TTX Series DC Actuator Installation & Maintenance Instructions |
27
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| 952.500.6200
Due to overcurrent protection, regulated supplies must
generally be rated for the peak power required by the drive.
Because the supplies limit output current, fuses between power
supply and drive may not be able to interrupt fault current to
the drive. The power supply must have output current foldback
and / or output cycling on overload. Foldback is where the
output current limit is reduced more or less proportionally with
the output voltage. Output cycling removes all output power on
overload and waits a few seconds before attempting to restore
power, limiting average power during faults. Fuses can still be
very useful in isolating a fault when a large power supply is
used to power several loads. Where conditions of use by an
approval agency require fuse protection, the fuses must be
installed even if they would not immediately clear a fault.
CAUTION!
During deceleration of the load the energy
generated from the motor and the load will increase the bus
voltage and could possibly damage the output of a regulated
power supply. If a regulated power supply is used for bus
power, a blocking diode should be installed to protect the power
supply. See Power Supply Wiring Diagrams section below
Regenerative energy due to deceleration, spring action, or
gravity on the mechanical load will increase bus voltage
and attempt to drive energy backward into a power supply.
Regulated supplies may trip on overvoltage or recover slowly
after being out of regulation causing a dip in output voltage at
the end of a regen event. It may be necessary to use a blocking
diode to allow the bus voltage at the drive to rise above normal
supply voltage without any reverse current.
Another aspect of BLDC drive loads is that it tends to take
pulses of current at twice internal switching frequency creating
high ripple current. Some regulated supplies may not be able
to tolerate high ripple current, depending on the final filter
capacitors. The Power Distribution and Surge Filter assembly
includes a small inductor that reduces ripple current. The
blocking diode (if used) also reduces ripple current. Power
wiring or power cables more than 30 ft (10 m) long provide
enough impedance to reduce ripple current as well. Contact
Exlar applications support for additional information.
5.3 POWER FROM BATTERY SYSTEMS
Tritex TTX DC is designed to be powered directly from 12 V and
24 V lead-acid batteries or other battery systems. Regen energy
and ripple current are not generally of concern with battery
applications of this type. Battery systems generally will be able
to supply peak power to the actuator. The average power may
be a consideration in sizing the charging circuits for the battery
system. Other battery powered applications are possible but
would require additional engineering considerations.
The product has not been tested for immunity to “load dump”
conditions. An external voltage clamp designed specifically for
load dump protection may be necessary on 24 V systems.
5.4 HANDLING REGEN ENERGY – INTERNAL SHUNT
RESISTOR AND REGULATOR
Tritex TTX DC has a built-in controller and small internal shunt
resistor that can handle up to 10 J of energy at a time as long
as average power does not exceed 8 W. Though not high
capacity, it is adequate to handle the inertia for many linear
applications. It is usually inadequate to handle energy from
a vertical load or spring return. The controller will turn off the
shunt upon reaching either energy or power limits. If there is
more regen energy, the bus voltage will rise, resulting in a high
bus fault.
Note: A poorly tuned system may have some oscillation that
results in the bus voltage pumping up and down enough to turn
on the shunt. This reduces the available capacity for handling
expected energy from deceleration. Likewise, if an overly
aggressive move profile results in significant following error,
there can be velocity overshoot followed by deceleration that
causes unnecessary regen energy to reach the internal shunt
resistor.
As shipped from the factory the internal regulator is set to
a value to protect the Tritex TTX from an overvoltage fault
condition (85 V). This parameter will not require adjustment
as long as the power supply can be back-driven to 85 V like
most unregulated 48 Vdc supplies or can handle all the regen
energy like most battery applications, or is isolated with a
blocking diode. For other applications, the built-in regulator can
be adjusted to restrict bus voltage to a level that will protect
the power supply from regen energy. Set the User Overvoltage
Fault Limit Parameter found in Expert software on the System
Set-up page / Limits tab to a value that the power supply can
tolerate. The Tritex TTX shunt regulator will operate at 90% of
the User Overvoltage Fault Limit value. The drive will trip with
a High Bus Voltage fault at the User Overvoltage Fault Limit
value or at 85 V, whichever is lower. The default setting of 0 is
a special case that means the factory parameter values of 85 V
for trip and 76.5 V for shunt operation will be used.
