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Old 1st December 2021, 12:16   #31
COLVERT
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Did you hope to initiate a discussion on the basis of the paper? If so, to what end?
Thought never crossed my mind.

I was using the report to show that modern alternators had high outputs even at low engine revs.

Due to the difference in pulley sizes between the alternator and engine the alternator would be running at quite high output even at tick-over.

Revving the engine would make very little difference to the approx. 14 4 volts already being output.
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Old 1st December 2021, 12:44   #32
MSS
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Originally Posted by COLVERT View Post
Thought never crossed my mind.

I was using the report to show that modern alternators had high outputs even at low engine revs.

Due to the difference in pulley sizes between the alternator and engine the alternator would be running at quite high output even at tick-over.

Revving the engine would make very little difference to the approx. 14 4 volts already being output.

The term output is ambiguous. Whilst alternators have a relatively constant voltage output vs engine RPM, their current output is related to the RPM by curve that roughly has the form of Imax(1-e^-(k*RPM)). The maximum current output is available at around 2500RPM.

It is the current that carries charge from the alternator to the battery meaning that the charging rate is dependent on RPM roughly in accordance with the shape of the above formula's curve.
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Old 1st December 2021, 19:29   #33
Ducati750cc
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Quote:
Originally Posted by COLVERT View Post
Thought never crossed my mind.

I was using the report to show that modern alternators had high outputs even at low engine revs.

Due to the difference in pulley sizes between the alternator and engine the alternator would be running at quite high output even at tick-over.

Revving the engine would make very little difference to the approx. 14 4 volts already being output.

But the report doesn't show what you say, quite the opposite, the charts / graphs, 3 & 7, I mentioned previously actually how low the output, in amps is at low engine revs



Talking about the difference in pulley sizes is irrelevant, the article and graphs are talking about output at engine speeds, RPM, not at the alternator rotor speed, RPM.


You are comparing apples with oak trees !


MSS explains the voltage, current thing excellently.
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