Jump starting a car - what I learned

[Dave T]

I thought I knew how to jump start a car.

+ to +, negative of good battery to ground of the bad car. Also don't have cars touch, don't let jumper cable clamps touch, etc.

I tried that. Nothing.

Then I connected the negative of the good battery to the negative of the bad battery. It worked. I wonder why even though this is not the correct or best way.

[GeoffR]

Most likely the ground you choose on the car with the flat battery wasn’t a good enough contact.

[tinytyler96]

Most likely the ground you choose on the car with the flat battery wasn’t a good enough contact.

Most likely this, I always like to try to find a bolt on the body of the car somewhere.

[Dave T]

Most likely the ground you choose on the car with the flat battery wasn’t a good enough contact.

Good answer! However, the ground that I chose was the spot recommended in the owner's manual, the ring to lift the engine. Perhaps the clamp didn't have enough contact or something. I will soon find out because the flat battery needs another jump start. I just ran the engine at 3000 rpm for 5 minutes 4 days ago. Maybe that was not enough to recharge the battery.

[GeoffR]

Good answer! However, the ground that I chose was the spot recommended in the owner's manual, the ring to lift the engine. Perhaps the clamp didn't have enough contact or something.

The other possibility is that the engine isn't actually a very good ground, possibly the ground strap is less than perfect?

I will soon find out because the flat battery needs another jump start. I just ran the engine at 3000 rpm for 5 minutes 4 days ago. Maybe that was not enough to recharge the battery.

Battery charge is determined by time and current, engine RPM has nothing to do with it. You need around 5 miles to recharge after a start, if the car hasn't been used for a while 30 or 40 miles might be required to reach full charge.