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power-system

Dec 14, 20245 min read

Power System Concept

Referencees

The power system is responsible for safely supplying power to the loads while also isolating other devices during different modes of operation or charging. This design incorporates on-board chargers that may only connect and charge the batteries under specific conditions. Most low cost off the shelf sealed lead acid (SLA) absorbent glass mat (AGM) float chargers [SLA battery maintainers] require the battery not be under load during charging. The design provides a solution for the following requirements.

Power Modes

  1. Charging mode: Shall use relays or contractors to isolate the 12V and 24V batteries from the loads. The relays or contractors shall also route power from an on-board 12V power supply to the 12V load such that the on-board computer can remain on during charging operations. The on-board computer (rpi) will have a dedicated UPS/Battery pisugar to operate during power source transitions such as (12V Battery to 12V Power Supply).
  2. E-stop mode: Shall use an emergency-stop button that disconnects power to the 24V Load and Pre-charge circuit such that the Pre-Charge, Start, and Stop buttons are disabled and Relay Z is opened. When releasing the e-stop button the system shall return to Standby-Mode.
  3. Pre-Charge mode: Shall provide a Pre-charge Momentary-On push button that supplies a reduced voltage (5V) from the 24V battery to reduced the in-rush current from the capacitive load characteristics of the motor controllers.
  4. Drive mode: Shall provide a Start button to latches the normally open switch Relay Z closed. Relay Z and Relay C shall be specified to handle at least 24V and 50A. Relay Z shall act as the main power switch to provide 24V to motors.
  5. Standby mode: Shall provide a Stop button to unlatch the normally open switch Relay Z.

Relay Behavioral Descriptions

  1. Relay A
    1. When not energized:
      1. Isolate the 12V Charger from the 12V Battery Circuit
      2. Connect the 12V Battery Circuit to the 12V Load Circuit.
      3. Isolate 12V Power Supply from the 12V Load Circuit
    2. When energized by the 12V Power Supply:
      1. Connect the 12V Charger to 12V Battery Circuit
      2. Isolate the 12V Battery Circuit from the 12V Load Circuit.
      3. Connect the 12V Power Supply to the 12V Load Circuit
  2. Relay B
    1. When not energized:
      1. Isolate the 24V Charger from the 24V Load Circuit during Standby Mode and Drive Mode.
    2. When energized the 12V Power Supply:
      1. Connect the 24V Charger to the 24V Battery Circuit during Charging Mode.
  3. Relay C
    1. When not energized:
      1. Connect the 24V Load Circuit to the 24V Battery Circuit to enable Standby Mode and Drive Mode.
    2. When energized the 12V Power Supply:
      1. Isolate the 24V Load Circuit from the the 24V Battery Circuit to enable Charging Mode.
  4. Relay X
    1. When energized by the 12V Load Circuit:
      1. Latch ON and subsequently latch ON Relay Z.
    2. When not energized by the 12V Load Circuit
      1. Latch OFF and subsequently latch OFF Relay Z.
  5. Relay Y
    1. When energized by the 24V Battery Circuit it enables the Start-Stop Latching Relay Circuit such that the start button will complete the Relay X Coil Circuit.
    2. The main purpose is to act as a stop button to unlatch Relay Z during anytime the Power from the 24V Battery Circuit cuts out. This may occur once the e-stop is engaged or the charging mode is engaged thus not energizing the coil.
  6. Relay Z
    1. When energized by the 24V Battery Circuit:
      1. Connect the power from the 24V Battery Circuit to 24V Load Circuit. The completion of the Relay Z Coil Circuit is dependent on Relay X Contacts, Relay Y Contacts, E-Stop Contacts, Start Button, and Stop Button.
    2. When not energized by the 24V Battery Circuit:
      1. Disconnect power to 24V Load Circuit.

24V Motor Battery System

Components

  • 2x12V-9AH SLA Batteries
  • 24 V 1.5 A Charger W13112099014
  • Fuse Holder
  • Fuses (procurement pendingtodo)

Loads

24 Volt Wire System

DC cable sizing calculator Voltage (V): 24 Current (Amps): 30 Cable run, including return (m) : 2 Voltage drop (%): 3 Calculated Minimum cable cross section (mm^2): 4 Closest American (AWG) gauge: AWG 11

Motor Battery Specs

  • Capacity: 216 Watt-Hours (Nominal)
  • Runtime:todo
  • 24V SLA Battery System (2x12V-9AH in Series)
  • Model: EXP1290
  • Terminals: F2 0.25in
  • Supplier Link: https://www.amazon.com/dp/B001NJ3H0C
  • Pre-Charger
  • Emergency Stop
  • Cycle use : >260 cyles
  • Floating and Standby use : 3-5 years
  • Self Discharge 3% per month @ 25 C
  • Charge Voltage @ 25C
    • 14.4-14.7 (-30mV/C), max. Current: 2.70A

Charger Specs

Logic Battery System

Components

  • 12V SLA Battery (procurement pendingtodo)
  • 12V SLA Charger (procurement pendingtodo)
  • 12V-to-5V Step Down Converter
    • Anker Dual USB-A Car Charger
  • Fuses (procurement pendingtodo)
  • Estimated Capacity =todo
  • (Battery Rated Capacity)
  • (Usable Capacity Correction Percentage)
  • (Battery Voltage/Converter Voltage)
  • (Converter Efficiency Percentage)
  • Lead Acid
  • Battery Rated Capacity ~= Usable Capacity (~65% of Rated Capacity) (50% of Rated Capacity, in high current applications)

Loads

  • nano 12.5Watts
    • Micro-USB Power: 5V 2.5 Amps (Current Configuration)
    • Barrel Jack Power: 5V 4 Amps
  • roboclaw (Logic Power)todo
  • rpi4todo
  • usb watt meter
  • Rate Capacity (amp-hours)

Logic Battery Specs

12V SLA Wall Charger

Step Down Converter Specs

  • 12V-to-5V Step Down Convert
  • Model:todo
  • Max Current:todo
  • Supplier Link:todo

PiSugar2

This UPS is only intended as a power fail safe for the Raspberry Pi in case the 12V logic battery fails

[[pisugar]]

CLI

  • Fetch battery charge percentage
echo "get battery" | nc -q 0 127.0.0.1 8423

WebUI

Local WebUI access

Remote WebUI access

  1. In a terminal enter
 ssh -L 8080:192.168.1.22:8421 proxy8.remoteiot.com
  1. Via web browser visit http://localhost:8080/index.html

power_system_requirements_specifications

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