wmbjk wrote:

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.

Should be comparable or better efficiency than a wind driven generator
charging batteries. In either case you're capturing and storing the
intermittently produced power for later use and a more convenient rate.
A compressor powered by water or a solar steam generator would work well
also.

Various electric utilities have been experimenting with compressed air
storage as a way to store power from excess generating capacity during
off peak times for use later during the peak times. They also do this
with pumped hydro, but CAS is far more practical than pumped hydro in a
homepower environment.


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.

No, not mechanically driven. The refrigeration compressor would be belt
driven from an air motor. The thermostat simply opens the air valve when
it needs to spin up the compressor. Again the ultimate source of power
does not have to be wind, and in fact with CAS it's even easier to
combine energy captured from multiple sources. No need to worry about
charge controllers when you're simply pumping air into a big tank.


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.

The point is that batteries can only accept a charge at a certain rate,
potentially wasting captured energy during peaks. There is no such
limitation with an air tank, unless it's already at max capacity. Air
tanks are also a lot less expensive and lower maintenance than battery
strings. By combining both an electrical generator and an air compressor
on the wind plant you can better capture peak output.

The efficiency of directly utilizing the energy of the compressed air
for mechanical applications is also higher. Instead of capturing wind
energy, converting to electricity, storing in a battery, converting to
AC, converting to mechanical energy with a motor, converting to
compressed air with a compressor coupled to the motor and then utilizing
the compresses air to fire your nail gun, you eliminate four conversion
steps.


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.

I know, but someone posted elsewhere in the thread that charging
cordless tools was horrifically inefficient.


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.

This is where you really need the hybrid system. You run the inverter to
power your conventional appliances. When you are not running the
appliances you turn the inverter off. You run your lighting and TV and
whatnot that are your much higher duty cycle items from DC and avoid the
conversion.


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. Instead we used
dual inverters, which eliminated the need for the transformer, and
provided sufficient power for most anything used in the usual home
shop.

Perhaps your home welding is less than mine. I've got a Miller
Syncrowave 250 that I love and it can see quite a bit of use on project
weekends. I'm thinking your inverters would gag at the 240v 100a gulps
the Syncrowave takes, even if the typical gulp is only about 10 seconds
duration. On a big project those 10 second gulps add up to quite a few
minutes.

I'm on-grid, but having recently moved to an area with much better solar
and wind potential I'm investigating options to take advantage of those
sources.


A decent welder / generator can serve two needs and may be the most
practical solution.

Welder generators aren't a good match for backup duty, or even for
backup charging. Their advantage is portability for welding, and
they're only best (in the home power context) when you need high amps
for short periods. For any application that needs longer run times
supplying small loads, something like the Honda EU series is far
better. After a few years of living off-grid, like many others I found
that a DC backup generator that works independently of the
inverter/chargers is nice to have. The one I built drives a $5 scrap
Delco 27SI, and only produces about 2000 Watts. When there's no sun or
wind, we can do nicely on about 4 hours run time per day, at a
charging rate that's similar to when the other sources are on line.

I didn't really intend the welder / generator to be used for backup to
the regular power system. I really meant it more as an option for
powering larger shop tools.

If you want to make it a bit more efficient in this capacity you can
build an automatic transfer switch so that when you are not drawing a
load from the generator to operate say a 5 hp table saw, the capacity
can be diverted to a charger to add some extra power to your regular
battery string.


If you've got really good water power available you could probably use
it to drive the head from an engine driven welder. A DC inverter type
welder could probably be modified to accept DC from a large battery
bank, but that would require you to have a fairly high voltage battery
string to be practical.

Like some of the other comments in this thread (line shafts for
instance), that suggestion may be feasible. But unless one has way
more time than money, conventional methods are more practical.

Modifying a DC inverter welder which are pretty inexpensive these days
is likely the most efficient way to get quality welding capacity from a
home power system. No line shaft required, and no need for oversized
inverters or load shedding.


Someone else posted about the differences in energy needs of a shop vs.
home. They had more or less the correct idea, but got their terminology
a bit out of whack. A shop has mostly high peak energy loads at low duty
cycles and a home has mostly low peak loads with high duty cycles. The
total energy consumption over the course of a day could be similar
depending on how busy the shop is.

That was probably me you're talking about, and my terminology was
quite correct for our setup. Occasionally our shop energy use is
higher than for our house, but usually it's the other way around by a
big margin. Normal power tool energy consumption in a home shop is
lost in the noise of an all-electric home's consumption. Welders,
plasma cutters, chop saws, table saws, planers, etc. are all high
power, but relatively low energy because of their short run times.

Shop = big gulps, house = long sips


Keep in mind that we're talking *home* shop here, which I consider to
be small projects by one person. Many off-gridders go the route of
putting a high percentage of their loads onto propane, leaving much
less for the actual power system to do. For them, shop energy
consumption may indeed cause the need for a much larger system, or the
pain and cost of running a big generator. But we're very nearly 100%
solar/wind powered. We don't even have propane, and fuel use for
backup generator and the welder/generator combined isn't much
different than what some folks consume in a season of mowing a big
lawn with a garden tractor.

Well, my home shop which is just for me, includes a Bridgeport mill, a
metal lathe, the big honkin' TIG welder mentioned earlier, a CNC router,
60gal compressor, 10" table saw, an electric forklift and a host of
smaller items like sawsalls and grinders.

This is of course partly attributable to my preference for metal
projects which tend to require bigger tools and more power tools than
woodworking.


Here are a couple of my projects from my off-grid shop. I only needed
the engine-driven welder a few times, mostly for its portability.

http://www.citlink.net/~wmbjk/images...als%20only.jpg top 40' of
a 65' free-standing wind generator tower (in progress)
http://www.citlink.net/~wmbjk/images/tower%20top.JPG tower nearly
finished and erected
http://www.citlink.net/~wmbjk/frank.htm cactus transport

Wayne

Nice projects. Someday I'd like to do that. Somehow it seems to cost
more to live self sufficient off-grid than it does to just pay the
utilities...

Just out of curiosity how do you make a living?

Pete C.