Single battery systems for FPV

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. 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.

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.

The goal for a battery system must be to provide the maximum amount of operation time of the whole system (R/C and video). As such, a single battery system is always the best as it guarantees that regardless of the electricity usage pattern, all systems always have the same amount of battery remaining. With a single battery, however, special attention must be paid to choosing the right components. When using a 3S system, 12V video transmitters or video cameras may not get sufficient power to operate when the battery power gets low or a cell fails. Relying on 5V gear and/or voltage converters to negate this problem is therefore necessary. Additionally, noise in the electronic circuitry caused by your speed controller (ESC) or servos needs to be filtered. For this, an LC filter is needed, or a device like the TBS CORE.

Careful though, reverse currents will quickly charge the remaining cells of the damaged battery and can cause fire. This is very crucial in setups using 2 cell lipo battery and still important on 3S batteries. With more cells, the reverse currents going into each cell are divided among more cells and should not cause havoc. Reverse currents can be prevented by using diodes. The problem here is that adequately sized diodes are heavy. If there is a way to monitor sudden voltage drops in your system and start a quick return home, it is possible to fly safely without such a diode.

Wiring Your Basic FPV System

You’ve determined which frequencies you want to use for RC and video, and purchased the necessary components to make your FPV goal reality. Now it’s time to wire all these items together into a wireless video system.

One tip to help make this process go more smoothly is to recall the operating voltage of each component. Video transmitters and receivers typically operate at 12 V. Many cameras also have an operating voltage range that includes 11-12 V. By using components that operate at 12 V, it will be easier to wire straight off of a 3S (12.6 V max) main battery supply. You’ll have to use additional voltage transformers to step down the voltage if you plan to use 4S batteries (16.8 V max).

One thing to be aware of when using the power straight off a battery is the minimum operating voltage for the video transmitter and camera. Although a 2200mah 3s lipo may start out at 12.6 V at full charge, during use the voltage of the cells will drop down to as low as 3.2 V*. You’ll want to make sure that the operating voltage of your FPV system components encompasses at least this 9 V threshold.