RC cars may be a hobby for some but knowing how to tweak the ESC to get the most out of your RC device is what distinguishes a true fanatic from a hobbyist. But even someone who is a professional RC driver may not know the nitty-gritty of its power system, like the electronic speed control or ESC. Don’t worry it isn’t your fault. It’s just the ESC manufacturers who don’t want to give you the inside scoop.

But what is an ESC?

Electronic speed control or just speed control is what differentiates a $100 RC toy from a professional RC racing vehicle. Basically, a speed control is what takes the signals from the receiver, decodes the signals and sends a power signal to your brushless motor. This is what helps in getting your RC vehicle moving. So, whether you are building your own RC car model or looking to make some changes in a pre-built model, having some information on the ESC might provide you with more insight to this mysterious box.

In this article, we will specifically highlight the information about ESC that manufacturers tend to hide from geeks like us.

BEC Voltage from ESC in RC cars

The BEC, or the battery eliminator circuit, is present on the ESC and it “eliminates” the need to use an external battery pack to supply power to the receiver and other servos onboard. The ESC has a circuit that utilizes the battery voltage of your vehicle and reduces it to the amount of voltage required for the receiver and servos. Simply, this would be a power source for an RC vehicle, just like the power supply found inside a PC or server room within an office. These power supplies convert the typical 120 volts to 5, 12, 24 volts. However, if the PC loads its power supply, it is unlikely that the voltage will sag significantly within this system.

The simplest way to understand this is by understanding the following scenario: A server room power supply for providing source power for an RC charger charging either a 6s pack or 2 6s packs at 10 amps each. No matter what the case, there is a negligible drop in the voltage going inside the RC charger.

However, this is not the case for an ESC. Why?

Manufactures don’t want you to know this but the BEC current as advertised by the manufacture of the ESC is not always accurate. When we tested speed controls at the mentioned continuous power, a 25% reduction in the voltage value was observed, however, this depends on the type of RC vehicle. Do be careful as this 25% drop can cause issues with receivers that we will cover here shortly.

Building your RC vehicle

Those who want to build their own RC vehicles by using an ESC must understand speed control’s BEC. That’s because modern-day radio devices have a minimum voltage level that needs a check and balance. If the voltage tends to fall below the minimum threshold, your vehicle might become unmanageable or even shut off. Following that, your RC vehicle’s receiver will restart and try to acquire signals from its transmitter to send them back to all systems onboard. This will take some time and even increase the chances of your RC vehicle crashing into something.

Key Takeaway

As long as the power onboard is stable, the radio system of your vehicle will be functional.  We also recommend checking the maximum threshold voltage on your servos as well as your RC car’s receiver. Next, set the BEC voltage on your speed control at the same maximum threshold. This will allow the servos to produce maximum torque within their operational range, and operate at a higher functional speed. If the voltage from BEC begins to drop, the voltage at the receiver may be below its minimum threshold. If this does happen, signals being sent to the receiver will be disrupted.

To help prevent this from happening, the recommended voltage for operating most systems is 5.5 to 6 volt or more. This is because most radio system begin to suffer from voltage loss between 3.5 and 4.5V.

Maximum Continuous Current Rating on an ESC

The maximum continuous current rating, mentioned on the labels of all speed control in boldface, is the maximum current the vehicle’s motor system can produce. All ESC manufacturers are mindful of mentioning this since it is a very important figure.

But what does it actually mean? Does it imply that an ESC with a 60-amp rating can sustain a continuous current of 60 amp?

Not necessarily.

This is because we are not sure if the ESC manufacturer has tested this rating based on their operating conditions. What are these operating conditions you might ask?

A certain amount of airflow could be one example. The airflow over the speed control will keep the ESC functional and stable to allow waste heat to pass. This is not always mentioned in the instruction manual of RC devices as it isn’t required for every speed control.

Another important figure for us is the amount of heat within the ESC. This will help us to determine what the actual continuous current is in our environment. Try to record the heat generated within the ESC. Measuring temperature is the easiest way to do this. If it exceeds the required amount, this will be the RC device’s new maximum limit.

Although a lot of RC drivers are running over the 60 amps limit, that is only recommended if you are fully aware of what you are doing and recording temperature changes within the ESC.

Key Takeaway

If you are not an expert, it is recommended that you run your RC car or airplane within the mentioned current rating or its maximum temperature. No matter which threshold is reached first, stick with that.

