Technosoft 2021
24
iPOS8015 BZ-CAT Technical Reference
Option 2. Connect a chopping resistor R
CR
between phase CR / B- and ground, and activate the software option of
dynamic braking (see below).
This option is not available when the drive is used with a step motor.
The chopping resistor option can be found in the Drive Setup dialogue within EasyMotion / EasySetUp:
The chopping will occur when DC bus voltage increases over U
CHOP
. This parameter (U
CHOP
) should be adjusted
depending on the nominal motor supply. Optimally (from a braking point of view), U
CHOP
should be a few volts above
the maximum nominal supply voltage. This setting will activate the chopping resistor earlier, before reaching dangerous
voltages – when the over-voltage protection will stop the drive. Of course, U
CHOP
must always be less than U
MAX
– the
over-voltage protection threshold.
Remark:
This option can be combined with an external capacitor whose value is not enough to absorb the entire
regenerative energy E
M
but can help reducing the chopping resistor size.
Chopping resistor selection
The chopping resistor value must be chosen to respect the following conditions:
1. to limit the maximum current below the drive peak current I
PEAK
= 40A
PEAK
MAX
CR
I
U
R
>
2. to sustain the required
braking power
:
d
CHOP
MAX
M
CR
t
U
U
C
E
P
)
(
2
1
2
2
−
−
=
where C is the capacitance on the motor supply (external), i.e:
CR
CHOP
CR
P
U
R
×
<
2
2
3. to limit the average current below the drive nominal current I
NOM
=21.15A
2
NOM
CYCLE
d
CR
CR
I
t
t
P
R
×
×
>
where t
CYCLE
is the time interval between 2 voltage increase cycles in case of repetitive moves.
4. to be rated for an average power
CYCLE
d
CR
AV
t
t
P
P
×
=
and a peak power
CR
MAX
PEAK
R
U
P
2
=
Remarks:
1. If
CR
CHOP
PEAK
MAX
P
U
I
U
×
>
2
2
the braking power P
CR
must be reduced by increasing either t
d
– the time to decelerate
or C – the external capacitor on the motor supply
2. If
CR
CHOP
NOM
CYCLE
d
CR
P
U
I
t
t
P
×
>
×
×
2
2
2
either
the braking power must be reduced (see Remark 1) or t
CYCLE
– the time
interval between chopping cycles must be increased
WARNING!
THE CHOPPING RESISTOR MAY HAVE HOT SURFACES DURING
OPERATION.
