Xantrex Technology 120 VAC/60 Parallel Stacked Operation, 240 VAC/60 HZ only Electrical Systems

OPERATION

240 VAC/60 HZ ONLY ELECTRICAL SYSTEMS

Two 120 VAC / 60 HZ inverters “series” stacked can be used to provide 240 VAC. This provides both 120 and 240 VAC since a center “neutral” is provided between the two inverters. If a 240 VAC only AC source is connected to the AC input terminals of the inverter without this center neutral, unacceptable operation will result. To allow connection of a 240 VAC only source to 120 VAC inverter’s, a small (2000 VA) auto- transformer must be connected across the 240 VAC source with the center of the transformer connected to the AC neutral terminals of the inverters. This will allow the inverter to operate properly. No transformer is required on the AC output side - the 240 VAC can be taken directly from the two AC hot output terminals (one from each inverter).

“PARALLEL” STACKED OPERATION

The parallel stacking interface allows twice the continuous and surge capacity to be available on a single output circuit from two inverters. The pass-through capacity is also doubled when connected to an AC source such as a fuel-powered generator or a utility grid. The inverter’s operate in parallel and split the loads between them. The inverters must be identical models and must have software revision REV 4.01 or higher software. The inverters must be connected to the same battery bank with equivalent cabling (both in length and in cable size). The inverter negative terminals of the inverters must be connected together either at the inverters or at a location close to the inverters (within 18 inches / 0.5 meters).

The parallel stacking interface cable (SWI/PAR) simply plugs into the stacking port on the left end of each inverter and allows the two inverters to operate as a single inverter. The interface method is based on the series stacking system offered for the SW Series inverters since their introduction for the North American market. The parallel stacking system operates the inverters in phase by having one of the inverters operate as the MASTER and the other as a SLAVE. When an AC source is connected, the MASTER first synchronizes to the AC source, then connects to it and battery charges. Since the SLAVE follows the master and is set-up with a longer warm-up delay, the SLAVE inverter is already synchronized when it transfers the loads and starts battery charging. This allows very smooth transitions from inverter mode to charger mode.

The parallel stacking interface system allows doubling of the AC pass through capacity. This is useful when large generators are used. Both inverters will battery charge as allowed by the settings in each of the inverters.

The hook-up depends upon the other components included in the system and whether it was ordered as only inverters, a power panel system, or a power module system. With the power module system, the paralleling enclosure is eliminated and all of the wiring is completed for you. With the individual inverters and the power panel system, the paralleling enclosure and parallel stacking interface cable must be installed on site. The paralleling enclosure is connected to each of the inverter’s outputs and is also connected to the AC loads being powered.

At this time, the paralleled inverters are intended to operate as a single unit. In case of an inverter fault or error condition, both inverters turn off as one. When the error has been corrected, the inverter will automatically or manually reset depending upon the type of error condition.

If an inverter failure occurs, the parallel stacking interface can be manually bypassed and the special parallel stacking interface cable can be removed to allow temporary operation on one unit.

GENERATOR CONTROL SETTINGS

When using two units in parallel, it is recommended that only the SLAVE inverter be used to control the generator. This is required because the generator control system includes a cool down timer that causes the controlling inverter to disconnect from the generator before it turns the generator off. If the MASTER controls the generator, then the SLAVE may not stay in sync with the MASTER during the cool-down period since it will remain in sync with the generator and not follow the MASTER. There currently is no adjustment for the cool-down period, so restricting the generator control to the SLAVE is the only solution available at this time.

The SLAVE also must be set with a longer warm-up period than the MASTER in order to prevent them from trying to synchronize to the generator at the same time. When the MASTER synchronizes first, the SLAVE will automatically sync after its warm-up period passes. This also makes the transfer from inverter to generator smoother and less noticeable.

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 2001 Xantrex Technology, Inc.	Telephone: 360/435-8826	SW Series Inverter/Charger
5916 - 195th Street N. E.	Fax: 360/435-2229	Part No. 2031-5
Arlington, WA 98223	www.traceengineering.com	Rev. C: February 2001