On Wed, Oct 20, 2004 at 01:23:21PM -0400, Peter Johansson wrote:
> Larry Bradley writes:
>
> [Snip]
> 
> My testbed is a 3.5 HP lawnmower engine (free) and an 80A alternator
> ($20 from the local junkyard) I'll be welding together a mounting
> frame this coming weekend. 

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

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.

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

> Phase one is to run the motor using the
> mechanical governor, and controlling field current on the alternator
> to provide proper charge current for a bank of deep-cycle batteries.
> Phase two will be to replace the mechanical governor with a stepper
> motor so the engine can throttled back and running the field current
> at maximum levels.  Phase three will be to develop an intelligent
> system that tracks usage, so that if I happen to be using power tools
> (perhaps via invertor) the system will keep the RPMs up and provide
> regulation via field current, and then reduce engine speed when power
> demands flatten out.

Cool.

> Once I get this setup working, I'm going to scale it up to a small
> water-cooled diesel and a much larger generator head.  The engine
> coolant will be used provide hot water, and use uC control to divert
> engine coolant between the hot water tank and an air-cooled radiator.
> There will also be a refrigeration compressor on the same shaft to
> keep the icebox cold -- using water/ice as the storage bank.  The goal
> is to run the engine briefly once each day to keep the system topped
> up.

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

> 
> 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?

> 
> > My area of concern is the "regulator" part - there are some areas I've no 
> > experience with, and would appreciate some advice.
> > 
> > I will use PWM to drive the alternator field. The question here is what 
> > sort of pulse rate should I be using? The field presumably looks like a 
> > large inductor (I've not a clue as to what the inductance might be) and a 
> > series resistance (which I can measure). Should I use a real low PWM rate? 
> > High? Not a clue as to what I should use.
> 
> I'm pretty much in the same boat (if you'll pardon the pun) on this
> one and this project is certainly going force me to catch up on my EE
> skills.  I found a datasheet for the CS3341/CS3351/CS387 chips which
> are aparently used inside automobile regulators and it provides a good
> basis for what your(our) regulator ought to be doing at a minimum.  If
> I am interpreting this datasheet correctly, it seems to recomend a 140
> Hz pulse frequency.  This seems counter to what I have read otherwise
> in regards to PWM control, where the selected frequency should be
> "just above the range of human hearing" i.e. 20 Khz or better.

Again, if the you have small alternator needs, then simply get one with the
voltage regulator built in.

[The rest snipped].
BAJ
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