On 02/05/2020 21:54, williamwright wrote:
On 02/05/2020 19:05, The Natural Philosopher wrote:
On 02/05/2020 17:31, Harry Bloomfield wrote:
Dave Plowman (News) formulated on Saturday :
So you are guessing it charges a low battery at 140 amps? ;-)

No, there would need to be a rather large difference in voltage
between the alternator and battery, to achieve that and as the
battery attains a charge, its voltage rises quite rapidly.

The alternator will deliver whatever voltage it meeds to but of course
there would not need to be a particularly large voltageÂ* to charge a
battery that is capable of delivering over 700 A to starter motors
without crapping out

I would suggest nearer an initial 20amps, which would rapidly fall to
maybe 3 to 6 amps. A flat to full charge time when being driven, can
require 6 to 10 hours of being driven. Which is why it is always best
to put such a battery on a mains charger for 24 hours, if at all
possible.


Total crap. There is no pint in having a 150A capable alternator to do
THAT

You are forgetting the internal resistance of the battery.

I am the one with the degree in that subject, I am not forgetting it.
You simply have no idea of its value.

The fact is
that the most charge a car will give a flat battery is around 30A, it it
drops off very rapidly. The high alternator output is to support
accessories.

Like I said the battery has sufficiently low internal resistance to be
able to deliver 700A to a starter motor, it can sure handle 50A with
only a half a volt or so increase in charge voltage.

Bill


--
There is something fascinating about science. One gets such wholesale
returns of conjecture out of such a trifling investment of fact.

Mark Twain