OPERATION
Copyright
Trace Engineering Company, 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. B: Sept 1, 1999
Page
95
USING MULTIPLE INVERTERS
Multiple SW Series Inverter/Chargers can be used in the same system. There are some limitations to the
design of the system for successful and reliable operation. For North American applications, the inverters
can be used in a “series” configuration to operate 240 VAC loads and to connect to 120/240 VAC power
systems. Series stacking of “E” versions (230 VAC / 50 Hz) would result in 230/460 VAC power.
Two inverters can also be connected together and operated in parallel to provide twice the power at the
same output AC voltage. 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 then be all in
parallel. The inverters will synchronize individually to the AC source and then connect.
“SERIES” STACKED OPERATION
As mentioned, in North America two inverters can be connected in a “series” stacked configuration to
provide 120 and 240 VAC output.
When series stacked, you get twice the power of a single inverter available for operating 240 VAC loads,
but only one inverter’s power is available for operating a single large 120 VAC load. Separate 120 VAC
loads can be operated from either inverter. Do not connect the AC output terminals of the inverters in
parallel - this will not work. A special stacking interface cable (SWI) is required to connect the series
stacking ports of the inverter to ensure the output voltage waveforms of the two inverters are phase
synchronized and locked 180 degrees from each other. This allows connection to 120/240 VAC
generators and utility grids. The 120 VAC loads are split and connected to either inverter. Both of the
inverters operate completely independently - except their frequency is locked. They do not operate as a
master-slave device as previous inverters have. One inverter can be in battery charger mode while the
other is inverting to power an AC load. This independent operation allows many new possible applications
and abilities that were previously not possible.
When inverters are series stacked, they do coordinate all operations that affect 240 VAC loads. This
requires that the inverters turn on together and switch to another AC source at the same time. If either
inverter shuts down, both inverters are inoperable.
If no 240 VAC loads are required to be operated, then the need and benefits of stacking are reduced.
Stacking adds complexity and will cause both of the inverters to shut down if either inverter goes into an
error condition. With separate (un-stacked) inverters, only one will shut down if over-loaded, etc.
When two inverters are connected to a 120/240 VAC distribution system without using the stacking
interface cable, the AC neutral wiring must be capable of handling twice the inverter output. This is due to
the lack of synchronization between the inverters. If both inverters are operating in exact synchronization
(as opposed to operating 180 degrees out of synch.), then the AC neutral will carry the current of both
inverters, which was split among the two AC hot conductors. This often is not a problem since the AC
distribution system may be oversized to handle the higher output level of a generator. When an AC source
is connected to the inverters, the inverters will synchronize independently and transfer at different times.
This is not a problem if no 240 VAC loads are connected to the output of the system.
Caution: You must connect the two chassis of the inverters together and to the grounding system by their
grounding lugs or a hazardous voltage may be present on the chassis of the inverters.
INPUT/OUTPUT BYPASS BREAKER SWITCH – 240 VAC LOADS
An inverter “bypass-breaker switch” diverts power around an inverter and is meant to be used only during
times of maintenance or to remove the inverter out of the installation. There is a possibility with a multiple
inverter installation stacked in “series” (120/240 VAC) with two bypass switches installed, that one inverter
bypass breaker switch could be in the Bypass Operation position (power diverted around the inverter’s)
and the other inverter bypass breaker switch could be in the Normal Operation position (power passing
thru the inverter). The resulting output of the two bypass switches may be less than 240 VAC, which could
cause problems with any 240 VAC loads that are not protected against an AC phase shift.
Summary of Contents for SW II - REV 4.01
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