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4291
Hubbell Industrial Controls
Euclid™ Lifting Magnet Controller
Varistor Type Automatic Discharge
Specification 4291 • May 2004 • Replaces July 1990
General Information
The Euclid Type 4291 Magnet Controller is
for use with all types and makes of lifting
magnets. It assures fast and clean release of
all types of magnet loads.
All or just part of the load may be dribbled, if
desired. In addition, because of the circuit
design, the magnet and magnet leads are not
subjected to high induced voltages.
♦Automatically discharges magnet.
♦Fast and clean release of load.
♦Peak magnet induced voltage limited to un-
der 700 volts.
♦Wide reverse current adjustment for differ-
ent types of magnet loads.
♦Mechanically interlocked mill-type “Lift” and
“Drop” contactors.
♦High-thermal capacity varistor discharge.
♦Permanently connected discharge path.
♦Discharge path completely independent
from the line.
♦“Drop” contactor opens automatically at
end of drop cycle.
♦Front wired, front removable components.
♦Long contact life.
♦Minimum maintenance.
♦Full voltage reverse current.
♦NEMA 3R Enclosed
Application
Euclid Type 4291 Lifting Magnet Controllers
have many uses from light scrap handling to
extremely heavy plate or billet handling. The
flexibility of this magnet controller is illustrat-
ed by the ease of proper “cleaning” that can
be accomplished when switching from one
type of material to another. A simple adjust-
ment of the potentiometer (P1) is all that is
necessary. An inherent dribble characteristic
is designed into each unit allowing material
sorting such as steel plate stacking, by re-
leasing one plate at a time.
Description
The Euclid Type 4291 Magnet Controller in-
corporates time proven components arranged
to provide a new concept in magnet controller
design and operation.
This controller includes all necessary power
and reverse current contactors in addition to
discharge path components.
Euclid’s standard mill-type contactors are
used to carry the power to the magnet. The
reverse current or “Drop” contactor is also a
mill-type contactor. The commonly used dis-
charge resistor has been replaced by a high
thermal capacity varistor connected in series
with a silicon rectifier to assure a permanently
connected independent discharge path at all
times around the magnet.
Main power of “Lift” contactors, due to the cir-
cuit design described herein, need only Eu-
clid’s exclusive arc-centering, high-arc inter-
rupting system to handle the highly inductive
magnet circuit.
The high thermal capacity of the nonlinear
varistor dissipates the energy stored in the
magnet at a much lower value of induced
voltage than does the usual fixed type dis-
charge resistor. The varistor assembly is a
bank of silicon-carbide composition discs
connected in parallel and cooled by alu-
minum radiating plates.
The maximum induced voltage permitted by
the varistor is a peak of 700 volts. This fea-
ture assures extra protection of the magnet
and lead system insulation. It also minimizes
destructive arcing on the "Lift" contactor.
Non-linear characteristics of the varistor
help maintain the discharge voltage at the
maximum allowable voltage until all of the
stored magnet energy is dissipated. The Eu-
clid Type 4291 Magnet Controller dissipates
stored energy as fast as any comparable de-
vice, but with a much lower induced voltage.
It is not necessary to close the "Drop" contac-
tor immediately to provide a discharge path.
Full line voltage, for cleaning the magnet, is
applied to the magnet terminals when the val-
ue of the induced magnet voltage declines to
nearly the line voltage value. Resistors are
eliminated from the reverse current circuit.
This allows the reverse current to build up as
fast as the magnet inductive characteristics
will permit.
During the time of the stored energy dissipa-
tion, the reverse voltage across the magnet
and the discharge varistor assembly signals
the discharge Sensor Module (DSM) that the
discharge cycle has begun. When the dis-
charge voltage falls to 250 to 300 volts, the
"DSM" closes a pilot Drop Relay (DR) that
energizes the Drop Contactor (D).
The adjustable time reverse current cycle be-
gins with the closing of the Drop Relay after
practically all the stored magnet energy is
dissipated by the Discharge Varistor (DVA)
assembly. The DSM also controls the length
of the reverse current cycle. After a preset
Page 1 of 4
Euclid Lifting Magnet Controllers Provide 3-Way Release of Load
Euclid Type 4291 automatic discharge type magnet controller is the only one on the market today that
will assure (1) fast and clean release of full load, (2) accurate release of partial load and (3) precise
control of dribbling. It can be used with all types and makes of lifting magnets in any industrial applica-
tion.