Why Additional Ceramic Capacitor for Carbon Motor ? Take a small toy motor as an example. When we are repairing some electronic toys, we often see a 0.1μF ceramic capacitor connected in parallel across the terminals of a DC small motor. Some curious electronic enthusiasts may even try to remove the capacitor to see if it has any effect. Surprisingly, the motor still operates normally. What is the purpose of the 0.1μF ceramic capacitor connected in parallel across the terminals of the motor?
The motors commonly used in electronic toys are usually DC motors. When the rotor of this type of motor rotates, it generates electric sparks and some high-frequency interference signals between the commutator contacts. To prevent this interference from being introduced into the power supply circuit through the motor power line, affecting the normal operation of other circuits sharing the same power supply with the motor, a ceramic capacitor of around 0.1μF is typically connected in parallel across the terminals of the DC motor to filter out this interference. Since the interference generated by DC motors has a relatively high frequency, a 0.1μF capacitor is sufficient. In addition to using a 104 small capacitor, sometimes we also connect a color ring small inductor in series.
After connecting a filtering capacitor across the terminals of a DC motor, most of the various high-frequency interferences generated inside the motor are bypassed by the filtering capacitor, thereby reducing its impact on the motor control circuit. By the way, if the motor control circuit is very simple without any control ICs, then this capacitor across the motor terminals can be omitted without affecting the circuit.
What If The 104 Capacitor Is Not Added?
The primary purpose of connecting a 0.1uF ceramic high-frequency capacitor across the terminals of a DC micro motor is twofold. We know that a motor is an inductive load, and when a DC motor runs at high speed, it generates relatively high harmonics. These higher-order harmonics can interfere with the electronic components in the motor control board, potentially affecting the normal operation of the circuit. For example, in some electric toys controlled by microcontrollers (MCUs), if the higher-order harmonics generated by the motor's high-speed operation interfere with the MCU, it may cause the MCU to malfunction, rendering it unable to operate normally. By installing a 0.1uF capacitor across the motor terminals, these higher-order harmonics can be filtered out or "absorbed," allowing the circuit board to operate normally. This is one aspect.
Another aspect is due to the inductive nature of the load. When controlled by a transistor or motor driver chip, at the moment the micro DC motor stops, a very high reverse electromotive force can be induced across the motor winding terminals. This induced voltage may break down the transistor or damage the motor driver chip, resulting in circuit board failure. Therefore, using a capacitor to absorb the peak induced voltage can provide protection. Sometimes, a resistor is also connected in series to further dissipate electromagnetic oscillation energy, and sometimes, one end of the capacitor is directly soldered to the motor casing.
The addition of this ceramic capacitor can also prevent the high-frequency electromagnetic waves generated by the motor from interfering with other electronic devices externally. Removing this capacitor can cause some interference to nearby electronic devices such as radios, Bluetooth headphones, and amplifiers when using the toy. This ceramic capacitor has no effect on the motor itself but mainly prevents high-frequency harmonics generated by the carbon brush from entering other circuits, primarily to prevent interference with other electronic devices.
Removing the ceramic capacitor does not affect the normal operation of the motor, but for European standards, there are strict requirements for EMC electromagnetic compatibility standards.
Extend: Common Used Ceramic Capacitors Parts on a Carbon Motor
In fact, in applications involving carbon brush motors, such as automotive windshield wipers and seat adjustments, ceramic capacitors with leads are commonly used.
The commonly used ceramic capacitor parts are as follows:
|
No |
UF Part Number |
UF Description |
|
CT4 Radial mlcc |
||
|
1 |
CT4B104K0100CC15R000 |
CT4 radial mlcc 0.1uF 100V X7R +/-10% (1206) P:5.08mm Tape & Reel RoHS |
|
2 |
CT4B475K0050CC15B000 |
CT4 radial mlcc 4.7uF 50V X7R +/-10% (1206 ) P: 5.08mm Bulk RoHS C1 Shape |
|
3 |
CT4B331K0050B0b2B000 |
CT4 radial mlcc 330pF 50V X7R +/-10% (0805) P:2.54mm Bulk RoHS b Shape |
|
CT42 Axial mlcc |
||
|
4 |
CT42B224M00500017A000 |
CT42 axial mlcc 0.22uF 50V X7R +/-20% (0805) Ammo RoHS |
|
5 |
CT42B104K01000017A000 |
CT42 axial mlcc 0.1uF 100V X7R +/-10% (0805) Ammo RoHS |
|
6 |
CT42B225K01000020A000 |
CT42 axial mlcc 2.2uF 100VDC +/-10% X7R (1206) Ammo RoHS |
|
7 |
CT42B331K00500017R000 |
CT42 axial mlcc 330pF 50V X7R +/-10% (0805) Tape & Reel Rohs |
Factory Recommendation
UF capacitors offers various radial type CT4 series and axial lead type CT42 series ceramic capacitors. It can cross to Murata RPE series, which now are obsolete, and can cross to AVX SR series with sorter delivery time and better price. Cross reference as below:
|
Photo |
Descriptiom |
UF Capacitors' |
Vishay |
TDK/Epcos |
Murata |
AVX/Mallory |
Kemet/Arcotronics |
|
|
CT4 Series |
K Series |
FK Series |
RPE Series |
SR Series |
C315~C350 Series |
|
|
|
CT42 Series |
A (Mono-Axial) |
*** |
*** |
SA Series |
C410~C440 Series |
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