Alternator Ripple, Smoothing Capacitor - Page 5 - PeachParts Mercedes-Benz Forum

leathermang · #1 01-11-2015, 02:19 PM

I have never needed to measure ' ripple '.... as far as I know...
but exactly what would identify a VOM ? as being able to measure that ?
I have a Fluke digital....
I have a scope also.. but doubt it has enough range... how much 'range' would be needed for the problem in this thread ?

oldtrucker · #2 01-11-2015, 03:07 PM

JamesDean nailed it right there.

Forgive me if there is something slightly incorrect, I am doing this out of my head....
The basics are true...

For each inductor in the altarnator, there are two diodes. The output of the alternator would be a 3 phase AC, if there is no rectifier built in. The rectifier alone will block the negative part of the sine and lets the positive part pass. At this point, the electronic community already talks about a DC (Direct Current) since there is no negative current flow anymore.
To get back to the original problem. Unfortunately, in modern Car design, the necesarry components to produce a flat DC (essentially without any ripple) are also built into the module e.g. rectifier. They have already the components to produce a clean DC with no significant load. The main Battery is the actual Load Capacitor. The condition can change with load, higher load means higher ripple. A lower load means a lower ripple.

Since the Alternator is attached to the crank in some way, the rpm of it will change with the engine RPM. So there is no 0815 formula to calculate a filter capactor that would take out any ripple. With more recent technologies and components, it is possible to make the filter somewhat smarter and dynamic. On the other hand, most board computer e.g. digital components, don't run directly from the battery voltage anyway. A few millivolt of ripple don't matter in regards of proper functioning of the computer. It can be significant with AM receiver equipment e.g. your AM reception on your radio that rectifies a few micro volts.

The digitlal onboard equipment is designed to take that ripple and still function properly.
The issue is "overvoltage" since the digital equipment is designed to only take a certain maximum voltage, probably no more than 16-17 Volt DC, perhaps a little more.
The voltage regulator and other devices are supposed to prevent that those over voltages and spikes, can happen.

Bottom line, if the supplement rectifier / regulator is regulating the alternator voltage to about 14 Volt, nothing will happen other than possibly a alternator wine on your favorite AM station.

The six diode design is partially, to minimize the interference with other very sensitive receiver equippment by multiplying the frequency (e.g. rpm's of alternator) by six and to move eventual harmonics outside this frequency spectrum. Doesn't work always, because it is still there and depend on it's amplitude, but may not interfer at a certain frequency.

There is a chance, if a interfering voltage (harmonic) is going into the RF spectrum and the amplitude is getting quite big. This can radiate off the wiring and could possibly distort the signals on the communication bus between control equipment. This has to be a real bummer.

leathermang · #3 01-11-2015, 04:14 PM

Are you saying we might be needing a Faraday shield ?

compress ignite · #4 01-11-2015, 06:31 PM

LM,

I Ain't Wearing ANY kind of Metal Hat whilst driving.

Norbert,
Thanks for the clarification.

Gregory · #5 01-14-2015, 02:45 PM

Here is what the Indy said"

Oil level warning: Rodent chewed wires, sensor OK, wires repaired.

Check tire pressure warning: batteries in the valve stems are flat, replace expensive valve stems.

No power issue, check engine light: Variable Inlet port shutoff motor shorted. 10 hour repair, ~$1400.

Is the Variable Inlet port shutoff motor the same as the swirl flap motor? Two different things?

JamesDean · #6 01-14-2015, 04:19 PM

Might be helpful?

OM642 intake port shutoff motor - MBWorld.org Forums