Cell board test fixture

Description and construction of a test fixture for cell boards for a Lithiumate™ BMS

• The board tests itself, with the help of a very simple test fixture
• The code for it is programmed in every board and runs once every time it is powered-up,
• In normal operation, in actual use:
  • The test fails right away, and therefore the LED blinks 2 times (repeated 3 times)
  • Then it runs the regular code
• In a test fixture:
  • The test proceeds, and the LED blinks once (if it passes) or n times (repeated 3 times) if it fails

If you don't want to build your own, you can buy it from us.

The test fixture consists of:

• A power supply
• A test fixture electronics board
• A test fixture head that mates to the Device Under Test (DUT) with test pins
• The fixture head mates to the B+, C+, C- and B- pads in the DUT

• The test fixture does the following:
  • The fixture powers the DUT with a fixed 3.0 V voltage through its B+ and B- pads
  • There is a resistor on that line, so that, if the DUT load resistor is on, the voltage drops below 3.0 V
  • The fixture routes the current out of the C- pad back into the C+ pad
  • At initial power-up, the test fixture applies a short pulse of current to the C- input, to get things started
• The fixture includes:
  • A push-button switch to run the test
  • Additional parts to test the positive and negative end boards

Qty	P/N							Value	Attribute	Component	Label	Manuf	Manuf P/N	Vendor	Vendor P/N
1	100EP901B	Test fixture, cell board, core	Rev B	PCB	PCB1
1	ECE2229RD	2200µ	6.3V, 105C, 10 x 20 x 5sp	Capacitor, elec	C3	United Chemi-Con	ESMG6R3ELL222MJ20S	Digikey	565-1006-ND
2	ECM2245XC	220n	50V X7R MONO 0.1" spcng	Capacitor, mono	C1-2	Kemet	C320C224K5R5TA	Digikey	399-4288-ND
1	EKP6405TG	5 x C-Grid SL	Male PCB hdr straight gold	Connector, PCB	P1	Molex	70543-0004	Digikey	WM4803-ND
1	EKX0069RC	2.5 ID 5.5 mm OD	Power barrel, RA	Conn., Coax	P2	CUI	PJ-037B	Digikey	CP-037B-ND
1	EOI2501BN	PS2501-1-L-A	200%~400% DIP4	Opto-isolator	OC1	NEC / CEL	PS2501-1-L-A	Digikey	PS2501-1-L-A-ND
1	EOL5090ET	RED	T1-3/4 10 mm tall clear 30°	LED	H1	Lite-On	LTL-2R3VEKNT	Digikey	160-1499-ND
2	ERE0103JB	10K	5% 1/4W	Resistor	R6-7	Yageo	CFR-25JB-10K	Digikey	10KQBK-ND
1	ERE0229JB	2.2	5% 1/4W	Resistor	R5	Yageo	CFR-25JB-2R2	Digikey	2.2QBK-ND
4	ERE1000FB	100.0	1% 1/4W	Resistor	R1-4	Yageo	MFR-25FBF-100R	Digikey	100XBK-ND
1	ERT5002KP	50	1 turn 1/4" cermet top adj	Trimmer	RV1	Copal	CT6EW500	Digikey	CT6EW500-ND
1	ESK1122SB	N.O.	Keyswitch square black	Switch, pushbutton	SW1	C&K	KS11R22CBD	Digikey	CKN4079-ND
1	ESS4232TG	DP3T sequential	straight 3.2 mm pitch	Switch, slide	SW2	C&K	OS203013MT8QN1	Digikey	CKN9550-ND
1	EXA0337ST	LM337	ADJ NEG REGUL TO220	IC, analog	U1	Fairchild	LM337T	Digikey	LM337TFS-ND
1	EXT3904BZ	2N3904	40V, .2A, .6W, NPN TO92	XSTR	Q1	Fairchild	2N3904BU	Digikey	2N3904FS-ND

• The wall-mounted power supply generates 5 Vdc, unregulated
• The internal regulator generates exactly 3.0 V (adjustable with a trimmer)
• The supply feeds a large capacitor through a resistor, so that its unloaded voltage is 3.0 V, but when loaded with 18 ohms (on the Cell Board), it drops to 2.67 V
• A push-button switch applies that voltage to the Cell Board; an LED lights up to indicate that there's power
• The fixture routes the Cell Board's output current back to the input, in ways that depend on the type of Cell Board:
  • Mid-bank Cell Boards:
    • The slide switch is flipped to the "Mid" position, enabling the normal current path through the opto-isolator on the test fixture
    • The test fixture head 'C+' and 'C-' test pins are both used
    • The current from the 'C-' pad is routed through a slide switch, an opto-isolator (with a gain > 100 %) to the 'C+' pad
  • Positive end Cell Boards:
    • The slide switch is flipped to the "End" position, disabling the normal current path through the opto-isolator on the test fixture
    • The test fixture head 'C-' test pin is used, but the 'C+' is not
    • The Cell Board already includes an opto-isolator on the input, across the 2-pin TX connector (or pads)
    • A pigtail from the test fixture is plugged into the TX connector (or pads)
    • The Cell Board's output current is routed from the 'C-' pad, through the slide switch, amplified by a transistor, routed through the pigtail, to the RX connector (or pads), to that opto-isolator input
  • Negative end Cell Boards:
    • The slide switch is flipped to the "End" position, disabling the normal current path through the opto-isolator on the test fixture
    • The test fixture head 'C+' test pin is used, but the 'C-' is not
    • The Cell Board already includes an opto-isolator on the output, across the 2-pin RX connector (or pads)
    • A pigtail from the test fixture is plugged into the RX connector (or pads)
    • The pigtail picks-up the opto-isolator output on the Cell Board, and feeds it directly back to the 'C+' pad of the Cell board
• In all 3 cases, the gain is greater than 100%, so that the current is latched on