Partial Throttle of ESC

A lot of RC drivers out there might not know but operating your speed control at partial throttle is inefficient and can be detrimental for your device. The closer the speed control operates to just above the 0% threshold, the less efficient it is going to be. Beware, efficiency here implies the resultant mechanical output from the electrical input to the system.

From an experimental point of view, we have observed that the speed control is most efficient at 100% throttle, and at the 50% threshold or below, efficiency drops.

Key Takeaway

To utilize your RC vehicle’s full potential, and if your primary concern is efficiency, try to operate its speed control at 100% throttle. For most general RC applications this is obviously not practical. We don’t recommend using a pylon racer at 100% throttle and operate the device at 3000 miles/hour in a circle. Not all that practical indeed.

However, your RC airplane’s cruise speed must be at 100% if you wish to get maximum range for an FPV long distance build. This also points to the discussion towards PWM switching.

PWM Switching Rate within ESC

An RC vehicle can make use of partial throttle, by reducing the signals sent to the motor. If the RC device operates at 100% throttle, its motor will reach its maximum rotational speed, however, to reduce that speed, the ESC will introduce PWM switching.

But here’s the catch.

ESC manufacturers don’t want you to know that by increasing the PWM switching rate, your speed control and the motor would become more efficient.

Why are they hiding this useful piece of information? ESC manufacturers don’t want you to know this because increasing the switching rate would burden the speed control. The speed control will introduce more heat in to the system, but the motor will become more efficient. The net result is efficiency gain as the motors gain is far more than the loss from the speed control.

Key Takeaway

Therefore, you want to make sure that you experiment with the PWM switching to attain maximum efficiency. However, be cautious about the temperature of the speed control.

Final words

Being an RC driver is about experimenting with speed control to get the most out of your RC device. However, take all precautionary steps to ensure proper operating temperature of your vehicle’s system.

C Rating of a LiPo Battery

In a previous article we talked about how the highest C rating has so many benefits that it makes it well worth it. However, because of all of these benefits, some LiPo manufactures use the C rating as not just a performance specification but more as a marketing tactic. This can make it very challenging for users such as us, to make a good selection for our true requirements. Some manufactures are recognizing this and try to provide the market with extra performance metrics that are not so vague. Also, the metrics provided by some manufactures are a lot more easily proved by consumers. Examples may include a simplified load test or using the internal resistance of the batteries cells.

What can you do about inaccurate C Ratings?

There are a few things that you would be able to do to help reduce chance getting stuck in these claims. The biggest and easiest method to avoiding these risks is to simply review the product reviews. Check what others are saying to see if the pack lives up to the standard you expect. Similarly, it is a good idea to check the forums to see what kind of reputation the LiPo manufacture has. Not only that but you may also run in to seeing what the popularity of the pack is. If many are using the LiPo and happy with it, chances are, it’s OK. Last item is to see if you can get any information as to the internal resistance of the pack. Using this data to compare against another pack, can tell you what performance to expect, Lower internal cell resistance will provide better performance. Check out this link to help determine the actual C rating of a LiPo.

Capacity of a LiPo Battery

There is no set standard to how a LiPo manufacture determines the capacity of a battery pack. Due to this, there is some variability in this performance specification. Some LiPo’s may not be able to deliver anywhere near their rated capacity. Now fortunately for us, the modeler, we can more easily prove and confirm these specifications just with the modern computer radio!

Capacity Varies Under Load

Yes, it’s true. Your 5000mAh battery may have just accepted 5000mAh that your charger put in to it. However, if you load the pack with a very light load you may get the full 5000mAh back out. Now if that load were to increase, you would get less total capacity out of the LiPo pack. This relationship is true based on how much load is placed on the pack up to a certain cutoff voltage.

This occurs as the minimum voltage of a LiPo battery comes in much quicker under significant load due to voltage drop. This is something to consider depending on the total amount of power that you RC vehicle will pull.

Soldered LiPo Battery Connectors

Many of the LiPo battery packs deliver some impressive numbers in terms of discharge current rates. Some of these rates easily exceed 100A continuous. However, In many cases you could see a high performing battery use such small wimpy connectors. Yep, it’s true. LiPo manufacture may choose to place small connectors on LiPo batteries for a few specific reasons. These reasons are primarily due to the market demand and cost. Some smaller connectors are more widely used. When a manufacture supplies a battery pack with a smaller more commonly used connector, less hobbyists would have to unsolder the connector only to replace with one of their own. The second primary reason manufactures may place smaller 60A connectors on a battery that can deliver well over 100A is purely due to cost. Smaller more popular connectors are inexpensive by nature. Reducing cost allows the manufacture to sell the battery more competitively and we in return get the pack for lesser overall cost.

