CapXon UJ series aluminum electrolytic capacitors

CapXon UJ series aluminum electrolytic capacitors

Introduction: When the aging of aluminum electrolytic capacitors threatens the reliability of the system

High voltage aluminum electrolytic capacitors are one of the most vulnerable components in the output filtering circuits of industrial frequency converters, server power supplies, automotive charging modules, and various switch power supplies. Engineers often face scenarios where a device that has been running for many years experiences increased output ripple, decreased power efficiency, and even frequent protection restarts. Upon disassembly, it is discovered that the top of the capacitor is bulging or leaking. Even more tricky is that the prototype capacitor may have been discontinued (EOL), or the original factory specifications may be difficult to find, making it impossible to accurately select a replacement.

The UJ series standard Snap in aluminum electrolytic capacitors launched by CapXon are designed as a solution to meet harsh application environments. This series is specifically optimized for working conditions at 105 ° C high temperatures, with rated voltages covering 200 V to 500 V DC, capacitance values ranging from 82 µ F to 3300 µ F, and providing 2000 hours of durability and 5000 hours of useful life. Additionally, an AEC-Q200 certified version is available to meet automotive grade reliability requirements. This article will deeply analyze the technical parameters, selection methods, life assessment, and common troubleshooting of the UJ series from a practical perspective, helping hardware engineers make optimal decisions when replacing old capacitors or designing new ones.

Product Series Overview: Core Features and Applicable Scenarios

2.1 Overview of Basic Specifications

Performance indicators for parameter items

Working temperature range -40 ℃~+105 ℃

Rated voltage (VR) 200 V, 250 V, 350 V, 400 V, 450 V, 500 V DC

Capacitor range (CR) 82 µ F to 3300 µ F (depending on voltage)

Capacitor tolerance ± 20% (120 Hz/20 ℃)

When the surge voltage (VS) VR is ≤ 315V, VS=1.15 × VR; when VR>315V, follow the standard

Leakage current (ILEAK) ≤ 3 × √ (CR × VR) [µ A] (after applying rated voltage for 5 minutes)

Loss tangent (tan δ) ≤ 15% at 200-400V (120 Hz/20 ℃)

Durability: 105 ℃/2000 hours (applied with rated voltage and ripple current)

Useful Life: 105 ℃/5000 hours (with rated voltage and ripple current applied)

Vibration test at 10~55 Hz, amplitude 0.75 mm, 2 hours on each axis, 10g force

Why choose UJ series?

Compared to conventional capacitors at 85 ℃ or 105 ℃/2000 hours, the UJ series has significantly improved in the following aspects:

Higher heat load capacity: 5000 hours of useful life means that at the same temperature, the degradation rate of capacitors is more than 60% lower than that of ordinary products, greatly extending the equipment maintenance cycle.

Stable loss tangent: Within the entire rated voltage range, tan δ is only 15% (maximum), which is beneficial for reducing self heating.

Extremely low leakage current: The formula ILEAK ≤ 3 ·√ (C · V) is much lower than some older capacitors (which may require 6 ·√ (C · V)), especially suitable for high impedance circuits or holding circuits.

AEC-Q200 optional: For automotive applications such as on-board chargers (OBC), DC-DC converters, and electric power steering, the UJ series can provide a stress tested version to ensure reliability under extreme temperature cycling and vibration.

In depth interpretation of key electrical parameters

3.1 Rated voltage and surge voltage

In practical applications, the voltage borne by capacitors may briefly increase due to power transients. The UJ series specifies the surge voltage VS:

When the rated voltage VR is ≤ 315 V, VS=1.15 × VR

For models with a voltage of 350 V and above, it is usually done according to 1.1 × VR or following IEC standards.

For example, a 250 V UJ capacitor can withstand a surge of 287.5 V for 30 seconds (according to standard requirements). The 400 V model can withstand a surge of approximately 440 V. This provides valuable transient margin for engineers, especially in situations where there are unresponsed spikes on the DC bus.

