I have a Range Rover 4.6l V8, and I'm wondering if anyone have some sort of estimate of how long time I need to keep my engine running, to charge the same amount of power that the starter took to start the engine.
I'm not really looking for exact figures here, but more if it's 5 minutes, or an hour.
(It starts in about 1-2 seconds)
We always used to say 7 miles of "decent" driving ie not idling in traffic, but the newer charging or smart charging systems may need slightly less...
Preferably you drive about 10 miles then you could be sure that your battery is rechared again. Or start up your engine and leave it running for about 5-10 minutes.
Given the AC is running, radio is on, and the headlights are on.... 15 minutes of actual driving is recommended to replenish the used current. 10 minutes if you keep some accessories off for the wait. Assuming you're not driving at higher speeds just drive for 6-8 miles and you should be good to go.
Edit: Headlights and AC are the first thing we ask someone to turn on if a suspected alternator needs to be tested. The actual load of both AC and Headlights are about equal, but on average turning both on dips roughly 1.5v off the alternator. And if it's a weaker (dying) or bad (dead) alternator it will no longer charge the battery with these on. Radio is only a major factor in the case of aftermarket setups which could take several tens to hundreds of watts to operate. A stock radio won't do anything as compared to the AC and Headlights.
There is a factor not considered in other answers, which is the original charge of the battery.
If you start the car with a healthy, fully charged battery, only a few minutes are needed, in particular if you are driving (higher revs). But, when the battery is depleted, the time could be really long. A few months ago I had to start an oldish friend's car that was left parked for a month. I had to jump start it, I let it run for a few minutes, and then drove it for 20km in a mixture of city and highway. I stopped it for 3 minutes, and when I tried to start it, it wouldn't crank at all. So I left it overnight with a battery charger, and from the next day the car would start and recharge normally.
This would vary from car to car. If you want to be safe I would hazard a guess of 10-15 minutes at a fast idle. With lead acid batteries you never want to go below %50 of their capacity and want to leave them charged when your done. An external trickle charger might fit the bill.
A P38 has a 100A+ alternator and Rover V8's require very little power to start - the older generation had facility for a hand crank handle through the front bumper.
I'd suggest 5 mins of running would be OK, maybe 10-15 if you're running lights/AC/heater as those can be quite a load.
Why are you asking - what issue are you having / worrying about?
If your stuck in snow storm with no help available. it's 20 minutes on 20 minutes off. Repeat.
Yesterday, I left my Honda Amaze in the parking lot with parking lights ON. When I came back after 6 hours, I saw that scary dying blink and cursed myself because, I knew that it would be hard to start the engine. Battery went almost completely dead !
It was midnight, thought of leaving my car and return back the next day with some solution. Just then, luckily, two guys from the nearby coffee shop which they had just closed, were passing by. They came to my rescue and pushed the car, the engine sprang to life. However I was worried what if the car stopped in the middle of 3 mile journey. I searched online and followed this post in the forum.
I drove in total 6 miles, then parked my car below my apartment with the engine ON, headlights, radio and the AC OFF. Revved it up on neutral at 2000 rpm for 20 mins. And praying that it must start now after I shutdown. And boom.. Thats exactly what happened. I could then start it normally. I tried twice and both the time, battery worked normally.
So to conclude, if you have a new gen car, and if your battery goes dead due to overdraining, then you must try the technique.
Thanks mighty V8 engine for the post.
