Battery Charging Guide

Charging and Maintaining Lipos

Warning! Lithium Polymer Batteries can be dangerous volatile batteries if not used properly. Keep them stored in a container that wont melt or catch other things on fire if a battery were to catastrophically malfunction.

Understanding your Batteries


This is a standard high discharge 2650mAh 3S lithium polymer battery.  

Specs:
Capacity: 2650mAh
11.1V Discharge
25C Constant /50C Burst
Weight: 215g
Dimensions: 148x44x18mm
Balance Plug: JST-XH

Capacity

Capacity is how much juice there is (in milliamps) that it has to offer over the course of an hour. So it will discharge 2.65 amps (2650mA x 10^-3) in one hour. What makes lithium polymer batteries so important is there ability to discharge way more amperage than their capacity ratings. 

How much you ask?


C Rating


Look at the 25C Constant/ 50C Burst. This C rating is simply a multiplier. Thus:

2650mAh or 2.65A x 25(c rating) = 66.25A Constant discharge. This is MASSIVE current. From the same logic that means this battery can, for short periods of time (burst), discharge 2.65A x 50 = 132Amps!! Note: the higher the C rating will result in a higher discharge rate but at the cost of slightly more battery weight.

Voltage

These batteries are rated to 11.1V. Mind you, fully charged it will output 12.6V. This is only because it is a 3 cell battery.

Lipos come in all kinds of cell configurations. Usually 1 to 8 cells. Each cell fully charged will output 4.2 volts. 4.2V x cell count = voltage of battery at full charge. Make sure everything that is wired directly into the battery's circuit is rated for the voltage of the battery your using.

Charging & Balancing

Multicell lipo batteries need to be maintained and charged. There are a few rules with lipos to ensure they are properly maintained:

  • Do not discharge the cells to below 3.3V. On a 3 cell lipo at 3.3V the battery will measure 10V at this point.
  • Keep the cells balanced! Use your charger's cell balancing feature to keep the lipo's cells balanced. The individual cell voltage can be measured through the balance plug with a battery checker of some kind. This is important for the health of the battery and can also be an indication of the batteries health. 
  • Do not store batteries for extended periods; charged or discharged. Most chargers will have a "storage" feature, use it!
  • Charge batteries within their recommended ratings. If a 2650mAh battery is rated to be charged at 1C, charge it at 2.65Amps. 2C, then charge at 5.3Amps, etc.. Stick to 1C or 2C for the sake of battery longevity.

Using Your New Lipo Knowledge in the Real World

Knowing what batteries to use for a multirotor is critical! I once had a person show me his quad that needed roughly 25 - 30 amps to hover, but using a 2200mAh 10C battery. Doing the math: 2200mAh x 15 = 33A. This is NOT ok. This battery is at it's limits just keeping the aircraft hovering; this is a classic mistake many new builders make when they don't read my guide :)

Choose the batteries to meet the requirements of the aircraft! Check the specs of your motors: max amperage, wattage, and any graphs showing power draw with certain propellor setups. Check to see what cell count the motors can handle. Choose a capacity that fits on the aircraft and doesn't create too much weight for the motors to handle. Take all of these factors into account and select the proper battery accordingly. Balance is key to a properly functioning multirotor! 


Congratulations, you're now a lithium polymer battery expert!

2 comments:

  1. Wow, thanks for the article, I had no idea that there were so many types of batteries for so many different things. I don't really know as much as I would want about batteries, so maybe I ought to research more into it and see what I can learn. I like when you said it is important to make sure you have the right battery for the right job, that seems like it would be important. http://www.all-trabattery.ca/en/

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