"Scott Willing" wrote in message
...
On 15 Jun 2005 11:36:20 -0700, "Too_Many_Tools"
wrote:
Thanks for the reply.
I would agree that cordless tools have a spot in the AHP workshop since
one can recharge them during off load hours.
Where would one find 12v motors in the suitable HP and speeds to
retrofit something like a table saw?
In considering this subject, a lineshaft approach does come to mind but
unfortunately you rarely see the needed equipment at HD or Lowes. I am
not to crazy about chucking all the stationary power tools that have
taken me decades to collect. Also, lineshafts take up room, linedriven
tools are required to stay in one place and cannot be mounted on wheels
to optimize shop space as needed. A workshop should be no larger than
necessary for the heating/cooling aspect that also takes energy.
TMT
I really hesitate to jump in on this topic, but I advise you to make
sure to do your research carefully before pursuing the replacement of
AC motors with DC motors.
In the early days of homepower which was nearly universally 12V on the
primary side, this was a pretty common practice, but in the overall
picture of things today I'm not sure it's warranted in the general
case.
At one time I was given to understand that DC motors are just innately
more efficient than AC. It appears that this is not necessarily so,
and has much to do with the crappy design and build quality of
"shovelware" AC motors than any basic electromechanical principles. To
know whether you would actually be further ahead after a DC
conversion, you would have to consider each case individually.
Ignoring power factor, a 12V load of power "x" draws 10 times the
current that an 120VAC load will draw. Will the losses you avoid by
bypassing the inverter get chewed up in the wire? How close to the
battery room will the workshop be?
I absolutely agree with what you are saying. This is why the on-grid folks
are using Tesla's design and not Edison's DC idea. For a house I also think
it's probably not worth the trouble to run massive wires everywhere in order
to use DC effeciently. Of course the higher the voltage the smaller the
wire required, which brings you right back to 115VAC. Probably better to
have a few extra batteries and a couple of extra solar panels (or whatever)
to cover the loss of effeciency. When I first started reading about wind
generators about 20 or so years ago they were talking about 120 volt
generators charging batteries in series equaling 120 VDC. According to the
author most appliances wouldn't care if it was AC or DC. This idea is
definately simpler than having to buy and connect an expensive sine wave
inverter but I suspect that today's electronics might be a bit more
particular about their input current than a 20 year old dishwasher or vacuum
cleaner. If someone wanted to try it I suppose the best thing to do would
be to buy a new whatever and make sure you can return it. If it explodes
you go get your money back. And of course there's always the problem of
short circuits burning the house down.
However, for a stand-alone workshop that is to be powered seperately I would
consider using DC as opposed to running a gasoline/diesel generator on one
or two tools that I use regularly. For those that I only use occasionally
for me it's no big deal to start up a little generator (most of my saws etc
run fine from a Honda eu2000). As someone else pointed out running a
compressor during peak sunlight or wind times (or when a generator happens
to be running) and filling the tank can, at least in my case, supply enough
air to do quite a bit of work later without having to use any additional
power. Leaks, in this case, cannot be allowed to exist!
I started out at 12V primary by virtue of buying a house with an
existing PV system. Like many frontier homebrew systems, it had
started as a purely DC system to which an inverter was added later.
Having no plumbing in the house, I've acquired a number of small 12V
pumps for various specific purposes, such as our bucket shower.
Fortunately this hasn't represented a significant investment. With
each system upgrade I left myself options for going to a higher
primary voltage, and recently made the move to 24V when we replaced
our chargerless mod square wave inverter with a sine wave
inverter/charger. At some distant point in the future we might even
make the jump to 48V, but for the moment, 24V was "just right."
The punchline is that our little pumps (and other 12V DC loads) are
now running off a 24V/12V DC-DC converter. In the overall picture of
things this crazy scenario actually still makes sense here, but again
these are *small* loads.
Lol. As long as you don't plug a battery charger into it to charge the
batteries it's running off of ;-)
The moral is that when you choose to run DC loads, you're creating
specialized equipment and there are serious implications that might
not be immediately obvious. If you stick with AC loads, your wire runs
can be far longer for a given power throughput / wire guage, you can
reconfigure the primary side of your system without affecting anything
on the load side, use a common AC generator when it's more convenient
or more sensible to do so, or take your gear with you and use it
elsewhere.
I keep toying with the idea (12 volt motors) but I still use a gasoline
generator for the sizeable, short use loads. When it comes right down to it
I'm probably only using about 2 to 3 gallons of gasoline per month to run my
tools to produce around $15,000 worth of revenue. From a business
standpoint this is an insignificant expenditure. I simply manage the use of
my power tools and do work in batches. I don't work after the sun goes down
(usually, unless it's a RUSH order).
Having "inherited" a mixed DC/AC system and lived with it, off-grid,
for five years, there is no question in my mind that the new house we
build here will be wired almost entirely for conventional AC and will
likely have only some emergency lighting (power room!), and perhaps a
few very special-purpose devices and outlets wired for DC.
YMMV.
-=s
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