Danaher Motion
05/2008
Appendix A – DC Power Supply Design
S200-VTS Product Manual
115
5. In most cases, a bus capacitor does not need to be mounted close to the drive.
The inductance of the bus and ground wiring is not critical because the internal drive bus
capacitance generally handles all the PWM current of the drive. A local capacitor is not needed
in the following cases:
3/9 ARMS DC S200
6/18 ARMS DC S200 with
HSTemp
less than 65° C
6/18 ARMS DC S200 mounted adjacent to other S200 drives with main bus supplies tied
locally together. The internal bus capacitors of the adjacent drives should provide the needed
capacitance.
The exception is a single, isolated 6/18 ARMS DC S200 drive running hot (HSTemp > 65° C).
In this case, connect across the bus within 1 ft of the drive, using twisted wire, a 470 µf (min),
100 V, low ESR, and an aluminum bus capacitor.
6. Bus capacitor for multiple drives
A conservative rule is to scale up the recommended output capacitance for one drive by the
number of drives. If this value is too large, the capacitor can be calculated from energy flows.
See the A.4
Bus Energy & Power Numerical Examples.
NOTE
Bus capacitance can be tweaked experimentally. Increase bus
capacitance if there are overvoltage trips. In general, there is
sufficient bus capacitance if the bus voltage variation is ± 5 V (from
75 VDC) during the machine cycle. Check the bus voltage with an
oscilloscope. Scope ground on J1-2 (Bus/Ctrl Gnd) and probe on J1-
3 (+bus), Hor: 5 ms / div.
NOTE
Some bus voltage variation is normal and required for the output
bus capacitor to supply or absorb energy.
7. Bus over-voltage fault (non-latching)
If regeneration is too high while bus capacitance is too low, the bus voltage rises to the bus
over-voltage fault threshold and disables the drive transistors. It typically takes 1 to 2 ms for the
motor current and torque to go to zero. After it has reached zero, there is no further rise in the
bus voltage. When the bus capacitors discharge to below the over-voltage threshold by a
hysteresis value, the over-voltage fault is cleared and normal operation resumes. While this
protects the drive by limiting the bus voltage rise, it may not be desirable because it interrupts
normal motor torque.
8. Unregulated power supply
External bus capacitance requirements are usually met by the output capacitor in an
unregulated power supply, as long as there is no diode between the drives and bus capacitor.
The same capacitor that filters the 120 Hz or 360 Hz line ripple also provides energy leveling
and regeneration absorption capability.
9. Regulated power supply
Some regulated supplies do not tolerate an increase in voltage above the supply voltage set
point. In this case, insert a diode between the positive supply terminal and the positive
capacitor terminal to prevent reverse current flow into the supply. The diode should be a
rectifier diode with a voltage and current rating equal to or greater than the supply.
A low ohm (< 1
Ω
) power resistor between the power supply and the capacitor may be
desirable. By reducing the stiffness of the voltage across the capacitor, it enhances the ability
of the capacitor to supply current to the drive during motor acceleration and prevents the
current limit of the regulated supply from cutting in.
10. Bus wire resistance
Bus wire current is the sum of DC current providing power to the drive and AC current between
the drive and external capacitor. The wire between the drive and external bus capacitance
should be a low enough resistance, so peak currents do not cause excessive voltage drop in
the wire. Peak instantaneous bus current can be up to 25 A per drive. Size the positive Bus
wiring to minimize the peak voltage drop. As a general guide, use no smaller than 16 AWG wire
to span 10 feet from the drive to the shared energy leveling capacitor.
The AC and DC bus currents also flow in the Control or Bus terminal. Size the ground wire to
the drive to be no smaller than the positive Bus wire. A larger wire size yields a cleaner ground.
If a separate control supply is used, connect the control supply ground and main bus supply
ground together at or near the drives not at the supplies.
11. Bus wire inductance and bus resonance