Burr King Model 800 - Manual (Page 7)

BURR KING MFG. CO., INC.
1220 TAMARA LANE
WARSAW, MO 65355
WWW.BURRKING.COM
(660) 438-8998 (800) 621-2748
FAX (660) 438-8991
Technical tip
May 16, 2006
As you may know we improved many of our 120 and 220-volt single-phase variable speed grinders and
buffers to use a three-phase AC motor with an inverter controller rather than the DC motors and a rectifier
controller previously used. This change is transparent to the end user since the machine is “plugged in” to
single-phase outlets. The use of a three-phase motor permits the use of computerized “inverter” controls to
achieve variable speed control. Current technology does not support the use of single-phase motors for
variable speed operation except through the use of mechanical systems. We made this change for the
following reasons:
• Customers frequently demand excess horsepower output from the machines. Regardless of the “labeled”
horsepower electric motors can deliver power well in excess to stated capability for short periods of
time. Since there is “no free lunch” this excess horsepower is sustained by high current drain on the
supply service (what comes out of the wall). Further this high current drain taxes the control module on
the grinder or buffer and all interconnect circuitry such as the electrical cord which can get warm as
evidence of the overstress. The new configurations are more tolerant of excess horsepower demand.
• The DC motors and controllers previously used had fuses that would “blow” when the customer
demanded even short periods of overload necessitating the customer searching for and replacing up to
two fuses at the machine and perhaps having to reset an wall circuit breaker. The new configurations
are more tolerant of overload, but in the event of an overload the customer needs only to reset the
controller.
• The DC motors require the use of “brushes” that have a specified service life of about 1200 hours with
normal loading. Excess loading greatly reduces this time. The three-phase motors used with the new
configurations do not have brushes and are inherently more reliable.
• The DC controllers previously used are very limited in their ability to be interfaced with external
controls as might be found with robotics or other automation devices. The new AC controllers have
greatly expanded interface capability.
• The DC motors and controls were often limited in their ability to drive the machines to maximum
specified belt or wheel speed. The new configurations can be readily set for optimum advertised
speeds.
• The cost of modern inverter controls is now competitive with the cost of the older DC control modules;
and three-phase motors are very competitive with DC motors. This allows us to deliver a superior
value to our customers and to expand the application utility of our products without negatively
impacting the price that our customers pay.
Because of the common and widely used 120 volt single-phase service (your home, office, and in factories)
there are some important application aspects that you and our customers need to bear in mind. These apply
to the new variable speed configurations or for that matter any electrical motor driven machine where the
horsepower is 1-½ or greater. People often do not understand the electrical supply beyond “it comes out of
the wall” and “if it is my garage it must work on everything specified 120 volts, single phase”. Many homes,
offices, and even factories (in accordance with local and national codes) are wired with 14-guage feeder
wire to the 120-volt outlets making the supplied service inadequate for machines with 1-½ horsepower
See our catalog at www.burrking.com Contact us at [email protected] 1