charging car battery

User2050

Hi,
I seem to have different answers to whether leaving a car in idle can charge the battery up or not.
Can anyone give me a more positive or authoritative answer?

Thanks

Netwizard

If you have jump started your car, leaving it running for 15 mins afterwards will charge the battery enough to restart it if you stall it, but you are better off taking it for a quick drive if you can.

Joe_Horner

Yes it can (assuming you don't have an old car with dynamo charging). That was the whole point of the change to alternators, that they give useful charge at much lower revs than a dynamo can.

That said, sitting at idle for the time it'll take to get a good charge in isn't all that kind to your engine so, unless it's just a case of getting enough in to start it for a run later, you're better off buying a cheap charger and doing it that way

Gloomendoom

There is normally a light on the dashboard that illuminates if the battery isn't being charged.

If your car is fitted with an alternator, as opposed to a dynamo, it will almost certainly go out as soon as the engine is running. If it doesn't, there is likely to be a high load on the electrical system or a fault somewhere.

Ebe_Scrooge

Joe has hit the nail on the head. And it'll be cheaper overall to use a proper charger, the amount of fuel you'll burn by leaving the engine ticking over is relatively high compared to the small amount of charge it'll give - quite apart from the wear on the engine. And if you've got anything electrical running on the car ( lights, screen heaters, etc. ) that'll further reduce the charge going into the battery.

So in general, leaving the engine ticking over will put a small amount of charge in, but far better is to give it a jump start when you need it then take it for a proper drive - around 20 minutes or so of reasonable driving ( not just pootling round town ) will near as makes no difference fully charge the battery.

SailorSam

Although the battery is starting to charge you're best turming off as much of the electrics that you can ........ the radio; heater; rear screen etc etc they're taking the charge back out.

gilbert_and_sullivan

If you jump start a completely flat battery then, on some cars, you need to put something on eg sidelights or heater fan, to trigger the alternator into giving.

Have known cars to be left ticking over for hours on end in compounds and the alternator hasn't put a single amp into the battery, the answer was to put the hazard flashers on, not only did it provide the needed drain, but visible reminder the engine was still running.

rememeber also make sure you have the keys on you, or the doors or windows are left open on the car you are about to connect to if the battery is completely flat, some cars will automatically lock all the doors when you connect jump pack/leads.

Oh and yes, whilst not particularly economical tickover will charge the battery.

Rover_Driver

gilbert_and_sullivan wrote: »

If you jump start a completely flat battery then, on some cars, you need to put something on eg sidelights or heater fan, to trigger the alternator into giving.

Not quite, an alternator needs an electrical supply to work, if the battery is completely flat you should leave the slave battery and jump leads connected for a while to build up the voltage in the flat battery.
If they are removed too soon, there may not be enough power for the alternator to work.
Everything else (side lights, heater fan etc.) should be switched off.

gilbert_and_sullivan

Rover_Driver wrote: »

Not quite, an alternator needs an electrical supply to work, if the battery is completely flat you should leave the slave battery and jump leads connected for a while to build up the voltage in the flat battery.
If they are removed too soon, there may not be enough power for the alternator to work.
Everything else (side lights, heater fan etc.) should be switched off.

I worked out of car compounds for years, jump starting the flat car then switching on lights or similar to give it something to work for...oh and blipping the throttle to get it going...always worked.

No time in a busy compound for the 'yardies' bus to sit for 10 mins with the jump leads connected to gee things up.
They could shift 20 cars in that 10 mins from the other side of the airfield.

Whilst what you say is true in a perfect world, the faster method does work just as well.

Rover_Driver

Nothing to do with giving it something to work for, once an alternator starts charging, any other load (lights etc.) just reduces the amount of power available to charge the battery, which is why they should be switched off.

gilbert_and_sullivan

Rover_Driver wrote: »

Nothing to do with giving it something to work for, once an alternator starts charging, any other load (lights etc.) just reduces the amount of power available to charge the battery, which is why they should be switched off.

Fine......