What is the DC-DC Converter & BMS Selection Calculator?

It helps select an appropriate DC-DC converter and battery management system based on input/output voltages, current demands, and battery pack specifications.

What input parameters are required?

Inputs typically include input voltage range, desired output voltage and current, battery pack voltage, cell count, cell chemistry, maximum charge/discharge current, and safety margins.

What outputs are provided?

The tool suggests suitable DC-DC converter ratings (voltage, current, power) and BMS specifications (voltage compatibility, max current, cell balancing, protections).

How does it match BMS to battery?

It ensures the BMS supports the cell count and chemistry (e.g. Li-ion, LiFePO4), handles the peak and continuous current requirements, and offers protections like overvoltage, undervoltage, overcurrent, and cell balancing.

What are the limitations?

The calculator assumes ideal electrical behavior, uniform cell performance, and does not account for thermal limits, ageing, or extreme operating conditions. Always verify with datasheets and incorporate safety margins.

DC-DC Converter and BMS Calculator

Battery type

Nominal voltage, V

Minimum voltage, V

Maximum voltage, V

Desired Vout, V

Pout, W (or 0)

Iout, A (if Pout=0)

Peak current, A

Capacity, Ah

Modern battery-powered systems require not only a well-selected battery but also a properly matched DC-DC converter and an appropriate Battery Management System. An incorrect choice may result in overheating, insufficient power for the load or even permanent failure of the electronics. This DC-DC and BMS selection calculator helps estimate the most suitable parameters for your design, highlights weak points in the configuration and provides essential formulas with recommendations for safe and efficient operation.

Table of Contents

Input parameters for the calculation

Before running the calculation, it is important to specify accurate initial data:

Nominal battery voltage Vnom — typical operating voltage such as 12 V, 36 V or 60 V.
Voltage range Vmin–Vmax — for instance, a lead-acid unit at 12 V works between 11.2–14.5 V, while a LiFePO₄ pack at 36 V may span 30–43 V.
Output voltage Vout — what the load requires: 5 V for electronics, 24 V for industrial modules, etc.
Load power Pout or current Iout — if one value is given, the calculator will compute the other.
Peak current Ipeak — typical for motors, inrush circuits and dynamic loads.
Battery type — Li-ion, LiFePO₄ or lead-acid, which directly influences BMS selection.
Battery capacity Ah — needed to estimate expected operating time of the system.

Key formulas

Load power:

\[ P_{out} = V_{out} \times I_{out} \]

Required module power including efficiency:

\[ P_{req} = \frac{P_{out}}{\eta} \]

where η is efficiency, usually 0.9.

Recommended power with safety margin:

\[ P_{rec} = P_{req} \times 1.25 \]

Battery runtime estimation:

\[ t = \frac{Ah \times V_{nom} \times DoD}{P_{out}} \]

Typical depth of discharge DoD: 0.8 for lithium-ion, 0.5 for lead-acid.

Wire cross-section reference

Load current	Minimum conductor size
up to 12 A	2.5 mm²
up to 25 A	4 mm²
up to 35 A	6 mm²
up to 60 A	10 mm²
above 60 A	calculated by length and installation

Battery Types and Key Parameters for DC-DC and BMS

Battery Type	Cell Voltage	Voltage Range	DoD	Main Applications
Lead-acid	2.0 V	1.8 – 2.4 V	50 %	Automotive, UPS, backup power
Li-ion (NMC)	3.7 V	3.0 – 4.2 V	80 %	Consumer electronics, EVs
LiFePO₄	3.2 V	2.5 – 3.65 V	80 %	Solar storage, marine, RV systems
NiMH	1.2 V	1.0 – 1.4 V	70 %	Portable devices, tools
Zinc-carbon	1.5 V	1.0 – 1.6 V	80 %	Low-power electronics, toys

How to select DC-DC topology

If Vmin is higher than Vout → use a buck converter.
If Vmax is lower than Vout → a boost converter is required.
If battery voltage spans across the output level → buck-boost or SEPIC is mandatory.

BMS selection criteria

Cell count ≈ Vnom divided by the nominal voltage of one cell: 3.7 V for Li-ion, 3.2 V for LiFePO₄, 2.0 V for lead-acid.
Rated BMS current must handle both average and peak demands. A multiplier of 1.5× Iout is often used.

BMS Selection 2

Design notes and risks

For power above 600 W add thermal management and ensure proper mounting.
If heat loss exceeds 25 W, active cooling or heatsinking is required.
For peak currents 1.5–2 times higher than nominal, use fuses and thicker wires.
If the input voltage span is too wide, choose industrial-grade converters with extended specifications.

The DC-DC and BMS selection calculator is not just a tool for quick numbers. It allows engineers and enthusiasts to evaluate converter type, BMS rating, wiring requirements and realistic battery runtime. It helps in identifying limitations of the system and prevents costly mistakes. Still, final hardware choice should always be confirmed with datasheets and manufacturer recommendations to ensure safety and compliance with standards.