The power supply is an unregulated wall-mounted, 5 V supply.

BOM:

Qty	PN	Value	Attributes	Label
1	5 Vdc, 250 mA	Wall wart	MOD1

The test fixture head is built using 2 blank Cell Board PCBs, separated by 0.315 inch standoffs.
The four pads ('B+', 'C+', 'C-' and 'B-') are drilled to fit spring loaded test pins.
The test pins' sockets are soldered in place.
A 4-wire pig tail is connected to all four test pins, and has a 4-pin connector at the other end for the test fixture board

BOM:

Qty	PN	Value	Attributes	Label
2	Cell Board	PCBs	PCB1-2
4	PIN	PIN	TERM	T1-4
1	4 x C-GRID SL	FEMALE	CON	J1
1	24 AWG black	wire	W1
1	24 AWG red	wire	W2
1	24 AWG orange	wire	W3
1	24 AWG gray	wire	W4
4	4-40 x 3/8"	M-F standoffs	ST1-4
2	4-40 x 1/2"	set screw
2	4-40 x 3/8"	F-F Nylon standoffs ST5-6

A generic test head can be used with all cell boards, even ones complete with wires, ahich cannot be tested in a regular test fixture head.

Connections:

• Positive cell board
  • 2-pin connector: communication connector
  • Red wire: B+ terminal or pad
  • Orange wire: C+ wire or pad
  • Gray wire: C- wire or pad
  • Black wire: B- terminal or pad
• Mid bank cell board
  • Red wire: B+ terminal or pad
  • Orange wire: C+ wire or pad
  • Gray wire: C- wire or pad
  • Black wire: B- terminal or pad
• Negative cell board
  • 2-pin connector: communication connector
  • Red wire: B+ terminal or pad
  • Orange wire: C+ wire or pad
  • Black wire: B- terminal or pad

The test head for a large cylindrical cell board (which has 2 cell board circuits on one assembly) contains test probes for both circuits.

The test fixture board is built on a piece of perf-board.

BOM:

Qty	PN	Value	Attributes	Label
1	perf-board	PCB	PCB1
1	1.0uF	50V X7R MONO	CAP	C1
1	1000uF	5V ELEC	CAP	C2
1	100n	50V X7R MONO 0805	CAP	C3
2	2 x C-GRID SL	FEMALE	CON	J2-3
1	LM337	ADJ NEG REGUL TO220	IC	U1
1	4 x C-GRID SL	MALE PCB HDR STR GLD	CON	P1
1	CNC1S101	OPTO-ISOLATOR	OPTO-ISO	OC1
1	RED	TINTED DIFF T1-3/4	LED	H1
2	130	1% 1/4W	RES	R1-2
1	2.2	5% 1/10W 0805	RES	R5
2	100	5% 1/10W 0805	RES	R3-4
1	20	1 TURN	RTRIM	RV1
1	SPDT	SLIDE STRAIGHT 0.1 inch	SW	SW2
1	N.O.	PUSHBUTTON	SW	SW1
1	MMBT3904	40V,  .2A, .6W, NPN	XSTR	Q3

The cell board performs the following tests, in order:

During the bus test, the following occurs:

• When the test fixture push-button is first pressed, the fixture puts a short pulse of current into the 'C+' pad
• The current goes through the DUT and out of the 'C-' pad, and back into the test fixture
• The test fixture amplifies that current, and feeds it back to the 'C+' pad, therefore completing a loop, and the current continues uninterrupted
• After 1.6 ms, the test program in the DUT block the current out of the 'C-' pad, and the pulse ends

The voltage at the C- input is a pulse, 3 V high, whose shape and duration depends on whether the cell board is working properly.

