Effects of Electric Shock on Man". IRE Transactions on Medical Electronics (PGME-5, July 1956).
[7] Lawrence Berkeley National Laboratory. Safe Soldering Work Practices.
https://eta-safety.lbl.gov/sites/default/files/Soldering Guidelines.pdf
[8] Massachusetts Institute of Technology. Soldering Safety and Health Guidelines.
[9] Nippon Chemi-Con. Precaution of Capacitor Disposal.
[10] University of Cambridge. Soldering Safety.
[11] Farnell. Managing Solder Fume Extraction.
[12] Dalziel, C. F. & Massoglia, F. P. "Let-Go Currents and Voltages". Transactions of the American Institute of Electrical Engineers, Part II: Applications and Industry (Volume 75, Issue 2, May 1956).
[13] Schwan, Herman P. & Kay, Calvin F. "Specific Resistance of Body Tissues". Circulation Research (Volume 4, No. 6, November 1956).
[14] Rush, Stanley, Abildskov, J. A. & McFee, Richard. "Resistivity of Body Tissues at Low Frequencies". Circulation Research (Volume 12, No. 1, January 1963).
[15] Nichicon. Application Guidelines for Aluminum Electrolytic Capacitors.
[16] Parler, Sam G., Jr. Reliability of CDE Aluminum Electrolytic Capacitors. Cornell Dubilier.
[17] Cornell Dubilier. AC Capacitor Application Guide.
[18] Nippon Chemi-Con. Judicious Use of Aluminum Electrolytic Capacitors.
[19] Parler, Sam G., Jr. Selecting and Applying Aluminum Electrolytic Capacitors for Inverter Applications. Cornell Dubilier.
[20] Parler, Sam G., Jr. & Macomber, Laird L. Predicting Operating Temperature and Expected Lifetime of Aluminum-Electrolytic Bus Capacitors with Thermal Modeling. Cornell Dubilier.
[21] Würth Elektronik. Afraid of Aging? The Effects of Time on Electrolytic Capacitors.
https://www.we-online.com/catalog/media/o467325v410 SN019_EN_d.pdf
[22] TDK Electronics AG. Aluminum Electrolytic Capacitors: General Technical Information.
[23] TDK Electronics AG. Film Capacitors: General Technical Information.
[24] TDK Electronics AG. Film Capacitors: Marking and Ordering Code System.
[25] TDK Electronics AG. Aluminum Electrolytic Capacitors: Quality and Environment.
[26] United Chemi-Con. Failure Modes.
[27] Digi-Key Electronics. Calculating Capacitor ESR from tan(δ).
[28] ELNA. Aluminum Electrolytic Capacitors.
[29] ELNA. Cautions for Using Aluminum Electrolytic Capacitors.
[30] ELNA. Soldering Conditions.
[31] Smith, Jim. A Practical Guide to Soldering Flux. Sierra Circuits.
[32] Indium Corporation. Soldering 101 — A Basic Overview.
[33] Nichicon. Plastic Film Capacitors.
Last edited:


Senior Member
Forum Donor
Feb 8, 2022
Supplementary Quotations
"As recycling electrical and electronic devices is good for the environment, the RoHS directive is not applicable to second-hand equipment. Repairing and even upgrading the devices marketed before 1st July 2006 may also be realized with non-RoHS compatible components, insofar as this product is not marketed as new. Products marketed as new products from 1st July 2006 must be repaired with RoHS compatible components."[1]

"Interestingly, products using leaded solder can still be sold, but only if they were introduced before July 1st 2006. In practice, though, this is only a short-term arrangement and will generally apply to only a few products, mainly from small manufacturers. However, the situation gets a little more involved when it comes to spare parts and repairs. Fortunately, the RoHS directive recognises that non-compliant components will be required to maintain 'legacy' equipment, and so permits their production and sale indefinitely — but whether the manufacturers will feel the market is sufficient to warrant their production is another matter!

"Related to all this is the fact that mixing leaded and lead-free solders is really not a good idea at all. So service centres will need to identify which kind of solder is employed in a product and use something compatible when making repairs. Reliability could be adversely affected by lead contamination of a lead-free circuit board, or by mixing lead-free and lead solders on an 'antique' PCB."[2]

"When the lead spacing of a capacitor does not match the hole spacing on your PCB, the capacitor should have its leads formed to avoid exposing the capacitor to excessive mechanical stress.

