At 05:46 AM 16/02/2013, you wrote:
Pretty sure the laws of physics apply as well in the UK as in the US.
If you charge a battery using an alternator driven by the battery you're
charging you'll just waste an extra 25% of your energy.
You don't get power for free.
Since the original message has yet to hit the EVDL, from the Nabble archive:
>[what if I sourced a front wheel drive (UK) ford focus, removed the
piston engine, fitted a 72v forklift motor and 6 x 12v batteries with
a controller, to aid range i thought about fitting a live rear axle
and power a big 12v alternator off that charging each 12v battery via
6 feeds through power diodes (for 1 way flow), the alternator would
be topping up the batteries at any time the car was moving, when not
moving the drive motor wouldnt be consuming power.... ]<
This is a basic "newbie" misunderstanding about how this electrickery
works, and is OK to repeat the explanation now and then, as this is
what the EVDL is here for.
This is a basic, very non-technical explanation that mis-uses
electrical units to explain the concept, so:
An electric vehicle is very efficient, about 80% of the energy
available from the batteries should make it into pushing the vehicle
down the road. Any added inefficiencies or loads reduces range.
The original poster asks what happens when an alternator is added to
the non-driven wheels. Unfortunately any generated energy looses
20-40% (or more) before it gets into the batteries, and another 20%
before getting back to the wheels.
So you have a vehicle that for example needs 100 amps to hold a
steady speed on a test road. Adding an alternator to give 20 amps
back into the battery requires the equivalent of say around 25 amps
of mechanical energy (being generous about the efficiency) and that
has to come from somewhere, unfortunately that somewhere is the drive
motor, which now has to deliver the extra power equivalent to that 25
amps - but it is only 80% efficient, so now the drive motor needs to
pull an extra 30 amps or more, so over 130 amps to maintain speed.
Your system is putting back 20 amps, so a nett loss of 10 amps and
reduced range is the result.
However, if you are in hilly country, or in "pushy" stop-and-go
traffic, where you are on and off the throttle all the time, adding
such a system can make sense - but you only turn it on when you start
to brake, so all the power that you get back would be otherwise
wasted as brake heat. This is regenerative braking, and is used in
all AC-motor drive systems (that I know of) and a few DC (harder to
do with DC).
Hope this helps.
Regards
[Technik] James
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