Installation and operational instructions for
ROBA
®
-servostop
®
Type 8982.00_01
Size 40
– 100
(B.8982.EN)
06/10/2022 GF
Chr. Mayr GmbH + Co. KG
Eichenstraße 1, D-87665 Mauerstetten
Phone: +49 8341 804-0, Fax: +49 8341 804-421
Page 20 of 27
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7.4.1.3 Calculation during Field Build-up with Overex-
citation
Required overexcitation time
Increased wear, and therefore an increasing air gap as
well as coil heating lengthen the separation times t
2
for
the brake. For this reason, at least 2 to 2.5 times the sep-
aration time t
2
at nominal current I
N
must be selected as
overexcitation time t
O
.
RMS coil capacity P
P
P
N
The coil capacity P must not be larger
than P
N
. Otherwise the coil may fail due
to thermal overload
.
Key and Calculations:
P
[W]
RMS coil capacity dependent on switch-
ing frequency, overexcitation, reduction in
capacity and duty cycle
P =
P
O
× t
O
+ P
H
× t
H
T
P
N
[W]
Coil nominal capacity (Technical Data,
type tag)
P
O
[W]
Coil power on overexcitation (Technical
Data)
P
H
[W]
Coil power on holding voltage (Technical
Data, type tag)
t
O
[s]
Overexcitation time
t
H
[s]
Holding time
t
on
[s]
Time with voltage
t
off
[s]
Time without voltage
T
[s]
Total time (t
O
+ t
H
+ t
off
)
U
O
[V]
Overexcitation voltage (bridge voltage)
U
H
[V]
Holding voltage (half-wave voltage)
U
N
[V]
Coil nominal voltage
I
O
[A]
Overexcitation current
I
N
[A]
Nominal current
M
Br
[Nm] Braking torque
7.4.1.4 Time Diagram:
7.4.2 Magnetic Field Removal
Determination of the connection time (t
1
)
7.4.2.1 Switching with Freewheeling Diode
Supply with DC voltage
The power circuit is interrupted in front of the freewheel-
ing diode. The magnetic field slowly reduces. This delays
the rise in braking torque and generates a slow connec-
tion time t
1
. The freewheeling diode is to be dimensioned
in accordance with the nominal current of the brake and
the maximum occurring supply voltage with the appropri-
ate safety factor.
Recommendation!
Connection time t
1
is of no consequence:
switch with the freewheeling diode.
No protective measures for the coil
and switching contacts required.
Switching with freewheeling diode means a longer brake
engagement time (approx. 6
– 10 times longer than with
DC-side switch-off), use for non-critical braking times.
L+
L-
Schematic wiring diagram 1
0
U
t
U
O
U =
H
U
N
T
t
off
t
on
t
O
t
O
t
H