Kohler Decision-Maker MPAC V2 (Kohler)

The Kohler MPAC driver monitors and controls a Kohler Decision-Maker MPAC V2 automatic transfer switch (ATS) controller — MPAC 1200 V2 or MPAC 1500 V2 — over Modbus/TCP. It polls the controller's system overview, source metering, setup, I/O, active events, and run-history registers and publishes them as device attributes with history enabled for graphing. It also exposes a small set of control commands: force-transfer-to-off, resume, loaded/unloaded test, preferred-source selection, transition-mode change, and service disconnect.

This is a single controller device — all values surface as device attributes, so you do not have to create zones for it. Register addressing follows Kohler TP-6113 §15 (the Decision-Maker MPAC V2 Modbus map), using Kohler's extended convention where register 400001 is holding register 0.

Status

Built against Kohler TP-6113 Section 15. Tested against the MPAC 1200/1500 V2 register map. Serial Modbus/RTU is supported by the underlying Modbus transport but most MPAC V2 controllers are commissioned over Ethernet (Modbus/TCP), which this page assumes.

Prerequisites

• An MPAC V2 controller (1200 or 1500) reachable on the LAN with its Modbus/TCP option enabled in the controller menus.
• The controller's Modbus TCP Unit ID — Kohler's default is 2 (not 1).
• Outbound TCP/502 from the GEM controller to the MPAC IP address.
• Know whether your unit is in legacy or non-legacy device-ID mode if you intend to confirm the model from the device_id attribute (see Identifying the model).

Live electrical infrastructure

An ATS switches a building between utility and generator power. The force transfer, test, service disconnect, and preferred source commands change how that switch behaves and can drop or transfer load. Only issue them when you understand the on-site consequences, and confirm the controller's front-panel switch is in Auto — many MPAC configurations reject Modbus writes while the front panel is in Manual or Off.

Setup

1. Enable Modbus/TCP on the MPAC controller and note its IP address and Unit ID (default 2).
2. Create the device — open Devices (System → Devices → Add Device), give it a name, and pick the Kohler Decision-Maker MPAC V2 driver. The form's View integration guide button opens this page inline.
3. Fill in the connection fields in the Device Attributes section:
   • Unit ID — match the controller (default 2).
   • Controller IP — the MPAC's LAN address (under Show optional attributes, in the Connection group).
   • TCP Port — 502 (default).
4. (Optional) Choose the register groups to poll — the Monitored Register Groups field controls how much is read each cycle (see Register groups below). Leave it at the default to poll live metering, setup, status, and history.
5. Pick a subsystem for the device. Of the driver's suggested subsystems (Power, Generator, Building Automation), only Power ships by default — create Generator or Building Automation under Subsystems first if you want a dedicated one.
6. Save (the button reads Create Device) and watch the device's attributes populate after the first poll completes.

tip

Use the Load sample: MPAC 1500 V2 on the LAN button on the Device Attributes header to pre-fill a typical configuration (ip, port 502, unit_id 2, a trimmed register-group list), then adjust the IP.

Device attributes

These are the configuration fields you set on the device. Everything else on this page is read from the controller automatically.

Attribute	Required	Type	Default	Notes
unit_id	yes	int	2	Modbus slave address. Kohler default is 2. Range 1–247.
ip	no	string	—	LAN IP of the MPAC controller (for Modbus/TCP).
port	no	int	502	Modbus/TCP port.
comm_port	no	string	—	Serial device path for Modbus/RTU wiring (e.g. /dev/ttyUSB0). See Serial wiring.
baud_rate	no	int	9600	Modbus/RTU baud rate.
timeout	no	int	10000	Modbus request timeout in ms.
polling_rate	no	int	30000	How often (ms) the selected register groups are swept.
reconnect_timeout	no	int	3000	Delay (ms) between reconnect attempts after a transport error.
monitor_registers	no	string	monitoring,setup,status,history	Comma-separated list of register groups to poll. See below.

Register groups

monitor_registers decides which blocks of the register map are read each cycle. The field renders as a dropdown offering each single group plus all; the default polls four groups at once. To poll a custom combination of several groups, set the monitor_registers value to a comma-separated list in the device's Attributes editor (e.g. monitoring,status,history).

