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E-bike Charging:Fast Or Slow?
Apr 03, 2018

We know that everyone appreciates a fast charge.the idea of charging an ebike battery in an hour is an exciting concept. Once you get into the ebike math, the first notion is to get as high an amp charger as possible. With a 10-amp charger you can charge a 10-amp battery in one hour.

But charging too fast is hard on the battery, and it will cause its life expectancy to go down, and also it can be a fire hazard in extreme cases of charging too fast.

We really recommend that if you are new to e-bike, and new to lithium batteries in general, that you stick with the slow charger that came with your pack, and do not fast charge. This is both safer and healthier for your pack.

One of the questions you should ask when buying an ebike is how large is the battery in Amp-hours (Ah) and how many amps is the charger it comes with? Then using ebike math you can quickly calculate how long your battery will take to charge. We know based on ebike math that charging a 10-Ah battery will take 10 hours with a 1-amp charger…or 2 hours with a 5-amp charger.

If  you divide the amp-hour rating of your battery by the amp rating of your charger, that is how long it will take you to fully charge your battery (if it is fully discharged). However all good lithium smart chargers dial back the charge at the end of the charge cycle, so they take a little longer than what they are rated for. So, for a 10 amp hour battery, it will take a 5-amp charger a little more than 2 hours to charge your pack.   

A high-amp charger will only actually use high-amps until the battery reaches about 90% of its full maximum possible charge…then it will use low amps to gently “top off” the pack.

BMS Limits and charger fast:

Commercially sold ebike batteries such as the Chengerxing battery packs have some kind of BMS (battery management system)  that protects the pack. One of the things the BMS does is limits how fast the pack is allowed to charge. If you plug a 10-Ah battery into a 5-amp charger, and the battery does not charge, the BMS might be refusing the charge.

Most lithium BMS’s have a limit of around 7 amps as the limit on how fast they will charge. Also, the BMS is in charge of balance charging your cells to further ensure you packs safety and longevity.

The Importance of Balance charging

Any good BMS not only protects the safety of your pack during charging and discharging it also ensures each series of cells is balance charged, which means all your cells are at about the same voltage.  Balance charging does not happen fast…in general most ebike  chargers will slow way down at the end of the charge to allow a proper ebike battery with advanced BMS to balance out each line of cells.  

           48 Volt Bicycle Battery


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