Electronics > Projects, Designs, and Technical Stuff
Car alternator. Ripple question.
cs.dk:
Hi,
I just replaced an alternator on a Peugeot 308 (if that matters). It came with a test report, and it just catch my eye, that it can make 42A in ripple current. I think it sounds terrible wrong.
They do however not mention the ripple voltage, which i find strange.
I also find it strange, that the ripple is negative sometimes. How can that happen?
Attached is the test report.
Thanks.
Psi:
Probably just because it's rectified but has no filter capacitor, so the output is full of ripple.
PKTKS:
Hmm what I find strange is a simple alternator with
specs. like "voltage regulation" and actually a full
table of regulation parameters.
Who can actually provide regulation is the proper
regulator module and that should be provided with
the rectifier.
Such class of regulators (for motor alternators) actually
use a "short coil" technique to achieve cheap and affordable
semiconductor currents and temperatures.
That is the most likely cause of "negative" currents being
absorbed (sunken) by the damped coils.. which can only be confirmed
by looking the proper coil schema. Y or delta with center ground
or not.
That thing should be a whole regulator with very high
brute force DIODE PACK and stupid (big) MOSFETS built in
Paul
Siwastaja:
I'm sure the I(t) curve is just AC coupled, i.e., offset to be drawn around zero. The "zero" is likely, according to the first graph, around 150A, so the Y axis of the second curve ranges from 120A to 180A, not from -30A to +30A.
This amount of current ripple seems understandable and normal, it's a rectified AC generator. The battery won't care about this ripple.
Voltage ripple cannot be given because it's a property of the complete system and depends on the ESR of the battery. Current ripple is the property of the alternator, and the voltage ripple is then easy to calculate by U = R * I, given the R of the battery is known.
coromonadalix:
In some circuits the battery is the "filtering capacitor"
Check every ground wires from the frame to the motor, i had an flat flexible copper (10 inch) wire who got corroded and "cutted" itself. i had more noise from the radio.
Found a new wire from a scrap yard, resolved all the noise issues ..
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