User Guide
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3
Guide to Lithium Polymer Battery’s
(brushless motors are rated by kV, which means 'RPM per Volt'). So if you have
a brushless motor with a rating of 3,500kV, that motor will spin 3,500 RPM for
every volt you apply to it. On a 2S LiPo battery, that motor will spin around
25,900 RPM. On a 3S, it will spin a whopping 38,850 RPM. So the more voltage
you have, the faster you're going to go.
Capacity (mAH )
The capacity of a battery is basically a measure of how much power the battery
can hold. Think of it as the size of your fuel tank. The unit of measure here is
milliamp hours (mAh). This is saying how much drain can be put on the battery
to discharge it in one hour. Since we usually discuss the drain of a motor
system in amps (A), here is the conversion:
1000mAh = 1 Amp Hour (1Ah)
It is said that the capacity of the battery is like the fuel tank - which means the
capacity determines how long you can run before you have to recharge. The
higher the number, the longer the run time. Airplanes and helicopters don't
really have a standard capacity, because they come in many different sizes, but
for R/C cars and trucks, the average is 5000mAh - that is our most popular
battery here in the store. But there are companies that make batteries with
larger capacities. Traxxas even has one that is over 12000mAh! That's huge,
but there is a downside to large capacities as well. The bigger the capacity, the
bigger the physical size and weight of the battery, and it is expensive to ship
due to IATA Dangerous Goods Regulation. Another consideration is heat buildup
in the motor and speed control over such a long run. Unless periodically
checked, you can easily burn up a motor if it isn't given enough time to cool
down, and most people don't stop during a run to check their motor temps.
Keep that in mind when picking up a battery with a large capacity.
Understanding “C” Rating
Let start off by understanding what the battery's "C" rating means. C rate
is the battery's maximum SAFE continuous discharge rate. If the label says
"20C" that means that the battery can be discharged at a rate of up to 20 times
the capacity of the battery, until it is depleted. Capacity refers to the milliamp-
hour rating of the battery, which will be listed as a number followed by "mAh" -
2200mAh. Some brands also use Amp ratings, which is pretty much the same,
just a different scale, so 2200mAh will be displayed as 2.2. Keep in mind that
1000mAh equal 1Amp. So here is an example with a 2200mAh 20C pack (pack
voltage does not play a part in determining C rating):
2200mAh = 2.2Amps
2.2Amps x 20C = 44Amps continuous discharge