Battery Configuration

This guide covers battery limits, voltage protection, and BMS integration for ASI BAC motor controllers.

Rated Limits Configuration

The BAC Controller's battery configuration involves three main settings:

1. Rated System Voltage

Enter the battery's rated voltage rather than the measured voltage at full charge.

Battery Type	Rated Voltage	Full Charge Voltage
10S Li-ion	36V	42V
13S Li-ion	48V	54.6V
14S Li-ion	51.8V	58.8V
16S Li-ion	59.2V	67.2V

2. Maximum Battery Current Limit

Specified as a percentage of the motor's rated current capacity.

Example calculation:

Rated motor power: 2880W
Rated system voltage: 48V
Rated motor current: 2880W ÷ 48V = 60A
For 45A battery limit: 45A ÷ 60A = 75%

3. Regeneration Battery Current Limit

Also expressed as a percentage of rated motor current.

Critical Safety Note

If the Regeneration battery current limit is set to 0%, even a slight rollback of a direct drive vehicle will not allow forward motion until the vehicle comes to a complete stop. Set this parameter to at least 20% to prevent this behavior.

Voltage Protection Parameters

Overvoltage Protection

Address	Parameter	Description
147	Fast over voltage threshold	Instant trip on single spike (% of rated voltage)
149	Slow over voltage threshold	Trip after >1 second averaged (% of rated voltage)

Example for 48V rated system:

Fast OVP at 120%: 48V × 1.20 = 57.6V trip threshold
Slow OVP at 110%: 48V × 1.10 = 52.8V trip threshold

Undervoltage Protection

Address	Parameter	Description
148	Fast under voltage threshold	Instant trip below threshold
150	Slow under voltage threshold	Trip after >1 second below threshold

Example for 48V rated system:

Fast UVP at 50%: 48V × 0.50 = 24V trip threshold
Slow UVP at 75%: 48V × 0.75 = 36V trip threshold

High Battery Voltage Foldback

These parameters control regen current reduction as voltage approaches limits:

Address	Parameter	Function
194	High battery foldback starting voltage	Regen reduction begins
195	High battery foldback end voltage	Maximum regen reduction

Battery Management System (BMS)

Purpose

BMS integration enables accurate state-of-charge (SOC) tracking, which is essential because SOC does not have a linear relationship with voltage.

Primary Applications

Reduce motor power when battery levels drop to extend range
Display remaining capacity to users
Override external BMS voltage protection behaviors

Configuration Options

Interface Type	Description
None	SOC reads 100% (configure voltage foldbacks separately)
Voltage Model	Internal software linearization
Analog 10V	Direct analog signal input
Remote	Network-based communication

SOC Calculation Formula

The controller applies this formula:

SOC = ((battery voltage / Rated system voltage) × Voltage model SOC gain) + Voltage model SOC offset

Results are clamped to 0-100%.

Battery Resistance Compensation

The Battery Resistance parameter compensates for voltage drops during high current draw.

Calculation method:

Measure no-load voltage
Measure full-load voltage
Calculate: (No-load V - Full-load V) ÷ Load current

Typical value: ~200 mΩ

Verification

Test using adjustable power supplies or live riding to confirm SOC tracking accuracy against actual battery depletion.

Battery Foldback Options

Option 1: Voltage Foldbacks

Monitors battery voltage to reduce peak motor current as voltage drops.

Address	Parameter	Function
141	Low battery foldback starting voltage	Current reduction begins
142	Low battery foldback end voltage	Maximum current reduction

Warning bit 7 activates when voltage falls below starting threshold.

Disable Option

Set both thresholds to 0V to disable voltage-based foldback.

Option 2: SOC Foldbacks

Uses state-of-charge data from the BMS:

Parameter	Function
Battery SOC foldback starting capacity	Triggers foldback initiation
Battery SOC foldback end capacity	Cuts current to zero

Option 3: Battery I²T Foldback

Enables thermal monitoring based on battery current rather than motor current.

Enable by: Setting Motor Features bit 3 to "Disable motor I²t enable battery I²t"

Overload Protection Thresholds

The system uses hysteresis between heating and cooling phases:

Parameter	Function
Continuous threshold	Normal operating limit
Heating current	Peak level before thermal accumulation begins
Cooling current	Level at which thermal accumulation dissipates
Overload heating time	Duration to reach 100% accumulation
Overload cooling time	Duration to reach 0% accumulation

Battery current rating = Rated motor power ÷ Rated system voltage

Dual-Battery Configurations

For systems with OR-ed battery packs:

Requirements

Current must flow bidirectionally between controller and DC source
Simple series diodes block regenerative current and cause overvoltage faults
Use ideal diode bridges with N-Channel MOSFETs

Considerations

Bus dynamics: Controller sees a stiff bus held by whichever pack has higher voltage
Impedance limits: Verify maximum allowed impedance during regen
BMS communication: Ensure charge-inhibit signals are properly routed

Regen Path

When using ideal diodes for reverse polarity protection, ensure the regen current path has sufficiently low impedance to prevent voltage spikes.

Configuration Checklist

Set Rated System Voltage

Enter your battery's nominal voltage (not full charge voltage).

Configure Current Limits

Set maximum battery current and regeneration limits as percentages.

Set Voltage Thresholds

Configure overvoltage and undervoltage protection thresholds.

Configure Foldbacks

Set up voltage or SOC-based foldbacks for battery protection.

Enter Battery Resistance

Measure and enter the battery's internal resistance for voltage compensation.

Select BMS Interface

Choose and configure your BMS communication method.

Save to Flash

Write all parameters to flash memory and power cycle.

Next Steps

Configure Braking Systems for regenerative charging
Set up Protection Systems for safe operation
Review the Technical Q&A for common questions