Normally:

• Starts with about 250 us of switch bounce
• then 1.6 ms total pulse length, at which point the DUT stops the current out of C- by shorting the base and emitter of Qout
• then a 330 us TC decay tail

Short pulse, if there's no feedback current from C+ to C-:

• Starts with about 250 us of switch bounce
• then a 330 us TC decay tail

Long pulse, if the cell board in unable to stop the current out of C-:

• Starts with about 250 us of switch bounce
• Remains high

The cell board test program does the following:

• Waits 100 us
• If the pulse has already ended, it reports a "Short Pulse" error: 2 blinks
• Forces off the current out of the 'C-' pad
• Waits another 300 us
• If the pulse doesn't end, it reports a "Long Pulse" error: 3 blinks

The Cell Board Program measures and checks the temperature reading.
The reading cannot be checked accurately, because the room temperature is not known.
It does the following:

• It measures the reading of the on-board thermsitor
• If the reading is very low, it reports a "Temperature = 0" error: 4 blinks
• If the reading is low, it reports a "Reads hot" error: 5 blinks
• If the reading is high, it reports a "Reads cold" error: 6 blinks
• If the reading is very high, it reports a "Temperature = FFh" error: 7 blinks

The Cell Board Program measures and checks the voltage reading.
The reading can be checked accurately, because the supply voltage is known: 3.0 V.
It does the following:

• It measures the reading of the on-board voltage sensor
• If the reading is very low, it reports a "Ref reading = 00h" error: 8 blinks
• If the reading is low, it reports a "Ref reading too low" error: 9 blinks
• If the reading is high, it reports a "Ref reading too high" error: 10 blinks
• If the reading is very high, it reports a "Ref reading = FFh" error: 11 blinks

The Cell Board software turn on the balancing load, which will drag the test fixture supply voltage down, because it includes a resistor in series.
It does the following:

• It turns on the load
• If waits 10 ms
• If the supply voltage hasn't dropped, it reports a "No load" error: 12 blinks

If the Cell Board software reaches this point without errors, the Cell Board passes the test: it reports "Pass": 1 blink

The test fixture can be used to test loose cell boards (that are not installed on cells).
Testing must be done at room temperature, or "too cold" or "too hot" failures will result.

• Power up the test fixture
• Connect the cell board to the test head (if multiple sections, connect just one of the sections)
• Slide the switch on the test fixture electronics board for the type of board: Positive end, Mid board or Negative end
• Install a cell board, matching the orientation of the PCB in the test head
• Press the test fixture's push button
• Note the behavior of the LED on the cell board, and use the table below to troubleshoot

The test fixture consists of two sets of electronics connected to a single test head.
Test one half of the cell board at a time.

• Power both test test fixtures
• Connect the cell board to the test head, one for the positive half (red cable), one for the negative half (black cable)
• On the test fixture electronics board to which the red cable goes, slide the switch for the type of board: Positive end or Mid board
• On the test fixture electronics board to which the black cable goes, slide the switch for the type of board: Mid board or Negative end
• For a negative cell board, fill the hole in the 'C-' pad with solder (otherwise the test proble will slip into that hole)
• Install a cell board, matching the orientation of the PCB in the test head
• Press one of the test fixture's push button
• Note the behavior of the LED on the cell board, and use the table below to troubleshoot
• Press the other test fixture's push button
• Note the behavior of the LED on the cell board, and use the table below to troubleshoot

LED	Result	Problem	Cause	Possible components
1 blink	Pass
2 blinks	Fail	Input pulse too short	no feedback from C- to C+	Micro pin 3 shorted, Rbus open, Qout bad/bridged, test fixture C- pin
3 blinks	Fail	Input pulse doesn't end	Unable to ground ouput	C+ shorted to B+, C+ shorted to V test point, 1 KOhm (R6) missing/open/blown, Qout (Q1) blown/bad/bridged. Micro pin 3 open, C- shorted to B-
4 blinks	Fail	Temperature = 0	No Therm reading	Thermistor shorted Rtherm open/missing Micro pin 7 open/bridged to pin 8 Open trace
5 blinks	Fail	Reads hot	Therm reading is low	Too hot in the room Bad thermistor Rtherm value too low
6 blinks	Fail	Reads cold	Therm reading is high	Too cold in the room Bad thermistor Rtherm value too high
7 blinks	Fail	Temperature = FFh	No Thermistor	Thermistor missing/open Rtherm bridged Micro pin 7 open open trace
8 blinks	Fail	Ref reading = 0	No Vref input	Uref bad/bridged, R4 open/missing, open trace
9 blinks	Fail	Ref reading too low	Vref reading is low	Micro pin 5 and 6 bridged, open trace
10 blinks	Fail	Ref reading too high	Vref reading is high	Micro pin 5 open
11 blinks	Fail	Ref reading = FFh	No Vref	Uref (U2) missing/open/bad, open trace
12 blinks	Fail	No load	Load doesn't come on	MOSFET missing/open/bad, Rload open, open trace
Off	Fail	No input pulse	Doesn't see fixture	Not programmed Ferrite missing / unsoldered R-LED missing / unsoldered LED missing / backwards / bad / unsoldered Micro missing / unsoldered MOSFET missing / unsoldered Rin open Cin shorted pin 4 open trace test fixture C+ pin
Always on	Fail	Load on	Load drive always on	MOSFET shorted/bridged