"The maximum amount of lead stress should be limited to 1.0 Kg in the vertical direction and 0.5Kg in the horizontal direction.

"You should also avoid bending the leads of your capacitor right next to the capacitor body itself - the internal connections from a capacitor’s leads to its actual capacitive material are delicate and can easily be damaged. Leave at least a millimeter or two between the capacitor body and the first bend in your leads to avoid breaking those delicate connections."[3]

"Aluminum electrolytic capacitors are polarized. Make sure that no reverse voltage or AC voltage is applied to the capacitors. Please use bi-polar capacitors for a circuit that can possibly see reversed polarity.
Note: Even bi-polar capacitors can not be used for AC voltage application.

"There are non-halogen types of flux that do not contain ionic halides, but contain many non-ionic halides. When these non-ionic halides infiltrate the capacitor, they cause a chemical reaction that is just as harmful as the use of cleaning agents. Use soldering flux that dose not contain non-ionic halides.

"1) Do not use any fixing or coating materials, which contain halide substance.
2) Remove flux and any contamination, which remains in the gap between the end seal and PC board.
3) Please dry the cleaning agent on the PC board before using fixing or coating materials.
4) Please do not apply any material all around the end seal when using fixing or coating materials.

"(1) Take either of the following methods in disposing of capacitors.
• Make a hole in the capacitor body or crush capacitors and incinerate them.
• If incineration is not applicable, hand them over to a waste disposal agent and have them buried in a landfill.

"(2) When removing a capacitor from the circuit board or when disposing of capacitor please ensure that the capacitor is properly discharged."[4]

"Parts which dissipate heat in quantities of 1 Watt or greater, or in quantities sufficient to damage the laminate shall be mounted with sufficient standoff [ > 1.5mm (0.060 in.) ] and shall be mechanically restrained.

"Components weighing in excess of 7 g (0.25 oz.) total, or 3.5 gm (0.12 oz.) per lead, shall be mechanically secured to the mounting surface by at least 4 evenly spaced bonds, when no other mechancial support is used.

"Parts having conductive cases, which are mounted over printed conductors or which are in close proximity to other conductive materials shall be separated by insulation of suitable thickness, or shall have an insulating jacket/sleeve.

"Exposed ends of leads on straight-through termination shall not be cause for rejection if the PWA is to be conformally coated.

"Parts shall be mounted in such a manner that, at a minimum, the markings are visible in the following order of precedence: polarity, traceability/lot code (if applicable), part value, part number/type.

"Contamination is a reliability concern.

"Parts with damaged seals shall not be used.

"Dewetting is caused when molten solder coats a surface and then recedes, leaving irregulary-shaped solder deposits separated by areas covered by a thin solder film.

"A disturbed solder joint is characterized by the appearance that there was motion between the metals being joined while the molten solder was solidifying.

"Parts shall not be mounted such that they obstruct solder flow to the component-side termination area (pad) or prevent cleaning and inspection.

"Leads shall be cut per engineering documentation and by methods, which do not impart stress to the lead seal or internal terminations.

"Parts shall be mounted parallel to the laminate surface, right side up and aligned to the lands within design and engineering specifications.

"The use of parts with nicks in the component body or termination area is prohibited.

"Poor wetting is an indicator of poor solderability, improper flux or contamination."[5]

"Flow (wicking) of solder along the conductor is permitted. Solder shall not make presence of the individual wire strands indistinguishable.

"Tin the iron tip, while the connection is cooling at room temperature. A small amount of solder should remain on the tip.

"Minimum steps to protect ESD-sensitive devices are:
• Always work at a grounded workstation
• Use only ESD-approved materials
• Handle ESD-sensitive devices only at static-safe workstations
• Always use a conductive wrist strap before handling ESD-sensitive devices
• Use an ESD bag or container to store or carry parts in.

"Hot tinning of solid conductors and part leads should not extend closer than 0.5mm (0.020 inch) to part bodies, end seals, or insulation unless the part configuration and mounting configuration dictate it.

