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BS2 as vehicle battery isolator controller - help request (with schematic) — Parallax Forums

BS2 as vehicle battery isolator controller - help request (with schematic)

SpereSpere Posts: 9
edited 2015-01-31 08:02 in Robotics
I'm putting together a BS2 controlled 'smart battery isolator controller' for use in a vehicle with multiple battery banks and various chargers.

System Basics:
  • This is being used on a Mobile Command Center (MCC/CIC) vehicle - think an RV with some communications and logistical gear in back.
  • There are 2 independent and electrically isolated battery systems (common ground), one for the chassis and another for the command center.
  • The chassis system consists of one 12vdc battery and is charged from the alternator at typical vehicle voltages (14.4 Vmax)
  • The rear system consists of a 12vdc battery bank and is charged using a 100amp programmable charger, itself powered from either shore power or an associated in vehicle generator.
  • The rear batteries require 15.3 Volts for absorption and 15.6 Volts for equalization.
  • The max voltage allowed on the chassis system is 14.4 Volts.
  • There is currently a 200 amp isolation solenoid which can combine the systems to allow the alternator to charge the command center batteries when the vehicle engine is running.
  • Currently, the solenoid is manually closed and opened via an spst.

Goal of BS2 integration:
  • Monitor the voltages of both the chassis (V1) and rear (V2) battery systems.
  • Monitor the current going from the chassis to the rear (or from the rear to the chassis - i.e. bidirectional).
  • Control the Solenoid based on the voltages, the current, or a user override.
  • Display operating conditions on an LCD.
  • Sound a warning for 'out of parameter' conditions.
  • Allow user input and parameter selection.

Functional Components:
  • ADC to acquire voltages - (MCP3204)
  • LCD display to display status and voltages (NHD-0216K3Z)
  • Solenoid control circuit - (NPN 2SC6144SG)
  • 1A @ 5vdc Switching power supply (R-785.0-1.0)
  • User input via a simple 5 button switch array

Notes:
  • It has been a long time (ok, a decade) since I worked with microcontrollers.
  • my electrical theory/circuitry classes I had in college were before that.

Where I would most appreciate help.

Circuit Components:

HAAS 200-s Current Sensor
Digikey page here: http://www.digikey.com/product-search/en?KeyWords=398-1064-ND&WT.z_header=search_go
Data sheet is here: http://www.lem.com/docs/products/hass_e_rev14.pdf

1A at 5vdc switching power supply
Data sheet is here: http://www.recom-power.com/pdf/Innoline/R-78xx-1.0.pdf

And, The Schematic:

Attachment not found.

Thanks much!

Comments

  • kwinnkwinn Posts: 8,697
    edited 2015-01-23 07:35
    Looks good to me. Just make sure the bypass capacitors for each chip are as close to the chip as possible when you lay out the board.

    Only concerns I have are the minimum current requirement for the regulator and if a blocking diode on regulator Vout is required.

    The recommended minimum current on the regulator data sheet is 10mA for it to meet the specs, so as long as the board draws more than that you should be ok.

    A blocking diode on the Vout pin is recommended to prevent current flowing back through the regulator where that is a possibility. Your schematic shows a total of 2.3uF on the board that could discharge back through the regulator if the 12V in was disconnected and the transistor controlling the relay was on. Not really much chance of that happening or damaging the regulator, but I would put the diode in the circuit.
  • $WMc%$WMc% Posts: 1,884
    edited 2015-01-30 18:01
    kwinn wrote: »
    Looks good to me. Just make sure the bypass capacitors for each chip are as close to the chip as possible when you lay out the board.

    Only concerns I have are the minimum current requirement for the regulator and if a blocking diode on regulator Vout is required.

    The recommended minimum current on the regulator data sheet is 10mA for it to meet the specs, so as long as the board draws more than that you should be ok.

    A blocking diode on the Vout pin is recommended to prevent current flowing back through the regulator where that is a possibility. Your schematic shows a total of 2.3uF on the board that could discharge back through the regulator if the 12V in was disconnected and the transistor controlling the relay was on. Not really much chance of that happening or damaging the regulator, but I would put the diode in the circuit.
    '
    If you add in the Vout Diode, This will cause a 0.6 volt drop across it throwing the regulated voltage off by -0.6 volts. You could add a Diode of same value between the ground pin of the regulator and physical GND to compensate for the drop. The GND Diode will raise the Reg. Voltage by 0.6 volts above GND. This would be lost across the output Diode to reach a null state. Corrected out-put voltage. Bread board this before you try it in a circuit that could damage something!!!
    '
    Keeping a load on the Regulator is important. I like to use a Jumbo Led for this. Your spec shows 10mA minimum, The Jumbo's pull 15mA to 20Ma. And they make a nice indication that their working.
  • SpereSpere Posts: 9
    edited 2015-01-30 19:20
    Thanks Walt,

    I was pondering how to maintain the regulated voltage at 5.0 v +/- 1% while including the blocking diode. This would seem critical as the Vout is used as Vref for the ADC.

    -- your idea is easy and elegant, much appreciated.

    I will most certainly breadboard it, I hate releasing the magic smoke.
    $WMc% wrote: »
    '
    If you add in the Vout Diode, This will cause a 0.6 volt drop across it throwing the regulated voltage off by -0.6 volts. You could add a Diode of same value between the ground pin of the regulator and physical GND to compensate for the drop. The GND Diode will raise the Reg. Voltage by 0.6 volts above GND. This would be lost across the output Diode to reach a null state. Corrected out-put voltage. Bread board this before you try it in a circuit that could damage something!!!
    '
    Keeping a load on the Regulator is important. I like to use a Jumbo Led for this. Your spec shows 10mA minimum, The Jumbo's pull 15mA to 20Ma. And they make a nice indication that their working.
  • kwinnkwinn Posts: 8,697
    edited 2015-01-31 07:42
    Since you are going to be monitoring the voltage on the two chassis you will need a voltage divider for each chassis to reduce the adc input voltage to a 0-5VDC range. The current measurement output is already 0-5VDC so no voltage divider is needed. In both cases you will need to do a little calculating to convert the raw reading to actual voltage and current readings. To get the calibration factors for these calculations you should use a calibrated meter to measure the actual voltage and current at minimum, middle, and maximum points of the ranges.
  • kwinnkwinn Posts: 8,697
    edited 2015-01-31 08:02
    Oh oh, noticed one problem on the schematic. You are using 100K and 300K resistors for the battery inpot voltage dividers. Those are much too high and will affect the accuracy of the readings. Values of 1K and 3K would be much better. See page 17 paragraph 3 of the Microchip data sheet (Analog Inputs) for an explanation. Adding a 0.1uF capacitor to the input from the voltage divider would also help filter out noise and improve accuracy.
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