Group	What it reads	In the default?
monitoring	System overview, source A/B voltages, line voltages, frequencies, currents, closed-transition phase delta.	yes
setup	Nominal voltages/frequencies, phase counts, rated amperage, transition/operation mode, preferred-source selection, service-disconnect type.	yes
status	Active time delay, MLB input/output state and hardware-output bits, accessory status, and active events.	yes
history	Last outage, switch-transfer counts, failures-to-transfer, loss-of-preferred counts, transfer times, run/standby minutes.	yes
ats	ATS designation, load/branch descriptions, location, serial number (text fields).	no
network	MPAC + FPGA firmware, controller IP, configured unit ID, present date/time, model device_id.	no
all	Everything above.	—

note

ats and network are not in the default set, so the controller's nameplate strings, firmware versions, and device_id only appear if you add those groups (or choose all). They change rarely, so polling them every cycle is wasteful — add them once to confirm, then drop back to the runtime groups.

Values are deduplicated: an attribute is only written when its value actually changes, and every published attribute has history enabled so you can graph it under History.

Telemetry attributes (auto-populated)

Read live from the controller by the poll loop. Bitmap registers are decoded into individual named attributes — e.g. the System Overview register becomes system_overview_contactor_position, system_overview_preferred_source, and so on. Enumerated values resolve to the exact strings below; use them verbatim when writing triggers or macro conditions on plant state.

System overview & events (monitoring + status)

Attribute	Values / unit
system_overview_contactor_position	off · source1 · source2 · source1_source2
system_overview_preferred_source	source1 · source2
system_overview_preferred_source_available	true · false
system_overview_standby_source_available	true · false
active_events	Comma-separated list of active event descriptions, or none.
active_event_codes	Comma-separated numeric event codes.
active_event_count	Number of active events.

active_events is a human-readable roll-up of every active alarm/state bit. Common entries include: not in auto, exerciser active, test mode active, peak shave mode active, load control active, source 1 under voltage / source 1 over voltage, source 2 under voltage / source 2 over voltage, loss of phase, fail to transfer, fail to acquire preferred, common alarm active, service disconnect, critical service required. A code with no friendly name shows as event <n>.

Source metering (monitoring)

Attribute	Unit
source_a_voltage_l1 / _l2 / _l3	V (line-to-neutral)
source_b_voltage_l1 / _l2 / _l3	V (line-to-neutral)
source_a_line_voltage_l1_l2 / _l2_l3 / _l3_l1	V (line-to-line)
source_b_line_voltage_l1_l2 / _l2_l3 / _l3_l1	V (line-to-line)
source_a_frequency / source_b_frequency	Hz
current_l1 / current_l2 / current_l3	A
phase_degree_delta	° (closed-transition phase difference)

Source A is typically the utility/normal source and Source B the generator/emergency source, but confirm against the controller's wiring.

Setup & mode (setup)

Attribute	Values / unit
service_disconnect_type	off · emergency · hold_current
nominal_normal_voltage / nominal_emergency_voltage	V
nominal_normal_frequency / nominal_emergency_frequency	Hz
normal_number_of_phases / emergency_number_of_phases	count
rated_amperage	A
preferred_source_selection	source1 · source2
transition_operation_modes_transition_mode	open · programmed · closed
transition_operation_modes_operation_mode	genset · genset_to_utility · utility_to_genset_genset · utility_to_utility
transition_operation_modes_transfer_switch_position	auto · manual

transition_operation_modes_transfer_switch_position is the one to watch before sending control commands: manual means the front panel is in control and Modbus writes will likely be rejected.

Status & I/O (status)

Attribute	Notes
time_delay_number	Which active time-delay timer is running.
time_delay_remaining / time_delay_preset	Seconds.
mlb_input_state / mlb_output_state	Raw MLB I/O state words.
mlb_hardware_output_engine_start_control	Engine start contact.
mlb_hardware_output_relay_k1 … _relay_k4	Programmable relay outputs K1–K4.
mlb_hardware_output_source_1_available / _source_2_available	Source-available contacts.
mlb_hardware_output_contactor_source_1 / _contactor_source_2	Contactor position contacts.
mlb_hardware_output_not_in_auto / _warning	Not-in-auto and warning flags.
accessory_status_exercise_in_progress	Exerciser running.
accessory_status_loaded_test_occurring / _unloaded_test_occurring	Test state.
accessory_status_peak_shave_in_progress / _load_control_in_progress	Demand-management state.
accessory_status_user_forcing_to_off	A force-transfer-to-off is active.

