A LiPo Battery packs C rating is a very important specification on a LiPo. It represents the ability for a LiPo battery pack to provide continuous current. Although, the C rating alone does not tell you how much current you can get out of a particular LiPo. There is a calculation for this and that calculation is quite simple to perform.

Consider a LiPo battery pack has a specified maximum continuous discharge C rating of 50C and a capacity of 3000mAh. Do not confuse the C ratings of the LiPo, there can be a continuous C rating and a Maximum Peak C Rating. We only want to use a continuous C rating. Firstly, 3000mAh must get converted to Ah. 3Ah. Next take the C rating and multiple it by the capacity in amp hours. 3Ah x 50C = 150A of maximum discharge current.

The question then becomes, how do you know that the C rating specified on a battery pack is accurate and not just some buy now bait from a marketing team? Or how do you know if a battery pack is weakening with age and or wear? Let’s look at 3 ways that we can do so. After all the C rating is just an arbitrary number that manufactures identify as a safe thermal limit.

Calculate the Actual C Rating of your Battery pack

The most simplistic approach to quickly estimate the actual C rating of a battery pack is to calculate it! To make this process as simple as possible, the calculator has already been complete and is located here: The Real LiPo C Rating Calculator

In order to calculate the C rating of your battery pack, you will need to know the C rating of your pack, the capacity of your LiPo and the average internal cell resistance. The average internal cell resistance is measured using a LiPo battery charger. The other items are simply read on the label of the pack.

It is recommended to follow the procedure in order to reduce error. Information that goes in to the calculator largely effects the overall accuracy of the calculation.

LiPo Battery Specification Comparison

This last method is both simple but also not so simple. The goal for this method is to compare internal resistances of battery packs with the same C rating. Once you know the internal resistance of your pack you can compare to other packs. This is the easy part. Where it gets more difficult is finding specifications of other LiPo battery packs for you to compare against. If you have multiple packs or have used these packs previously, you may already know where the internal resistance should be at. Use this as the baseline comparison. But if you don’t?

Consider having a 5000mAh battery pack that has an average internal resistance of 3.5 milliohms. If you happen to compare your data up against other known data (yours or others) and determine that the internal resistance is 2.5 milliohms, you can draw conclusions. Having a higher internal resistance does suggest that either the C rating of the pack may be weaker than you thought, or that the battery has aged.

Use a Load to Stress Test the LiPo – Manufactures Test

This test is not one that I can recommend, however it would be what I’d expect LiPo manufactures to be completing. Or some variation of the test.

If you have access to a large power dissipation bank that can apply a load to your battery pack, this is one way you can verify discharge current. There are such units that exist on the market today specifically for our RC battery packs.

The idea is that you would take your LiPo pack and wire it to the load bank. The load bank would then be configured to load the battery pack at the specific amount of current that the test requires. What you’d want to do is load your battery pack to the specified C rating. As the battery is being discharged, temperature should be recorded. The duration of the test would last until the pack is discharged to 80% of it’s rated capacity. During this time the LiPo would have to not exceed the manufactures maximum recommended temperature. If the maximum temperature is exceeded then the LiPo could not deliver the amount of power required for the C rating specified.

Concerns with the LiPo Load Test

Not only can this test be dangerous but it also places a lot of stress on the LiPo. For these reasons alone, is why I start off by saying it’s not my recommended test to confirm C rating. a) I don’t want to cause any harm to myself when conducting such a test and b) I don’t want to harm the LiPo’s.

Load Test Alternate

Another version of this test can be completed placing less stress on the battery and also decreased safety risks. This would be testing at a lower C rating then what the battery pack is rated at. However, the difference is that the expected manufactures maximum temperature would also decrease. The expected temperature would have to be verified with the new load to be applied.

I hope these points in this article provide you with an idea as to how LiPo batteries should be tested by the manufacture. It doesn’t matter what any of these tests say about your battery pack. keep in mind that if the battery stays within temperature specifications and operates your RC’s, that is what is most important.

Keeping your LiPo within its limitations can prolong your LiPo Batteries lifespan.