"Cut the lead.
• Straight-through leads may be bent up to 30 degrees from a vertical plane to retain parts during the soldering operation.
• Part leads terminated straight through the PWB shall extend a minimum of 0.51 mm (0.020 in.) and a maximum of 2.29 mm (0.090 in.).

"Position the soldering iron tip so as to touch both the lead and the printed wiring pad at the same time.

"Apply solder to the junction where the iron and lead meet in order to produce a thermal (solder) bridge.

"Touch the solder to the end of the cut lead to cover the exposed copper.

"Add solder as needed to complete the soldered connection.

"Remove the solder; remove the iron.

"The end of the part body must be mounted with at least 0.51 mm (0.020 in.) to a maximum of 1.27 mm (0.050 in.) clearance above the PWB surface. The end of the part is defined to include any extensions such as coating meniscus, solder seal, or weld bead.

"Inspect the solder joints under 4 X to 10 X magnification to the specified requirements.
• Free of flux residue and other contaminants.
• The solder shall wet all elements of the connection.
• The solder shall fillet between connection elements over the complete periphery of the connection."[6]

"Adhesive materials, when used, shall not⁴ preclude the formation of an acceptable solder connection. Adhesive materials extending from under SMT components shall not⁵ be visible in the termination area.

"When hand soldering a component identified as heat sensitive, a thermal shunt or heat sink shall² be attached to the device lead between the area to be soldered and the component body to minimize component heating.

"Wetting cannot always be judged by surface appearance. The wide range of solder alloys in use may exhibit from low or near zero degree contact angles to nearly 90° contact angles as typical. The acceptable solder connection shall¹ indicate evidence of wetting and adherence where the solder blends to the soldered surface.

"Lead-free and tin-lead connections may exhibit similar appearances but lead free alloys are more likely to have surface roughness (grainy or dull) or different wetting contact angles.

"The lead and wire ends should not extend beyond the terminal more than one (1) lead diameter.

"Part and component leads should be preformed to the final configuration excluding the final clinch or retention bend before assembly or installation. The lead forming process shall not⁵ damage lead seals, welds, or connections internal to components."[7]

"At soldering iron temperature, solder will stick to oxides and contaminants to produce a visually acceptable connection. However, the connection lacks an intermetallic bond and the high temperature degrades bonds inside components. The altered bonds change electrical values and shorten component life. In just a few seconds of improper application, a soldering iron can shorten the life expectancy of components by decades.

"The arrival of solid-state components meant that, for the first time, solder was applied directly to the component rather than wires and sockets. In other words, the components were subjected to the soldering heat. And this had profound reliability consequences because heat degraded the component electrical properties.

"To prevent heat damage during soldering, metal clamps were attached to leads next to the component body. Heat flowed from the soldering iron towards the component but was absorbed by the clamps before it could reach the component body. The clamps were called “heat sinks” and they provided absolute protection against heat damage."[8]

"No-clean solder paste generally doesn’t require cleaning.

"In reality, no-clean solder paste leaves behind flux with low residue. The reflow process leaves trace amounts of resinous residue, noncorrosive in nature. Present on or around solder joints, the residue can vary in color from amber to transparent. The residue left on the board after reflow depends directly on the solid content in the solder paste, mainly made up of activators, gelling agents, and resins.

"The primary intention for removing the no-clean flux and its residue from the board surface is to prevent interference with signal transmission and malfunction in circuit functioning.

"Numerous no-clean flux removers are available in the market, and their strengths vary."[9]

"Activated rosin fluxes contain small quantities (0.2% to 5%) of organic activating agents. The purpose of these activators is to catalyze the rosin copper oxide reaction so that a better soldering job can be obtained. The catalytic agents do not enter into the reaction and do not cause subsequent corrosion. However, the presence of these activators does impel the rosin (abietic acid) to combine with the copper oxide to form the green copper abietate compound. Copper abietate is not conductive and forms a green insulating coating on copper. Usually the dark rosin residue conceals this normal formation of green copper abietate."[10]

"Electrolytic capacitors are able to survive some transient current abuse, typically more than their metallized film counterparts. As a rule of thumb, for brief ripple current excursions such as several seconds of 2 to 4 times the rated load ripple current, the thermal mass of the capacitor winding will absorb a lot of the extra energy dissipation of such an event.

