In essence, a “capacitor is a capacitor”, although there are differences in design based on TOPOLOGY, type, and materials of manufacture. Sometimes capacitors will carry a dual rating, for AC and DC – the AC rating for a capacitor of the same capacitance is typically much lower than its DC rating (often at least 3-4x less SINCE AC MAX voltage peak-to-peak is ~2.8x rms), to accommodate the significant heating internal to the cap caused by FREQUENCY/alternating polarity. Some manufacturers manufacture AC caps which are essentially TWO DC caps in series back-to-back; these limit current flow through either cap but their internal resistance is somewhat high, which can lead to eventual break down due to heating as well.

Use of a DC cap across alternator terminals is often done to filter alternator whine (noise) caused by voltage ripple, the “AC” component of rectified DC output. When the capacitance is properly installed and matched to the frequency of the noise, it provides a low-impedance path to “divert” the voltage ripple to ground.

In essence, a “capacitor is a capacitor”, although there are differences in design based on topology, type, and materials of manufacture. Sometimes capacitors will carry a dual rating, for AC and DC – the AC rating for a capacitor of the same capacitance is typically much lower than its DC rating (often at least 3-4x less since AC max voltage peak-to-peak is ~2.8x rms), to accommodate the significant heating internal to the cap caused by frequency/alternating polarity. Some manufacturers manufacture AC caps which are essentially two DC caps in series back-to-back; these limit current flow through either cap but their internal resistance is somewhat high, which can lead to eventual break down due to heating as well.

Use of a DC cap across alternator terminals is often done to filter alternator whine (noise) caused by voltage ripple, the “AC” component of rectified DC output. When the capacitance is properly installed and matched to the frequency of the noise, it provides a low-impedance path to “divert” the voltage ripple to ground.