There are many RC’s on the market that are setup in such a way to use 2 LiPo battery packs. Theoretically, you can have any RC Airplane, Car, Boat, Helicopter or Drone setup using 2 battery packs. However, it is fairly common that RC manufactures would setup higher powered vehicles in this way. In this article we break it down using 2 LiPo battery packs in a RTR setup or even your own build!

Why RC’s are setup with 2 LiPo Batteries?

Manufactures of RTR vehicles setup an RC in this way for a few primary reasons. Let’s take a look.

Placement of Batteries

As we have mentioned above, it’s more common to use 2 LiPo batteries in a high powered RC. Higher powered RC vehicles just by inherited nature use larger batteries to be able to pump out higher amounts of power. It is more simple to break down the 1 large battery in to 2 smaller packs. Depending on the vehicle, it may be easier to physically locate 2 smaller packs on a chassis rather than 1 larger pack.

Weight Balance

In addition, placing 2 battery packs on an RC car will allow better balance of weight. Most 2 battery rigs will have the packs placed symmetrically about the length of the vehicle. Since the battery is usually the heaviest component to be placed in to your RC, balance of it is very important.

Availability of Battery Packs

It becomes more apparent as to the availability of LiPo batteries when running an RC car or boat using a cell count of 6 or more. There are not as many 6s LiPo batteries on the market as there would be for 3s LiPo’s for example. Then consider an 8s – 12s setup and purchasing 8s – 12s LiPo’s. I have not seen one in a very long time.

Is Parallel Or Series Better for 2 Packs

There are a few advantages to both a parallel setup and a series setup. However the true answer to this question lies in the Manufactures recommendation and your personal preference. Most manufactures already have the appropriate battery harness selected. This way you can simply take your charged batteries, plug them in and run the RC.

Parallel Advantages

• Parallel setups do not increase the wire length leading to the ESC
• Allows smaller Capacity Batteries to be used
• Boosts maximum continuous current output
• Condition or Health is not as critical

Series Advantages

• Series wiring can be achieved in many different setups (If you are trying to parallel a setup that requires 12s, this may be quite difficult as 12s packs are very rare to be sold in one pack)
• Boosts voltage of the setup

Conclusion to Wiring 2 Battery Packs

In general, if you are using a RTR vehicle, it is best to use the batteries that were intended to run in the vehicle. However, if you are comfortable with wiring and understand wiring, you can make a change to the RTR setup! Just keep in mind that this may void any warranty or support the manufacture may offer.

When I select which wiring I want to use for my specific RC car, boat, or plane, I generally don’t look at it as a parallel vs series. My main focus is trying to match up against the batteries that I own.

Wire 2 LiPo’s Based on What Packs you Own

Batteries are expensive. They have an average life of about 3 years, even if you do not use them. There is no point to purchasing additional batteries just for a new RC vehicle when you have packs that can already work.

Consider requiring a 6s 5000mAh setup for an RC car. The first thing I do is look at what packs I already own and pull out 2 6s 2500mAh. These packs come from an RC airplane but could work very well in the 6s RC car. In this case to get to the 5000mAh that I require, I must parallel the 2 battery packs.

On the other hand if I were to already own 2 3s 5000mAh packs from an offroad 1/10 scale car, wiring would be different. In this case, using a series wire harness would achieve 6s 5000mAh.

It’s a lot more simple to decide which batteries to use when your setup starts to get up to 8s or higher. Here you are forced in to running 4-6s packs placed in to series in order to hit the higher voltage requirement.

Don’t forget to consider how many cells in series your charger can charge. This limitation may determine the path that you must take.

Parallel Wiring Quick Tips

• Only wire packs in parallel that have the same voltage
• It is a good idea to wire packs in parallel that are around the same age and condition (otherwise power will be split based on health of the battery where the healthier pack delivers more)
• The C rating of a battery pack does not double, the battery capacity doubles

Series Wiring Quick Tips

• Wire packs that both have the same capacity (mAh) and C rating
• Packs wired in series must be around the same age and condition (Otherwise the least healthy pack will be pushed harder)

Firstly, I have to state that cogging is actually not the term to use here. However, since this term is commonly used within the RC community, I want to be sure that all can still find the improvements to the motor hesitation that we will be covering.

