BatteryDummy/contactorProblemInvestigation at master · JimsterCoder/BatteryDummy · GitHub

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1   Problem
When contactors are controlled by the Pi and relay boards the inverter does not work correctly. Symptoms are:
  1/ Inverter refuses to operate battery
  2/ Possibly voltage drops @inverter when inverter tries to draw power from battery on initialisation.
When contactors are operated by direct connection to 12V battery the inverter seems to work bsolutely fine.

2 Hypothesis:
  1/ Insufficient current flow to close contactors correctly, causing contact reistance and voltage drop with current flow.
  2/ Incorrect wiring meaning pre-charge circuit is main circuit.
  3/ Incorrect program with same effect as 2
3 Testing plan:
  1/ Establish that the correct leads are being operated by the pi and that the current flow is adequate.
  Ensure 12V battery is being backed by charger so that there is no effect due to source voltage differences.
  Remove pack breaker so that there is no output voltage
    i/ Measure current on individual contactor leads with direct connection
    ii/ Reapeat with pi control
  2/ Measure voltages on Leaf data connector for each pin
  3/ Measure voltages on GPIO control leads. Both should be high (3.3V?)

4 Results

  1/
    i & ii/ Current in contactor leads
    Measuring Device       Jaycar clampmeter
    Situation              Direct Control   Pi Control
    Lead                      Current       Current
    Overall from 12V            0.95        0.6
    Yellow (+ve contactor)      0.4         0.1
    Blue (-ve contactor)        0.34        0.5
    Green (PreCharge relay)     0.0         0.2
    Overall from 12V (confirm)  0.97        0.6

    Note: clampmeter is not terribly accurate at these low values

  2/
  Measuring Device       Jaycar clampmeter
  Situation              Direct Control   Pi Control
  Lead                      Volt          Volt
  Overall from 12V                        14.24
  Yellow (+ve contactor)                  0
  Blue (-ve contactor)                    14.24
  Green (PreCharge relay)                 14.24
  Overall from 12V (confirm)
  Ensure measurement is to appropriate -ve lead. These are what part of the switching.

  3/
  Relay Lead                  Function        Volts (free)  Volts (connected to relay board)  Relay Operational?
  2     GPIO26 purple/grey    PC/Main switch  3.189         1.258                             No
  1     GPIO13 orange/yellow  On/Off          3.287         1.542                             Yes

  4/
  All control leads swapped between relays. Relay behaviour the same, independent of control wiring*
  And then went weird. Relay 1 comes on without control line connected. LED2 (powered by GPIO26) is on dimly.

5 Conclusion:
  (Up until *: Relay board defective. Replace.)
  After *: More investigation needed.

6 Further work
  Up until *:We have had this before with Southern Research. Are these boards flawed or are we doing something bad to them?
  Possibly transients when switching on the coil of the contactor while simultaneously switching off the coil of the relay?
  The switching side electronics should be seperate from the power side. Worth investigating?
  After *:

Pololu Relay Investigation
https://www.pololu.com/product/2482:
"The control signal is fed directly to a BSS138 N-channel MOSFET, which in turn actuates the relay coil when the
control voltage exceeds approximately 2.5 V, up to a maximum of 20 V (see BSS138 datasheet (92k pdf) for details)."
https://www.pololu.com/file/0J620/BSS138-7-F.pdf:
Gate threshold: 1.2V Typ, 1.5V max
So it could be that the pi isn't giving enough V to the mosfet?

In beginning investigation I found that the leads to the relay control power pins were in a very bad state so I repaired & improved the joint.
Using banch power supply I tested engage and release of each relay

Relay Rising V 'On' Falling V 'Off'
      V     A       V         A     Notes
2     1.7V  0.04A   1.4V      0.03A Drops out occasionaly at 1.7V
1     NA!   0.4A              @3V It started smoking

Replace Pololu relay board with unknown spec chinese board
        Coil Res  A @12V (calc) P(calc)
Pololu  356 Ohm   0.034         0.4W
Chinese 70        0.17          2W
=> Relays on Chinese board are not 12V capable.