Run history (history)

Attribute	Unit
last_outage_time / last_outage_date	clock / calendar
last_outage_duration	min
switch_transfers_total / switch_transfers_reset	count
failures_to_transfer_total / failures_to_transfer_reset	count
loss_of_preferred_total / loss_of_preferred_reset	count
transfer_time_src1_to_src2 / transfer_time_src2_to_src1	ms
minutes_operation_total / minutes_standby_total / minutes_not_preferred_total	min

The _total counters are lifetime; the _reset counters are since the last controller reset.

Nameplate & network (ats + network)

Only polled when you add the ats and/or network groups.

Attribute	Notes
ats_designation / ats_load_description / ats_branch_description / ats_location	Free-text labels configured on the controller.
ats_serial_number	ATS serial number.
mpac_firmware_version / fpga_firmware_version	Firmware (major.minor).
ip_address / modbus_tcp_unit_id	As reported by the controller.
present_date / present_time	Controller clock.
device_id	Resolved model name — see below.

Identifying the model

When the network group is polled, device_id resolves the controller's model code to a label:

Code	Model
78	MPAC 1500 V2
77	MPAC 1200 V2
23	MPAC 1500 V2 (legacy addressing)
27	MPAC 1200 V2 (legacy addressing)

A code the driver doesn't recognize is reported as unknown (<n>).

Commands

Issue these from a macro, a trigger, or the device's command surface. The read-only commands are always safe; the rest write to the controller and should be used with the warning above in mind.

Command	Args	What it does
get_status	—	Returns the last cached register values (no controller write).
poll	—	Forces an immediate poll of the selected register groups.
force_transfer_off	—	Forces the transfer switch to the off position.
resume_operation	—	Clears a force-transfer and resumes normal operation.
start_test	loaded	Starts a generator test. loaded = true for a loaded test, false for an unloaded test.
stop_test	—	Ends an in-progress remote test.
set_preferred_source	value	Sets the preferred source. 0 = source 2, 1 = source 1.
set_transition_mode	value	Sets the transition mode. 0 = open, 1 = programmed, 2 = closed.
service_disconnect	value	Sets the service-disconnect type. 0 = off, 1 = emergency, 2 = hold current.

note

start_test takes its argument as a string — pass loaded as true or false. Out-of-range values on set_preferred_source / set_transition_mode / service_disconnect are rejected with an error rather than written, so a mistyped value can't put the controller in an undefined state.

Serial (Modbus/RTU)

If the MPAC is wired to GEM over RS-485 instead of Ethernet, the underlying Modbus transport opens a serial device at the configured baud rate. Set the Baud Rate to match the controller and wire A/B per the controller's terminal markings. For serial commissioning detail — adapters, wiring, and the unit-ID scanner — see the Modbus integration page. Ethernet (Modbus/TCP) is the recommended and most common path for MPAC V2.

Troubleshooting

Symptom	Check
No attributes populate	Wrong Unit ID (Kohler default is 2, not 1), Modbus/TCP not enabled on the controller, or TCP/502 blocked. Confirm the IP and that Modbus is on in the controller menus.
connection refused / timeouts on 502	Modbus/TCP option is disabled, or another Modbus master already owns the connection. The MPAC serves one master.
Control commands have no effect	The front panel is in Manual or Off — check transition_operation_modes_transfer_switch_position; it must read auto. Many configurations reject Modbus writes otherwise.
Nameplate / firmware / IP attributes are missing	The ats and network groups aren't in the default poll set. Add them to Monitored Register Groups (or choose all) for one cycle to capture them.
Values feel slow to update	Lower Poll Interval (ms) from the 30000 default — but keep it reasonable; the driver only writes attributes that actually changed, so frequent polling is cheap but still loads the bus.
device_id reads unknown (<n>)	Your controller reports a model code outside the known set; the rest of the register map still reads correctly.

Related Documentation

• Modbus — generic Modbus transport, unit-ID scanner, and register browser this driver builds on
• Devices — adding and managing devices (the MPAC is a single device with telemetry as device attributes; it creates no zones)
• Subsystems — where to place the controller (Power by default)
• Attributes — viewing and editing the device's attributes, including monitor_registers
• History — graphing the controller's metered and history attributes over time
• Triggers — react to active events, source loss, or transfer state changes
• Power Management — the energy dashboard where power devices surface