gull
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response 34 of 40:
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Apr 7 17:42 UTC 2003 |
Re #33: My Honda will increase the idle if the electrical load is high
enough. Actually, it's kind of interesting. Honda lets the engine
computer control the alternator field voltage. It's not uncommon, on a
summer day with the blower fan and most other accessories off, for me to
look down when the car's idling and see only 12V on my voltmeter. If I
switch on some high-current accessories, or idle long enough for the
battery voltage to get down farther, the ECU will switch the alternator
back on, the voltage will jump up to 13.75 or so, and the idle will kick
up a hundred RPM or so. I suspect this is a way to improve fuel economy
and idle emissions. I've also noticed that in this mode, the ECU will
sometimes switch the alternator off when I accellerate and back on when
I coast in gear.
I've noted three distinct charging "modes" on this car. One is no
charging -- the alternator field is essentially switched off, and the
car is running on the battery, with an electrical system voltage around
12V. Another is a sort of float charge, where the battery is being kept
charged but the voltage is around 13.5-13.75V. (I don't have a digital
voltmeter, just an expanded-scale analog one, so this is approximate.)
Then there's the "the battery is really low and we need to charge it
fast" mode, like when I start the car and turn the heater blower on high
on a very cold winter day. Under those circumstances I've seen charging
voltages as high as 14V.
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