Byron A Jeff writes:

> I've looked at this task a couple of times. It's an activity that
> off-gridders like to tackle for equalizing battery packs.
> 
> One helpful resource can be found here:
> 
> http://theepicenter.com/tow02077.html

That's the page that first got me interested in the project.  ;-)

> It points out that certain GM alternators have a built in voltage
> regulator. So essentially you power the alternator, provide the field
> current and it'll put out 14V (or so) automagically.

The problem with the built-in regulators is that they are very simple
voltage control units.  This is just fine to maintain the float charge
on an auto starting battery, but will provide far too much current on
deeply cycled storage batteries.  Even more than that, the built-in
regular uses a sense directly on the output windings which does not
not account for resistance in the lines or the temperature of the
batteries.  Anyone who has ever dealt with storage batteries will tell
you just how important proper charging is to their capacity and
lifespan!

If you just want a 14V supply (say, to power hand tools or run an
invertor) the internal regulator will be just fine.  You could just
buy a pre-made 14V charge controller and use it in conjuction with the
factory regulator, but where is the fun in that?  ;-)

> Finally you can get that alternator in the $20 USD ballpark NEW at the
> auto store.

The cheapest NEW alternators I found were still over $70.  What you
get for $20 is a 35A remanufactured unit.  The best price I found for
an 80A unit (remanufacturered) was still almost $100.  Tell me where I
can find any (new or remfg, with or w/o regulator) 80A or better
alternator for $20 and I'll go out and buy a half-dozen of them.
That's how many used mowers I picked up for free in the past week
alone.  ;-)

> Wow! The gas driven compressor sound interesting. How in the heck do you
> drive one of those puppies?

Just the same way you drive the A/C compressor in your car.  ;-)

> > At some point I'll add solar as well, of course building a maximum
> > power point tracker (intelligent DC-DC convertor) into the same charge
> > controller.
> 
> Solar is also on my list. How hard is it to build high power inverters
> say 1800 - 2400 watts with a modified sine wave setup?

What I was really referring to here was one of these:

http://www.windsun.com/ChargeControls/PPT.htm

There is no point in building your own (2-step) modified sine wave
invertor these days.  Commercial units of this variety are dirt
cheap.  I would consider building my own true-sine invertor as
commercial units of this variety are still quite expensive, but a
project of this nature is quitely likely beyond my abilities.  I did
find a design for a ferroresonate true-sine invertor which used a PIC
to do sine via PWM, then driving 200A @ 12V using IGBTs to one side of
a transformer to get 120VAC on the other.  I'm really not sure how the
commercial true-sine units work.

> Again, if the you have small alternator needs, then simply get one with the
> voltage regulator built in.
> 
> [The rest snipped].

Unfortunately, this is not suitable for my needs.  :(

I also neglected to mention one of the *other* cool things you can do
with an automotive alternator once you have uC control over field
current.  If you spin the alternator up to full speed and give it full
field current you will get 100-200 VDC at the drive side, which is
quite suitable for driving many 120 VAC loads.  This is also enough
juice for basic DC stick (or even TIG) welding -- all you need are the
apropriate cables (and gas for TIG) and stinger.  Pretty cool, huh?

-p.

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