APC7921

APC7921 overview


Ethernet w activity-leds
Serial
2x 7-segment display
1x 3-color LED
Button
factor-reset-switch (hole)

8x female outlets
8x leds
1x male inlet
   
                          FRONT
+---------------------------------------------------+-----+
|  Controller | |                                   |     |
+-------------+ |          Relay board              |     |
| IN     OUT    |J131                          J132 |     |
|               +-----------------------------------+     |
|                     +-----------------------------+     |
|                     |     PSU Board               |     |
|                     |J231             J266        |     |
+---------------------+-----------------------------+------
                        BACK


PSU overview:
PSU -> PSU -> controller wiring

10-wire flat-cable with 2mm pitch 2x5 connectors runs from J266->J231->Controller-IN
See connector J266 and J231

The PSU board has two identical PSU's onboard that provide 24VDC
The right-most PSU also has a set of pins used for connecting current-transformer circuitry to the controller.
The left-most PSU only has 2 pins connected for 24VDC, nothing else.


Controller overview:

The controller provides ethernet and serial connectivity; as well as a 2-digit display and a 3-color status-led to indicate errors and/or amperage. It also has a single button to interact with the device, as well as a pin-hole switch that allows for factory-resets.

Main things to replicate:
- 24VDC 'merging'
- Faulty PSU detection
- Ethernet function
- Serial function (if desired)
- 24VDC->3.3VDC conversion (for relay-board logic)
- I2C bus to control relay-board
- Adress-bus lines (can be hard-wired)


The controller drives the relay-board with a similar 10-conductor flatcable with 2x5pin 2mm headers.
It provides 24VDC and 3.5VDC power to the relay-board with seperate GND's.
It also provides an I2C bus (SDA/SCL) and 3 'address-lines'.
See connector J131

Relay board:
There are 2 main parts to the relay-board. The IO-logic and the relay-logic.

Relay-board IO logic:

The relay-board uses a PCF8574 'Remote 8-Bit I/O Expander for I2C Bus' to provide 8 outputs that drive the relays.
It is powered with 3.5VDC from the controller-board which creates it from the 24VDC available there.
The PCF85674 has 3 address-strapping lines A0,A1,A2 that allow selecting the I2C slave-addresses for both READ or WRITE operations. See table later in the document.
In single-board operation, strapping all pins to L would put the READ address at 0x41 and WRITE at 0x40
The relay-boards can be daisy-chained by connecting a next board to the J231 of the first.
For this to work, however, at least one, and at most two, address-lines will need to be strapped H
The reason for this is the manner in which the A0-A2 lines are presented on the J231 connector. They are shifted one pin, 

Signal    J131         +-------------+                 J132
  A0        7 ---------|---------+   +------  7   
  A1        9 ---------|--+      +----------  9
  A2       10 ---------+  +----------------- 10


The PCF8574 provides 8 outputs that drive the relays using a circuit that first INVERTS the data via a NOR port (one pin strapped to ground, the other connected to the PCF8574) before running to one of the 8 relay-circuits that switch the 220VAC power provided to one of the 8 output terminals.
The 8 NOR ports for this setup are provided by 2x 7402 IC's and seem to function both as a signal-conditioner as well as a way to ensure the power-on state is 'on' for each of the relay circuits (needs to be verified).

Relay-board relay circuit:

Each of the 8 relay-circuits is identical and consists of:
- A small switching-transistor driven from a NOR-gate, switching 24VDC
- A Relay-coil being driven by the switching-transistor
- A flyback diode across the relay in reverse-polarity for circuit-protection
- An ESD-protection diode ( -->|-+->|-- ) that is employed to help drive an LED
                                 |
- An LED
- A series resistor to current-limit

------- Connector pinouts-----------

J266 (right, next to current-transformers) PSU1


+----+
|10 9|
|8  7|
|6  5|
|4  3|
|2  1|
+----+

1	Sense Phase C
2	Center of 3phase
3	Sense Phase A
4	Center of 3phase
5	24VDC PSU1
6	24VDC PSU1
7	Sense Phase B
8	GND PSU 1
9
10



J321 (left, on edge of board) PSU2

+----+
|10 9|
|8  7|
|6  5|
|4  3|
|2  1|
+----+

1
2
3
4
5
6
7
8
9	GND PSU 2
10	24VDC PSU2


Note: GND PSU1 and GND PSU2 are connected together via screws that fasten PCB to chassis.




J131 on relais PCB  INPUT

+----+
|1  2|
|3  4|
|5  6|
|7  8|
|9 10|
+----+


	J131		PCF8574
1	GND IO		8
2	GND relais
3	VCC IO		16
4	SDA IO		15
5	24VDC relais
6	24VDC relais
7	A0 IO		1
8	SCL IO		14
9	A1 IO		2
10	A2 IO		3


J132 on relais PCB , Daisychain OUTPUT

1	GND IO
2	GND Relais
3	VCC IO
4	SDA IO
5	24VDC RELAIS
6	24VDC RELAIS
7	A2 IO
8	SCL IO
9	A0 IO
10	A1 IO


PCF 8574 DW (16 pin)

       +----------+
  A0  -| 1 *   16 | VCC (2.5-6vdc)
  A1  -| 2     15 |- SDA
  A2  -| 3     14 |- SCL
  P0  -| 4     13 |- _INT_
  P1  -| 5     12 |- P7
  P2  -| 6     11 |- P6
  P3  -| 7     10 |- P5
  GND -| 8      9 |- P4
       +----------+