Roger Wiegand wrote in 090203 MMDigest:

> You may be amazed by the start-up current drawn by a blower -- I was!

All AC induction motors draw higher current when starting than they
do when running.  You see the effect of this when starting a circular
saw and the lights momentarily dim while the saw comes up to speed.
Ideally it is preferable to deal with this by starting the motor under
conditions of minimal load.

Apart from this motor phenomenon, there is a more serious matter
regarding blowers: blowers require the most power when they are running
under conditions of low pressure.  In other words, the maximum power
for a blower will be found when running a blower connected to no
ductwork at all in free air.

You can see this effect when you place your hand over a vacuum cleaner
hose and notice the motor speeds up even though the blower is producing
the maximum pressure.  This is due to the fact that the blower is not
doing any work -- no air is flowing.  Pressure blowers normally run at
speeds sufficient to draw excessive power at low pressure and this can
easily over draw the household circuit or trip a motor overload.  This
high current will be drawn as the system pressurizes and will taper off
to normal as pressure builds.  There are a couple of ways I can think
of to deal with this:

1. Someone pointed out that a reservoir is not needed with a blower in
use.  Filling the reservoir is a primary delay factor in bringing the
system up to pressure.  You could choose to block it off and reduce the
time the blower will be in a high demand state if this suits your
needs.  If you eliminate the reservoir the system pressure will vary
with the demand for air by the organ.  Reservoirs are a primary method
of moderating this effect.

2. Put a restricting aperture in the line to the reservoir.  You would
not want this restriction to be in the line leaving the reservoir
however as this would limit the usefulness of the reservoir to supply
high air flow when the organ demands it.  Accomplishing this might
require some plumbing changes to provide separate ducts in and out of
the reservoir with one-way valves in the lines.

3. Put a restricting aperture in the line to the reservoir with a
bypass that will open once the reservoir is at operating pressure.  The
bypass can be pressure activated or timed on with an electronic or
pneumatic timer.  This effectively provides a low flow bleed into the
reservoir and reduces the load on the blower and motor only during
startup, leaving the system as designed when running under operating
conditions.

4. Do not begin playing the organ until the system is at full pressure.

There are several ways to produce 3-phase power from a single phase
source.  The best way for a residential user is to use a rotary
converter.  There are inverter supplies that can produce variable speed
3-phase power (VFD = variable frequency drive) but these almost always
produce high voltage spikes of 1200 to 1600 volts on a 460-volt output
and those spikes will blow holes in motor wiring varnish insulation
unless the motor is made for industrial use with VFDs.

Rotary converters do not generally provide for variable frequency
(speed control), but are often made for frequency conversion such as
50 Hz to 60 Hz or 60 Hz to 50 Hertz.  Soft start starters may be
available that do not produce the high voltage spikes VFDs produce.
This is an ideal solution if you can find one.  I don't know the state
of these devices as they fell out of vogue when VFDs became available
with the soft start and soft stop ramping features built in.

Considering the cost of VFDs, soft start reactors and 3-phase motors,
it may be worth looking at using a DC motor with a ramping speed
control.

As always, be aware that all blowers have a limiting speed beyond
which they can fail structurally and turn into shrapnel, destroying
everything within twenty feet as well as causing injury and death.
Never exceed a blower's rated maximum impeller speed even if you have
tested it in a block house and believe it to be safe.  This can become
a particular problem when introducing variable speed controls in blower
systems where a push of a button can cause overspeed inadvertently.

Don Shenbarger