Xantrex Technology SW Series - Manual (Page 105)

OPERATION
 2001 Xantrex Technology, Inc.
5916 - 195th Street N. E.
Arlington, WA 98223
Telephone: 360/435-8826
Fax: 360/435-2229
www.traceengineering.com
SW Series Inverter/Charger
Part No. 2031-5
Rev. C: February 2001
Page
97
BATTERY CHARGING WITH MULTIPLE INVERTERS
The inverters can operate in parallel as battery chargers from the same AC source connected to the same
battery. The AC input terminals and DC terminals would all be in parallel. The inverters will synchronize
individually to the AC source and then connect.
When multiple inverters are connected to the same battery and operated as in battery charger mode, the
settings of the inverters are best set to the same settings. Only when a system is being operated in
automatic generator control mode should staggered settings be used.
The most significant problem with multiple inverters charging the same battery is the voltage ripple caused
on the battery. This causes the chargers to not reach their full output - two battery chargers on the same
battery may not provide twice the charging rate to fill the battery in half the time. The higher the charger
rate and/or the smaller the battery, the more pronounced this problem would be. The only way to reduce
the problem is to individually cable each inverter and to connect them at opposite “corners” of the battery
bank. Keeping the cable size as short as possible also helps.
Since the inverters will all be charging the same battery, one inverter may taper off first and finish the bulk
stage before the others. When a single inverter has reached the float stage, it is best to turn off the
generator at this time. It may take a longer period of time for the remaining inverters to reach the float
stage. Running the generator to only power an inverter that is float charging is very inefficient and should
be avoided.
If multiple Battery Temperature Sensors are installed, ensure they are all connected to the same location
(battery). This will also help prevent one inverter from tapering off first.
AUTOMATIC GENERATOR CONTROL WITH MULTIPLE INVERTERS
Several considerations must be taken into account when using the automatic generator controlling system
with multiple inverters. The inverter that controls the generator – referred to as the “generator controlling”
inverter - along with the other inverter which does not control the generator - referred as the “non-
generator controlling” inverter - must be programmed differently to achieve the best results. The two
inverters should be programmed with the same BULK VOLTS DC and FLOAT VOLTS DC settings, but
with the ABSORPTION TIME on the “non-generator controlling” inverter to a longer setting. This will
ensure that the charge current is shared between the two inverters more equally during the absorption
stage by preventing one of the inverters from switching to float before the other. When the inverter that
controls the generator reaches float, it will shut down the generator.
The same consideration should be made if you are trying to equalize the batteries. The two
inverter/chargers should be programmed with the same EQUALIZE VOLTS DC settings, but with the
EQUALIZE TIME on the “non-generator controlling” inverter to a longer setting. When you are ready to
start the equalization process (either manually or automatically) you must select EQ from the SET
GENERATOR menu item on both inverters (accessible by pressing the green GEN MENU button on the
Control Panel). This will allow both units to help bring the voltage to the EQ voltage level. During the
equalization process, the BULK LED will flash slowly on each inverter to indicate that the EQ position has
been selected from the SET GENERATOR menu item.
If you manually equalized your batteries – by using a manually started generator or utility power - the
FLOAT LED will come on to indicate that the equalization process has finished. You must return the
cursor to the OFF position in the SET GENERATOR menu item on both inverter/chargers once the
equalization period has been completed.
If the automatic generator control system is used to equalize your batteries, the equalization process will
begin during the next - automatically started - generator run period. When the equalization period has
been completed, the generator will automatically stop and the cursor under the SET GENERATOR menu
item will return to the AUTO position on the “generator controlling” inverter. At this time, you must
manually return the cursor in the SET GENERATOR menu item on the “non-generator controlling” inverter
from EQ back to OFF or you will allow this inverter to charge up to the EQ voltage the next time the
generator comes on.