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Car alternator. Ripple question.

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DBecker:

--- Quote from: langwadt on December 22, 2019, 08:32:37 pm ---
--- Quote from: Benta on December 22, 2019, 07:38:29 pm ---41 A is absolutely realistic as ripple current. The alternator has a 6-diode, 3-phase rectifier feeding current into the battery. This only happens when the phase voltage from the alternator is at a peak.
Same situation as with a transformer -> bridge rectifier -> storage capacitor.

--- End quote ---

but the ripple out of a  6-diode, 3-phase rectifier should only be ~15%

--- End quote ---

You might be thinking of an ideal 3-phase source.

This is the spec from a real-life device, with lots of imperfections.  It's useful to document the current variation into an ideal sink, in this case apparently a 13.00V load.
Presumably the ripple current is measured with a inductive clamp, thus a zero-centered graph.
The rest of the specs are normal for a modern alternator, with the regulator permanently connected to the 12V supply and monitoring one of the phase outputs to activate rotor current when the rotor RPM hits 1533 RPM.  With a pulley ratio of 2.38 (which is a parameter of the engine pulley configuration, not the alternator itself), the engine must spin at 645 RPM before the alternator wakes up.  It then waits briefly (perhaps the 2 seconds listed) before ramping the output current.  A typical ramp is 20 amps/second, so a 140 amp alternator takes about 10 seconds before it is putting out its maximum power.

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