"For aluminum electrolytic capacitors, dielectric absorption will allow up to 10% recovery of a previously applied voltage. Thus with high-voltage aluminum electrolytic capacitors rebound voltages of 40 to 50 V are possible. While such voltages are not usually a shock hazard, they can certainly cause sparking and even arc damage during installation.

"During charging the voltage on each capacitor connected in series is proportional to the inverse of the actual capacitance, but upon reaching the applied voltage, the steady-state DC voltage that each capacitor approaches no longer depends upon its capacitance at all, instead shifting to follow the inverse of the capacitor’s leakage current.

"Ripple current is the AC current flowing through the capacitor. It’s called ripple current because the associated AC voltage rides on the capacitor’s DC bias voltage as a ripple rides on the surface of water. The ripple current heats the capacitor, and the maximum permitted ripple current is set by how much heat rise can be permitted while still meeting the capacitor’s load life specification. Too much temperature rise will cause the capacitor to exceed its maximum permitted core temperature and fail; even operation close to the maximum permitted core temperature dramatically shortens expected life.

"Don’t exceed the maximum storage temperature while preheating the capacitors [...] Don’t contact insulating sleeve or other plastic parts with a soldering iron or molten solder.

"When gluing, don’t apply glue to the full capacitor circumference, and don’t cover the capacitors’ pressure-relief vent with potting or glue.

"In the case of electrolyte contact to skin, immediately rinse the exposed area with soap and water. If electrolyte contacts eyes, flush for 10 minutes with running water and seek medical attention. If vapors are present, ventilate the room."[11]

"1) A capacitor with more than a certain case size has the pressure relief vent functioning to escape abnormal gas pressure increase.
If gas expels from a venting capacitor, disconnect the power supply of the device or unplug the power supply cord. If not disconnecting the power supply, the device circuit may be damaged due to the short circuit failure of the capacitor or short-circuited with the liquid that the gas was condensed to. It may cause secondary damages such as device burnout in the worst case scenario.
The gas that comes out of the open vent is vaporized electrolyte, not smoke.
2) The gas expelled from a venting capacitor is more than 100°C. Never expose your face to the capacitor. If your eyes are exposed to the gas or you inhale it, immediately flush your eyes and/or gargle with water. If the electrolyte comes in contact with the skin, wash with soap and water."[12]

[1] Willems, Geert. The RoHS Directive: An Answer to Your Questions. Sirris.
[2] Sound on Sound. Has the EU Directive on Hazardous Substances (RoHS) Impacted Equipment Sales?
[3] Digi-Key Electronics. Lead Spacing/Bending.
[4] Nichicon. Aluminum Electrolytic Capacitors.
[5] National Aeronautics and Space Administration. NASA Workmanship Standards.
[6] National Aeronautics and Space Administration. NASA Training Program: Student Workbook for Hand Soldering.
[7] IPC. Requirements for Soldered Electrical and Electronic Assemblies. IPC J-STD-001D.
[8] Smith, Jim. How to Achieve Perfect PCB Soldering. Sierra Circuits.
[9] Roy, Akber. Is It Necessary to Clean No-Clean Flux? Electronic Design.
[10] Kester. Green Corrosion with Rosin Flux?
[11] Cornell Dubilier. Aluminum Electrolytic Capacitor Application Guide.
[12] Nippon Chemi-Con. Precautions and Guidelines (Aluminum Electrolytic Capacitors).
Last edited:


Major Contributor
Feb 6, 2020
If I think there is a possibility of stored charge in a piece I will be working on, I just poke around with a DC voltmeter and have a look-see. If I find any charge, I use a well-insulated probe to bleed it down through a resistor. It's never a good idea to short the leads of a charged cap together; bleed the charge away though a current limiting resistor to make life easy for the cap.


Senior Member
Forum Donor
Feb 8, 2022
If I think there is a possibility of stored charge in a piece I will be working on, I just poke around with a DC voltmeter and have a look-see. If I find any charge, I use a well-insulated probe to bleed it down through a resistor. It's never a good idea to short the leads of a charged cap together; bleed the charge away though a current limiting resistor to make life easy for the cap.
Do you check for voltage on capacitor terminals or somewhere else?


Major Contributor
Feb 6, 2020
If cap terminals are accessible to test probes, I look there first; otherwise, I poke around circuits supplied by the voltage on the capacitor.
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