KEPCO EL Series Electronic Load Operator Manual P/N 243-1295 Firmware Version 3.22 through 3.41 - Manual (Page 29)

SERIES EL 062011
2-11
2.6.2.3 GROUNDING
It is recommended that the 1/4-inch bolt with wingnut and flat washers (supplied) at the top left
of the rear panel be connected to earth ground.
The LOAD Bus bars are isolated from the chassis and from the control circuits well into the 100s
of volts. The PGM (Program) input is isolated from the control circuits (and are therefore doubly
isolated from the LOAD Bus) up into the 100s of volts. The I-Load output is independently iso-
lated from the control circuits and therefore is double-isolated from all other external connec-
tions. Lastly, all of the Remote Interface inputs (RS-232, USB 2.0, RS-522) are optically isolated
from the control circuits and are therefore doubly isolated from all other circuits.
2.6.3 PARALLEL MASTER/SLAVE CONFIGURATIONS
Up to 15 Series EL Electronic Loads may be paralleled for additional current and/or power han-
dling capability. All units must have the same voltage rating. One load is designated as the Mas-
ter, and the rest are designated as slaves. Master/slave communications are via proprietary
protocols using special cable(s) connected to the MSTR (Master) and SL-I and SL-O (Slave In
and Out) connectors on the rear panel. (see Table 1-5). Connections are from MSTR to SL-I,
then for subsequent slaves, from SL-O to SL-I. Computer/load communications are via either
the RS 232 or USB connections applied to the master only. Figure 2-9 illustrates connections for
a typical master/slave system.
In a Master-Slave configuration, two or more Loads operate in parallel to increase the total cur-
rent and power capacity.
CAUTION: Loads in Master-Slave configuration are always operated in PARALLEL,
never in series. Each Load in the system must have exactly the same maxi-
mum voltage limit-otherwise the Load internal software will not allow the
Loads to configure as a Master-Slave system. Paralleling two Loads of
unequal voltage rating and applying a voltage greater than the limits of the
Load with the lower voltage rating can result in the destruction of the Load,
the connected source or both.
Typically Loads are stacked vertically to minimize the distance between the ± LOAD terminals. It
is essential to keep this cabling as short as possible due to the high currents flowing during
operation. One of the Loads is designated as the Master and the other as the Slave. Any Load
may be designated as the Master.
Master-Slave configuration is achieved by two interconnections at the Load rear panel (see Fig-
ure 2-9): First connect the ± LOAD terminals of master and all slaves in parallel using sufficiently
heavy cable to carry the maximum current expected to be drawn by any of the individual loads.
Next connect the UUT (Unit Under Test) to the ± LOAD terminals. Use of No. 6 (or larger) Weld-
ing Cable is recommended for flexibility, current carrying capacity and insulation.
For remote operation use the supplied RJ-22 Master-Slave communications bus cables (these
use miniature modular connectors - do not try to use conventional modular telephone cables).
Connect an RJ-22 bus cable from the MASTER (Master Out) which is the upper most RJ-22
Jack, to the SLAVE (Slave In) which is the lower RJ-22 Jack on the slave. For more than one
slave, connect Slave Out to the next Slave in, and so on. No terminations are needed at the final
slave in the daisy chain.