In general, I replace the connectors on more than 75% of the LiPo battery packs I purchase. This is because primarily, I use an old connector that is rarely used these days. I also prefer a beefy connector for minimum voltage loss.

Wire Gauge used On the Battery

Very similarly as above with connectors, it may be possible that a manufacture chooses to use a gauge of wire that is smaller than what would be expected. However, the big difference here is that if you are going to be pushing packs extremely hard and want top performance – select a battery that has the wire gauge you are looking for. Otherwise what you may find yourself doing is re-soldering cables.

As for my setups. It’s rare that I run in to a situation where the wire on the battery pack is not large enough for my application. in general for most hobbyists out there, it really won’t make much of a difference at all. Wire gauge is a topic for the experienced hobbyists, otherwise run what you have.

It is fairly common that a new hobbyist to RC may think too high of a C rating would be bad for their RC. In fact the higher the C rating, the better off your entire system will be. Here is a quick review of how we use the C rating to calculate the maximum continuous discharge current the battery can output. C ratings can come in the form of either continuous or peak ratings. Be certain that you are using the continuous ratings.

Continuous Discharge Current = Continuous C rating x Battery capacity (Ah)
Discharge Current = 35C x 4.5Ah
Discharge Current = 157.5A

There are three primary reasons that you will want to get the highest C rating possible for your RC, let’s go through them.

Get the Highest Performance Possible

When a LiPo battery is under load a voltage drop occurs. It is this voltage drop that can hurt performance. If your power system is experiencing a significant voltage drop under load, the motor will not be able to hit maximum RPM. Lost RPM is exactly where we lose performance. Your RC vehicle will have a reduced top speed. However, batteries with a higher C rating will be able to maintain voltage under load. This will mean your power system will be able to produce more power output in watts leading to a higher top speed.

Another area where you will see the greatest benefit is under heavy acceleration. A higher C rated battery will be able to sustain higher voltages but also at higher current output. This will allow an RC car to accelerate out of a corner more aggressively, or for an RC boat to get out of the hole faster.

For these reasons, it is a great idea to select a pack with the highest C ratings that you can.

Reduce the Temperatures on your LiPo Battery

Temperatures effect all electrical components and it is in our best interest to keep them as cool as possible. For a LiPo battery, temperatures below 140F are acceptable. Above 140F should not be acceptable and will cause permanent damage. To maximize the lifespan of the battery reducing temps much below 140F will help.

Moving up to the highest C rating that you can will reduce the temperatures of the LiPo battery. This is due to the fact that the battery will be able to sustain a higher amount of output. For example, consider a load that you need to satisfy at 70A. Two battery options for simplicity allow for a 100A and 200A maximum continuous draw. The 100A pack would be loaded at 70% of its maximum capability. The second battery pack would be loaded at 35% of its maximum capability. The reduced amount of stress on the second battery is going to result in lower temperatures and longer life.

Reduce Ripple Voltage within Your ESC

Ripple voltage is described in detail within this article. A higher C rating will be able to reduce the amount of ripple voltage that the ESC will see. This is due to the fact that the voltage under load would be reduced. Furthermore, if an adequate C rated battery is not selected for the power system, ripple voltage can be excessively high. If the amount of ripple voltage present in the ESC is too high, the capacitors on the ESC can fail. Once this happens the ESC will ultimately fail.

It’s quite obvious that we would want to avoid this scenario at all cost. To reduce the ripple voltage within the ESC and maximize reliability of the ESC, select the highest C rated batteries that you can.

In the image above, ripple voltage is produced by a 4s 4000mAh 35C battery. The current draw is around 80A where the battery is rated for 140A. Ripple voltage is over 10% of the batteries nominal voltage which is very concerning. This must be addressed before it takes out the ESC. This LiPo battery is no longer performing at 35C due to many possibilities. Read more about LiPo batteries and what ages them here.

What can Limit C rating?

Size of the LiPo Battery

A major factor that can limit the C rating that you can use in your RC, is the size of the battery pack. As you increase the C rating of an RC LiPo battery, the physical size tends to increase. In addition to the increase in size is also the increase in overall weight. I have a battery pack that has one of the highest, accurate C ratings, that you can buy. However, it is far to heavy to place in to the RC plane that I bought it for. As a result, I have decided to use another pack instead. The new pack is lighter, improving the low speed flight characteristics of the plane. **A lighter plane will allow a less stressful landing for the pilot.** The pack is also smaller allowing an easier fitment upon strapping the pack within the planes battery bay.

Cost of the Higher C rating

Another factor that comes in to play is of course the almighty dollar. (Or which ever currency you have in your country – we use the dollar in Canada) Higher C rating batteries tend to get very pricey very quickly. Biggest thing here is that your budget should be met. If you can’t grab the 65C LiPo battery but the 45C fits within budget and your RC’s requirement, then buy it!

Since LiPo battery packs have been used in RC vehicles, performance levels have jumped up significantly. LiPo batteries have a lot of advantages such as being light weight, having high power output, high charge rates, low internal resistance and more. However, there are some disadvantages too. In particular LiPo batteries only perform their best for a short period of time relatively speaking.

How do LiPo Batteries Age?

Age of Battery Pack

LiPo batteries age for a number of reasons. One of the most obvious reasons a LiPo battery will age is due to time. Typically you can expect a LiPo battery to perform its best for the first year of use. The battery has an average lifespan of about 3 years. At the end of the 3 year mark, it doesn’t mean that the LiPo is completely useless, but it does mean that the performance of the battery is not going to be the same as when it was new.

Cycle Count

Another reason a LiPo battery pack ages is due to cycle count. The more times you charge and discharge a battery pack, the more wear that battery will experience. A cycle is considered a cycle when ever you are discharging and charging the battery. It doesn’t matter if you are only charging the battery pack 20% from 80% charged. Expect your high performance LiPo battery pack to provide about 500 cycles on average. After this point, performance drops off.

Battery Maintenance and Care

Here are a bunch of points that can help you avoid aging your battery quicker.

Maximum Discharge or Run Time

Using 100% of the packs capacity will significantly degrade the lifespan. What you want to do instead is time your run so that you end up with at least 20% of the batteries capacity remaining. Doing so will allow you to reach maximum lifespan of the battery pack.

Maximum Discharge Rate

Your batteries will get very hot if you plan to discharge the packs at the exact specification they are rated at. For example drawing 100A from a battery that can support a 100A load. What you must do instead is give yourself at least a minimum 50% headroom to a recommended 100%. This would be a battery that can support a minimum 150A or 200A recommended. Moving up to a pack that can support additional load will decrease the temperatures and increase lifespan.

Storing a LiPo Battery

When there is no plan to use your LiPo batteries for than 10 days, it is recommended to store them correctly. Not placing your batteries in to storage mode will significantly impact the lifespan of the packs.

The recommended storage voltage for a LiPo battery pack is 3.80 to 3.85 volts. This voltage is a resting voltage. Battery capacity will be approximately 40-45% at the correct storage voltage. Many chargers on the market are able to automatically bring the LiPo batteries to this storage voltage. If not, you will have to do this manually.

Leaving your battery pack at 100% charged is one of the worst things you can do to the battery when you are not using it. At the same time leaving the battery near empty is also far less than ideal. Be certain to leave your battery pack at the storage voltage specification to maximize your LiPo battery lifespan.

Operating Temperatures

Temperature in any electronic component is important. Operating a LiPo battery pack outside 140F or 60C will decrease the lifespan. Make certain to stay under these specifications for maximum reliability.

Summary and Conclusion

The 3 main issues we can face for battery packs aging is:

1. Age of Battery pack in years. Typical lifespan of a High Performance LiPo battery is 3 years.
2. Cycle Counts. LiPo Batteries have an average cycle count of about 500.
3. Battery Pack Maintenance and Care

There’s not much that we can do about the age of the LiPo. Try to maximize the total amount of RC vehicles that you can use with that particular LiPo battery and only buy the pack when you plan to run the vehicle.

As for cycle counts, again not much at all that we can do here. We don’t want to let the LiPo just sit around unused. Throw them in your RC and don’t worry about cycle counts.

The most important item here is maintenance and care for your packs. Make certain that you are following the proper guidelines to maximize the life of your battery.