CapXon UJ series aluminum electrolytic capacitors

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.