"wmbjk" wrote in message
...
On Thu, 16 Jun 2005 15:43:10 GMT, "Pete C."
wrote:

Too_Many_Tools wrote:

I would agree but an VFD that is unnecessary is a current draw that is
not needed.

Like any system, one needs to plan a workshop as a whole.

At this point, I could go single phase, 3 phase or DC motors on on all
my machines. One of the reasons why I started this discussion was to
make that decision based partially on the experiences of others who
have hopefully gone before me.

TMT

I've been following this thread with some interest and now have some
thoughts and comments to add to it.

I may have missed something along the way, but I don't recall you
specifying what type(s) of alternative energy sources you have
available. This makes quite a difference in determining the best
options.

As an example, if your alternate source(s) provide mechanical power such
as found with water power, wind power, or a solar boiler driving a
turbine or steam engine, then air power could be quite advantageous.

A source of mechanical energy can directly drive a compressor head,
saving the extremely inefficient conversions to electricity and back.
Compressed air is easy and economical to store in large volumes and is
free from the chemical hazards of batteries. Useable service life of
compressed air tanks is much higher than batteries as well.

Wind driven compressor - storage tank - air motors? Could be OK if
one had a really windy site, lots of surplus pressure vessels, and a
plenty of rotor diameter. To get an idea of the diameter versus work
produced, check out the size and pumping rates of Bowjon well pumps.

In addition to the obvious air tools, compressed air can also be used to
power things such as refrigeration if you use the belt driven type
refrigeration compressors.

Mechanical drive all the way to the pump? That would work well with a
large mill, when the wind is blowing, and be as efficient as these
http://www.deanbennett.com/windmills.htm. But in that application
there's the advantage of easy storage for when there's no wind.

Those mechanical energy sources can also simultaneously drive electrical
generators to charge conventional batteries for loads such as lighting.

Which is why the conventional rotor/alternator is so popular with home
power users. Ours is similar to this one
http://www.windenergy.com/whisper_200.htm.

Battery charging for cordless tools is no less efficient that the
charging of your "regular" battery string, as long as the charging is
limited to peak energy generation times.

For the usual home power setup, cordless tools are no more and no less
advantageous than they are on-grid. Unless the power setup is very
small, the double conversion isn't worth trying to work around.

The efficiency of converting DC from your battery string to AC so you
can use conventional appliances is fairly good with modern inverters.
The conversion efficiency also improves when you use a higher voltage
battery string since inverters switching higher voltages at lower
currents will have lower resistive / heat losses.

Solar PV conversion efficiency is incredibly low to begin with and PV
cost is high so if that is your only energy source you really do need to
watch every miliamp.

That depends. On very small systems, it's often true. Our setup isn't
huge, and costs about as much as a medium priced SUV. The idle loads
are about 100 Watts 24-7. That's a waste versus
convenience/practicality issue, and it's a long way from watching
every milliamp.

Of course, even with that inefficiency a solar PV
panel charging batteries for your cordless tools is just fine as long as
it has the capacity to keep up with your usage.

For items like welders that require huge gulps of power it's really
difficult to get away from an IC engine / generator for practicality.

Not necessarily. Home welding tends to be short duration. The hardware
to supply that kind of power is actually affordable, and if one is
designing the power system from scratch for what most would consider a
normal home, then the extra inverter capacity isn't a big deal. In our
case, for the house loads alone we could have gotten away with a
single SW4024 plus a transformer for the 220V loads.

How is this done, getting 220V from 110? How do you get the two "hot"
wires? Are there 2 secondary windings on the transformer? Wouldn't they
need to be out of phase with each other?