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Page 45

Using AC Coupling

5.0 Using the MS-PAE Series in an AC Coupled Application

This section covers the use of MS-PAE Series inverter/chargers in an AC coupled system.

5.1 What is an AC Coupled System

Many homeowners utilize renewable energy (e.g., PV, wind, etc.) by installing high efﬁ ciency,

battery-less, grid-tie inverter systems to offset their power consumption from the utility grid.

However, during a utility power outage, the grid-tie inverter is required to shut down. This can

cause considerable frustration as the homeowner realizes that the critical loads in the home (e.g.,

refrigerator, lights, water pump, etc.) are no longer powered, and all the energy produced by the

renewable energy source is being wasted while the utility power is out.

In an AC coupled system, all the energy sources and loads are connected directly to the AC side.

Installing a bi-directional battery-based inverter (i.e., MS-PAE Series) allows the existing battery-

less, grid-tie inverter to operate, and therefore to continue to utilize the renewable energy to

power the home’s critical loads during the power outage—all from the AC side.

However, in an AC coupled system—during a utility power interruption—the main panel loads are no

longer connected and the utility grid is not available to export any excess power that is generated.

This means there may be more power on the AC side than the critical loads can consume, causing

current to be pushed back through the output of the inverter into the battery bank. Since this is

not the normal path for the inverter to sense incoming current, it is unable to control the battery

voltage or regulate the current, providing the possibility that the battery voltage will rise and

damage your batteries. The MS-PAE Series inverter (≥Rev. 4.1) has a feature (“frequency shift”)

that can be enabled with an optional remote control (ME-RTR, ME-ARC, or ME-RC) and allows

the AC output frequency to shift when the battery voltage rises to a high level (see Section 5.2).

However, this protection feature does not ensure effective battery charging and should only be

used as a backup to a primary battery management system

5.2 Conﬁ guring a Remote to use the MS-PAE in an AC Coupled

System

An optional remote control display (RTR, ARC, or RC) must be conﬁ gured in order for the MS-PAE

inverter to work optimally in an AC coupled system—as described below:

1. Enable Frequency Shift: Adjust the SETUP button’s Battery Type menu setting to “Custom”.

This feature monitors the inverter’s battery voltage and causes the MS-PAE inverter’s output

frequency to increase—causing the grid-tie inverter to cease producing power to avoid

overcharging the system’s batteries. This feature activates (i.e., raises the MS-PAE’s ouput

frequency from 60.0 Hz to 60.6 Hz) when the battery voltage rises 2 volts (24-volt units) or 4

volts (48-volt units) above the Absorb Voltage setting. The MS-PAE inverter’s output frequency

returns to 60.0 Hz when the battery voltage falls 2 volts (24-volt units) or 4 volts (48-volt

units) below the Absorb Voltage setting—allowing the grid-tie inverter to reconnect. Again,

because the frequency shift feature activates at a high voltage level, it should only be used as

a secondary (i.e., back-up) method to regulate the battery voltage.

2. Turn off Search mode: Adjust the SETUP button’s Search Watts menu setting to “OFF”.

3. Turn off Parallel Threshold (ME-RTR only): Adjust the SETUP button’s Inverter Threshold to

Start Parallel menu setting to “OFF”.

4. Ensure the MS-PAE is set to automatically accept grid power when available (ARC & RTR only):

Adjust the CTRL button’s AC In Control menu setting to “Auto Connect”.

Note

: The battery bank voltage can be managed by installing a diversion controller and a load

capable of absorbing the majority of the expected surplus energy. Options include: 1) a DC diversion

controller and DC resistance loads; 2) AC diversion using AC resistance loads driven by DC controlled

relays; or 3) Sensata’s AC Load Diversion controller (ACLD-40). Now in development, Sensata’s AC

Load Diversion controller will enable customers to maximize the use of onsite generated renewable

power and to provide multiple-stage battery charging with temperature compensation using AC

loads. For more information on the release of the ACLD-40, continue to monitor our website at