WCL488 Series Water Cooled Electronic Loads
Operation & Programming Manual
TDI-Dynaload Division
Page 32
402828, Rev. B1
EXAMPLE:
If the previous example required 15 feet of total cable length or 6.25 microhenries, which
would be 12.5V of inductive drop, then the capacitor would have to supply 5.5V @ 100A
for 50 microseconds. The capacitance of this capacitor is computed using Equation 2
below:
Equation 2. Formula to Establish Capacitor Requirements
Effects Of Cable Length
Current Oscillation
The Dynaload regulation loop is designed to operate at a maximum response time of 10
µ
S. This
is not affected by manipulating the slew rate. When operating in any of the constant DC modes,
the external cable length can effect the performance of the load. If the total inductance of the
power cables is excessive, a parasitic oscillation could occur. It is always recommended to
monitor the current sample output to verify that the load is operating without current oscillation.
If this situation occurs, refer to the
Effects of Cable Inductance On Pulse Loading
section earlier
in this chapter.
Line Loss
If the Dynaload is not configured for remote voltage sensing, the voltage display and voltage
readback will reflect what may appear to be an erroneous number. The voltage display will
indicate the voltage present at the input terminals. This number will be affected by the current
level. Wire is a resistor, and will lose voltage as the current is increased. A general rule of thumb
is to size your wire at 500 circular mils per amp of load current. This will allow a maximum of 10
degrees centigrade rise in temperature of the wire. The resistance of wire is approximately 107
ohms per 1000 feet for 100 circular mils of cross-sectional area. Use Ohm’s law (E = I x R) to
calculate the line losses for your particular application. For detailed information about the
maximum current capacity of conductors refer to Table H.
402825-02-13.C D R
=
W here:
is current in Am ps (A)
is tim e in m icroseconds ( s)
is Voltage in Volts (V)
is capacitance in m icrofarads (
µ
µ
F)
C = = 910 F
µ
100A x 50 s
5.5V
µ
Substituting the values from the exam ple into this equation results in: