Electric Motors: More Efficient Than Combustion Engines

The RC industry has recently gone through a transformation, with many people switching away from nitro engines to electric motors. A big part of that is due to the efficiency and power of electric brushless motors, but the other big reason is due to the recent advances in battery technology.

Previously, the biggest challenge with electric RC cars was that they were underpowered compared to their nitro counterparts. Lithium Polymer (LiPo) batteries have changed that now because they are lighter and more powerful than regular NiCad and NiMH batteries.

Unlike NiCad and NiMH, LiPo batteries also do not self-discharge when connected in parallel which means that LiPo batteries can be connected in parallel to double their capacity which means longer run times for your RC. They can also be connected in series to increase their voltage.

By combining LiPo batteries in different parallel and series configurations, manufacturers can create LiPo packs to suit any of your RC needs. For example, the voltage on the pack can be increased by wiring LiPo packs in series. One LiPo cell has a nominal voltage of 3.7 volts so two LiPo batteries connected in series produce 7.4 volts, three produce 11.1 volts etc. batteries that best in class for the trolling motor

LiPo packs also have something called a “C” rating which is the maximum average discharge current recommended for the cell. The “C” rating on a LiPo pack can be used to determine the maximum discharge amperage by multiplying the “C” rating by the capacity of the pack.

For example, a 5000 mAh LiPo pack with a “C” rating of 20 would have a maximum discharge rating of 5,000 mAh x 20C = 100,000 mA which is 100 amps. The higher the “C” rating on a battery pack, the higher discharge amperage it can handle continuously without stressing the battery. Therefore it is important to match your LiPo’s “C” rating with the needs of your electric motor.

Some of the newest RC cars on the market can handle two 11.1v LiPo packs running in parallel, delivering 22.2 volts of power to the motor.

The kind of power these LiPo batteries are delivering to the brushless motors in electric RC cars is allowing them to reach maximum speeds in excess of 100 m/h, while at the same time increasing run time before needing to charge the battery again.

DC Motors are arguably the most useful type of electrical motors, and with good reason, they are designed to be used with batteries, solar cells or similar cell based energy sources, and as a result are used in systems where you don’t have to be tied to a wall. Furthermore, even in systems where they are tied to the wall, sometimes it can be more efficient and cost effective to run DC Motors even in certain situations. Motors generally though give the impression of a gas guzzling car. In this article, I hope to dispel that myth, and educate you on where and when DC Motors can be and are used.

Low Power DC Motors

The lower power motors aren’t really useful for things commonly associated with motors. Lifting and transportation applications require more power & torque for them to work. However, what they lack in power they make up in precision. Low power DC motors are particularly useful as speed changes from 0 to 1 are almost instantaneous. Therefore, they can be used successfully in digital systems.

A low speed, low power brushless DC motor can be found in most turntable devices, particularly precision turntable devices. Devices with such motors are things like personal computers (usually, with 3 motors in it, one for the hard drive, and one for the processor cooler), CD & DVD players.

Medium Power DC Motors

Medium power DC Motors have a use too in systems. Generally they are connected to the mains, and use a rectifier to convert the AC current into a DC current to be used for the task in hand. As a result of this, they also need to be stepped down (voltage reduced) so that the current doesn’t overpower the circuit and burn out the motor. This limits their usage to larger systems that require room for both a stepper and a rectifier. But they still serve a purpose, particularly in systems where size nor speed is an issue, just reliability. One such place is in pinsetters in a bowling alley, for example.

High Power DC Motors

Arguably the most common and useful motors are High Power DC Motors. These motors are generally used in open systems, and generally used in systems were torque and power, as well as drive are paramount. Examples of such systems include electric wheelchairs, electric scooters, Segways, hybrid cars, as well as in elevators.

Of course, with power comes great power usage, and whilst the most energy efficient form of motor, they can require a lot of energy to run. Part of the creative process of using them is to be efficient (drive systems in hybrid cars use the petrol motor’s momentum to recharge a battery, which will be then used to power the DC motor), but generally the battery will need to be recharged or replaced at regular intervals. Even so, it’s usually infrequently the battery needs replacing. Furthermore, any systems attached to the mains don’t suffer from this problem.