Even with the best FPV gear on the market, you won’t get very far without a decent knowledge of batteries and how to get the most out of them. The choice of batteries depends on the type of FPV aircraft and the flying characteristics of the pilot.
The LiPo Battery in RC FPV
Almost all FPV aircraft use Lithium-Ion (LiPo) batteries for power. LiPo batteries used in the RC hobby have similar characteristics to the batteries that power your smart phone, computer, and other small electronic gadgets.
However, LiPo RC batteries have a different sort of covering over them, a flexible wrapper, rather than a rigid container. This saves on weight, and makes them an ideal choice for RC aircraft.
Two LiPo Batteries.
LiPos typically have identical cells inside them that are connected to make up the desired total voltage. Each cell is typically 4.23 V fully charged, and can be discharged down to around 2.7 V, but usually no less than 3.2 V in practice.
It’s important not to discharge LiPos all the way because they won’t hold a recharge. You can find out more about the design and history of LiPos by visiting the lithium polymer battery Wikipedia page. Let’s focus on just the basics and on how to identify and read a LiPo battery label.
LiPo Battery Basics
In the image with the two LiPo batteries, you’ll see a few numbers. On the top LiPo battery, you see a 5.0 in large font on the right, and on the left face of the battery “5000 mAh.” The 5.0 stands for amp-hrs and is a measure of the capacity of the battery.
The 5000 mAh is just another way of expressing the 5 amp-hr capacity, as milli is simply the prefix for 1/1000.
This means that this particular battery can be discharged at a rate of 5 amps for 1 hour. In practice, the usable capacity is about half of that.
The “35-70C Discharge” statement on the center of the battery refers to how fast the battery can be discharged safely, and is a multiple of the total mAh capacity with units of amps. For example, this battery has a capacity of 5 amp-hr and a discharge of 35-70C.
That means that this LiPo battery can be discharged at 5 * 35 = 175 amp continuously and up to 5 * 70 = 350 amp in a burst (usually a few seconds). This sort of discharge rate is really far more than is necessary for even the most aggressive RC or FPV flying.
A typical single-motor mid-size FPV aircraft operating at full throttle only pulls about 30 – 40 amps, so you can see how the battery companies are marketing a capability that is basically useless to the normal FPV hobbyist.
Various LiPo Batteries and Charger.
Voltage and Number of Cells
Both the batteries above have three cells and are termed 3C. Since each cell is 4.23 V, the total battery voltage is 3 * 4.23 V = 12.69 V. For more power, you could use a 4C battery, with a total voltage of 16.92 V.
One Battery or Two?
LiPo batteries power not only the motor or motors, but also the on-board electronics, video transmitter, camera, servos, etc. There are various ways to wire the on-board electronics, motor, and battery. Some veteran FPV pilots recommend a wiring scheme that utilizes two LiPo batteries.
In this type of setup, one large LiPo battery powers the main flight motors while a second, smaller LiPo battery powers the on-board electronics, including the control servos.
This redundant setup allows for control of the aircraft if the motor or main flight battery were to fail inflight. Others recommend a single battery setup to save on weight at the expense of added redundancy.
The basic wiring diagram for an FPV setup with no flight stabilization electronics, GPS, or on screen display (OSD) is not too complicated. The difficulty occurs when one wishes to add some of the advanced features described above.
The matching of voltage, current limits, added sources of RF interference, and increased wiring length and clutter all make the placement and connection of these components more tedious. Separate posts will cover the details about wiring an FPV setup, recommended connectors for a LiPo battery, and how to charge LiPo batteries successfully.