Car battery, replacing charge used to start the car

Everything in good order and low electric loads, about a 15 minute drive

mrcheerful

Thanks :)

mrcheerful. ( snipped-for-privacy@hotmail.com) gurgled happily, sounding much like they were saying :

If the battery had been fairly well depleted. If the car had started easily, then barely any time.

The message from "mrcheerful ." contains these words:

Of course, a re-start from hot generally takes less than a second, so for that, considerably less. Even if the starter's taking 400A and the charging efficiency is 25% then a 100A alternator will make good the shortfall in 16 seconds.

Things ain't as simple as that, of course, but you get the idea.

Not a simple question since it depends on many things. A hot start where the engine fires instantly will take a fraction of the total power of a cold start on a winter's day where the engine needs some churning. It also depends on how much current the alternator can dump into the battery after starting - some are quite marginal if other things are on like lights and heated rear window, etc.

The speed of the car makes little difference - the alternator reaches peak output at about 1500 engine RPM.

Much less, unless there is a real problem getting it to fire in the first place.

Many, many people have a commute of under 15 minutes. Some lazy gits only drive 2-3 minutes.

Ah, another usefull fact, thanks :)

Hi Dave,

I certainly agree with you on many factors on recharging car batteries. I would also add temperature, State-of-Charge and condition of battery to your list. Depending on the crank and alternator pulley sizes, I believe that you will find that 2000 RPM or above is more common for peak alternator output for today's high compression car engines.

Kindest regards,

BiLL.....