Measuring ripple voltage

[avant]

I’m having a problem measuring ripple voltage on my system.

I have 3 multi meters, a cheap one, a ‘good’ (more expensive, autoranging, more measuring modes, etc.) one and a clamp one (also autoranging) with probes

Using all three, the dc voltage is the same on my system.

Measuring ac in the dc system (ripple voltage), the cheap one measures 28.6vac, the expensive one 0.06vac, and the clamp on meter (using the probes) can’t decide, but see-saws between a low value and over range alarm.

Values don’t change when the shoreside battery charger is turned on and off, or the shore power is disconnected completely. The specs on the three meters for vac measurement are essentially identical.

I’m at a bit of a loss as to what’s going on here, the values being so out of whack. Anyone have any wisdom to offer up as to what might be happening?

[moctrams]

I think you can only see the AC component on the DC line with an oscilloscope. Then, you could see the frequency too.

[avant]

Numerous online forums and instructional posts in electrical and boating forums mention and describe using a multi meter to quantify ripple.

[AKA-None]

Meters will show you rms ac voltage but it depends on the frequency of the ac. Otherwise you really need an oscilloscope

[CassidyNZ]

Originally Posted by avant

I’m having a problem measuring ripple voltage on my system.

I’m having a problem understanding the need to measure ripple voltage on my system?

[transmitterdan]

The “cheap” one must not be blocking DC. Some cheap RMS meters will measure DC+AC when in AC RMS mode.

Why do you think it’s important to measure AC ripple on your DC system? If you have batteries then AC ripple will be very low.

Are you searching for the source of AC hum on your radio?

[GordMay]

Checking Alternator Ripple Voltage or (AC voltage) can be measured by switching your DMM to AC, and connecting the black lead to a good ground, and the red lead to the "BAT" terminal on the back of the alternator (not at the battery).
A good alternator should measure less than 0.5 VAC, with the engine running. A higher reading indicates damaged alternator diodes.