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car engine battery charger

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Posted by Q on July 30, 2007, 2:52 am
 
For years I've been using an engine/alternator to top up my battery bank
during those no sun/low sun days during the winter. I have a 16 hp OHV
Briggs engine off a lawn tractor coupled to a 100 amp truck alternator,
and a 5 hp Honda engine coupled to a 65 amp alternator. Both have worked
well and are pretty quiet with extra large mufflers. This winter I'm
considering trying something different, a truck alternator attached to a
Geo Metro. Someone gave me a free one that runs well. I've heard the 1L,
3 cyl, TBI engines are very efficient and am wondering if the idling Geo
engine would be more efficient than the small engines. Anyone have any
thoughts on the subject?

Q

Posted by Gordon on July 30, 2007, 4:03 am
 
@newsread4.news.pas.earthlink.net:


We had a discussion here awhile back about that.  I had asked
about using a car and an inverter as a blackout power supply.
The consensus seemed to be that the car engine would be a very
ineficient for that purpose.

OTOH.  YOu have the parts, why not just try it.  If it doesn't
work, just go back to using your other methods.

And While your at it.  You could use the big alternator
in the Geo as the beginnings of a gas/electric hybryd
experiment.

Posted by Neon John on July 30, 2007, 5:46 am
 

You're experiencing engine overkill!  100 amps at 14 volts is 1400 watts, a
little
less than 2 hp.  Even with the lousy efficiency of an automotive alternator
factored
in, call it 3 hp.  That 5 hp engine is more than enough.

A few years ago I built a 10KW generator around a Metro engine.  It worked quite
well
and was very quiet.  It was economical to run but since economy wasn't my primary
concerns (clean power and quiet operation for that application), I don't have any
concrete numbers.  I'd save that engine for a larger generator and go back to the
utility engine for your application.

I suggest using the 5 hp engine, gearing it to run at a low speed.  That's the
approach I take with my Cordless Battery Charger.  You'll want to experiment
with the
combination of field excitation and engine speed that gives the best economy.  

The built-in voltage regulator by itself is not a good solution for this
application,
as it slams full field current to the alternator whenever the voltage is lower
than
setpoint.  This results in the alternator attempting to operate at low speed and
high
torque which isn't a good match to the engine's power curve.

Controlling/limiting the field current externally lets you position the
alternator's
speed and torque requirements to match the engine.  A simple power rheostat in
the
field lead will do the trick.

In general, it is better to operate the alternator at higher speed (weak field)
because that enables the fan to provide adequate cooling. Copper's resistance
goes up
with temperature and that increases the losses in the stator which causes more
heating, etc.  Both the stator and diodes are happier and healthier with the
rotor
spinning fast enough for good cooling.

Here are some very old photos of the prototype of my Cordless Battery Charger.
This
one used an off-the-shelf analog smart charge controller and a fixed resistor in
the
field circuit to limit the alternator's torque demand.  Now I do it digitally but
this analog system worked almost as well for basic battery charging.

The alternator is a 150 amp model from a late 90s Cadillac.  I chose that
alternator
because this particular caddy used a conductive thin film on the windshield for
defrost which resulted in a high and continuous current draw.  This is one of
the few
automotive alternators that can sustain its rated output in continuous duty.  I
have
a local alternator shop build these for me sans regulators as I need them.

If you want to go for the ultimate in economy and noise reduction then you might
consider duplicating my CBC (or maybe talking me into building some more :-)  It
operates similarly to the Honda EU series, with a servo-controlled throttle that
chooses the optimum engine speed for each point in the charge regime.  I use an
RC
model servo which is trivially easy to control from a BASIC Stamp or something
similar.

RE: drive.  I highly recommend the cog belt drive pictured in my photos.  The
drive
is quite efficient, very quiet and very durable.  Other than breaking a belt
early on
from debris getting between the belt and pulley, I've never had a belt failure.
My
personal CBC that I use when RVing has close to 1000 hours on it.

One last comment.  Were I designing a CBC from scratch today I'd go with a
permanent
magnet alternator, perhaps followed by a PWM controller.  This would be a much
more
efficient arrangement for two reasons.  One, car alternators are designed to
saturate
early and limit the current output over a wide range of voltage and speeds.  Not
terribly efficient.  Two, the field consumes considerable power and contributes
to
the heat load on the alternator cooling system.  

I'd take a good hard look at the larger motorcycle and 4-wheeler alternators.
These
use the cup shaped flywheel/permanent magnet field and an inside stator.  The
larger
ones are capable of a KW and that can probably be increased with careful
rewinding
and cooling.

John
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com  <-- best little blog on the net!
Tellico Plains, Occupied TN
Some people are only alive because it is illegal to kill.


Posted by Q on July 30, 2007, 7:35 pm
 I've tried using a brand new 3 hp Tecumseh engine to turn a 60 amp
alternator and it didn't have enough power. The 5 hp Honda does the
trick but with not much to spare. Evidently a lot of inefficiencies in
the alternator, belt drive, etc.. The Geo engine has a ribbed sheave
meant to drive the air conditioning pump that will be used to drive the
added on alternator.

The 5 hp Honda engine runs nice at low RPM but if you want to crank up
the amperage it needs a certain number of RPMs to get into the power
band. The 16 hp engine/alternator has a 10" diameter sheave because I
like to run it at low RPM.

I don't use automotive regulators on these units. Instead I have rigged
up several switches and nichrome wire resistors to control the fields.
I've built a couple electronic controllers over the years but always
managed to fry them somehow.

Q



Neon John wrote:


little

factored

quite well

primary

any

the

with the

application,

than

and high

alternator's

the

goes up

rotor

 This

in the

but

alternator

the few

I have

might

that

an RC

drive

early on

failure.  My

permanent

more

saturate

Not

contributes to

These

larger

rewinding


Posted by Neon John on July 30, 2007, 9:12 pm
 

Go back and read my post and try to understand what I'm telling you.  The reason
you
could not drive the 60 amp alternator with the Tecumseh engine was that you
didn't
have it properly mated to the engine.  The 4 hp Honda engine in the photos of my
first CBC easily drives the 150 amp alternator to full output precisely because
I DID
match it to the engine.

John
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com  <-- best little blog on the net!
Tellico Plains, Occupied TN
Okay, okay, I'll take it back ... UNfuck you!


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