Summary of "Embedded Systems and Design & Development - Feb 3, 2026 | Afternoon | VisionAstraa EV Academy"

Summary — Embedded Systems and Design & Development

VisionAstraa EV Academy — Feb 3, 2026 (afternoon)

Main ideas and lessons

This session covered core battery‑pack design fundamentals, calculating pack metrics from cell data, practical worked examples, safety and imbalance issues, and recommended engineering practices. A step‑by‑step methodology for designing packs and selecting chargers was presented. A concrete design mistake (mismatched parallel counts across series strings) was highlighted with its consequences and fixes.

Core battery‑pack design fundamentals

Series (S) increases pack voltage; parallel (P) increases pack capacity (Ah).
Per‑cell parameters to know:
- Nominal voltage
- Full‑charge voltage
- Cutoff (0%) voltage
- Capacity (Ah)
Typical chemistries and example per‑cell voltages used:
- NMC (Li‑ion): nominal ≈ 3.7 V, full ≈ 4.2 V, cutoff ≈ 3.0 V
- LFP: nominal ≈ 3.2 V, full ≈ 3.6 V (used in examples)
- Lead‑acid: nominal ≈ 2.0 V per cell (noted)

How to calculate pack metrics from cell counts and ratings

Use the cell ratings and series/parallel counts to compute pack values:

Pack nominal voltage = S × cell_nominal_V
Pack full‑charge voltage = S × cell_full_V
Pack cutoff voltage = S × cell_cutoff_V
Pack capacity (Ah) = P × cell_Ah
Total number of cells = S × P

Worked examples and numbers used

14P where each cell = 3.7 V / 2.6 Ah → pack = 3.7 V nominal, 36.4 Ah
Two identical 14P packs in series → 7.4 V, 36.4 Ah (voltage adds; Ah unchanged)
Larger example: 14P × 16S → nominal ≈ 3.7 × 16 = 59.2 V (often rounded to 60 V)
- Full ≈ 4.2 × 16 = 67.2 V
- Cutoff ≈ 3.0 × 16 = 48 V
- Total cells = 14 × 16 = 224
- (Note: an associated practical design error is discussed below)
Charger selection examples:
- 60 V LFP pack: S ≈ 60 / 3.2 ≈ 19S → full = 19 × 3.6 = 68.4 V → charger should supply ≈ 68.4 V (not simply a generic 70 V charger unless validated safe)
- NMC 16S pack: full = 16 × 4.2 = 67.2 V; cutoff = 16 × 3.0 = 48 V
Computing number of cells from pack specs:
- 60 V, 30 Ah pack with 5 Ah cells → S ≈ 60 / 3.7 ≈ 16; P = 30 / 5 = 6 → total cells = 16 × 6 = 96
- 48 V, 50 Ah pack with 3 Ah cells → S ≈ 48 / 3.7 ≈ 13; P ≈ 50 / 3 ≈ 17 → total ≈ 13 × 17 = 221

Amp‑hour (Ah) explained

Ah is current (A) × time (h) deliverable at the rated discharge. Examples:

5 Ah battery → 5 A for 1 hour; 10 A for 0.5 hour; 2.5 A for 2 hours

Safety, imbalance and BMS

A highlighted assembly/design mistake: one series string had 14P while other strings had 15P (mismatched parallel counts). This causes imbalance.

Consequences of imbalance:

During charging: strings/cells that are already higher can overcharge while charger continues to pack full voltage → overcharge, thermal stress, leakage, fire risk
During discharging: weaker strings/cells reach cutoff earlier → deep discharge of that string, irreversible damage, loss of capacity

Required protections and mitigations:

Over‑charge protection and under‑voltage (cutoff) protection for pack and individual strings/cells
Cell balancing so all series strings/cells stay at comparable state‑of‑charge (SOC)
Implement a Battery Management System (BMS) that monitors voltages, balances cells/strings, and enforces cutoffs and protections
Avoid mismatched P counts across series strings; plan for aging and replacements and include balancing/BMS for long‑term drift

Design mistake (emphasized): mismatched parallel counts between series strings (e.g., 14P vs 15P) leads to uneven charging/discharging, thermal risks, premature failure. Fix by using consistent P counts, proper balancing, and a BMS.

Practical design and engineering recommendations

Determine chemistry first (NMC, LFP, etc.) to obtain correct per‑cell nominal/full/cutoff voltages before sizing S or selecting a charger
Use the formulas above, step‑by‑step, when designing/sizing packs and chargers
Avoid mismatched P counts across series strings; plan for cell aging and replacement
When specifying a charger, size its output to pack full‑charge voltage (S × cell_full_V) and integrate with the BMS for charge control
For hands‑on learning, practice designing packs for common industry nominal voltages (48 V, 60 V, 72 V, etc.) and for different chemistries

Methodology — step‑by‑step instruction

Identify cell chemistry and per‑cell ratings (cell_nominal_V, cell_full_V, cell_cutoff_V, cell_Ah).
Determine required pack nominal voltage (V_pack_nominal) and capacity (Ah_pack).
Calculate series count (S): S = round(V_pack_nominal / cell_nominal_V) (choose nearest integer consistent with system).
Calculate full and cutoff pack voltages:
- V_full_pack = S × cell_full_V
- V_cutoff_pack = S × cell_cutoff_V
Calculate required parallel count (P): P = Ah_pack / cell_Ah (round appropriately for manufacturability).
Total cells: N_cells = S × P
Charger selection:
- Charger maximum voltage must match V_full_pack (or slightly below depending on BMS/tolerance)
- Choose charger current based on desired C‑rate and pack Ah
Safety and BMS:
- Implement voltage monitoring, balancing, over‑current, over‑voltage, under‑voltage protections
- Ensure all series strings have equal P; do not assemble if mismatched without corrective measures
Validate with numerical examples and arithmetic checks.
Account for aging: include balancing and monitoring for long‑term mismatches.

Design mistake highlighted and implications

Fault: mismatch in parallel counts across series strings (e.g., one string 14P vs others 15P)
Effects: uneven charging/discharging, overcharging some cells, deep discharging others, heat generation, safety hazards, premature cell failure
Remedies: consistent P counts, robust BMS with balancing, careful cell management and replacement practices

What will be covered next

Detailed BMS design: balancing strategies, embedded systems and microcontroller selection, how the BMS enforces protections and performs balancing — to be covered in the next session. Notes from this session will be shared.

Speakers / sources featured

Primary speaker: Instructor/presenter (unnamed) from VisionAstraa EV Academy (session host)
Participants: several attendees who made brief interjections (counts, confirmations); no named participants quoted
Video source: “Embedded Systems and Design & Development - Feb 3, 2026 | Afternoon | VisionAstraa EV Academy”