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by 8 Jan 2004-10 Dec 2009 on January 22nd, 2007
Usually, but not always. Most vehicles (>95% of them) will spin the alternator fast enough at idle to charge the battery.
However there are some with the wrong sized pulleys, electrical issues, design flaws, and/or too low idle speeds to give the battery a meaningful charge while the engine is idling. My current vehicle falls under that category. Every part is within spec when tested, but for some reason my battery will not charge at warm-idle RPM. (Cold-idle is a little higher and actually driving isn't idling unless I'm at a red light, so it isn't a major problem for me.)
by Metaphiz on January 22nd, 2007
Yes.
by ShaunAnthonyMcCarthy on January 31st, 2011
The battery is used to start the car and that's all it's needed for, but it does indeed charge over time, replenishing the charge it released during the start up. It also serves as a backup when the alternator isn't outputting high enough or a sudden need for power introduces itself...
You can disconnect the battery, but the battery is also an electronic filter for osculations in current/polarity, removing it from the loop can damage electrical systems and computer systems, which is why if you suspect your battery is dead beyond repair, replace it ASAP
but to correct others, the Alternator is part of the Charging system
by DA BEN DAN yanggui zi on December 18th, 2010
It should.
by csimme01 and Ninja Cooper UNMASKED on December 18th, 2009
The alternator will output charging current at idle. The problem is this current may be less than the current used by the vehicle. Lights, fans, heated seats, heated rear window, heated mirrors all use current and can consume way more that the alternator can output at low speeds. Newer vehicle have a current sensor on the battery and can sense if the current draw is to great. In some cases this system will turn off non-required devices. This system also controls the alternator to achieve zero current at the battery. This reduces engine load to save fuel.
by steve.grahovac on December 18th, 2010
>The Alternator does not charge the battery. The battery is used to initially start up the car, then the alternator will use that power. (for example, you could have your car running and disconnet the battery, the car should still run becaue the car is not running off of the battery charge, but the alternator) It's takes a lot to charge a battery, you would need to drive at least a half hour to an hour on the interstate.
I'm not sure, but that doesn't sound accurate, I think the alternator does indeed charge the battery. Just because the battery can be disconnected while the car is running does not mean the alternator is not charging.
by SilverBells789 on December 18th, 2009
The Alternator does not charge the battery. The battery is used to initially start up the car, then the alternator will use that power. (for example, you could have your car running and disconnet the battery, the car should still run becaue the car is not running off of the battery charge, but the alternator) It's takes a lot to charge a battery, you would need to drive at least a half hour to an hour on the interstate.
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Comments
Was gonna answer but I was gonna say pretty much what you have here.
by geek860 on January 22nd, 2007
Thanx.
by justme32 loves the weekends on January 23rd, 2007
Re the question “Does the alternator charge at idle” the answer is probably NO. European Bosch alternators usually have two current ratings on the ID label. The high figure is what the alternator can give when it is turning at 5000rpm. The lower figure is what the alternator can produce when it is turning at 1500rpm. IMHO it is best if the alternator can handle all loads at idle speed but often this is not the case. Some of the newer cars allegedly have an engine idle speed as low as 600rpm so a speed up ratio from the pulleys of about 3:1 is required. This will cause the alternator to turn at 1800rpm. If the engine is thrashed up to 6000rpm the alternator will turn at 18,000rpm but modern alternators are capable of handling this and more for a short time. Virtually all alternators produce no current when only turning at 1000rpm. Unfortunately car manufacturers usually test their cars on test tracks at high speed but forget about traffic congestion, 20mph speed limits, “sleeping policemen” etc. All these features can cause flat batteries.
In winter cars are driven more slowly because of snow and ice but the dark nights and the cold weather cause the greatest power demand when the charging performance is at its worst. If a home battery charger can be used it is a tremendous help as even a 4 amp charger can achieve overnight what would otherwise take many miles of highway driving. The cost of the electricity is just a few pennies unlike the cost of several gallons of fuel. My present car, a Rover 800 Turbodiesel cannot handle “granny cycle” in winter. Firstly the glow-plug controller has to heat the plugs for 20 to 30 seconds, that’s one hundred amps! Next comes the cold cranking which takes 300-400 amps in freezing weather. During the cold cranking there still has to be enough voltage to work the drive-by-wire computer so unless the battery is fully charged the engine won’t start. Considering that there is also the constant drain from the burglar alarm/immobiliser “flat” batteries can be a regular event. I am so unhappy with the performance of the OEM alternator that an upgrade is planned. I have a Bosch “N Type” recycled from a Jaguar XJS 3.6 According to the label this alternator gives 40 amps at idle (115 amps at high speed) so hopefully this will solve the problem.
The main beam on these cars is four 60 watt bulbs (dip is 2 x 40W) and prolonged use of main beam flattens the battery unless one has the petrol V6 which has a 120 amp alternator as standard. Very odd that the diesel, which needs more electrical power, has a weaker alternator. Perfectly OK though if one doesn’t drive at night!
Tools needed:- An inexpensive (or borrow one) digital volt meter should show 14.2 volts with the engine idling. If the voltage falls back to 13.8 or less as more items are switched on the alternator isn’t coping. If one has an automatic transmission ensure that the transmission is in “P” as people have been known to rev the engine and run themselves over.
by davey1000 on January 9th, 2010