Lithium Polymer Batteries July 23, 2008
Does Temperature Affect Lithium Polymer Batteries?
Yes, lithium polymer batteries are affected by temperature. All batteries use a chemical reaction to provide electricity, and a low temperature slows this reaction down significantly. You cannot harm a lithium battery by running it at a low temperature, but you will notice a significant decrease in performance. Allowing lithium polymer batteries to freeze is generally not recommended, so be sure to store the lithium battery in a cool, dry location over the winter months.
What does “3S4P” mean?
Every lithium polymer battery consists of a set of individual cells, which can be wired in either series or parallel. Cells wired in series (positive to negative) increase the overall voltage of the pack, while cells wired in parallel increase the capacity. As an e 3S4P pack consists of 3 cells wired in series, and each array of three cells is wired in parallel four times. This means that the pack consists of twelve cells in total. Because all 3S batteries consist of the same number of cells wired in series, they all have the same voltage.
How can I calculate theoretical flight time?
In order to calculate the maximum theoretical flight time of your models, you will need to know some information about your battery and motor equipment:
- Motor Amperage
- Pack capacity in Mah (milliamp hours)
After you have that information, you can use the following formula to compute the maximum theoretical flight time of your model:
Time (hours) = (battery capacity (amps) / (motor current (amps)
Notice how the battery capacity must be given in amps. To find your battery capacity in amps, divide the capacity in milliamps by 1000. You will probably want the result expressed in minutes. so multiply the time you just calculated by 60.
By this formula, a 33.5 amp motor powered by a 5000 Mah battery would have a run time of a run time of 8.96 minutes. This is a theoretical maximum, if you actually ran the above set up for the calculated maximum time you would destroy the battery. Most lipo batteries shouldn’t be discharged below 80%, so multiply the calculated time by .8 to account for this.
What does the C rating mean?
The C rating is a measure of how long it takes a battery pack to discharge under a given load, expressed in fractions of an hour. As an example, a battery discharging at 1C would be empty in 1 hour, a 2C discharge would empty it in 1/2 an hour, and so on. For example: a 4000 Mah battery being discharged at 4000 ma, then it would be empty after an hour, and discharging at a rate of 1C.
I’m converting my RC vehicles from Nicd or Nimh to Lipo – what equipment do I need?
That depends on the type if speed controller that you’re using. If it’s marked as lipo friendly, then you don’t need to replace anything but the battery. Otherwise, it’s best that you get a speed controller that has been specifically designed for lipo batteries.
How many cycles will a lipo battery last for?
There is really no clear and concise answer for this question. The lifetime of the lipo battery really depends on how it was used. If you over discharge, over charge, or drain the battery at a higher C rating than it was intended for it will not last long. If you take care of your batteries, and are careful to follow the manufacturers instructions, you can expect to get at least 300 cycles during the lifespan of the batteries.
Is it true that the storage of the battery can effect the performance?
Yes, it is. How you store the battery severely affects it’s capacity, and thus it’s useful lifetime. You should not store lipos at 100 percent charge, and you should not store them at near minimum voltage. Either of these situations will result in the battery internally “rusting away”, and will decrease it’s capacity over time. The best way to store a lipo is at about a 50% charge, in a cool, dry location.
Is there really a way to “recover” over discharged batteries?
No. Despite claims that some chargers and settings can miraculously “restore” over discharged lipos, no charger will undo the permanent chemical reactions which take place within an over discharged cell.