Charge or jump start?

[Mr2Mike]

kambites said:

Or you just increase the number of turns and hence the field strength.

More turns of the same sized wire would give more copper loss at high currents (i.e. more heat to get rid off, and lower efficiency). If you increase the diameter of the wire as well as the number of turns, then the weight, size and cost of the alternator increases. It would also increase the maximum possible output current for a given copper loss, so you are back where you started; the alternator only producing some fraction of it's maximum possible output at low shaft speeds.

The bottom line is that an alternator will provide some charge at idle, but if you want to get some charge into battery as quickly as possible then you'll need higher RPM.

[skyrover]

battered said:

normalbloke said:

But then the 2 battery in parallel trick comes in handy.

I've heard this one, never used it myself. However in the motor trade it's a favourite. Connect a spare battery to the dead one with jump leads, connect the charger to the spare, walk away for a few hours or overnight. Charger sorts them both out, spare battery gives the dead one enough oomph to wake it up, possibly by passing heavy current through the cells and dislodging the sulphate film, who knows?

Makes sense... something I will certainly remember for the future

[R8VXF]

Hooli said:

R8VXF said:

Talking of jump starting, I was told in Halfords that it would be dangerous to jump start my 1.2 Corsa with the VXR8. Any truth to this?

It's bks.

However I wouldn't leave a car with a big battery connected to a car with a small battery for ages. The car with the larger battery will normally have much higher alternator output to charge the larger battery. This can mean the charging ampage is too great for the smaller battery on the other car.

I can't see it ever being an issue with cars, just something to bear in mind with bikes etc.

I thought it might be, but got a jump start pack for £40 quid that did the trick anyway. It also means I can take it on long road trips in-case of flat batteries.