Primary Power Controller
Primary Power Controller (PPC) - is a power electronics board, designed to control the process of battery charge/discharge, merge separate battery current into one or multiple power rails, control the current flow of output rails and simple filtering. The core of the PPC is a µC which contiguously reads voltage of each battery assembly, incoming charger voltage, control the current of output power rails. At the same time it controls switching of each output rail, enables charging of individual battery, communicates with each of the Battery Charge Controllers, controls air flow and fan speed by taking each section's temperature into account.
Contents |
Version 2
This version is in production.
The main concept is splitting the charging and control functions into separate boards. The Primary Power Controller's functions are:
- 1) Connecting external power for charging;
- 2) Connecting six battery assemblies for charge and use;
- 3) Allowing manual switching off the separate battery assembly;
- 4) Communicating with each of the Battery Charge Controllers and receive its charge/discharge level, wear level, temperature, duty time, also monitor the voltage and current level of each battery from an assembly; (I2C interface is used for this purpose)
- 5) Extend output power rails count to 6 output rails, with separate LC filtering. Up to 4 output rails should have additional external logic TTL output (for service functions).
- 6) Software switch On/Off of the separate output rail. Monitor each rail power consumption;
- 7) Communicate with PC board (via UART/COM-port), and report detailed power status information;
- 8) Control fan speed and internal temperature climate;
- 9) Wait for the (several) external triggers and run previously programmed functions as a response (such as switching on all the power rails, when external signal is emitted).
- 10) Reset peripherals
The board have a single µC. Independent charging of battery assemblies is controlled by separate effective switched mode DC-DC converters on each of the Battery Charge Controllers.
Schematic capture
PCB
Device photo
Specifications
Test results
- FAN2 is not working properly (always enabled)
- Power diodes are warm and dissipate much power
- Schematic is poorly protected from EMP (occasionally starts up when high-power electromagnetic pulse emits)
- Several separate connectors for inputs/outputs is not very good solution (a lot of separate connectors)
- Temperature sensing using DS18B20 has failed (or not implemented correctly)
Recommendations
- modify transistor for FANs control - logic level ones alone does not have enough power
- Ensure there is a single switch to disable filtered output of batteries
- fix FAN2 operation
- split entire board into two boards: Logic and Power
- put current sensing resistor into each charger rail (current sensing with evaluating resistor voltage drop)
- reduce LEDs power below nominal by increasing LED resistors to 500-800 Ohms
- put more power transistors to output rail to decrease power losses
- make some schematic splitting to reduce standby power consumption
- apply current-limiting to remove sparks when connecting charger
- add 100-330 Ohm limiting resistor to each input-output port pin
- add optically-coupled device to sense PC start-up
Parts list
- Charger socket 4-pin: MF-4MA (p/n Molex 50-30-4461)
- Battery connector 8-pin: MF-8MA (p/n Molex 44472-0857)
- Motor connector: PWL-2 (3.96mm pitch)
- Sensor connectors: WF-2 (for Signal, Fan and Pull-Down connector), WF-3 (for DS18B20), WF-6 (for Railcontrol connector)
- Current sensor: Allegro ACS712, 8-pin SOIC (ACS712ELCTR-20A-T and ACS712ELCTR-30A-T)
- MCU: ATMega64A-AU
- Oscillator [BQ1]: 14.7456 MHz
- LEDs: HV1 (FYLS-1206UGC green,2.1V, 20mA), HV2 (FYLS-1206URC red, 2.0V, 20mA)
Notes
- Do not try to update Primary Power Controller's firmware with running embedded computer. This will lead to immediate powering down computer and devices rails (Motion controllers, etc.).
- While reprogramming, the only rail that always stays powered up is Vsb. However the rail of PSU is always connected. To enable +5V or other powerful output of the PSU while PPC has not yet commanded to turn the power on, force it by shorting a corresponding jumper on the PSU board.
Device specific commands
<TODO>
Version 1
Is a current implementation. There are inputs for the 6 Li-Ion battery assemblies (22.2V / 4800 mAh each). Power rail's current of all 6 batteries is merged using multiple power Schottky diodes. There are outputs for sensing battery voltage, through limiting resistor but with no voltage divisor (22.2V, 330 Ohm resistor). A single, up to 27 VDC, input socket power connector (5.5 mm x 2.5mm) is provided to connect external charger (AC/DC power supply), however with no overcharge detection. A transformer based charger (220VAC/27VDC @ 2A) is used to charge batteries. There are 2 output rails with 4 output connectors. Each output rail have its separate LC filter.
