If you own a drone then the chances are you probably have Lipo batteries to make it fly. But you probably have no idea what it is.
What is a LiPo battery?
A LiPo battery is a Lithium Polymer battery. Its a rechargeable battery that is lightweight and offers amazing energy density….Meaning you get a lot of available power in a small package, ideal for your drone.
Funnily, lithium ion batteries have actually only been available since 1991 with the modern batteries we use in our drones being far more recent than that!
Advantages to LiPo battereis over other types
- Hugely powerful
- Light weight
- Reasonably cheap
- They don’t explode….Although they can set on fire
- Widely available for drones
Disadvantages of LiPo batteries
- Balanced charging required
- Can set on fire
- Sensitive to voltage levels and being left uncharged
- Sensitivity to overcharging, over-temperature, undercharging….Basically, conditions need to be perfect!
What the hell are all the numbers for on the outside of a LiPo?
The numbers aren’t just there for show, they let you know exactly what the battery is capable of and what you need to do to charge it. Heres an example LiPo battery number :
5000mAh 11.1V 3S 40C
And heres the random battery it is off:
lets break this down so we know what all the numbers mean.
5000mAh is the capacity of the battery. This is how much power your LiPo can hold….To drain your battery you would need to drag 5000mA out of your battery for one hour….If you drag 10000mA you battery will last half an hour etc.
3S is the number of cells the battery is made from. Why is this important? because it tells you the voltage the battery provides and more voltage equals faster motors. 3S means we have 3 cells in series which adds the output voltage up to 11.1v….If you had 2S (2 cells) the voltage would be 7.4v. Roughly 3.7 volts per cell. As a side note, this isn’t the maximum voltage of your battery, it is the nominal voltage – the voltage in-between the fully charged voltage and the minimum charge voltage. The max voltage for a cell is 4.2v and the minimum is 3.0v.
40C – The C rating of the battery is the discharge rating, it tells you how much current you can drag out of the battery without it setting on fire or getting damaged. To calculate the maximum current just multiply the capacity of the battery by the C number. In this case, the discharge rating tells us that we can drag 40 x 5000 mA out of the battery without it getting damaged….Thats 200 Amps! You will usually have burst and a continuous discharge rating.
LiPo Battery Charging
One of the major issues with LiPo batteries is their charging requirements. You can’t just put a voltage to it and it will suck it all on board. You need to use something called constant current and constant voltage charging. And the charger needs to sense when the voltage reaches the magic numbers stated above (4.2v per cell).
Another issue is that your charger needs to have a built in balancer. because, as stated above, your LiPo is actually a collection of cells, wired to give you the correct voltage, if they aren’t all charged the same you get problems. The balancer ensures that all the cells are charged with the same voltage. THIS IS EXTREMELY IMPORTANT! Your drones controller cannot tell if all the cell voltages are equal. If LiPo voltage drops below 3.0v then the battery will be ireversibly damaged, so your controller will sometimes have something called a low voltage cutout which cuts the power if the voltage drops below this threshold……But how can it tell if individual cells are below 3.0v? it can’t, so it just keeps on pulling power from the battery.
The auto cutoff that is a good safety feature but if all cells aren’t balanced the LiPo voltage could be well over this cutoff point, even if the voltage has dropped below 3.0v in one of the cells. ALL CELLS NEED TO BE CHARGED EQUALLY. This is why there are two leads on your LiPo, specifically for balancing the charging and sensing voltages on individual cells.
The charging current is also important. Most LiPo batteries should be charged at an absolute maximum current of the capacity rating of the battery…..But some are now actually stating 2 or 3 times the battery capacity.
Storing your LiPo Batteries
LiPo batteries need to be charged up to be stored. Your charger might have a storage option on it that charges your LiPo’s up to 3.8v per cell. You can then store them at room temperature.
What happens if you don’t do this? The battery will deteriorate and may get damaged. And it doesn’t take very long either. A few weeks without voltage will damage them.
Getting rid of LiPo’s
Getting rid of LiPo batteries is also somewhat challenging. You can’t just toss them in the trash because they are dangerous and might set on fire. So how do you get rid of them safely?
To get rid of your LiPo battery you need to take them to a recycling centre where they have specific bins for used LiPo batteries, but before that you need to run them right down to zero volts.
Your LiPo charger probably has an option for this discharging, but will only run it down to 3.0v.
What you need is to connect your battery to a load to drain it completely and stop the fire risk. An old filament light bulb is the best option as they are cheap and effective and don’t pull a particularly big load. Connect it up and wait until the bulb goes out!
One of the main issues with LiPo batteries is that they don’t last very long, compared to other rechargeable batteries. A standard rechargeable battery will probably last for 1,000 charge and discharges…A LiPo might last 300.
Don’t puncture your LiPo or you might end up with a fireball! They can be a little temperamental if you puncture or smash them about, or even if you don’t charge them properly.
Are LiPo Batteries that dangerous?
From the above you might think LiPo’s are just too much hassle to work with. They arent that bad as long as you follow the correct procedures and the amount of power you get from the size makes them ideal for drones.
Should you use LiPo batteries?
YES! They are an incredible source of drone power. Use them correctly, be careful and you will be fine.