3.2 Capacitor Tolerance and Temperature Characteristics

The tolerance of the UJ series is ± 20% (20 ℃/120 Hz), which is a common level for electrolytic capacitors. However, it should be noted that the capacitance value will significantly decrease with decreasing temperature. The low-temperature characteristic table provides the impedance ratio Z:

For the 200-250 V model, Z (-25 ℃)/Z (+20 ℃) ≤ 4, Z (-40 ℃)/Z (+20 ℃) ≤ 7.

This means that at -40 ℃, the equivalent series resistance (ESR) of the capacitor will increase several times, leading to an increase in ripple voltage. If the device operates outdoors in cold weather (such as charging stations in the north), it must be used with a reduced ripple current or a larger capacity capacitor must be selected.

3.3 Engineering significance of leakage current

The leakage current formula for the UJ series is ILEAK ≤ 3 ·√ (C · V) (µ A). Example:

470 µ F/400 V capacitor: ILEAK ≤ 3 ·√ (470 × 400)=3 ·√ 188000 ≈ 3 × 433.6=1300 µ A=1.3 mA.

This value is measured after applying the rated voltage for 5 minutes. For long-term holding circuits (such as RTC power supplies or energy storage capacitors), the leakage current will further decrease. If the leakage current of the old capacitor exceeds the standard and causes unstable voltage in the later stage, the low leakage characteristics of the UJ series can directly improve the problem.

3.4 ESR and Ripple Current

Typical ESR and maximum allowable ripple current (120 Hz/105 ℃) can be extracted from the standard rating table. For example:

UJ331M200M300A: 330 µ F/200 V, diameter 30 mm, length 30 mm, typical ESR 330 m Ω, maximum ripple current 1550 mA rms.

UJ102M400P550A: 1000 µ F/400 V, diameter 35 mm, length 55 mm, typical ESR 110 m Ω, ripple current 3160 mA rms.

Frequency compensation of ripple current: Due to the decrease in ESR of electrolytic capacitors with increasing frequency, higher frequencies generate less heat under the same ripple current. The UJ series provides a frequency multiplier table Kf:

Voltage range 50/60 Hz 100/120 Hz 300 Hz 1 kHz 10 kHz 50k-100 kHz

200~250V 0.81 1.00 1.17 1.32 1.45 1.53

350~550V 0.77 1.00 1.16 1.30 1.41 1.43

For example, a 400 V capacitor with a rated ripple of 2 A at 120 Hz can actually allow a ripple of 2 × 1.41=2.82 A when operating at a switching frequency of 10 kHz. Conversely, if it is mainly used for 50 Hz rectification and filtering, the rated value needs to be multiplied by 0.77 for derating.

Mechanical structure and pin configuration

4.1 Packaging size

The UJ series adopts standard Snap in packaging, with diameters ranging from 22 mm to 45 mm and lengths ranging from 25 mm to 80 mm (see column L in the table). For example:

22 × 25 mm: commonly used for 100~220 µ F/400 V

35 × 50 mm: commonly used for 820~1000 µ F/400 V

45 × 80 mm: up to 1800 µ F/400 V

4.2 Pin version

According to the PDF diagram, three terminal configurations are provided:

2-pin standard type: two pins, with spacing determined by diameter. The standard lead length H is 6 ± 1 mm, and a short leg version of 4 ± 1 mm can also be customized to reduce installation height.

3-pin polarity protection type: used to prevent accidental insertion, with one pin being dummy or used for positioning. The diameter is usually ≥ 30 mm.

Multi pin version: Used for large-sized capacitors with a diameter ≥ 30 mm to increase mechanical stability.

When replacing old capacitors, it is necessary to check the pin spacing and aperture of the original PCB. The standard snap in package is usually compatible, but some brands may use non-standard hole positions (such as specific layouts for 4-pin bases). CapXon offers multiple terminal styles, and you can contact the manufacturer for detailed packaging information documents.

Selection and Replacement Guide: How to Replace Discontinued or Faulty Capacitors with UJ Series

Step 1: Identify the key parameters of the original capacitor

When the capacitor bulges or the identification cannot be read, it is necessary to infer from circuit analysis:

Rated voltage: Measure the highest steady-state voltage of the DC bus, plus a 20% margin. For example, choose a 400V capacitor for the 310V bus.

Capacitor value: Commonly used in power output filtering, the larger the value, the smaller the ripple, but if it is too large, it may affect the startup surge. It can be selected according to the nominal value of the original model.

