FAQs: In-Vehicle Battery Management Systems, All Your Questions Answered

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In-vehicle battery management systems (BMS’s) come in all shapes and sizes. And while it’s great to have choice, the terminology can be confusing.

Here, we answer all your questions on BMS’s… what they are, why you need one, how they work and so on.

Have a look through these FAQs and if you have any other questions, please ask in the Comments at the end of this post.

We’ve also done a comprehensive review on our REDARC Manager30 Battery Management System. Go here for more information.

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My Generator stock a wide range of battery management systems, at a range of price points. Go here for details.

What are battery management systems?


Battery management systems are electronic devices which manage and protect rechargeable batteries. Functions include:

✔︎ Protecting the battery from overcharge (over-voltage and over-current),

✔︎ Maintaining a battery at optimum charge,

✔︎ Monitoring the battery for faults or conditions that could damage the battery (over-temperature for example),

✔︎ Protecting the battery from undercharge, and

✔︎ Protecting the voltage source (starting battery in vehicle) from being drained, by isolating the incoming power supply once it gets below a certain voltage.

Why is a BMS needed?


A BMS (Battery Management System) is needed to protect a battery from operating outside of safe operating conditions. Examples of conditions that may damage a battery are:

✔︎ Over-voltage,

✔︎ Over-current,

✔︎ Over-temperature,

✔︎ Under-temperature.

What is a BCDC Charger?


It’s a DC to DC charger. “BCDC” stands for Battery Charger, Direct Current.

A BCDC charger is also a simple battery management system. Compared to a Manager30, its features are limited.


How does a BCDC charger work?


A BCDC charger takes power from your vehicle’s battery and/or solar, then converts it to charge your auxiliary (second) battery.

Depending on the model, a BCDC charger will:

✔︎ Convert incoming power to a voltage suitable for your auxiliary battery,

✔︎ Maintain your second battery at optimum charge,

✔︎ Monitor your second battery for faults,

✔︎ Protect your battery from over-voltage and over-current, and

✔︎ Protect your vehicle’s battery from being drained by the second battery.

What does DC to DC mean?


A DC-DC charger is an electronic device that converts a source of direct current from one voltage level to another.

For example, a REDARC BCDC charger accepts an incoming voltage between 5 and 32 volts then converts this to a voltage suitable for your second battery.

It will then regulate the voltage to the second battery, depending on its state of charge.

What is State of Charge?


State of Charge or SOC is a measure of the level of charge of your battery relative to its capacity.

For example, a battery which is half-drained has a 50% SOC and a battery which is ¾ drained has a SOC of 25%.

Where can I get a REDARC Manager30 manual?


You can get a complete Manager30 manual here.

Where can I get a REDARC BMS 30 wiring diagram?


You’ll find a wiring diagram of a typical setup on Page 20 of the Manager30 manual.

What do I need for dual battery setup?


We’ve written a detailed guide on selecting and setting up a dual battery system. You’ll find all the information you need, whether it’s a 12V or 24V system.



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