It is important to choose the right charger for your battery. The right charger will make your battery function as safely and efficiently as possible. There are a few different factors that go into choosing a charger, each of which is detailed below.
This one is critical. Most lithium battery chargers are designed for either lithium-ion batteries or lithium iron phosphate (LiFePO4) batteries. The difference is the charge voltage. You have to choose the right type of charger to ensure that you will have the correct charge voltage.
That leads us to our next issue: charging voltage. If you’re using a VRUZEND battery building kit then you’re almost certainly using li-ion cells that should be charged to 4.2 V per cell. That means you’ll need a charger that has an output voltage that is 4.2 V x the number of cells in series in your battery.
For a 10s battery with 10 cells in series, that means you need a charger that outputs 4.2 V x 10 cells = 42.0 V.
For a 13s battery with 13 cells in series, you’d need a 54.6 V charger.
For a 14s battery with 14 cells in series, you’d need a 58.8 V charger.
And so on.
You can actually increase the life of your battery by slightly undercharging it, but we’ll talk about that further down in this article.
You also want to consider charging current. Most lithium ion cells should not be charged above 1 C, though most prefer to stay below 0.5 C. The “C” rating is simply the capacity of the battery. So for a 3.5 Ah cell, 1 C would be 3.5 A. For a 10 Ah battery pack, 0.5 C would be 5 A. Got it?
You should aim to not charge your cells at more than 0.5, or half of their capacities. So if you use 3.5 Ah cells, and you have 4 in parallel, that means you should charge at no more than 7 A. Even 7 A is a pretty high charging rate for lithium batteries. The lower current you charge at, the happier your batteries will be and the longer they will last.
Lastly, you have to consider your BMS, if you have one. Most BMS units are rated for around 5A charging, unless you specifically have a higher power BMS.
I generally charge my batteries at around 1/3 C, which means they take around 3 hours to fully charge, when nearly empty. For a 10 Ah battery, 1/3 C would be 3.3 A. Most common lithium battery chargers, especially those meant for electric bicycles, are found in the 2 A to 5 A range. These are all reasonable current levels for most batteries. But if you have a very small battery, such as a 5 Ah battery pack, a 5 A charger would be 1 C, which would be the limit of most cells. So always remember to keep that in mind when choosing your charging current.
Studies have shown that charging to a slightly lower voltage can have a dramatic improvement on the number of cycles you can get out of your battery. Charging to 4.1 V instead of 4.2 V (which is the equivalent to charging to around 90%) has been shown to add nearly 50% more cycles to a battery over its entire life. To do this, you’ll need a fancier charger though.
Some chargers are adjustable and can be set to different charging profiles, such as 50%, 80%, 90% or 100% charging. These are more expensive than simple chargers though.
One note: if you use a BMS and want to do sub-100% charging, it is a good idea to still charge to 100% every now and again. Most BMSs use ‘top balancing’, which means that they don’t balance the cells until the cells are full. By always charging to nearly full, these types of BMSs will never get the chance to balance the cells. So remember to charge to 100% every now and again, between every 10-20 charges, depending on how well your cells stay in balance on their own.
Quality levels of chargers
There are a few main quality levels of chargers on the market. They look like this:
Cheap plastic chargers – While most cheap plastic lithium batteries are crap, there are a few good ones out there. It’s hard to know which are which though, as they all basically look alike. They are the least expensive, but they make up for it in low quality. They are usually low powered, which means they don’t have a cooling fan. They make a good back up charger, but use them at your own risk as a primary charger.
Aluminum case chargers – These are a step up. There are many different types, but they are generally better quality than most plastic lithium battery chargers. They can also support higher power levels and usually come with a cooling fan. Some are even adjustable.
Balance chargers – These are discussed more in the article on balance charging. There are many different types of different qualities and most are built for the RC world of toy cars and drones. You really need to know what you’re doing with balance chargers though, as they don’t use a BMS to protect the battery. Make sure you read that article if you are considering going this route.
High end adjustable and programmable chargers – This includes chargers like the Cycle Satiator. These are really high quality chargers that have a number of features that allow you to customize charging profiles. You’ll pay a pretty penny for them though.
There are so many different chargers out there that you’ll want to make sure you take your time and choose the right one for you. The most important things are to check that the voltage matches your battery and that the quality is of the level you want. Cheap chargers are ok, as long as you know what you are getting into and use them safely. I always have one as a back up in a pinch. If you can afford it though, better chargers will last longer and keep your battery healthier.