Size: Center distance between two mounting holes on the PCB (commonly 10mm, 12.5mm, etc.) and maximum allowable height.

Ripple current requirement: difficult to measure directly, can refer to the original power level estimation. For example, a 500 W PFC output stage typically requires a ripple capability of 2-3 A.

5.2 Step 2: Match the model from the standard rating table

Example of model coding rules for UJ series: UJ331M200M300A

UJ=Series

331=330 µ F (first two digits, third digit is a power of 10)

M=tolerance (M is ± 20%)

200 = 200 V

M=Pin Style/Package Code (M represents standard 2-pin, N, O, P, Q, V represent different diameter/length combinations)

300=Length 30 mm (L)

A=Optional suffix (may indicate standard or special requirements)

When replacing, not only should the voltage, capacitance value, and size be consistent, but also ensure that the ripple current capability is not lower than the original design. If the original capacitor is severely aged, it is recommended to choose a model with a ripple current of more than 20% to extend its lifespan.

Step 3: Consider AEC-Q200 version

If the device is used for automobiles (such as car chargers, DC-DC converters, ADAS power supplies), it is strongly recommended to choose the UJ series version certified by AEC-Q200. This certification includes strict tests such as temperature shock, humidity, and vibration resistance, and is not interchangeable with ordinary industrial capacitors. Although the model suffix may be different, the specific order number for the automotive grade version can be obtained from the CapXon agent.

5.4 Replacement case: Refurbishment of DC bus capacitor for frequency converter

A 7.5 kW frequency converter originally used a brand of 680 µ F/400 V capacitor (size 35 × 50 mm), but after 5 years of use, frequent overvoltage alarms occurred. After testing, the capacitance value decreased to 480 µ F (-30%), and the ESR increased by three times. Replace with CapXon UJ681M400P400A (680 µ F/400 V/35 × 40 mm), which has a ripple current of 2350 mA higher than the original product's 2100 mA. The installation height is slightly reduced, but the original snap spring can be fixed. After replacement, the full load ripple voltage of the frequency converter decreased from 8 Vpp to 3.5 Vpp, and the operation returned to normal.

Life estimation and reliability design

6.1 Life cycle model

The lifespan of aluminum electrolytic capacitors is mainly affected by temperature and follows Arrhenius' law. CapXon provides a useful life curve (see the Useful Life chart on page 8 of the PDF), with the core formula being:

L=L0×two T0−Ta ten

L=L0×2 ten T0−Ta

among which

L0=5000 hours (at 105 ℃, under rated ripple current conditions)

T0 = 105℃

Ta=Hot spot temperature inside the capacitor (ambient temperature+ripple current self heating)

In practical applications, it is necessary to consider the temperature rise (Δ T) caused by ripple current. Usually, Δ T ≤ 5 ℃ can ensure the service life. By using derating (reducing ripple or lowering ambient temperature), the lifespan can be doubled. For example, at an ambient temperature of 85 ℃ and a ripple current of 80% of the rated value, with an internal temperature of approximately 88 ℃, the estimated lifespan is 5000 × 2 ^ ((105-88)/10) ≈ 5000 × 2 ^ 1.7 ≈ 5000 × 3.25 ≈ 16250 hours. If the device works for 10 hours a day, its theoretical lifespan exceeds 4 years.

6.2 Engineering measures to improve reliability

Parallel use: Using multiple small capacitors in parallel instead of a large capacitor can reduce the ripple current load of each capacitor, while the ESR is lower after parallel connection, resulting in a smaller overall ripple.

Leave sufficient heat dissipation space: The horn capacitor should avoid being in close contact with heating power devices (such as rectifier bridges and MOSFETs), and air vents should be opened on the PCB.

Voltage derating: At 105 ℃, it is recommended to reduce the operating voltage to within 80% of the rated value. For example, a 400 V capacitor is used for a 320 V DC bus.

Regular monitoring: The lifespan can be predicted by measuring the appearance, capacitance value, and ESR of the capacitor top. At the end of its lifespan, the UJ series has a capacity change of within ± 20% (after 2000 hours of durability testing), and after 5000 hours, the capacity change may exceed -20%. It is recommended to replace it at this time.

