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Technosoft 2015
56
iPOS4808 BX-CAN Technical Reference
(U
BRAKE
) should be adjusted depending on the nominal motor supply. Optimally (from a braking
point of view), U
BRAKE
should be a few volts above the maximum nominal supply voltage. This
setting will activate the brake resistor earlier, before reaching dangerous voltages – when the over-
voltage protection will stop the drive. Of course, U
BRAKE
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 brake resistor size.
Brake resistor selection
The brake resistor value must be chosen to respect the following conditions:
1. to limit the maximum current below the drive peak current I
PEAK
= 20A
PEAK
MAX
BR
I
U
R
>
2. to sustain the required
braking power
:
d
brake
MAX
M
BR
t
)
U
U
(
C
E
P
2
2
2
1
−
−
=
where C is the capacitance on the motor supply (external), i.e:
BR
BRAKE
BR
P
U
R
×
<
2
2
3. to limit the average current below the drive nominal current I
NOM
=8A
2
NOM
CYCLE
d
BR
BR
I
t
t
P
R
×
×
>
where t
CYCLE
is the time interval between 2 brakes in case of repetitive moves.
4. to be rated for an average power
CYCLE
d
BR
AV
t
t
P
P
×
=
and a peak power
BR
MAX
PEAK
R
U
P
2
=
Remarks:
1. If
BR
BRAKE
PEAK
MAX
P
U
I
U
×
>
2
2
the braking power P
BR
must be reduced by increasing either t
d
– the
time to decelerate or C – the external capacitor on the motor supply
2. If
BR
BRAKE
NOM
CYCLE
d
BR
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 braking cycles must be increased
WARNING!
THE BRAKE RESISTOR MAY HAVE HOT SURFACES
DURING OPERATION.
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