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What size Lithium battery charger do I need?

This entry was posted on 06/12/2018 11:53:09 AM by Valen

How to calculate what size Lithium Charger is needed

Lithium Phosphate (LiFePO4) batteries are now widely used in a range of applications, from mobility scooters to caravans to providing back up power for remote communications towers. 

When you install a Lithium battery for any type of application, you need to ensure you’re using the correct battery charger for the technology and the size of the battery.

So how do you determine what battery charger you need?

In this blog, the team at Valen take you through the steps of calculating what size Lithium battery charger you need for your battery.


Free Download: Advantages and Disadvantages of Different Batteries Guide


What information do I need to know?

To calculate what size battery charger you need, the first step is making sure you know:

  • Battery Amp Hour (total capacity)
  • Battery Voltage (total voltage)
  • How fast do you need to charge your battery (in hours)

It’s also recommended to check the charging capacity of the Battery Management System (BMS).

If you have more than one Lithium battery, you’ll also need to decide what way you’ll be connecting them.

It is highly recommended to parallel connect Lithium batteries instead of series connecting.

When connected in series, one battery will say it’s fully charged and cut the charging before the second battery is fully charged. So it’s not recommended to series connect Lithium batteries as you have no control over the voltage of the individual cells. With parallel connection, you always have control over the voltage.


What are the Advantages and Disadvantages of different batteries?


How do I calculate what size charger I need?

Once you’ve confirmed the above information, follow the below calculation steps:

  • Charging (Hours), divided by two = the Charging Time
  • Battery Capacity (Ah), divided by the Charging Time = the Charger Capacity
  • Charger size = battery voltage (Voltage of the charger) and the Charger Capacity (calculated above).

For example, Bob has a 24V250Ah Lithium battery he would like to charge for 10 hours. Let’s take a look at how he would calculate his required charger size using the steps above.

  • 10 hours (charging (Hours)) / 2 = 5 hours (Charging Time)
  • 250Ah (Battery Capacity) / 5 hours (Charging Time) = 50A (Charger Capacity)
  • Therefore, Bob requires a 24V50A Lithium battery charger


What can happen if I use the wrong size battery charger?

Using the incorrect sized Lithium battery charger can damage your Battery Management System (BMS). The BMS is installed in the battery to protect the battery against overcharging and over-discharging.

If you are using a cheap Lithium battery that does not contain a BMS or has a cheap version installed, it’s highly likely your batteries will overcharge and will not be safe to use.

You have a greater chance of purchasing the incorrect technology specified battery charger than calculating the wrong size. Every battery charger is designed for a specific battery technology. Just as Gel battery chargers are designed for Gel batteries, Lithium Phosphate battery chargers are designed for Lithium Phosphate batteries.

So always ensure you are using the correct technologically specified battery charger for your battery before charging.

We recommend purchasing your Lithium Phosphate batteries and charger from the same supplier/manufacturer to reduce the risk of using the incorrect battery charger.

Related: How to Safely Handle Lithium Phosphate Batteries


Need further advice on Lithium battery chargers?

The industrial battery experts at Valen are happy to check your calculations for your Lithium battery charger or walk you through the calculations to ensure you purchase the correct charger for your system.

If you’d like more information, please click here to get in touch with our expert team. We’d be happy to answer any questions you have.


Written by Valen

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