Since the introduction of LiPo batteries(Lithium Polymer) cells to the RC world, the older NiMh technology has become nearly obsolete. LiPo cells or battery packs have a much greater energy density than NiMh cells making them a better choice in almost every application. Greater energy density from LiPo – Lithium Polymer Battery Packs results in Cells that can hold more capacity at a higher voltage in a lighter weight package. Perfect for RC!
Typical Terms found on LiPo batteries cells are:
Cells in Series – A 4s LiPo battery pack, for example, would have a total of 4 LiPo cells electrically wired in series to make a complete battery pack. Each Lithium Polymer cell has a nominal voltage of 3.7v. A 4s pack would be rated at a nominal voltage of 14.8v. 4s2p LiPo battery pack would mean two 4s packs in parallel. A LiPo pack in parallel doubles the capacity, and discharge rate. Total nominal voltage and C rating remains the same. 4s2p at 5000mAh each would add to
10 000mAh in total.
C Rating – The C rating of a Lithium Polymer LiPo Battery Pack is specific to the maximum continuous rate of discharge the battery can perform safely. The recommended maximum discharge for a LiPo is calculated using the C rating and battery capacity. A 25C 5000mAh battery has a max discharge of 5Ah * 25C = 125A.
mAh – mAh stands for milli-amp-hour. In simpler terms it is best related to the capacity of the LiPo battery Pack. A higher value would result in delivering an equal amount of power for longer. A 1000mAh battery would deliver (1000mA) 1 Amp for 1 hour.
Selecting the Best LiPo Battery Pack for your RC application.
It is highly recommended to use the highest capacity LiPo cells as possible with C ratings of 25 or higher. In most cases the only reason to use cells of a lesser capacity or discharge rating would be for weight and size savings. C rating is usually a matter of budget. They effect weight at a small level and do effect cost at a higher level.
LiPo Battery Packs with a larger mAh rating will naturally be heavier and have a larger physical size. Choose cells that will fit in the location they are intended to be in.
Use of LiPo Battery Packs
Using LiPo batteries are just as simple or more simple than using NiMh cells. As long as manufacture warnings and instructions are followed, use of LiPo is very safe.
Charging LiPo Battery Packs
Charge LiPo’s at the rate specified by the manufacture. In most cases this is 1C. C = capacity. A 5000mAh pack would be charged at 5.0A – 1C. In some cases LiPo’s can be charged at faster rates but this must be specified on the LiPo. It is not uncommon to see values as high as 3C or more. 5000mAh cells could be charged at 15A if they are rated for a 3C charge rate. Be certain to use a charger that either has a balancer or use a seperate balancer. Balance the cells in a pack so that all cells have equal voltage. Set your charger to the proper current rate, and voltage and initiate the charge.
Storage/First Use of LiPo Battery Packs
LiPo Battery Packss can be charged up and used immediately after purchase. They do not require a break in period. For storage, keep the cells around 40-50% capacity.
Long LiPo Life
To ensure long life of cells:
– Try to avoid getting them wet. Although the cell is completely water proof, the balance taps are not and can easily corrode from excessive water. If a pack becomes wet, one may cut the shrink wrap off, dry out the taps and re-shrink the pack.
– Discharge a maximum of 80% of the spec’d maximum discharge rate. Running 2P will greatly take the pressure off the cells in high drain applications. (More common for RC Boats) This is depandant on C rating and capacity.
– Discharge the cells to the manufacture specified voltage when storing. This is typically around 40-50% capacity.
– Only discharge a maximum of 70-80% of the cells total capacity. This means, bring the car, plane or boat in well before any voltage cut off kicks in if it is set at the default 3.0v cutoff. Or increase the cut off to a higher voltage using ESC programming tools/software
– Avoid temperatures higher then 60C or 140F.