Car Alternator used to charge batteries

[SteveC]

if you could somehow power a car alternator to run, could you charge a bank
of batteries somehow? Like using solar power to power an electric motor,
which in turn, turns the alternator which charges up the batteries?

Time to hit the junkyard for a couple of cheap alternators for an
experiment!!

 

[Ray King]

Steve,
Car Alternators can be efficient but a major modification is needed first.
The field is about 3 amps. 3 amps times 14 volts is 42 watts. You have 30-42
watts to satisfy before you can push any current into a battery, so replace
the rotating field ( removing the brushes also ) and replacing the field
with a donut magnet. You may not have quite as much current but you start
off with a much more efficient generator.

Ray

 

[Eeyore]

if you could somehow power a car alternator to run, could you charge a bank
of batteries somehow? Like using solar power to power an electric motor,
which in turn, turns the alternator which charges up the batteries?

If you have solar electricity you'd use it to charge the batteries directly not
waste power driving mechanical things.


Graham

 

[s_sus]

I saw windgenerator with car alternator that used screenwiper motor for
field exitation.
Screenwiper motor was DC and mech connected on alternator shaft and runned
on same windmill.


s_sus

 

[clare at snyder dot ontario dot canada]

I've looked at this concept before and based on an idea I had seen many
years ago at a US Naval base in Northern Ireland where they had a large (7T)
flywheel spinning a standby generator. In the event of a power loss the
flywheel would drive the standby generator for almost 24 hours thus
maintaining power to the base. The principle was that once the flywheel was
up to speed it would only need kicking every now and again to keep it there
thereby reducing the energy needed to keep it turning.

Applying this to this discussion if you had an alternator driven by the
flywheel which in turn charged a bank of batteries then a smaller electric
motor could be used to maintain the flywheel at speed. This motor could be
powered by a single battery which could be charged by a small wind turbine
or a small array of solar panels. If the single battery was fully charged
they the charging circuit could be switched to the main bank of batteries.

A suitable flywheel might be from an old lister steam engine about 24" in
diameter and perhaps 3 - 4" thick. Granted there would be losses along the
drive mechanism but the momentum in the flywheel would drive the alternator
and reduce the impact of load.

Just a thought

But it won't work.First, it takes a LOT of power to get the flywheel
up to speed.
Second, the amount of power taken out by the alternator needs to be
put back in to keep the flywheeel from slowing down. Due to efficiency
issues, this WILL be more than you are getting out of the alternator -
no matter what technology you use.

Flywheels are EXCELLENT for smoothing out power spikes. If your
alternator only needs to put out high power for short bursts, you can
use a small motor full time instead of a larger motor periodically to
provide the power.

 

[Ray King]

Todd,

It works for you but to get up to 14 volts you have wasted about 30 watts
before you begin to push current into your batteries. The auto alternator is
designed to push 100amps or so at 3000 rpm. It takes 3 amps to generate the
amplification factor for 100amps or 100/3 = 33. If you rewind the field with
smaller wire to double the amp turns you could not get the amplification
factor to 66 or even higher. A better way ( if you only need a few amps ) is
to run the negative output of the alternator ( grounded to the fields
negative out put ) back through the field so that the output current is
feeding the field in series. this looses very little energy but you do not
loose the field power. This is easy just float the alternator from ground
and disconnect any regulators and take the positive output from the
alternator from the normal positive output and the negative output is the +
field connection. When you exceed 3 amps you should rewind the field with
larger wire and fewer turns. This can increase the alt output to the limit
of the field brushes. You may have to flash the field if you bang the field
frame and it looses its magnetism.

Ray

 

[Ray King]

Todd,

It works for you but to get up to 14 volts you have wasted about 30 watts
before you begin to push current into your batteries. The auto alternator
is designed to push 100amps or so at 3000 rpm. It takes 3 amps to generate
the amplification factor for 100amps or 100/3 = 33. If you rewind the
field with smaller wire to double the amp turns you could get the
amplification factor to 66 or even higher. A better way ( if you only need
a few amps ) is to run the negative output of the alternator ( grounded to
the fields negative out put ) back through the field so that the output
current is feeding the field in series. this looses very little energy but
you do not loose the field power. This is easy just float the alternator
from ground and disconnect any regulators and take the positive output
from the alternator from the normal positive output and the negative
output is the + field connection. When you exceed 3 amps you should rewind
the field with larger wire and fewer turns. This can increase the alt
output to the limit of the field brushes. You may have to flash the field
if you bang the field frame and it looses its magnetism.

Ray

 

[Ray King]

The loss in the alternator causes heat to be developed in the diesel. The
diesel engine is only 30% efficient. If you are driving 30 watts that is un
necessary in the load that produces about 100 extra watts in the diesel
engine minimum.

Ray

 

[Ray King]

Todd,

Your voltage regulator circuit could use a 3 amp 100v ( fast recovery would
be preferrable but not absolutely necessary because you are not "hard
switching" ) to clamp the energy that is stored in the field coil. When your
2N3773 transistor turns off the voltage jumps up to the avalanche the
transistor. Very few transistors can stand this for very long. By adding the
diode you will also notice the 2N3773 runs cooler when the voltage is at the
regulator set point. The cathode of the diode goes to the plus field
connection and the anode to the 2N3773 collector. Because your regulator is
mostly running in the linear mode the voltage across the 2N3773 does not see
a lots of voltage. However if a heavy load is removed ( similar to load dump
in autos ) the above condition occurs and your 2N3773 shorts out.

Ray