For a deeper understanding as to what cogging is, visit the cogging explained page. That leads us to our next question, if the brushless motor is experiencing hesitation on startup or acceleration from 0 speed, what is this called?

Typically this is referred to as the syncing process between the ESC and motor at extremely low speeds. Once the motor is in sync with the ESC, this issue is resolved entirely until the next time the motor comes to a stop or enters extremely slow speeds.

How a Sensorless System Works

A sensorless motor is exactly as it sounds. It is a system that does not use sensors to understand what position the rotor of the motor. In other words the ESC has no information as to the position of the rotor.

The ESC figures it out by first sending power to the motor, rotating the rotor slightly. While the rotor of the motor rotates, what is known as Back EMF is produced. This back EMF is read by the ESC. Back EMF is just a fancy term for voltage fed back to the ESC. This process of power sent to the motor and then back EMF sent to the ESC happens several times over a short period of time until the ESC and motor are fully in sync. During this process is where you would experience motor hesitation, chugging, poor synchronization, unsmooth operation or whatever you’d like to call it. Now we will figure out how to improve it or even completely remove it if you’d like to go that far.

It’s important to note that this occurs most commonly in RC land vehicles.

How to Completely Eliminate ESC/Motor Sync Issues

Switching to a sensored system will be able to completely eliminate hesitation within your setup. A sensored motor will be able to tell the ESC the exact position that the motor is in. Understanding position, the ESC will send power at exactly the correct time it’s required.

Does this mean that you need to switch all of your setups to a sensored system? My answer, is simply no. 9/10 of the radio controlled RC’s I have use a sensorless system. There would be very little point to run a brushless boat, plane or helicopter with a sensored system. It would be added weight and complexity for not much benefit. However, if your RC vehicle happens to be a rock crawler, then a sensored system is nearly required. Just think about how often the motor on a rock crawler would be close to 0 RPM with quite a high load to overcome.

Improving Startup Hesitation

Inspect for Binding / Unnecessary Load

Inspect gear train to be certain there is no binding or unnecessary load in the drivetrain.

This is very easy to do and well worth the check. If you find areas of binding, removing this will improve the amount of start up hesitation that your ESC/Motor combination experience. Areas to check are around dogbones, CV joints, and meshing gears.

The reason why this is important is that any additional load the motor has to rotate will make it more difficult for the ESC and motor to sync up.

LiPo Battery Discharge Strength – Improve Motor Hesitation

Be certain the battery that you are using can supply the current required for a brushless motor. The startup synchronization process takes a lot of power to initially get the motor in Sync with the ESC. Weaker Battery packs will struggle to supply the necessary power required for startup.

NiMh batteries contribute to ESC / motor synchronization problems as they generally can not deliver the power required to get moving effectively. In this case swap them out for a more reliable LiPo battery.

3 Wire Connection from the Motor to ESC

Ensure there is a good connection between the 3 wires from the motor to ESC. A good strong connection is an absolute must. As mentioned above, there is quite a bit of power that must be consumed in order to get the motor started up and in sync with the ESC. Having good connections on all 3 motor to ESC wires will allow transfer of power at the least amount of resistance. Lowest resistance means the motor receives maximum power to get going!

Gear Ratio – Improve Motor Hesitation

The gear ratio is important for hesitation within the motor at startup. Having a higher gear ratio increases the load on the motor at all speeds. What is most critical is at 0 RPM. High Gearing can make motor hesitation much more exaggerated. This may be especially true for the guys who are doing speed runs well over 160km/h. (100mph) With such high gearing to achieve these speeds, motor hesitation during startup may be significant.

Often times with my high speed RC Car, I will give it a shove to assist off the line. Once moving I engage power and the synchronization of the motor/ESC is nearly instant. Dropping a few teeth on your motors pinion gear, thus, moving to a lower gear ratio will help with hesitation.

Switching to a Motor with More Poles

In general, motors with more poles at the same kv tend to (but not always) have a smoother startup. This is due to having more ESC / Motor switching steps for every one revolution of the motor. If you have the opportunity to move up to a good quality motor with a higher pole count, try it out.