Download For those who are quite entrenched in the vacuum industry you have

For those who are quite entrenched in the vacuum industry you have undoubtedly had
lingering technical questions in the back of your mind. One major issue that has never
been fully addressed in any public articles has been the pros and cons of 120 volt and 240
volt motors.
For most central vacuum power unit manufacturers this has never been an issue because
they only produce a few options of units, all of which draw under 15 Amps of 120 volt
power. Any time a central vacuum system is proposed for a home over 5,000 square feet
you should be considering a product of substantially higher power. While some central
vacuum manufacturers might claim that their single-motor power unit will handle homes
up to 10,000 square feet, there are a few other factors to consider. Yes, motors may have
adequate suction to clean properly at 150 feet away on a 10,000 square foot home but you
must also consider the much-higher volume of traffic in the home. If a 2400 square foot
home takes 1 hour per week to clean, a 10,000 may require five to six hours. Add to this
the fact that larger homes will typically be cleaned by paid employees and the vacuum
would get used for much longer periods of time. Six hours per week times 50 weeks per
year equates to 300 hours per year. The motors are only designed to last 800-1000 hours!
Many of the high performance motors on the market today employ motors that are
operating at a much higher speed. Rather than 20,000 RPM, they may be turning at
almost 40,000 RPM. This additionally reduced motor life down to 600-700 hours. So
this wonderful, powerful single-motor unit might last only two years in this expensive
home!
A few manufacturers have offered higher-powered power units that require greater
amounts of electricity to operate. This presents a whole new set of issues: To provide
electricity to two large motors, the amperage will exceed the standard circuit normally
provided for the central vacuum. Any appliance over 7.5 Amps should be on its own
dedicated circuit but these units would require 25-26 Amps of 120 volt power. You
cannot simply exchange the breaker for a 30 Amp breaker! A 30 Amp breaker requires
10 gauge wire rather than standard 12 gauge. The only other option would be exchange
the circuit with a 240 volt circuit. This would cut the amperage requirement in half and
allow it to operate on the smaller 12 gauge wire.
This drives us to the original purpose of this article. Which configuration would be best?
Let’s analyze it on two fronts: Technical and Practical. You can then make the decision
which will best suit your applications.
From a technical aspect, motor manufacturers do not have exact cross-over’s for every
single motor. Although they may have two motors that are both 2-stage, tangential
exhaust, bypass, ball-and-ball with the exact same fans but one is 120 volt and the other
is 240 volt, they may not both have the exact same performance specifications.
According to Don Johnson of Electro Motor Inc., “the wire size on the 240 volt motor is
half the size but twice as long. The wire is turned twice as many times around the stator
and armature.” Don continued, “In fact, if you melted down the copper from a 120 volt
motor and the basic equivalent 240 volt motor, you would end up with just the same
amount of weight of copper.”
I used to think that one had less copper than the other and the copper would act to
dissipate heat. Now I understand that this is not a correct statement. But heat is certainly
a factor in vacuum motors. Because most vacuum motors are only 28-35% efficient,
much of the energy gets expended as heat. According to Pete Pavlick of Ametek Electric
Motors, “In the ideal world there should be no differences in the temperatures between
equal 120 and 240 units given the same fan system and same input power. However,
there are differences in the current draw. The lower current of the 240 would be a
positive. Within the motor there is a difference in the commutation voltages. The 240V
would have a higher bar to bar voltage and this can be a negative.”
Because in a 240 volt setting, a higher voltage is being transferred across the bars of the
commutator, this motor would have a slightly higher total temperature. But Pete brings
up another very important issue. Because the 240 volt is operating at a lower current
(amperage) it would also use less electricity and be less expensive to operate. Essentially
240 volt motors use both legs of electricity simultaneously whereas 120 volts uses only
one leg and the other half might be wasted if there is not a balance of appliances using the
same amount of voltage on opposing breakers. But even so, on a 26 Amp vacuum motor
used 6 hour per week, at a cost of $.15 per kilowatt the 120 volt version would be an
increased total of $60 per year. (For that 2400 square foot home the total central vac
electrical operating cost would be about $10 per year!) So there is a tangible higher cost
for the 120 volt but these figures assume there would be no other appliances operating on
the opposite phase that would counteract the usage. The true annual increase in cost for
this 10,000 sq. ft. home might be more like $25 per year.
Consider also that the 240 volt motors are less available on the open market. It would be
far easier for you to stock only one voltage of motor on your service vehicle knowing it
would fit all your units out in the field. According to Don Johnson, Electro Motor sells a
disproportionately higher volume of 120 volt motors despite sales to foreign markets. If
the factories set up their operation for 120 volt motors and run a million motors and then
change to 240 volt motors which use a smaller gauge wire, there has been some wear on
the spindles that lay the windings down and this wear may translate into an unevenness
that is not found on the 120 volt, more popular motors. So they have to be more careful
building 240 volt motors. In fact, because most of Electro Motor’s 240 volt motors are
destined for Europe they must meet stringent EMI (Electro Mechanical Interference)
guidelines. This calls for a reduction in the arcing between bars and makes balancing
more critical. “Varnish also plays a very important part of this process” states Pete
Pavlick. Lastly, the differences in the winding resistances and the bar to bar voltages
mandate a different carbon brush composition. So don’t go putting 120 volt brushes in
240 volt motors as it will not provide the proper voltage into the motor.
For normal residential application the home may also only be receiving 220 or 230 volts
rather than 240 volts. Running a 240 volt motor on 220 volts will only reduce motor
speed and output performance. Running a 220 volt unit on 240 volts will actually over
rev the motor and could greatly reduce the motor life. Most manufacturers install 240
volt motors to be on the safe side but some can actually provide the 220 volt versions.
You can also run many central vacuums on 208 volts but not on three phase power. Be
sure to check with your manufacturer to see if the circuit board and motors can handle
this before specifying it.
On the practical side, for the 120 volt version of a two-large-motor unit such as MD
Manufacturing’s S5 or SV, you will need to be sure to have the electrician provide the
proper 30 Amp, 20-gauge wire. If he forgets and installs only a 20 Amp, 12 gauge wire
he can still convert it to a 240 volt circuit if it is dedicated. I have seen cases where the
electrician has installed the circuit after the power unit has been hung and the electrician
mistook the 30 Amp 120 volt for a 240 volt plug and wired it incorrectly. This will
destroy the transformer in the unit, but is easily repaired by replacing the entire circuit
board.
The 240 volt unit will be harder to maintain service parts because it will be out of the
normal pattern but with good record-keeping you should be able to be properly prepared
for service. Both Ametek and Electro Motor stated it is really a toss-up between the two.
Neither the 120 volt nor the 240 volt motor stood out in their minds as superior to the
other. At MD Manufacturing we agree but we emphasize that you always would rather
install a unit that exceeds their suction needs rather than disappoints them. So 120 volt or
240 volt MD would love to meet your needs!
Grant Olewiler is the General Manager of M.D. Manufacturing, Inc. in Bakersfield, CA
and has been in the central vacuum business over 30 years. He speaks from the
perspective of an assembler, installer, marketer, and research specialist. MD
Manufactures the Modern Day, Silent Master, Air Force, and FloMaster Central
Vacuums. MD’s centralvacuum.com website is the industry’s most comprehensive data
source for central vacuum information and this article will be posted there.
Reproductions are not permissible unless written permission has been granted. Feel free
to contact Grant at [email protected].