Common fault modes and troubleshooting methods

Possible causes of malfunction using UJ series solutions

The top of the capacitor bulges (pressure relief valve action), causing excessive ripple current or overvoltage and resulting in excessive internal gas pressure. Choose a model with a higher ripple current level; Check if the bus voltage exceeds the surge specification; Increase the number of parallel capacitors

Leakage (electrolyte seeping out from the bottom or top) during long-term high-temperature operation or sealing failure to ensure that the working temperature is below 105 ℃ and improve heat dissipation; Choose AEC-Q200 version to cope with harsh environments

The capacitance value significantly decreases (>30%), the electrolyte dries up, and the lifespan is terminated. Re evaluate the thermal load; Choose the UJ series with a longer lifespan (5000h); Reduced usage voltage/ripple

Abnormal increase in ESR (>2 times the initial value), increase in internal contact resistance, or local overheating measurement to determine if the actual ripple current exceeds the standard; Check if the capacitor installation is loose and causing poor contact

Low frequency (50/120 Hz), excessive ripple, insufficient capacitor capacity or high ESR, increase capacity; Confirm if the frequency multiplier Kf is correctly applied (allowing for lower ripple at low frequencies)

Installation and welding precautions

8.1 Mechanical Installation

The pins of the horn capacitor usually need to be inserted into the pre opened circular holes on the PCB, and then soldered by wave soldering or manual soldering. Suggest inserting it all the way through, leaving a gap of 0.5~1mm between the bottom of the capacitor and the PCB, so that the soldering flux gas can escape during soldering.

For large capacitors with a diameter of ≥ 30 mm, it is strongly recommended to use clamps or adhesives to fix them on the PCB or chassis to resist vibration. The UJ series has passed the IEC 60068-2-6 vibration test (10~55 Hz, 0.75 mm amplitude, 10g), but the installation method directly affects the actual reliability.

8.2 Welding conditions

Manual soldering: Iron temperature ≤ 350 ℃, time ≤ 5 seconds.

Wave soldering: preheating temperature ≤ 100 ℃, soldering temperature ≤ 260 ℃, time ≤ 10 seconds.

Excessive temperature or prolonged time can damage the internal sealing structure, leading to early leakage.

8.3 Storage and Aging

Unused capacitors should be stored in their original packaging at an ambient temperature of 0-35 ℃ and a relative humidity of ≤ 75%.

If stored for more than 2 years, it is recommended to apply rated voltage through a 1 k Ω resistor for aging treatment for 1-2 hours before use to repair the oxide film and reduce leakage current.

Practical case: Upgrade and replacement of PFC output capacitor for charging piles

9.1 Original design issues

A 3.3 kW AC charging station PFC output stage uses two 680 µ F/450 V capacitors in parallel (ordinary 105 ℃/2000h product). At an outdoor temperature of 45 ℃ in summer, the measured surface temperature of the capacitor reached 78 ℃, with a ripple current of about 3.5 A (sharing 1.75 A per capacitor). The rated ripple of the original capacitor is 1.9 A @ 105 ℃. Although there is some margin when converted to 78 ℃, some products still have bulges after 1.5 years.

9.2 Selection improvement

Replace with CapXon UJ series UJ681M450P500A (680 µ F/450 V/35 × 50 mm), with a rated ripple current of 2580 mA @ 105 ℃, much higher than the original product's 1900 mA. Moreover, the useful life of UJ series is 5000 hours @ 105 ℃. According to the doubling of life for every 10 ℃ decrease in temperature, the theoretical life at 78 ℃ exceeds 5000 × 2 ^ ((105-78)/10) ≈ 5000 × 2 ^ 2.7 ≈ 5000 × 6.5 ≈ 32500 hours, and the actual use can reach more than 5 years.

9.3 Transformation Results

After replacement, the surface temperature of the capacitor on the charging pile decreased by 3 ℃ at the same ambient temperature (due to lower ESR reducing self heating), the ripple voltage decreased from 12 Vpp to 8 Vpp, and the overall efficiency increased by 0.2%. It has been running for 3 years now and there have been no capacitor failures.